Evaluation of Semiochemical-Baited Traps for Monitoring the Pea Leaf Weevil, Sitona lineatus (Coleoptera: Curculionidae) in Field Pea Crops

Evaluation of Semiochemical-Baited Traps for Monitoring the Pea Leaf Weevil, Sitona lineatus... Abstract The pea leaf weevil (PLW), Sitona lineatus L., is a pest of field pea (Pisum sativum L.) and faba bean (Vicia faba L.) that recently invaded the Canadian Prairie Provinces. Although most damage is done by larvae that feed on root nodules, adults are easier to monitor than larvae. Both male and female weevils respond to a male-produced aggregation pheromone and to volatiles released by host plants. The current study tests the attractiveness of synthetic aggregation pheromone, 4-methyl-3,5-heptanedione, and host plant volatiles linalool, (Z)-3-hexenol, and (Z)-3-hexenyl acetate to PLWs in spring when weevils are reproductively active and in fall when weevils seek overwintering sites. Different combinations of semiochemical lures at various doses, released from a variety of devices were tested in pitfall traps. Semiochemical-baited traps captured both male and female weevils in both seasons but the sex ratio varied with season. Weevils did not respond in a dose-dependent manner to pheromone, as all pheromone lures were equally attractive. Pheromone release rate was determined by the release device and not the pheromone dose in the lure. The addition of plant volatiles sometimes increased weevil captures but plant volatiles alone were not attractive to PLW adults. An additional study tested the effect of trap type on weevil capture. Of the 12 different trap types tested, pheromone-baited pitfall traps were most successful in attracting and retaining weevils. Bycatch of other Sitona species was limited to a few specimens of the sweet clover weevil, Sitona cylindricollis Fahraeus. The pea leaf weevil (PLW), Sitona lineatus L. (Coleoptera: Curculionidae) is an invasive pest of field pea (Pisum sativum L., Fabaceae) and faba bean (Vicia faba L., Fabaceae) that is expanding its range in the Canadian Prairie Provinces (Vankosky et al. 2009). PLW was first reported in the Prairie Provinces in 1995 near Swift Current, Saskatchewan (Pepper 1999) and in 1997 near Lethbridge, Alberta (Coles et al. 2008). Climate projection models (Olfert et al. 2012) predict continued expansion of PLW into the Prairie Provinces as an effect of global warming. Field pea is an important pulse crop in Canada, with an average of 2.3 million hectares seeded or 4.5–5 million tonnes of peas produced per year (Pulse Canada 2016). Canadian pea and the small acreage of faba bean crops in the Prairie Provinces are at risk to PLW damage. PLWs are univoltine and overwinter as adults (Jackson 1920). Adult weevils display two periods of activity per year when weevils are in different physiological states. Before overwintering, weevils are sexually immature and seek overwintering sites in shelter belts or perennial legumes. In the spring, PLW seek mates and migrate to reproductive hosts for feeding, mating, and egg production. During both periods of adult activity, adult weevils feed aboveground on legumes, causing characteristic feeding notches at the margins of leaves (Jackson 1920). While sexually immature in the fall, PLW adults feed on leaves of most legumes but prefer to feed on their reproductive host plants, pea or faba beans, when mating in the spring (Fisher and O’Keeffe 1979, Landon et al. 1995, Landon et al. 1997). An 11% loss in photosynthetic area of pea seedlings can result from heavy adult PLW damage (Cárcamo et al. 2012). Adult foliar feeding is temperature dependent, with feeding activity highest between 12°C and 21°C (Landon et al. 1995). Damage from larval feeding on root nodules is considered more important than adult foliar feeding and can reduce yields by decreasing nitrogen availability (Nielsen 1990, Williams et al. 1995, Vankosky et al. 2009, Cárcamo et al. 2015). The current method of estimating PLW activity in the Prairie Provinces is to survey adult feeding damage in pea crops (Saskatchewan Ministry of Agriculture 2016, Alberta Agriculture and Forestry 2017). This approach is labor intensive and variable as adult feeding is temperature dependent (Landon et al. 1995). As PLW aggregation and host location behavior is tied to olfaction, semiochemical-baited traps are a possible alternative tactic to monitor adult PLW populations (Vankosky et al. 2009, Evenden et al. 2016). A male-produced aggregation pheromone, 4-methyl-3,5-heptandione (Blight et al. 1984) attracts both male and female PLW adults in the spring (Blight et al. 1984, Nielsen and Jensen 1993, Quinn et al. 1999, Evenden et al. 2016) and fall (Evenden et al. 2016). PLW adults also use host plant volatiles to locate suitable host plants (Blight et al. 1984, Landon et al. 1995, Landon et al. 1997) and are responsive to these cues during both periods of adult activity but not during the winter (Landon et al. 1997). Exploitation of these semiochemicals as artificial lures in insect traps could be a useful tool for monitoring the PLW range expansion in the Prairie Provinces (Vankosky et al. 2009, Evenden et al. 2016). Synthetic copies of the male aggregation pheromone in combination with volatiles released from faba beans ((Z)-3-hexenol, (Z)-3-hexenyl acetate, and linalool) attract PLW (Blight et al. 1984, Evenden et al. 2016). Semiochemical-baited cone traps have been successfully used to monitor PLW during the spring migration in faba bean crops in Denmark (Nielsen and Jensen 1993) and in North America (Quinn et al. 1999). Evenden et al. (2016) were the first to show that adult PLW respond to semiochemical-baited traps in both the spring and fall activity periods in studies conducted in the Canadian Prairie Provinces. Although studies using cone traps to capture PLW in Europe were successful (Blight et al. 1984, Blight and Wadhams 1987, Nielsen and Jensen 1993), cone traps did not retain attracted weevils in Alberta (Evenden et al. 2016). Besides the attractiveness of the semiochemical lure, the type, color, and placement of an insect trap contribute to its effectiveness as a monitoring tool (Reddy et al. 2011). The objective of this research was to develop a semiochemical-baited trap to monitor established and expanding populations of PLW in the Prairie Provinces. A successful semiochemical-baited trap will reliably capture PLW, be easy to use and cost-effective. In this study, various doses of semiochemicals released from a variety of devices are tested to develop an appropriate semiochemical lure for PLW. Various types of traps are also tested in an attempt to find an effective, efficient, and user-friendly trap to adopt for a semioochemical-based monitoring system that can delineate the range expansion of this pest in the Prairie Provinces. Materials and methods Semiochemical Lures: Dose and Release Device A series of field experiments was performed in 2013 and 2014 to test the attraction of PLW adults to various semiochemical lures that consisted of the PLW aggregation pheromone, with or without various host plant volatiles (Tables 1–3). Lures tested in 2013 compared two different doses of pheromone in two types of Eppendorf tube release devices (250 and 400 µl) alone and in combination with host volatile lures. Pheromone doses tested were 21 mg, a dose that was previously shown to attract PLW (Blight et al. 1984, Nielsen and Jensen 1993, Evenden et al. 2016), and a higher dose of 42 mg. Host volatile lures tested were those developed by Blight et al. 1984 and previously tested by Evenden et al. (2016) (Table 1). In 2014 (Table 2), different devices releasing host plant volatiles were tested in combination with the aggregation pheromone. Release rates of lures tested in both years are shown in Table 3. Table 1. Composition of semiochemical treatments tested for attractiveness to PLW adults in spring (8 May–19 June) and fall (31 July–13 September) 2013 Treatment  Pheromone lure composition  Host volatile lure composition  Pheromonea dose (mg)  Pheromone release device  (Z)-3-hexenyl acetate dose (mg) in 250 μl Eppendorf  (Z)-3-hexenol dose (mg) in 250 μl Eppendorf  Linalool dose (mg) in 250 μl Eppendorf  1  21  250 μl Eppendorf  0  0  0  2  21  250 μl Eppendorf  21  34  3 x 50  3  21  400 μl Eppendorf  0  0  0  4  21  400 μl Eppendorf  21  34  3 x 50  5  42  250 μl Eppendorf  0  0  0  6  42  250 μl Eppendorf  21  34  3 x 50  7  42  400 μl Eppendorf  0  0  0  8  42  400 μl Eppendorf  21  34  3 x 50  9  0    0  0  0  Treatment  Pheromone lure composition  Host volatile lure composition  Pheromonea dose (mg)  Pheromone release device  (Z)-3-hexenyl acetate dose (mg) in 250 μl Eppendorf  (Z)-3-hexenol dose (mg) in 250 μl Eppendorf  Linalool dose (mg) in 250 μl Eppendorf  1  21  250 μl Eppendorf  0  0  0  2  21  250 μl Eppendorf  21  34  3 x 50  3  21  400 μl Eppendorf  0  0  0  4  21  400 μl Eppendorf  21  34  3 x 50  5  42  250 μl Eppendorf  0  0  0  6  42  250 μl Eppendorf  21  34  3 x 50  7  42  400 μl Eppendorf  0  0  0  8  42  400 μl Eppendorf  21  34  3 x 50  9  0    0  0  0  aPea leaf weevil pheromone: 4-methyl-3,5-heptanedione. View Large Table 2. Composition of semiochemical treatments tested for attractiveness to PLW adults in spring (30 April–19 June) and fall (5 August–16 September) 2014 Treatment  Chemical lure composition per treatment  Host volatile release device  Pheromonea dose (mg) in 250 μl Eppendorf tube  (Z)-3-hexenyl acetate  (Z)-3-hexenol  Linalool  1  0  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  2  21  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  3  42  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  4  0  700 μl  700 μl  200 μl  Bubble cap  5  21  700 μl  700 μl  200 μl  Bubble cap  6  42  700 μl  700 μl  200 μl  Bubble cap  7  21  0  0  0  -  8  42  0  0  0  -  9  0  0  0  0  -  Treatment  Chemical lure composition per treatment  Host volatile release device  Pheromonea dose (mg) in 250 μl Eppendorf tube  (Z)-3-hexenyl acetate  (Z)-3-hexenol  Linalool  1  0  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  2  21  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  3  42  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  4  0  700 μl  700 μl  200 μl  Bubble cap  5  21  700 μl  700 μl  200 μl  Bubble cap  6  42  700 μl  700 μl  200 μl  Bubble cap  7  21  0  0  0  -  8  42  0  0  0  -  9  0  0  0  0  -  aPea leaf weevil pheromone: 4-methyl-3,5-heptanedione. View Large Table 3. Release ratesa of semiochemical lures tested in 2013 and 2014 Semiochemical  Dose  Release device  Release rate (mg/day) @ 20°C  Release rate (mg/day) @ 30°C  4-methyl-3,5-heptanedione  21 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  42 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  21 mg  400 μl Eppendorf  0.2  0.5  4-methyl-3,5-heptanedione  42 mg  400 μl Eppendorf  0.2  0.5  (Z)-3-hexenyl acetate  21 mg  250 μl Eppendorf  0.35  1.6  (Z)-3-hexenyl acetate  700 μl  Bubble cap  13  Not tested  (Z)-3-hexenol  34 mg  250 μl Eppendorf  0.15  0.28  (Z)-3-hexenol  700 μl  Bubble cap  3.7  17  Linalool  50 mg  250 μl Eppendorf  Not detected  0.04  Linalool  200 μl  Bubble cap  4  Not tested  Semiochemical  Dose  Release device  Release rate (mg/day) @ 20°C  Release rate (mg/day) @ 30°C  4-methyl-3,5-heptanedione  21 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  42 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  21 mg  400 μl Eppendorf  0.2  0.5  4-methyl-3,5-heptanedione  42 mg  400 μl Eppendorf  0.2  0.5  (Z)-3-hexenyl acetate  21 mg  250 μl Eppendorf  0.35  1.6  (Z)-3-hexenyl acetate  700 μl  Bubble cap  13  Not tested  (Z)-3-hexenol  34 mg  250 μl Eppendorf  0.15  0.28  (Z)-3-hexenol  700 μl  Bubble cap  3.7  17  Linalool  50 mg  250 μl Eppendorf  Not detected  0.04  Linalool  200 μl  Bubble cap  4  Not tested  aRelease rates were determined gravimetrically by the semiochemical supplier: Scotts Canada. View Large The PLW aggregation pheromone, 4-methyl-3,5-heptanedione, was synthesized by collaborators at Scotts Canada, (Delta, BC, Canada) (Evenden et al. 2016) and dispensed into various release devices depending on the experiment. The bean volatiles tested were those identified previously as released from faba bean shoots: (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, and linalool (Blight et al. 1984). Commercial sources of the bean volatiles ((Z)-3-hexen-1-yl acetate (Sigma Aldrich, St. Louis, MO); (Z)-3-hexen-1-ol (Bedoukian Research, Danbury, CT); and linalool (Lancaster, Ward Hill, MA) were used to formulate the lures at Scotts Canada. Lures were shipped in refrigerated containers to the University of Alberta and stored at 4°C before transport to the field in refrigerated containers and at −20°C for longer-term storage between trapping experiments. At each field site (n = 9–14) in southern Alberta, lures were positioned in Solo cup pitfall traps that consisted of two 473 ml plastic cups (Solo, Lakeforest, IL). The rim of one cup was trimmed off at the 414 ml fill line and placed as an insert in an intact cup for easy removal at trap service. Cups were positioned in the ground so that the top of the intact cup was flush with the soil surface. Pitfall traps were filled halfway with propylene glycol (Prestone Plumbing Antifreeze, Honeywell Consumer Products Group, Danbury, CT) to preserve captured insects. Propylene glycol was replenished at each trap check. Lures were secured with wire to a 15 × 15 cm piece of white plastic Coroplast (Home Hardware, Edmonton, AB, Canada) that was positioned above each trap and secured into the ground with four 10-cm nails. The white Coroplast also served as a canopy to protect the trap from rain and evaporation (Fig. 1a). Traps were positioned 25 m apart in random order along a linear transect 1 m from the edge of pea fields at each site. Sites were located >1 km apart to ensure independence of weevil populations. Although it is not known how far PLW can fly, dispersal to pea fields in the spring has been described as a migratory flight (Fisher and O’Keefe 1979). Once weevils arrive in a reproductive host crop following spring migration, dispersal occurs by walking (Hamon et al. 1987).Experiments were performed throughout the adult weevil activity period in the spring and fall of 2013 and 2014. Traps were placed in the field within 5-days post-seeding in mid-May and were checked every 5–8 days for 4–6 weeks in both years. Semiochemical lures were replaced and the trap order was re-randomized at the beginning of the fall activity period in early (2013) to mid-August (2014) and were checked weekly until the end of adult activity in both years. Fig. 1. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2013. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include (a) a white Solo cup pitfall trap; (b) ground-based, hand-constructed yellow cone trap; (c) hand-constructed yellow cone trap placed 1 m above the ground on a rebar stake; (d) hand-constructed yellow cone trap placed 0.6 m above the ground on a yellow pyramid; (e) hand-constructed yellow bucket trap; and (f) green unitrap. Also tested but not shown here were yellow unitraps, multicolored unitraps and yellow sticky cards (Table 4). Fig. 1. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2013. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include (a) a white Solo cup pitfall trap; (b) ground-based, hand-constructed yellow cone trap; (c) hand-constructed yellow cone trap placed 1 m above the ground on a rebar stake; (d) hand-constructed yellow cone trap placed 0.6 m above the ground on a yellow pyramid; (e) hand-constructed yellow bucket trap; and (f) green unitrap. Also tested but not shown here were yellow unitraps, multicolored unitraps and yellow sticky cards (Table 4). Weevils were removed from propylene glycol, and the number of PLW in each trap was recorded by sex. In 2014, PLW captured in the fall trapping period were further separated into overwintered or newly eclosed based on wing morphology. Newly eclosed PLW had intact scales and flexible elytra whereas overwintered weevils had heavily worn scales, rigid or fused elytra, and some had evidence of previous mating (damaged pygidia in females or everted aedeagi in males). In 2014, nontarget Curculionidae captured in semiochemical traps were also collected and identified to genus (Otiorhynchus, Ceutorhynchus, Perapion, Hypera, and Sitona) using the keys in Bright and Bouchard (2008). Statistical Analyses All analyses were conducted using the statistical program R (version 3.1.3). To determine which semiochemical lures were most attractive to PLW, trap capture was analyzed using generalized linear mixed models with negative binomial error distributions created using the function glmer.nb in the lme4 package (version 1.1–10). Models were selected based on best fit by comparing AIC values, –log likelihood values, and the distribution of residuals. For the statistical analyses, the total number of PLWs captured per trap in each season (i.e., the sum of PLW captured each week) was used as a response variable, with (1|Site) as a blocking term. Repeated measures models with a (Week|Site) random term were also built, but season total models with (1|Site) were selected based on better fit. Models were first constructed with all possible interaction terms included and nonsignificant interaction terms were subsequently removed in a step-wise manner. Relevant P values were calculated using the ANOVA function in the package car (version 2.0–25). Post-hoc Tukey’s multiple comparisons tests were performed on significant factors with more than one level using the function ghlt in the package multcomp (version 1.4–4). The effect of seasonality on PLW trap capture was tested only in 2014. To determine if traps were differentially attractive to male and female PLW, total trap capture in each baited trap in 2014 was subjected to a Two-Sided Exact Binomial Test using the function binom.test in the package stats which determined the proportion of males to females captured in each semiochemical-baited trap. To compare the sex ratio of trap capture within a given season, Chi-Square Contingency Table Analyses were performed using the function chisq.test in the package stats (2 × 6 table for spring 2014; 2 × 8 table for fall 2014). For the analysis of sex ratio in spring 2014, the following treatments were excluded due to low PLW captures: blank traps (n = 3), traps baited with low (n = 2), or high dose (n = 3) host plant volatile lures without pheromone. For the fall 2014 sex ratio analysis, capture in blank traps was excluded due to low PLW capture (n = 1). To compare the proportion of newly eclosed to overwintered, male or female PLW within each semiochemical-baited trap, Two-Way Tests of Equal Proportions were performed using the function prop.test in the package stats (version 3.1.3). The number of male and female PLW that were newly eclosed or overwintered PLW were compared among semiochemical traps with a 6 × 4 chi-square contingency table analysis. PLW captures were again excluded from unbaited traps (n = 1) or in traps baited with either low host plant volatile lure (n = 18) or high host plant volatile lure (n = 17) without pheromone (n = 17) due to low PLW captures in these traps. Trap Type To determine if a trap design more suitable than the Solo cup pitfall trap (Evenden et al. 2016) could be developed to attract and retain PLW in Alberta, various trap types were evaluated in the fall trapping period of 2013, 2014, and 2015. In each of these experiments, the various types of traps tested (Figs. 1–3; Table 4) were baited with a low dose (21 mg) of pheromone released from a 250 µl Eppendorf tube and positioned in pea fields in August of each year, after the pea crop was harvested at each site when weevils are dispersing to feed prior to overwintering. Table 4. Trap types tested in 2013, 2014, and 2015 Year  Trap typea  Placement  Trap source  2013  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Yellow Unitrap, 1 m above the ground on rebar stake  Above crop  Scotts Canada  Green Unitrap, 1 m above the ground on rebar stake  Above crop  AgBio Inc., Westminister, CO  Multicoloured Unitrap, 1 m above ground  Above crop  Scotts Canada  Yellow sticky card (18 × 14 cm), 1 m above the ground on rebar stake  Above crop  Alphascents, West Linn, OR  Yellow cone trap, 1 m above the ground on rebar stake  Above crop  Hand constructed  Yellow cone trap, 0.75 m above ground on a yellow pyramid  Crop level  Hand constructed  Yellow cone trap secured on ground with tent pegs  At ground  Hand constructed  Yellow bucket trap with ½ of a Vapona insecticide strip  Pitfall  Hand constructed  2014  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent, with a ring of 6 mm × 6 mm chicken wire mesh to exclude large bycatch  Pitfall  Hand constructed  Yellow pan trap  Pitfall  Flexahopper Plastics Ltd., Lethbridge, AB Canada  Boll weevil (Legget) trap  At ground  ISCA Technologies Inc., Riverside, CA  Legget trap modified with all holes >2 mm sealed with hot glue  At ground  ISCA Technologies Inc.  PVC pitfall trap with small holes (20, 2 × 2 mm holes)  Pitfall  Hand constructed  PVC pitfall trap with large holes (six, 20 × 10 mm holes)  Pitfall  Hand constructed  Cylinder of yellow sticky cards on a wooden stake  Crop level  Modified from commercially available  2015  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Vernon ramp trap for wireworms, lined with yellow sticky cards  Pitfall  Scotts Canada  Vernon pitfall trap for wireworms, with propylene glycol as a killing agent  At ground  Scotts Canada  Year  Trap typea  Placement  Trap source  2013  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Yellow Unitrap, 1 m above the ground on rebar stake  Above crop  Scotts Canada  Green Unitrap, 1 m above the ground on rebar stake  Above crop  AgBio Inc., Westminister, CO  Multicoloured Unitrap, 1 m above ground  Above crop  Scotts Canada  Yellow sticky card (18 × 14 cm), 1 m above the ground on rebar stake  Above crop  Alphascents, West Linn, OR  Yellow cone trap, 1 m above the ground on rebar stake  Above crop  Hand constructed  Yellow cone trap, 0.75 m above ground on a yellow pyramid  Crop level  Hand constructed  Yellow cone trap secured on ground with tent pegs  At ground  Hand constructed  Yellow bucket trap with ½ of a Vapona insecticide strip  Pitfall  Hand constructed  2014  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent, with a ring of 6 mm × 6 mm chicken wire mesh to exclude large bycatch  Pitfall  Hand constructed  Yellow pan trap  Pitfall  Flexahopper Plastics Ltd., Lethbridge, AB Canada  Boll weevil (Legget) trap  At ground  ISCA Technologies Inc., Riverside, CA  Legget trap modified with all holes >2 mm sealed with hot glue  At ground  ISCA Technologies Inc.  PVC pitfall trap with small holes (20, 2 × 2 mm holes)  Pitfall  Hand constructed  PVC pitfall trap with large holes (six, 20 × 10 mm holes)  Pitfall  Hand constructed  Cylinder of yellow sticky cards on a wooden stake  Crop level  Modified from commercially available  2015  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Vernon ramp trap for wireworms, lined with yellow sticky cards  Pitfall  Scotts Canada  Vernon pitfall trap for wireworms, with propylene glycol as a killing agent  At ground  Scotts Canada  aAll tested trap types were baited with 21 mg of pea leaf weevil aggregation pheromone in a 250 µl Eppendorf tube. View Large In 2013, nine trap types (Table 4) were tested at eight pea fields in southern Alberta. Traps were placed 25 m apart along a linear transect 1 m from the edge of the field in early August and checked every 5–7 days for a total of five trap collections. Trap capture was transported to the laboratory where PLW were identified and counted. Trap types tested in comparison to the Solo cup pitfall trap (Fig. 1a) included modified cone traps constructed from an inverted 946 ml yellow plastic drinking cup (Jean’s Plastics Party Supplies Gifts, Ebay). Cone traps were modified by drilling five, 1-cm diameter holes into the cup base for insect entry and gluing a clear polypropylene powder funnel (104 mm diameter, 243 ml capacity; Fisher Scientific) to the top of the inverted cup with a 37 ml plastic snap cap vial (Sigma Aldrich) attached to collect attracted insects. The inside of the plastic cup and funnel were sanded to increase traction and insect movement up the traps. Three versions of this cone trap were constructed: 1) a ground-based version (Fig. 1b); an aerial cone trap (Fig. 1c) positioned 1 m above the ground; and 3) a cone trap positioned on a pyramid (Fig. 1d) constructed out of two interlocking yellow Coroplast triangles (27 × 60 cm, base × height). Yellow bucket traps (Fig. 1e), similar to those used to monitor palm weevils (Vacas et al. 2013), were also tested in 2013. Yellow bucket traps were constructed from the same yellow plastic drinking cups but had a circular yellow Coroplast lid. Six, 2 cm diameter holes were drilled into the top of the cup for insect entry and cups were dug into the ground. Half of a Vapona insecticide strip (Scotts Canada) was secured to the inside of the cup to kill captured insects. In 2013, we also tested three different colors of Unitraps (Scotts Canada) (17 × 23 cm, diam × height), which were positioned 1 m above the ground on rebar stakes. Unitraps were either entirely green, entirely yellow or multicoloured (Fig. 1f) with a green lid, yellow cone, and white bucket. Each Unitrap contained half of a Vapona insecticide strip to kill captured PLW. Yellow rectangular sticky card (18 × 14 cm) traps (Alpha Scents, West Linn, OR) were also tested in 2013. Each yellow sticky card was attached with wire to a rebar stake at 1 m. In 2014, PLW capture was compared in eight types of insect trap (Table 4) at each of 5 sites. The Solo cup pitfall trap (Fig. 1a) was tested again with the addition of a cylinder (12 cm diam.) of 6 mm × 6 mm wire mesh attached to the Coroplast lid to exclude large bycatch (Fig. 2a). Additional pitfall traps tested in 2014 included two traps constructed from white PVC piping (Fig. 2b and c). In each PVC pitfall trap, a 10 cm length of 10 cm diameter PVC pipe with fitted cap had either, 20, 2 mm holes (Fig. 2b) or six, 20 mm × 10 mm oval holes (Fig. 2c) cut into the cap. PVC pitfall traps were half-filled with propylene glycol to preserve captured insects. Yellow pan traps (6.5 × 20 × 27 cm) (Fig. 2d) were also tested. Pan traps were buried into the soil so that the top of the pan trap was level with the soil surface, and were half-filled with propylene glycol as a trapping medium. In 2014, an unmodified and modified version of the Leggett cone trap (Leggett et al. 1975) (Fig. 2e) was tested. As the Legget traps were previously unsuccessful in retaining PLW in Alberta (Evenden et al. 2016), a modified Leggett cone trap was constructed to minimize the hole size in the mesh cone to less than 2 mm. Cone traps were placed on the ground and secured in place with tent pegs. The final trap type tested in 2014 was a cylinder (14 cm high, 50 cm circumference) (Fig. 2f) (Fisher and O’Keeffe 1979) constructed from three overlapping yellow sticky cards (14 × 18 cm) stapled to a 30 cm wooden stake to position the cylinder just above the crop stubble. Fig. 2. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2014. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were placed 25 m apart in a linear transect in random order at the edge of five pea fields in southern Alberta after crops were harvested. A second transect was positioned 25 m into the field so that traps formed a 2 × 8 grid. Trap types include: (a) a white Solo cup pitfall trap modified with mesh to exclude large bycatch; (b) white PVC pitfall traps with small or (c) large entrance holes; (d) yellow pan traps; (e) green Legget cone traps modified with hole size <2 mm; and (f) the cylindrical yellow sticky card trap. Also tested were the unmodified white Solo cup pitfall traps (Fig. 1a) and the unmodified green Legget cone traps (not pictured). Fig. 2. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2014. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were placed 25 m apart in a linear transect in random order at the edge of five pea fields in southern Alberta after crops were harvested. A second transect was positioned 25 m into the field so that traps formed a 2 × 8 grid. Trap types include: (a) a white Solo cup pitfall trap modified with mesh to exclude large bycatch; (b) white PVC pitfall traps with small or (c) large entrance holes; (d) yellow pan traps; (e) green Legget cone traps modified with hole size <2 mm; and (f) the cylindrical yellow sticky card trap. Also tested were the unmodified white Solo cup pitfall traps (Fig. 1a) and the unmodified green Legget cone traps (not pictured). In addition to trap type, the effect of trap position within the field was tested in 2014. Two transects each containing one trap of each of the 8 tested trap designs were positioned 25 m apart at each pea field. One transect was erected along the edge of each field and another 25 m into the field, so that the traps formed an 8 × 2 grid. These traps were placed in five pea fields post-harvest in mid-August and trap capture was checked every 2 weeks until mid-September. Trap capture was transported to the laboratory where PLW were identified and counted. In 2015, only three insect trap types were evaluated (Table 4): 1) the Solo cup pitfall trap (Fig. 1a); 2) a commercially available (Scotts Canada) box trap (Fig.3a) developed for monitoring wireworms (Vernon 2004); and 3) a commercially produced (Scotts Canada) Vernon pitfall trap (Fig. 3b) designed to capture wireworms (Vernon and van Herk 2014). The 15 cm × 15 cm × 4 cm box trap was lined with yellow sticky cards to capture insects. Two ramps leading into the box allow insect entry. Two, 1 mm holes were drilled into the lid of each box trap to attach semiochemical lures with wire. The Vernon pitfall traps consist of a brown lower cup (400 ml) which is set into the ground, a clear lining cup (200 ml) that is inserted into the lower cup and filled with propylene glycol, and a brown plastic top which snaps onto the bottom and excludes large bycatch with small plastic pegs. Two, 1 mm holes were drilled into the lid of each Vernon pitfall trap to attach semiochemical lures with wire. Structurally, the Vernon pitfall traps are very similar to the Solo cup pitfall trap, but with a slightly smaller capacity (200 ml vs 400 ml). Two of each type of trap were randomly placed 25 m apart on a linear transect at the edge of each pea field (for a total of 6 traps per transect). Traps were placed in three pea fields in mid-August and were serviced three times, until mid-September. Trap capture was transported to the laboratory where PLW were identified and counted. Fig. 3. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2015. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order along a linear transect at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include: (a) the Vernon ramp trap; and (b) the Vernon pitfall trap. Also tested in 2015 was the unmodified Solo cup pitfall trap (Fig. 1a). Fig. 3. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2015. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order along a linear transect at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include: (a) the Vernon ramp trap; and (b) the Vernon pitfall trap. Also tested in 2015 was the unmodified Solo cup pitfall trap (Fig. 1a). Statistical Analyses Separate generalized linear mixed effects models were used to analyze the effect of trap type on total PLW capture for all 3 years of experimentation. Models were constructed using the function lmer in the lme4 package (version 1.1–10) in R (version 3.1.3). Total PLW captured during the experiment was the dependent variable and trap type and position (2014 only) were specified as explanatory variables. In all models, site was specified as a random variable. Post-hoc Tukey’s multiple comparisons tests were performed on significant factors with more than one level using the function ghlt in the multcomp package (version 1.4–4) (R version 3.1.3). Results Semiochemical Lures: Dose and Release Device In the spring 2013 trapping period, the semiochemicals used to bait traps significantly impacted the season-long trap capture of PLW (χ2 = 131.15, df = 2, P < 0.001; Fig. 4). Traps baited with aggregation pheromone alone (Z-value = −10.34, P < 0.001) or in combination with host plant volatiles (Z-value = −11.45, P < 0.001) captured significantly more PLW than unbaited control traps. Traps baited with pheromone and host plant volatiles also captured significantly more PLW than traps baited with pheromone alone (Z-value = 2.52, P = 0.03). Similarly, in fall 2013, there was a significant effect of semiochemical lure on the season-long catch of PLW (χ2= 18.84, df = 2, P < 0.001; Fig. 4). Significantly more PLW were captured in traps baited with pheromone alone (Z-value = −2.12, P = 0.08) or pheromone with host plant volatiles (Z-value = −3.97, P < 0.001) than in unbaited control traps. More weevils were caught in traps baited with pheromone and host plant volatile lures than in traps baited with pheromone alone (Z-value = 2.94, P = 0.009) (Fig. 4). Fig. 4. View largeDownload slide Box plot of season-long capture of PLW in semiochemical-baited traps baited with different lures tested in spring and fall, 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Captures of weevils were pooled across pheromone dose and device size. Boxes marked with different capital and lowercase letters represent significantly different seasonal PLW captures at α = 0.05 and α = 0.10, respectively. Fig. 4. View largeDownload slide Box plot of season-long capture of PLW in semiochemical-baited traps baited with different lures tested in spring and fall, 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Captures of weevils were pooled across pheromone dose and device size. Boxes marked with different capital and lowercase letters represent significantly different seasonal PLW captures at α = 0.05 and α = 0.10, respectively. The 2013 data was also analyzed without the trap capture from the unbaited control traps. In the spring, neither pheromone dose (χ2 = 1.69, df = 1, P = 1.9) nor release device (χ2 = 0.40, df = 1, P = 0.4) affected PLW captures. In the fall, there was a trend toward increased PLW captures in traps baited with the lower dose of 21 mg of pheromone over traps baited with 42 mg pheromone (Z-value = 1.87, P = 0.06). Release device did not affect PLW captures (χ2 = 0.242, df = 1, P = 0.62) in the fall or interact with pheromone dose, or addition of host plant volatiles in the spring or fall. Trap capture from both spring and fall trapping periods was analyzed together in a single model in 2014. Trapping season significantly affected PLW capture through an interaction with pheromone dose (χ2 = 6.19, df = 2, P = 0.05). The interaction between season and pheromone dose was largely driven by the relative attractiveness of the low compared to the high dose lures at two sites in the spring that was less pronounced in the fall. In the spring, the low dose of pheromone tended to capture more PLW, but in the fall, the high dose of pheromone captured numerically more PLW. The presence of host plant volatiles significantly affected PLW captures through an interaction effect with season (χ2 = 8.14, df = 2, P = 0.02) and as a main effect (χ2 = 9.44, df = 2, P = 0.009). The addition of host plant volatiles to the pheromone lure increased PLW captured in the fall but not in the spring. A direct comparison of trap capture of in each type of baited trap in both seasons in 2014 showed that PLW captures were significantly affected by the semiochemical lure in both the spring (χ2 = 107.77, df = 8, P < 0.001) and the fall (χ2 = 68.52, df = 8, P < 0.001) (Fig. 5). All traps baited with either dose of pheromone with or without host volatiles captured more weevils than unbaited control traps or traps baited with host volatiles alone at either dose (Fig. 5). Fig. 5. View largeDownload slide Box plot of season-long capture of PLW in all semiochemical-baited traps tested in spring and fall of 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Comparisons among treatments were made in each season separately. Boxes marked with different capital letters represent significantly different seasonal PLW captures at α = 0.05. Fig. 5. View largeDownload slide Box plot of season-long capture of PLW in all semiochemical-baited traps tested in spring and fall of 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Comparisons among treatments were made in each season separately. Boxes marked with different capital letters represent significantly different seasonal PLW captures at α = 0.05. The proportion of male and female PLW caught in spring 2014 did not differ by semiochemical treatment (χ2 = 7.70, df = 4, P = 0.17). Binomial tests, however, performed to determine the ratio of male to female PLWs captured within each treatment found that the sex ratio sometimes differed from 1:1 (Fig. 6). Trap capture was male-biased in traps baited with the low pheromone and low host plant volatile dose lures (63% male, P < 0.001, n = 184), the low pheromone and high host plant volatile dose lures (65% male, P < 0.001, n = 221), the high pheromone dose lure (61% male, P = 0.05, n = 92), the high pheromone and low host plant volatile dose lures (58% male, P = 0.04, n = 154), and the high pheromone and high host plant volatile doses (66% male, P < 0.001, n = 119). Traps that lacked the pheromone lure, including the unbaited control trap and traps baited with either the low or high host plant volatile lures alone, captured few insects (n = 3, n = 1, n = 3, respectively). Traps baited with the low pheromone dose lure alone captured 209 PLWs in spring 2014, but trap catch was not significantly male- or female-biased (54% male, P = 0.27, n = 209) (Fig. 6). Fig. 6. View largeDownload slide Proportion of male and female PLW captured in semiochemical traps in 2014. Semiochemical lures are described in Table 2. Trap capture was separated by sex in each semiochemical trap and the proportion of males and females captured was compared with a two-sided binomial test within trap type. Significant differences from a 1:1 ratio of the proportion of male and female PLW captured within a single semiochemical trap treatment are denoted with “.” for α = 0.10, “*” for α = 0.05, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Numbers within bars on the graph denote the total number of male and female PLW captured in a given trap. Fig. 6. View largeDownload slide Proportion of male and female PLW captured in semiochemical traps in 2014. Semiochemical lures are described in Table 2. Trap capture was separated by sex in each semiochemical trap and the proportion of males and females captured was compared with a two-sided binomial test within trap type. Significant differences from a 1:1 ratio of the proportion of male and female PLW captured within a single semiochemical trap treatment are denoted with “.” for α = 0.10, “*” for α = 0.05, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Numbers within bars on the graph denote the total number of male and female PLW captured in a given trap. The proportion of male and female PLW caught in fall 2014 also did not differ with the semiochemical-baited trap (χ2 = 7.12, df = 7, P = 0.42). Binomial tests on PLW captured within each trap showed that sex ratio of PLW captured was not always 1:1 (Fig. 6). In fall 2014, the majority of traps did not display a significant sex-biased capture and no traps had a significantly male-biased capture (Fig. 6). Trap capture was female-biased in traps baited with the high dose of host plant volatile without pheromone (24% male, P = 0.05, n = 17). Blank traps were not included in the analysis for fall 2014 as PLW captures were low (n = 1). In the fall of 2014, 194 individuals or 15.8% of the captured PLW were suspected to have overwintered and belong to the parental generation. There was a marginal effect of semiochemical lure on the proportion of newly eclosed: overwintered male and female PLW captured in semiochemical traps (χ2 = 24.14, df = 15, P = 0.06). Proportions of newly eclosed to overwintered PLW within each trap type tested with Exact Proportion Tests sometimes differed by sex in a given semiochemical trap (Fig. 7). There was a greater proportion of males than females in the parental generation for weevils captured in traps baited with 1) low pheromone dose (χ2 = 5.47, df = 1, P = 0.02); 2) low pheromone dose and low host plant volatile dose (χ2 = 9.16, df = 1, P = 0.002); 3) low dose of pheromone and high host plant volatile dose (χ2 = 6.27, df = 1, P = 0.01); 3) high pheromone dose and low host plant volatile dose (χ2 = 17.58, df = 1, P < 0.0001); and 4) high pheromone dose and high host plant volatile dose (χ2 = 12.36, df = 1, P < 0.001). Traps baited with the high pheromone dose alone also followed this same trend (χ2 = 3.5, df = 1, P = 0.06). In unbaited traps or traps baited with only host plant volatile lures, the proportion of parental versus newly eclosed PLW did not differ between the sexes. PLW captures in these traps, however, were low overall. Fig. 7. View largeDownload slide Proportion of newly eclosed and overwintered male and female PLW captured in each semiochemical trap type tested in fall 2014. For each semiochemical-baited trap, a Two-Way Test of Equal Proportions was used to determine if the proportion of overwintered and newly eclosed PLW was similar between males and females. Significant differences between the proportion of newly eclosed male and female PLWs are denoted with “.” for α = 0.10, “*” for α = 0.05, “**” for α = 0.01, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Fig. 7. View largeDownload slide Proportion of newly eclosed and overwintered male and female PLW captured in each semiochemical trap type tested in fall 2014. For each semiochemical-baited trap, a Two-Way Test of Equal Proportions was used to determine if the proportion of overwintered and newly eclosed PLW was similar between males and females. Significant differences between the proportion of newly eclosed male and female PLWs are denoted with “.” for α = 0.10, “*” for α = 0.05, “**” for α = 0.01, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. In 2014, 98% of the 998 Sitona specimens captured in semiochemical-baited traps were identified as PLW (S. lineatus). Only 12 individuals were identified as S. cylindricollis, the sweet clover weevil. Trap Type There was a significant difference between the number of PLWs captured in the different trap types tested in 2013 (χ2 = 99.31, df = 8, P < 0.0001) (Fig. 8). The Solo cup pitfall traps captured significantly more PLW than any of the other traps tested in 2013 (P < 0.0001). The remaining trap types captured a similar (negligible) number of PLW. In addition, Unitraps captured a high level of Hymenopteran bycatch. In 2014, there was also a significant effect of trap type on the number of captured PLW (χ2 = 125.84, df = 7, P < 0.001). The Solo pitfall cup, the Solo pitfall cup modified with wire mesh to exclude large bycatch, and the yellow pan trap all successfully captured PLW (Fig. 9). The remaining traps captured few PLW. There was no effect of trap position in the field on the capture of PLW as traps placed on the edge of the field captured a similar number of PLW as those placed on a parallel transect 25 m into the field (χ2 = 0.063, df = 1, P = 0.802). A low number of PLW were captured in the trap type experiment in 2015 (n = 5) that precluded statistical analysis. Fig. 8. View largeDownload slide Box plot of PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 8 August to 6 September 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Trap capture of PLW in the Solo cup pitfall trap was greater than in all other trap types tested. Fig. 8. View largeDownload slide Box plot of PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 8 August to 6 September 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Trap capture of PLW in the Solo cup pitfall trap was greater than in all other trap types tested. Fig. 9. View largeDownload slide Box plot PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 7 August to 15 September, 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Fig. 9. View largeDownload slide Box plot PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 7 August to 15 September, 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Discussion Semiochemical Lures: Dose and Release Device After comparing various doses and combinations of the PLW pheromone and host plant volatiles, the best lure tested was 21 mg of PLW pheromone, 4-methyl-3,5-heptanedione, in a 250 μl Eppendorf tube. A combined lure of 21 mg of PLW pheromone in a 250 μl Eppendorf tube with host volatile lures (21 mg of (Z)-3-hexenyl acetate in a 250 μl Eppendorf tube, 34 mg of (Z)-3-hexenol in a 250 μl Eppendorf tube, and three 250 μl Eppendorf tubes, each with 50 mg of linalool) was at least equally as attractive and sometimes more attractive than the pheromone lure alone. The added efficacy of the combined lure over the pheromone lure alone was not consistent enough to justify future effort and expense of inclusion of the host plant volatiles as part of a semiochemical lure. Evaluation of various ground-based and aerial insect traps found that the most successful trap type is a wet pitfall trap, which is easily constructed from Solo cups, Choroplast, and nails. Semiochemical-baited traps successfully attracted and retained PLW adults in both the spring and fall, corroborating the findings of Evenden et al. (2016). Capture of PLW in baited traps in the fall allows assessment of pre-overwintering populations that could assist producers in planning pest management tactics including whether to plant insecticide-treated pea seed the following spring. Trap capture in semiochemical-baited traps can vary with semiochemical dose (Byers 2013) because the active space of the signal changes with dose (Byers 2008) causing the signal to be variably sensed by insects in space (Dolzer et al. 2003). The insect may also show plasticity in response to signals released from lures containing different pheromone doses (Roelofs 1978). PLWs, however, did not respond differently to the two pheromone doses tested in the semiochemical-baited traps tested in 2013 and 2014. Because PLW captures were similar between both release devices and doses of pheromone tested, the best lure would be the least expensive to produce: 21 mg of pheromone in a 250 μl Eppendorf tube. Blight et al. (1984) found that more PLW were captured in traps baited with a 21 mg pheromone dose released from a polythene vial as compared to a 5 mg dose. PLW in the current study did not respond differently to the different pheromone doses used to bait traps. The release rate of 0.3 mg/day of pheromone from the 21 mg dose in a 250 μl Eppendorf tube (Table 3) is similar to the stable attractive release rate tested in a small plot push-pull study of PLW in the United Kingdom (Smart et al. 1994). Response to a broad range of semiochemical doses may relate to the aggregating mating behavior of PLW, as aggregations may vary from a few to a few thousand males and females. It would therefore be adaptive for PLW to respond to a wide range of pheromone release rates. Similarly, attraction of plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) weevils to trap trees at the perimeter of apple orchards was not enhanced by a 5-fold increase in pheromone dose (Leskey et al. 2014). The red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) exhibits a dose-dependent response to male-produced aggregation pheromone at low release rates, but this relationship breaks down at high release rates (Vacas et al. 2013). If the pheromone signal increases with weevil aggregation size, enhanced response to high release rates would be advantageous only to a certain point, depending on the optimal aggregation size. This may be similar to the behavior of granary weevils, Sitophilus granaries L. (Coleoptera: Curculionidae) that are attracted to low concentrations but arrested to high concentrations of aggregation pheromone (Plarre 1994). Electrophysiological responses of antennae of male and female Sitona discoideus Gyllenhål to pheromone presented at medium (100 µg) and high (1,000 µg) doses was significantly greater than that to low doses (0.1–10 µg) (Unelius et al. 2013) suggesting that Sitona weevils are capable of processing strong pheromone signals. Future studies which test a broader range of PLW pheromone release rates should be conducted to determine if PLW behavioral response is dose-dependent at lower release rates or if high doses repel or arrest PLW. In this study, PLW response to pheromone was enhanced by the presence of host plant volatiles in three of the four trapping periods. Blight et al. (1984) and Evenden et al. (2016) also found that PLW response to pheromone was sometimes synergized by the presence of host plant volatiles. Both doses of host plant volatile lures tested here were not attractive alone. This is in contrast to laboratory studies that showed PLW orient to plant volatile compounds in an olfactometer assay (Landon et al. 1997) and could suggest that natural host cues are masking the host plant volatile lures in our experiments. Similarly, Anthonomus rubi Herbst (Coleoptera: Curculionidae), is weakly attracted to traps baited with pheromone, exhibits a synergistic response to traps baited with pheromone and host plant volatiles, but does not respond to traps baited with host plant volatiles alone (Wibe et al. 2014). Response by the cotton boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), to pheromone is enhanced by host plant volatiles (Dickens 1989). A synergistic effect of host plant volatiles with pheromone would be expected to occur if calling or mating behavior occurs in association with the host plant (Landolt 1997). The PLW orient to reproductive host plants prior to mating and producing eggs (Vankosky et al. 2009) and males release pheromone while feeding on the host plant (Blight et al. 1984). PLWs consistently respond to pheromone lures in both the spring and fall. Host plant volatiles enhance response to pheromone, primarily in the fall which may be due to a scarcity of host plants at this time of year that makes the semiochemical signal from the trap more apparent. In the fall, PLW may also be better tuned to respond to host plant cues as they need to find plants after the fall migration away from pea fields to feed before overwintering (Jackson 1920, Landon et al.1997). The olfactory response of other insects can be influenced by background volatiles. A volatile compound released by strawberry flowers enhances the response of A. rubi to its aggregation pheromone throughout the growing season (Wibe et al. 2014) when the plants in the background are both in vegetative and flowering states. Despite the presence of olfactory neurons sensitive to the strawberry leaf volatile (-)-germacrene D on the antennae of A. rubi, this compound did not synergize weevil response to pheromone traps positioned in strawberry fields (Wibe et al. 2014). During the spring trapping period, the pea crop is green and edible to PLW (Jackson 1920, Landon et al. 1995). As pea plants enter the flowering or bud stages, relative emission of (Z)-3-hexenol and (Z)-3-hexenyl acetate decreases compared to other volatiles (Thöming et al. 2014). By the fall, PLW are not attracted to desiccated pea plants (Landon et al. 1995) but likely still use host volatiles in the fall to orient to plants after migration for feeding before overwintering. In the current study, the sex ratio of weevils captured in semiochemical-baited traps did not vary statistically among the various semiochemical-baited traps. The sex ratio within individual trap treatments, however, sometimes varied from an expected 1:1 ratio and this difference was dependent on the season of trapping. PLW captures in spring 2014 were predominantly male-biased. In fall 2014, traps captured weevils in even sex ratios except for those baited with a high release rate of host plant volatiles in which capture was female-biased. This may be because female PLW need to feed before overwintering to maximize egg production (Schotzko and O’Keeffe 1986). Blight et al. 1984) also reported male-biased captures of PLW in semiochemical-baited traps in the spring. Interestingly, Evenden et al. (2016) reported female-biased PLW captures in semiochemical-baited traps in the spring and an even number of males and females in the fall. Both male-biased and female-biased PLW captures in semiochemical-baited traps were also reported to vary by crop (Nielsen and Jensen 1993). It is also possible that PLW sex ratios vary with population density, if sex-specific costs and benefits change with density, as occurs in other insects such as the sandfly, Lutzomyia longipalpis, França (Diptera: Phlebotominae) (Jones and Quinnell 2002). Laboratory feeding experiments by Schotzko and O’Keeffe (1988) found that female PLW have greater longevity than male PLW when maintained in single reproductive pairs, but male and female PLW have similar longevity when maintained in groups of 13 reproductive pairs, indicating that PLW density may affect PLW mortality in a sex-specific way. This is supported in our study by the finding of relatively even sex ratios of newly eclosed weevils in the fall but uneven sex ratios in the spring when mortality agents have had more time to act. Future studies should determine if PLW sex ratios in pea fields are density dependent and if PLW sex ratios in semiochemical traps mirror PLW sex ratios in surrounding crops. Future studies should investigate state-specific plasticity of PLW response to semiochemicals. Our trap catch data illustrate that some PLW that overwinter remain active throughout the following season and are sensitive to semiochemical cues as they are captured in semiochemical-baited traps the following fall. Similarly, weevils from the spring and summer generation of A. rubi responded to semiochemical-baited traps in northern Europe (Wibe et al. 2014). In general, more overwintered male PLW were captured in traps the following fall than overwintered females. Landon et al. (1995) tested the response of male and female PLW to pea volatiles in the laboratory at various times of year and found that weevil response was decreased only in the winter and there was no effect of PLW sex on response to plant volatiles. The closely related clover root weevil, Sitona lepidus Gyllenhål (Park et al. 2013) and S. discoideus (Unelius et al. 2013) exhibit sexual dimorphism in the expression of olfactory receptor neurons. Sitona discoideus also exhibits sexual dimorphism in electrophysiological response to the various enatiomers of their pheromone 5-hydroxy-4-methyl-3-heptanone (Unelius et al. 2013). The pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), exhibits sexual dimorphism in response to semiochemicals as male response to pheromone is synergized with the addition of host plant volatiles, but female response to pheromone is not (Muniz-Merino et al. 2014). Both sexes of PLW respond to pheromone in spring and fall in our trapping studies and those of Evenden et al. (2016), but little is known about the effect of season or sex on the neurophysiological response to pheromone. The semiochemical traps tested here were specific for PLW. A few specimens of the sweetclover weevil, Sitona cylindricollis were captured in 2014. The aggregation pheromone of S. cylindricollis likely overlaps slightly with that of the PLW and other Sitona species. Tóth et al. (1998) captured multiple Sitona species in traps baited with 4-methyl-3,5-heptanedione in Hungary. Information on the specific aggregation pheromone identity of various Sitona species is limited, but S. discoideus utilizes a two-component blend: 4-methyl-3,5-heptanedione and (4S,5S)-5-hydroxy-4-methyl-3-heptanone as an aggregation pheromone (Unelius et al. 2013). Sitona lepidus also uses these components in its aggregation pheromone but only males are responsive to 4-methyl-3,5-heptanedione (Park et al. 2013). Sitona weevils utilize legumes as host plants (Jackson 1920) and it is likely that there is overlap in attractive host plant volatiles. Besides PLW, the Sitona species present in the Prairie Provinces are S. cylindricollis, S. flavescens, S. hispidulus, S. lineellus, and S. californius (Bright 1994) and their chemical ecology is virtually unknown. Knowledge on the chemical ecology of the non-Sitona weevil bycatch is also limited. Non-Sitona bycatch included weevils in Hypera, Ceutorhynchus, Otiorhynchus, and Perapion. These weevils may also have similar pheromones to the PLW. The alfalfa weevil, Hypera postica (Gyllenhål), was captured in significant numbers in traps targeting PLW in the Pacific Northwest, United States (Quinn et al. 1999). Nontarget weevil species might also be attracted to the host plant volatiles used to bait the traps tested here. For example, Otiorhynchus sulcatus is responsive to linalool and (Z)-3-hexenol (van Tol and Visser 2002). Despite some non-PLW bycatch, the overall specificity of these semiochemical-baited traps is high. Trap Type The pitfall trap was the most successful trap type tested for attraction and retention of PLW in the fall trapping period across three field seasons. As we conducted the trap type test in the fall, when less than 10% of newly emerged adults are estimated to leave the crop by flight (Hamon et al. 1987) it is not surprising that a ground-based trap was most effective. The pitfall trap constructed from Solo cups consistently captured the most PLW, but it is not the most user-friendly trap. The addition of a ring of wire mesh around the pitfall cup does not hinder PLW captures and may successfully exclude some of the large bycatch, such as small mammals, amphibians, or large carabid beetles, captured in this study. Vertebrates are common bycatch in pitfall traps, and there can be a trade-off between the utilization of pitfall traps for insect monitoring and the loss of vertebrates and arthropod predators, such as carabids (Thompson and Thompson 2008). Lemieux and Lindgren (1999) found that the addition of a lid to open-top pitfall traps reduced vertebrate bycatch. By similarly reducing the entrance size, the addition of mesh to covered pitfall traps is expected to also reduce vertebrate bycatch, although this was not statistically tested in this study. The Vernon pitfall trap is expected to be a suitable trap for capturing PLW. Unfortunately, an overall low number of PLW were captured in the 2015 trapping experiment, and we were unable to demonstrate that the Vernon pitfall trap successfully captures PLW in the field. Similar to the pitfall trap modified with mesh, the Vernon pitfall trap includes pegs that limit the entrance size. The Vernon pitfall trap warrants further testing for PLW in the future. The Vernon pitfall traps tested here were brown, but yellow or green traps are also available and may be more visually attractive to PLW (Reddy et al. 2011). Yellow pan traps also successfully attracted and retained PLW in similar numbers to the two pitfall traps tested in 2014. Yellow pan traps are used in canola fields in the Prairie Provinces to monitor the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) (Fox and Dosdall 2003, Blake et al. 2010) and Delia spp. (Diptera: Anthomyiidae) (Broatch and Vernon 1997). Yellow pan traps positioned in pea fields in this study, however, were more susceptible than pitfall traps to evaporation of propylene glycol and unintended bycatch. The remaining traps tested did not successfully capture PLW in the fall trapping period and should not be adopted as traps for a semiochemical-based monitoring system. Traps placed above the ground may be more successful in the spring trapping period as weevils fly to locate pea crops in the spring and then disperse throughout the field by walking (Hamon et al. 1987). Unitraps placed 1 m above the ground did not capture PLW in the fall and also had a high level of hymenopteran bycatch as previously reported in other systems (Mori and Evenden 2013) that could result in removal of pollinators from the cropping area. The various yellow sticky card traps tested in our study rarely captured PLW and were difficult to handle. In contrast, unbaited sticky traps captured PLW during peak flight in the spring in studies in Europe (Fisher and O’Keeffe 1979, Nielsen and Jensen 1993). Semiochemical-baited Legget cone traps have been used to monitor PLW during the spring migration in Europe (Blight et al.1984, Blight and Wadhams 1987, Nielsen and Jensen 1993, Smart et al. 1994), but were unsuccessful in the spring in the Prairie Provinces (Evenden et al. 2016). Legget traps and other hand-constructed cone traps were also unsuccessful in the current study, even when modified to prevent escape. Future experiments testing semiochemical-baited trap types should assess aerial traps against ground-based traps during the spring migration but focus on pitfall traps during the fall trapping period. The Solo pitfall trap is inexpensive and easy to make, but the Vernon pitfall trap is likely as effective and more user-friendly. The experiments reported here support the potential for semiochemical-based monitoring of PLW in the Canadian Prairie Provinces. All of our experiments were performed in Alberta, where the PLW is established but similar results are expected in the other Prairie Provinces. These experiments have identified 21 mg of 4-methyl-3,5-heptanedione released from a 250 μl Eppendorf tube as a reliable lure. The addition of host plant volatiles (21 mg of (Z)-3-hexenyl acetate in a 250 μl tube + 34 mg of (Z)-3-hexenol in a 250 μl Eppendorf tube, and three 250 μl tubes, each with 50 mg of linalool) sometimes enhanced PLW captures in pheromone-based traps, especially in the fall. The next step in the development of this semiochemical-based trapping system is to identify if PLW captures in traps are related to PLW populations or to PLW-induced damage in the field. This system will be especially useful for pulse producers if a predictive model for PLW activity can be developed. A predictive model based on fall trap captures would be particularly useful for Canadian pea producers, as it would allow producers to make informed decisions on the use of insecticide-treated pea seed. Acknowledgments The authors thank Shelley Barkley and Scott Meers, Alberta Agriculture and Forestry, for assistance with site location and establishment. Lawrence Vanderark and J.-P. 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Evaluation of Semiochemical-Baited Traps for Monitoring the Pea Leaf Weevil, Sitona lineatus (Coleoptera: Curculionidae) in Field Pea Crops

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Abstract

Abstract The pea leaf weevil (PLW), Sitona lineatus L., is a pest of field pea (Pisum sativum L.) and faba bean (Vicia faba L.) that recently invaded the Canadian Prairie Provinces. Although most damage is done by larvae that feed on root nodules, adults are easier to monitor than larvae. Both male and female weevils respond to a male-produced aggregation pheromone and to volatiles released by host plants. The current study tests the attractiveness of synthetic aggregation pheromone, 4-methyl-3,5-heptanedione, and host plant volatiles linalool, (Z)-3-hexenol, and (Z)-3-hexenyl acetate to PLWs in spring when weevils are reproductively active and in fall when weevils seek overwintering sites. Different combinations of semiochemical lures at various doses, released from a variety of devices were tested in pitfall traps. Semiochemical-baited traps captured both male and female weevils in both seasons but the sex ratio varied with season. Weevils did not respond in a dose-dependent manner to pheromone, as all pheromone lures were equally attractive. Pheromone release rate was determined by the release device and not the pheromone dose in the lure. The addition of plant volatiles sometimes increased weevil captures but plant volatiles alone were not attractive to PLW adults. An additional study tested the effect of trap type on weevil capture. Of the 12 different trap types tested, pheromone-baited pitfall traps were most successful in attracting and retaining weevils. Bycatch of other Sitona species was limited to a few specimens of the sweet clover weevil, Sitona cylindricollis Fahraeus. The pea leaf weevil (PLW), Sitona lineatus L. (Coleoptera: Curculionidae) is an invasive pest of field pea (Pisum sativum L., Fabaceae) and faba bean (Vicia faba L., Fabaceae) that is expanding its range in the Canadian Prairie Provinces (Vankosky et al. 2009). PLW was first reported in the Prairie Provinces in 1995 near Swift Current, Saskatchewan (Pepper 1999) and in 1997 near Lethbridge, Alberta (Coles et al. 2008). Climate projection models (Olfert et al. 2012) predict continued expansion of PLW into the Prairie Provinces as an effect of global warming. Field pea is an important pulse crop in Canada, with an average of 2.3 million hectares seeded or 4.5–5 million tonnes of peas produced per year (Pulse Canada 2016). Canadian pea and the small acreage of faba bean crops in the Prairie Provinces are at risk to PLW damage. PLWs are univoltine and overwinter as adults (Jackson 1920). Adult weevils display two periods of activity per year when weevils are in different physiological states. Before overwintering, weevils are sexually immature and seek overwintering sites in shelter belts or perennial legumes. In the spring, PLW seek mates and migrate to reproductive hosts for feeding, mating, and egg production. During both periods of adult activity, adult weevils feed aboveground on legumes, causing characteristic feeding notches at the margins of leaves (Jackson 1920). While sexually immature in the fall, PLW adults feed on leaves of most legumes but prefer to feed on their reproductive host plants, pea or faba beans, when mating in the spring (Fisher and O’Keeffe 1979, Landon et al. 1995, Landon et al. 1997). An 11% loss in photosynthetic area of pea seedlings can result from heavy adult PLW damage (Cárcamo et al. 2012). Adult foliar feeding is temperature dependent, with feeding activity highest between 12°C and 21°C (Landon et al. 1995). Damage from larval feeding on root nodules is considered more important than adult foliar feeding and can reduce yields by decreasing nitrogen availability (Nielsen 1990, Williams et al. 1995, Vankosky et al. 2009, Cárcamo et al. 2015). The current method of estimating PLW activity in the Prairie Provinces is to survey adult feeding damage in pea crops (Saskatchewan Ministry of Agriculture 2016, Alberta Agriculture and Forestry 2017). This approach is labor intensive and variable as adult feeding is temperature dependent (Landon et al. 1995). As PLW aggregation and host location behavior is tied to olfaction, semiochemical-baited traps are a possible alternative tactic to monitor adult PLW populations (Vankosky et al. 2009, Evenden et al. 2016). A male-produced aggregation pheromone, 4-methyl-3,5-heptandione (Blight et al. 1984) attracts both male and female PLW adults in the spring (Blight et al. 1984, Nielsen and Jensen 1993, Quinn et al. 1999, Evenden et al. 2016) and fall (Evenden et al. 2016). PLW adults also use host plant volatiles to locate suitable host plants (Blight et al. 1984, Landon et al. 1995, Landon et al. 1997) and are responsive to these cues during both periods of adult activity but not during the winter (Landon et al. 1997). Exploitation of these semiochemicals as artificial lures in insect traps could be a useful tool for monitoring the PLW range expansion in the Prairie Provinces (Vankosky et al. 2009, Evenden et al. 2016). Synthetic copies of the male aggregation pheromone in combination with volatiles released from faba beans ((Z)-3-hexenol, (Z)-3-hexenyl acetate, and linalool) attract PLW (Blight et al. 1984, Evenden et al. 2016). Semiochemical-baited cone traps have been successfully used to monitor PLW during the spring migration in faba bean crops in Denmark (Nielsen and Jensen 1993) and in North America (Quinn et al. 1999). Evenden et al. (2016) were the first to show that adult PLW respond to semiochemical-baited traps in both the spring and fall activity periods in studies conducted in the Canadian Prairie Provinces. Although studies using cone traps to capture PLW in Europe were successful (Blight et al. 1984, Blight and Wadhams 1987, Nielsen and Jensen 1993), cone traps did not retain attracted weevils in Alberta (Evenden et al. 2016). Besides the attractiveness of the semiochemical lure, the type, color, and placement of an insect trap contribute to its effectiveness as a monitoring tool (Reddy et al. 2011). The objective of this research was to develop a semiochemical-baited trap to monitor established and expanding populations of PLW in the Prairie Provinces. A successful semiochemical-baited trap will reliably capture PLW, be easy to use and cost-effective. In this study, various doses of semiochemicals released from a variety of devices are tested to develop an appropriate semiochemical lure for PLW. Various types of traps are also tested in an attempt to find an effective, efficient, and user-friendly trap to adopt for a semioochemical-based monitoring system that can delineate the range expansion of this pest in the Prairie Provinces. Materials and methods Semiochemical Lures: Dose and Release Device A series of field experiments was performed in 2013 and 2014 to test the attraction of PLW adults to various semiochemical lures that consisted of the PLW aggregation pheromone, with or without various host plant volatiles (Tables 1–3). Lures tested in 2013 compared two different doses of pheromone in two types of Eppendorf tube release devices (250 and 400 µl) alone and in combination with host volatile lures. Pheromone doses tested were 21 mg, a dose that was previously shown to attract PLW (Blight et al. 1984, Nielsen and Jensen 1993, Evenden et al. 2016), and a higher dose of 42 mg. Host volatile lures tested were those developed by Blight et al. 1984 and previously tested by Evenden et al. (2016) (Table 1). In 2014 (Table 2), different devices releasing host plant volatiles were tested in combination with the aggregation pheromone. Release rates of lures tested in both years are shown in Table 3. Table 1. Composition of semiochemical treatments tested for attractiveness to PLW adults in spring (8 May–19 June) and fall (31 July–13 September) 2013 Treatment  Pheromone lure composition  Host volatile lure composition  Pheromonea dose (mg)  Pheromone release device  (Z)-3-hexenyl acetate dose (mg) in 250 μl Eppendorf  (Z)-3-hexenol dose (mg) in 250 μl Eppendorf  Linalool dose (mg) in 250 μl Eppendorf  1  21  250 μl Eppendorf  0  0  0  2  21  250 μl Eppendorf  21  34  3 x 50  3  21  400 μl Eppendorf  0  0  0  4  21  400 μl Eppendorf  21  34  3 x 50  5  42  250 μl Eppendorf  0  0  0  6  42  250 μl Eppendorf  21  34  3 x 50  7  42  400 μl Eppendorf  0  0  0  8  42  400 μl Eppendorf  21  34  3 x 50  9  0    0  0  0  Treatment  Pheromone lure composition  Host volatile lure composition  Pheromonea dose (mg)  Pheromone release device  (Z)-3-hexenyl acetate dose (mg) in 250 μl Eppendorf  (Z)-3-hexenol dose (mg) in 250 μl Eppendorf  Linalool dose (mg) in 250 μl Eppendorf  1  21  250 μl Eppendorf  0  0  0  2  21  250 μl Eppendorf  21  34  3 x 50  3  21  400 μl Eppendorf  0  0  0  4  21  400 μl Eppendorf  21  34  3 x 50  5  42  250 μl Eppendorf  0  0  0  6  42  250 μl Eppendorf  21  34  3 x 50  7  42  400 μl Eppendorf  0  0  0  8  42  400 μl Eppendorf  21  34  3 x 50  9  0    0  0  0  aPea leaf weevil pheromone: 4-methyl-3,5-heptanedione. View Large Table 2. Composition of semiochemical treatments tested for attractiveness to PLW adults in spring (30 April–19 June) and fall (5 August–16 September) 2014 Treatment  Chemical lure composition per treatment  Host volatile release device  Pheromonea dose (mg) in 250 μl Eppendorf tube  (Z)-3-hexenyl acetate  (Z)-3-hexenol  Linalool  1  0  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  2  21  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  3  42  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  4  0  700 μl  700 μl  200 μl  Bubble cap  5  21  700 μl  700 μl  200 μl  Bubble cap  6  42  700 μl  700 μl  200 μl  Bubble cap  7  21  0  0  0  -  8  42  0  0  0  -  9  0  0  0  0  -  Treatment  Chemical lure composition per treatment  Host volatile release device  Pheromonea dose (mg) in 250 μl Eppendorf tube  (Z)-3-hexenyl acetate  (Z)-3-hexenol  Linalool  1  0  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  2  21  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  3  42  21 mg  34 mg  3 × 50 mg  250 μl Eppendorf  4  0  700 μl  700 μl  200 μl  Bubble cap  5  21  700 μl  700 μl  200 μl  Bubble cap  6  42  700 μl  700 μl  200 μl  Bubble cap  7  21  0  0  0  -  8  42  0  0  0  -  9  0  0  0  0  -  aPea leaf weevil pheromone: 4-methyl-3,5-heptanedione. View Large Table 3. Release ratesa of semiochemical lures tested in 2013 and 2014 Semiochemical  Dose  Release device  Release rate (mg/day) @ 20°C  Release rate (mg/day) @ 30°C  4-methyl-3,5-heptanedione  21 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  42 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  21 mg  400 μl Eppendorf  0.2  0.5  4-methyl-3,5-heptanedione  42 mg  400 μl Eppendorf  0.2  0.5  (Z)-3-hexenyl acetate  21 mg  250 μl Eppendorf  0.35  1.6  (Z)-3-hexenyl acetate  700 μl  Bubble cap  13  Not tested  (Z)-3-hexenol  34 mg  250 μl Eppendorf  0.15  0.28  (Z)-3-hexenol  700 μl  Bubble cap  3.7  17  Linalool  50 mg  250 μl Eppendorf  Not detected  0.04  Linalool  200 μl  Bubble cap  4  Not tested  Semiochemical  Dose  Release device  Release rate (mg/day) @ 20°C  Release rate (mg/day) @ 30°C  4-methyl-3,5-heptanedione  21 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  42 mg  250 μl Eppendorf  0.03  0.18  4-methyl-3,5-heptanedione  21 mg  400 μl Eppendorf  0.2  0.5  4-methyl-3,5-heptanedione  42 mg  400 μl Eppendorf  0.2  0.5  (Z)-3-hexenyl acetate  21 mg  250 μl Eppendorf  0.35  1.6  (Z)-3-hexenyl acetate  700 μl  Bubble cap  13  Not tested  (Z)-3-hexenol  34 mg  250 μl Eppendorf  0.15  0.28  (Z)-3-hexenol  700 μl  Bubble cap  3.7  17  Linalool  50 mg  250 μl Eppendorf  Not detected  0.04  Linalool  200 μl  Bubble cap  4  Not tested  aRelease rates were determined gravimetrically by the semiochemical supplier: Scotts Canada. View Large The PLW aggregation pheromone, 4-methyl-3,5-heptanedione, was synthesized by collaborators at Scotts Canada, (Delta, BC, Canada) (Evenden et al. 2016) and dispensed into various release devices depending on the experiment. The bean volatiles tested were those identified previously as released from faba bean shoots: (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, and linalool (Blight et al. 1984). Commercial sources of the bean volatiles ((Z)-3-hexen-1-yl acetate (Sigma Aldrich, St. Louis, MO); (Z)-3-hexen-1-ol (Bedoukian Research, Danbury, CT); and linalool (Lancaster, Ward Hill, MA) were used to formulate the lures at Scotts Canada. Lures were shipped in refrigerated containers to the University of Alberta and stored at 4°C before transport to the field in refrigerated containers and at −20°C for longer-term storage between trapping experiments. At each field site (n = 9–14) in southern Alberta, lures were positioned in Solo cup pitfall traps that consisted of two 473 ml plastic cups (Solo, Lakeforest, IL). The rim of one cup was trimmed off at the 414 ml fill line and placed as an insert in an intact cup for easy removal at trap service. Cups were positioned in the ground so that the top of the intact cup was flush with the soil surface. Pitfall traps were filled halfway with propylene glycol (Prestone Plumbing Antifreeze, Honeywell Consumer Products Group, Danbury, CT) to preserve captured insects. Propylene glycol was replenished at each trap check. Lures were secured with wire to a 15 × 15 cm piece of white plastic Coroplast (Home Hardware, Edmonton, AB, Canada) that was positioned above each trap and secured into the ground with four 10-cm nails. The white Coroplast also served as a canopy to protect the trap from rain and evaporation (Fig. 1a). Traps were positioned 25 m apart in random order along a linear transect 1 m from the edge of pea fields at each site. Sites were located >1 km apart to ensure independence of weevil populations. Although it is not known how far PLW can fly, dispersal to pea fields in the spring has been described as a migratory flight (Fisher and O’Keefe 1979). Once weevils arrive in a reproductive host crop following spring migration, dispersal occurs by walking (Hamon et al. 1987).Experiments were performed throughout the adult weevil activity period in the spring and fall of 2013 and 2014. Traps were placed in the field within 5-days post-seeding in mid-May and were checked every 5–8 days for 4–6 weeks in both years. Semiochemical lures were replaced and the trap order was re-randomized at the beginning of the fall activity period in early (2013) to mid-August (2014) and were checked weekly until the end of adult activity in both years. Fig. 1. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2013. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include (a) a white Solo cup pitfall trap; (b) ground-based, hand-constructed yellow cone trap; (c) hand-constructed yellow cone trap placed 1 m above the ground on a rebar stake; (d) hand-constructed yellow cone trap placed 0.6 m above the ground on a yellow pyramid; (e) hand-constructed yellow bucket trap; and (f) green unitrap. Also tested but not shown here were yellow unitraps, multicolored unitraps and yellow sticky cards (Table 4). Fig. 1. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2013. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include (a) a white Solo cup pitfall trap; (b) ground-based, hand-constructed yellow cone trap; (c) hand-constructed yellow cone trap placed 1 m above the ground on a rebar stake; (d) hand-constructed yellow cone trap placed 0.6 m above the ground on a yellow pyramid; (e) hand-constructed yellow bucket trap; and (f) green unitrap. Also tested but not shown here were yellow unitraps, multicolored unitraps and yellow sticky cards (Table 4). Weevils were removed from propylene glycol, and the number of PLW in each trap was recorded by sex. In 2014, PLW captured in the fall trapping period were further separated into overwintered or newly eclosed based on wing morphology. Newly eclosed PLW had intact scales and flexible elytra whereas overwintered weevils had heavily worn scales, rigid or fused elytra, and some had evidence of previous mating (damaged pygidia in females or everted aedeagi in males). In 2014, nontarget Curculionidae captured in semiochemical traps were also collected and identified to genus (Otiorhynchus, Ceutorhynchus, Perapion, Hypera, and Sitona) using the keys in Bright and Bouchard (2008). Statistical Analyses All analyses were conducted using the statistical program R (version 3.1.3). To determine which semiochemical lures were most attractive to PLW, trap capture was analyzed using generalized linear mixed models with negative binomial error distributions created using the function glmer.nb in the lme4 package (version 1.1–10). Models were selected based on best fit by comparing AIC values, –log likelihood values, and the distribution of residuals. For the statistical analyses, the total number of PLWs captured per trap in each season (i.e., the sum of PLW captured each week) was used as a response variable, with (1|Site) as a blocking term. Repeated measures models with a (Week|Site) random term were also built, but season total models with (1|Site) were selected based on better fit. Models were first constructed with all possible interaction terms included and nonsignificant interaction terms were subsequently removed in a step-wise manner. Relevant P values were calculated using the ANOVA function in the package car (version 2.0–25). Post-hoc Tukey’s multiple comparisons tests were performed on significant factors with more than one level using the function ghlt in the package multcomp (version 1.4–4). The effect of seasonality on PLW trap capture was tested only in 2014. To determine if traps were differentially attractive to male and female PLW, total trap capture in each baited trap in 2014 was subjected to a Two-Sided Exact Binomial Test using the function binom.test in the package stats which determined the proportion of males to females captured in each semiochemical-baited trap. To compare the sex ratio of trap capture within a given season, Chi-Square Contingency Table Analyses were performed using the function chisq.test in the package stats (2 × 6 table for spring 2014; 2 × 8 table for fall 2014). For the analysis of sex ratio in spring 2014, the following treatments were excluded due to low PLW captures: blank traps (n = 3), traps baited with low (n = 2), or high dose (n = 3) host plant volatile lures without pheromone. For the fall 2014 sex ratio analysis, capture in blank traps was excluded due to low PLW capture (n = 1). To compare the proportion of newly eclosed to overwintered, male or female PLW within each semiochemical-baited trap, Two-Way Tests of Equal Proportions were performed using the function prop.test in the package stats (version 3.1.3). The number of male and female PLW that were newly eclosed or overwintered PLW were compared among semiochemical traps with a 6 × 4 chi-square contingency table analysis. PLW captures were again excluded from unbaited traps (n = 1) or in traps baited with either low host plant volatile lure (n = 18) or high host plant volatile lure (n = 17) without pheromone (n = 17) due to low PLW captures in these traps. Trap Type To determine if a trap design more suitable than the Solo cup pitfall trap (Evenden et al. 2016) could be developed to attract and retain PLW in Alberta, various trap types were evaluated in the fall trapping period of 2013, 2014, and 2015. In each of these experiments, the various types of traps tested (Figs. 1–3; Table 4) were baited with a low dose (21 mg) of pheromone released from a 250 µl Eppendorf tube and positioned in pea fields in August of each year, after the pea crop was harvested at each site when weevils are dispersing to feed prior to overwintering. Table 4. Trap types tested in 2013, 2014, and 2015 Year  Trap typea  Placement  Trap source  2013  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Yellow Unitrap, 1 m above the ground on rebar stake  Above crop  Scotts Canada  Green Unitrap, 1 m above the ground on rebar stake  Above crop  AgBio Inc., Westminister, CO  Multicoloured Unitrap, 1 m above ground  Above crop  Scotts Canada  Yellow sticky card (18 × 14 cm), 1 m above the ground on rebar stake  Above crop  Alphascents, West Linn, OR  Yellow cone trap, 1 m above the ground on rebar stake  Above crop  Hand constructed  Yellow cone trap, 0.75 m above ground on a yellow pyramid  Crop level  Hand constructed  Yellow cone trap secured on ground with tent pegs  At ground  Hand constructed  Yellow bucket trap with ½ of a Vapona insecticide strip  Pitfall  Hand constructed  2014  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent, with a ring of 6 mm × 6 mm chicken wire mesh to exclude large bycatch  Pitfall  Hand constructed  Yellow pan trap  Pitfall  Flexahopper Plastics Ltd., Lethbridge, AB Canada  Boll weevil (Legget) trap  At ground  ISCA Technologies Inc., Riverside, CA  Legget trap modified with all holes >2 mm sealed with hot glue  At ground  ISCA Technologies Inc.  PVC pitfall trap with small holes (20, 2 × 2 mm holes)  Pitfall  Hand constructed  PVC pitfall trap with large holes (six, 20 × 10 mm holes)  Pitfall  Hand constructed  Cylinder of yellow sticky cards on a wooden stake  Crop level  Modified from commercially available  2015  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Vernon ramp trap for wireworms, lined with yellow sticky cards  Pitfall  Scotts Canada  Vernon pitfall trap for wireworms, with propylene glycol as a killing agent  At ground  Scotts Canada  Year  Trap typea  Placement  Trap source  2013  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Yellow Unitrap, 1 m above the ground on rebar stake  Above crop  Scotts Canada  Green Unitrap, 1 m above the ground on rebar stake  Above crop  AgBio Inc., Westminister, CO  Multicoloured Unitrap, 1 m above ground  Above crop  Scotts Canada  Yellow sticky card (18 × 14 cm), 1 m above the ground on rebar stake  Above crop  Alphascents, West Linn, OR  Yellow cone trap, 1 m above the ground on rebar stake  Above crop  Hand constructed  Yellow cone trap, 0.75 m above ground on a yellow pyramid  Crop level  Hand constructed  Yellow cone trap secured on ground with tent pegs  At ground  Hand constructed  Yellow bucket trap with ½ of a Vapona insecticide strip  Pitfall  Hand constructed  2014  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent, with a ring of 6 mm × 6 mm chicken wire mesh to exclude large bycatch  Pitfall  Hand constructed  Yellow pan trap  Pitfall  Flexahopper Plastics Ltd., Lethbridge, AB Canada  Boll weevil (Legget) trap  At ground  ISCA Technologies Inc., Riverside, CA  Legget trap modified with all holes >2 mm sealed with hot glue  At ground  ISCA Technologies Inc.  PVC pitfall trap with small holes (20, 2 × 2 mm holes)  Pitfall  Hand constructed  PVC pitfall trap with large holes (six, 20 × 10 mm holes)  Pitfall  Hand constructed  Cylinder of yellow sticky cards on a wooden stake  Crop level  Modified from commercially available  2015  Pitall trap with Solo cup base, Coroplast lid, propylene glycol killing agent  Pitfall  Hand constructed  Vernon ramp trap for wireworms, lined with yellow sticky cards  Pitfall  Scotts Canada  Vernon pitfall trap for wireworms, with propylene glycol as a killing agent  At ground  Scotts Canada  aAll tested trap types were baited with 21 mg of pea leaf weevil aggregation pheromone in a 250 µl Eppendorf tube. View Large In 2013, nine trap types (Table 4) were tested at eight pea fields in southern Alberta. Traps were placed 25 m apart along a linear transect 1 m from the edge of the field in early August and checked every 5–7 days for a total of five trap collections. Trap capture was transported to the laboratory where PLW were identified and counted. Trap types tested in comparison to the Solo cup pitfall trap (Fig. 1a) included modified cone traps constructed from an inverted 946 ml yellow plastic drinking cup (Jean’s Plastics Party Supplies Gifts, Ebay). Cone traps were modified by drilling five, 1-cm diameter holes into the cup base for insect entry and gluing a clear polypropylene powder funnel (104 mm diameter, 243 ml capacity; Fisher Scientific) to the top of the inverted cup with a 37 ml plastic snap cap vial (Sigma Aldrich) attached to collect attracted insects. The inside of the plastic cup and funnel were sanded to increase traction and insect movement up the traps. Three versions of this cone trap were constructed: 1) a ground-based version (Fig. 1b); an aerial cone trap (Fig. 1c) positioned 1 m above the ground; and 3) a cone trap positioned on a pyramid (Fig. 1d) constructed out of two interlocking yellow Coroplast triangles (27 × 60 cm, base × height). Yellow bucket traps (Fig. 1e), similar to those used to monitor palm weevils (Vacas et al. 2013), were also tested in 2013. Yellow bucket traps were constructed from the same yellow plastic drinking cups but had a circular yellow Coroplast lid. Six, 2 cm diameter holes were drilled into the top of the cup for insect entry and cups were dug into the ground. Half of a Vapona insecticide strip (Scotts Canada) was secured to the inside of the cup to kill captured insects. In 2013, we also tested three different colors of Unitraps (Scotts Canada) (17 × 23 cm, diam × height), which were positioned 1 m above the ground on rebar stakes. Unitraps were either entirely green, entirely yellow or multicoloured (Fig. 1f) with a green lid, yellow cone, and white bucket. Each Unitrap contained half of a Vapona insecticide strip to kill captured PLW. Yellow rectangular sticky card (18 × 14 cm) traps (Alpha Scents, West Linn, OR) were also tested in 2013. Each yellow sticky card was attached with wire to a rebar stake at 1 m. In 2014, PLW capture was compared in eight types of insect trap (Table 4) at each of 5 sites. The Solo cup pitfall trap (Fig. 1a) was tested again with the addition of a cylinder (12 cm diam.) of 6 mm × 6 mm wire mesh attached to the Coroplast lid to exclude large bycatch (Fig. 2a). Additional pitfall traps tested in 2014 included two traps constructed from white PVC piping (Fig. 2b and c). In each PVC pitfall trap, a 10 cm length of 10 cm diameter PVC pipe with fitted cap had either, 20, 2 mm holes (Fig. 2b) or six, 20 mm × 10 mm oval holes (Fig. 2c) cut into the cap. PVC pitfall traps were half-filled with propylene glycol to preserve captured insects. Yellow pan traps (6.5 × 20 × 27 cm) (Fig. 2d) were also tested. Pan traps were buried into the soil so that the top of the pan trap was level with the soil surface, and were half-filled with propylene glycol as a trapping medium. In 2014, an unmodified and modified version of the Leggett cone trap (Leggett et al. 1975) (Fig. 2e) was tested. As the Legget traps were previously unsuccessful in retaining PLW in Alberta (Evenden et al. 2016), a modified Leggett cone trap was constructed to minimize the hole size in the mesh cone to less than 2 mm. Cone traps were placed on the ground and secured in place with tent pegs. The final trap type tested in 2014 was a cylinder (14 cm high, 50 cm circumference) (Fig. 2f) (Fisher and O’Keeffe 1979) constructed from three overlapping yellow sticky cards (14 × 18 cm) stapled to a 30 cm wooden stake to position the cylinder just above the crop stubble. Fig. 2. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2014. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were placed 25 m apart in a linear transect in random order at the edge of five pea fields in southern Alberta after crops were harvested. A second transect was positioned 25 m into the field so that traps formed a 2 × 8 grid. Trap types include: (a) a white Solo cup pitfall trap modified with mesh to exclude large bycatch; (b) white PVC pitfall traps with small or (c) large entrance holes; (d) yellow pan traps; (e) green Legget cone traps modified with hole size <2 mm; and (f) the cylindrical yellow sticky card trap. Also tested were the unmodified white Solo cup pitfall traps (Fig. 1a) and the unmodified green Legget cone traps (not pictured). Fig. 2. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2014. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were placed 25 m apart in a linear transect in random order at the edge of five pea fields in southern Alberta after crops were harvested. A second transect was positioned 25 m into the field so that traps formed a 2 × 8 grid. Trap types include: (a) a white Solo cup pitfall trap modified with mesh to exclude large bycatch; (b) white PVC pitfall traps with small or (c) large entrance holes; (d) yellow pan traps; (e) green Legget cone traps modified with hole size <2 mm; and (f) the cylindrical yellow sticky card trap. Also tested were the unmodified white Solo cup pitfall traps (Fig. 1a) and the unmodified green Legget cone traps (not pictured). In addition to trap type, the effect of trap position within the field was tested in 2014. Two transects each containing one trap of each of the 8 tested trap designs were positioned 25 m apart at each pea field. One transect was erected along the edge of each field and another 25 m into the field, so that the traps formed an 8 × 2 grid. These traps were placed in five pea fields post-harvest in mid-August and trap capture was checked every 2 weeks until mid-September. Trap capture was transported to the laboratory where PLW were identified and counted. In 2015, only three insect trap types were evaluated (Table 4): 1) the Solo cup pitfall trap (Fig. 1a); 2) a commercially available (Scotts Canada) box trap (Fig.3a) developed for monitoring wireworms (Vernon 2004); and 3) a commercially produced (Scotts Canada) Vernon pitfall trap (Fig. 3b) designed to capture wireworms (Vernon and van Herk 2014). The 15 cm × 15 cm × 4 cm box trap was lined with yellow sticky cards to capture insects. Two ramps leading into the box allow insect entry. Two, 1 mm holes were drilled into the lid of each box trap to attach semiochemical lures with wire. The Vernon pitfall traps consist of a brown lower cup (400 ml) which is set into the ground, a clear lining cup (200 ml) that is inserted into the lower cup and filled with propylene glycol, and a brown plastic top which snaps onto the bottom and excludes large bycatch with small plastic pegs. Two, 1 mm holes were drilled into the lid of each Vernon pitfall trap to attach semiochemical lures with wire. Structurally, the Vernon pitfall traps are very similar to the Solo cup pitfall trap, but with a slightly smaller capacity (200 ml vs 400 ml). Two of each type of trap were randomly placed 25 m apart on a linear transect at the edge of each pea field (for a total of 6 traps per transect). Traps were placed in three pea fields in mid-August and were serviced three times, until mid-September. Trap capture was transported to the laboratory where PLW were identified and counted. Fig. 3. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2015. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order along a linear transect at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include: (a) the Vernon ramp trap; and (b) the Vernon pitfall trap. Also tested in 2015 was the unmodified Solo cup pitfall trap (Fig. 1a). Fig. 3. View largeDownload slide Types of traps evaluated for PLW capture in the trap type experiment in 2015. Each trap was baited with 21 mg of 4-methyl-3,5-heptanedione in a 250 μl Eppendorf tube. Traps were positioned 25 m apart in random order along a linear transect at the edge of eight pea fields in southern Alberta after crops were harvested. Trap types include: (a) the Vernon ramp trap; and (b) the Vernon pitfall trap. Also tested in 2015 was the unmodified Solo cup pitfall trap (Fig. 1a). Statistical Analyses Separate generalized linear mixed effects models were used to analyze the effect of trap type on total PLW capture for all 3 years of experimentation. Models were constructed using the function lmer in the lme4 package (version 1.1–10) in R (version 3.1.3). Total PLW captured during the experiment was the dependent variable and trap type and position (2014 only) were specified as explanatory variables. In all models, site was specified as a random variable. Post-hoc Tukey’s multiple comparisons tests were performed on significant factors with more than one level using the function ghlt in the multcomp package (version 1.4–4) (R version 3.1.3). Results Semiochemical Lures: Dose and Release Device In the spring 2013 trapping period, the semiochemicals used to bait traps significantly impacted the season-long trap capture of PLW (χ2 = 131.15, df = 2, P < 0.001; Fig. 4). Traps baited with aggregation pheromone alone (Z-value = −10.34, P < 0.001) or in combination with host plant volatiles (Z-value = −11.45, P < 0.001) captured significantly more PLW than unbaited control traps. Traps baited with pheromone and host plant volatiles also captured significantly more PLW than traps baited with pheromone alone (Z-value = 2.52, P = 0.03). Similarly, in fall 2013, there was a significant effect of semiochemical lure on the season-long catch of PLW (χ2= 18.84, df = 2, P < 0.001; Fig. 4). Significantly more PLW were captured in traps baited with pheromone alone (Z-value = −2.12, P = 0.08) or pheromone with host plant volatiles (Z-value = −3.97, P < 0.001) than in unbaited control traps. More weevils were caught in traps baited with pheromone and host plant volatile lures than in traps baited with pheromone alone (Z-value = 2.94, P = 0.009) (Fig. 4). Fig. 4. View largeDownload slide Box plot of season-long capture of PLW in semiochemical-baited traps baited with different lures tested in spring and fall, 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Captures of weevils were pooled across pheromone dose and device size. Boxes marked with different capital and lowercase letters represent significantly different seasonal PLW captures at α = 0.05 and α = 0.10, respectively. Fig. 4. View largeDownload slide Box plot of season-long capture of PLW in semiochemical-baited traps baited with different lures tested in spring and fall, 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Captures of weevils were pooled across pheromone dose and device size. Boxes marked with different capital and lowercase letters represent significantly different seasonal PLW captures at α = 0.05 and α = 0.10, respectively. The 2013 data was also analyzed without the trap capture from the unbaited control traps. In the spring, neither pheromone dose (χ2 = 1.69, df = 1, P = 1.9) nor release device (χ2 = 0.40, df = 1, P = 0.4) affected PLW captures. In the fall, there was a trend toward increased PLW captures in traps baited with the lower dose of 21 mg of pheromone over traps baited with 42 mg pheromone (Z-value = 1.87, P = 0.06). Release device did not affect PLW captures (χ2 = 0.242, df = 1, P = 0.62) in the fall or interact with pheromone dose, or addition of host plant volatiles in the spring or fall. Trap capture from both spring and fall trapping periods was analyzed together in a single model in 2014. Trapping season significantly affected PLW capture through an interaction with pheromone dose (χ2 = 6.19, df = 2, P = 0.05). The interaction between season and pheromone dose was largely driven by the relative attractiveness of the low compared to the high dose lures at two sites in the spring that was less pronounced in the fall. In the spring, the low dose of pheromone tended to capture more PLW, but in the fall, the high dose of pheromone captured numerically more PLW. The presence of host plant volatiles significantly affected PLW captures through an interaction effect with season (χ2 = 8.14, df = 2, P = 0.02) and as a main effect (χ2 = 9.44, df = 2, P = 0.009). The addition of host plant volatiles to the pheromone lure increased PLW captured in the fall but not in the spring. A direct comparison of trap capture of in each type of baited trap in both seasons in 2014 showed that PLW captures were significantly affected by the semiochemical lure in both the spring (χ2 = 107.77, df = 8, P < 0.001) and the fall (χ2 = 68.52, df = 8, P < 0.001) (Fig. 5). All traps baited with either dose of pheromone with or without host volatiles captured more weevils than unbaited control traps or traps baited with host volatiles alone at either dose (Fig. 5). Fig. 5. View largeDownload slide Box plot of season-long capture of PLW in all semiochemical-baited traps tested in spring and fall of 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Comparisons among treatments were made in each season separately. Boxes marked with different capital letters represent significantly different seasonal PLW captures at α = 0.05. Fig. 5. View largeDownload slide Box plot of season-long capture of PLW in all semiochemical-baited traps tested in spring and fall of 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Comparisons among treatments were made in each season separately. Boxes marked with different capital letters represent significantly different seasonal PLW captures at α = 0.05. The proportion of male and female PLW caught in spring 2014 did not differ by semiochemical treatment (χ2 = 7.70, df = 4, P = 0.17). Binomial tests, however, performed to determine the ratio of male to female PLWs captured within each treatment found that the sex ratio sometimes differed from 1:1 (Fig. 6). Trap capture was male-biased in traps baited with the low pheromone and low host plant volatile dose lures (63% male, P < 0.001, n = 184), the low pheromone and high host plant volatile dose lures (65% male, P < 0.001, n = 221), the high pheromone dose lure (61% male, P = 0.05, n = 92), the high pheromone and low host plant volatile dose lures (58% male, P = 0.04, n = 154), and the high pheromone and high host plant volatile doses (66% male, P < 0.001, n = 119). Traps that lacked the pheromone lure, including the unbaited control trap and traps baited with either the low or high host plant volatile lures alone, captured few insects (n = 3, n = 1, n = 3, respectively). Traps baited with the low pheromone dose lure alone captured 209 PLWs in spring 2014, but trap catch was not significantly male- or female-biased (54% male, P = 0.27, n = 209) (Fig. 6). Fig. 6. View largeDownload slide Proportion of male and female PLW captured in semiochemical traps in 2014. Semiochemical lures are described in Table 2. Trap capture was separated by sex in each semiochemical trap and the proportion of males and females captured was compared with a two-sided binomial test within trap type. Significant differences from a 1:1 ratio of the proportion of male and female PLW captured within a single semiochemical trap treatment are denoted with “.” for α = 0.10, “*” for α = 0.05, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Numbers within bars on the graph denote the total number of male and female PLW captured in a given trap. Fig. 6. View largeDownload slide Proportion of male and female PLW captured in semiochemical traps in 2014. Semiochemical lures are described in Table 2. Trap capture was separated by sex in each semiochemical trap and the proportion of males and females captured was compared with a two-sided binomial test within trap type. Significant differences from a 1:1 ratio of the proportion of male and female PLW captured within a single semiochemical trap treatment are denoted with “.” for α = 0.10, “*” for α = 0.05, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Numbers within bars on the graph denote the total number of male and female PLW captured in a given trap. The proportion of male and female PLW caught in fall 2014 also did not differ with the semiochemical-baited trap (χ2 = 7.12, df = 7, P = 0.42). Binomial tests on PLW captured within each trap showed that sex ratio of PLW captured was not always 1:1 (Fig. 6). In fall 2014, the majority of traps did not display a significant sex-biased capture and no traps had a significantly male-biased capture (Fig. 6). Trap capture was female-biased in traps baited with the high dose of host plant volatile without pheromone (24% male, P = 0.05, n = 17). Blank traps were not included in the analysis for fall 2014 as PLW captures were low (n = 1). In the fall of 2014, 194 individuals or 15.8% of the captured PLW were suspected to have overwintered and belong to the parental generation. There was a marginal effect of semiochemical lure on the proportion of newly eclosed: overwintered male and female PLW captured in semiochemical traps (χ2 = 24.14, df = 15, P = 0.06). Proportions of newly eclosed to overwintered PLW within each trap type tested with Exact Proportion Tests sometimes differed by sex in a given semiochemical trap (Fig. 7). There was a greater proportion of males than females in the parental generation for weevils captured in traps baited with 1) low pheromone dose (χ2 = 5.47, df = 1, P = 0.02); 2) low pheromone dose and low host plant volatile dose (χ2 = 9.16, df = 1, P = 0.002); 3) low dose of pheromone and high host plant volatile dose (χ2 = 6.27, df = 1, P = 0.01); 3) high pheromone dose and low host plant volatile dose (χ2 = 17.58, df = 1, P < 0.0001); and 4) high pheromone dose and high host plant volatile dose (χ2 = 12.36, df = 1, P < 0.001). Traps baited with the high pheromone dose alone also followed this same trend (χ2 = 3.5, df = 1, P = 0.06). In unbaited traps or traps baited with only host plant volatile lures, the proportion of parental versus newly eclosed PLW did not differ between the sexes. PLW captures in these traps, however, were low overall. Fig. 7. View largeDownload slide Proportion of newly eclosed and overwintered male and female PLW captured in each semiochemical trap type tested in fall 2014. For each semiochemical-baited trap, a Two-Way Test of Equal Proportions was used to determine if the proportion of overwintered and newly eclosed PLW was similar between males and females. Significant differences between the proportion of newly eclosed male and female PLWs are denoted with “.” for α = 0.10, “*” for α = 0.05, “**” for α = 0.01, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. Fig. 7. View largeDownload slide Proportion of newly eclosed and overwintered male and female PLW captured in each semiochemical trap type tested in fall 2014. For each semiochemical-baited trap, a Two-Way Test of Equal Proportions was used to determine if the proportion of overwintered and newly eclosed PLW was similar between males and females. Significant differences between the proportion of newly eclosed male and female PLWs are denoted with “.” for α = 0.10, “*” for α = 0.05, “**” for α = 0.01, and “***” for α = 0.001. Bars marked with “NT” signify that trap capture was too low to conduct the analysis. In 2014, 98% of the 998 Sitona specimens captured in semiochemical-baited traps were identified as PLW (S. lineatus). Only 12 individuals were identified as S. cylindricollis, the sweet clover weevil. Trap Type There was a significant difference between the number of PLWs captured in the different trap types tested in 2013 (χ2 = 99.31, df = 8, P < 0.0001) (Fig. 8). The Solo cup pitfall traps captured significantly more PLW than any of the other traps tested in 2013 (P < 0.0001). The remaining trap types captured a similar (negligible) number of PLW. In addition, Unitraps captured a high level of Hymenopteran bycatch. In 2014, there was also a significant effect of trap type on the number of captured PLW (χ2 = 125.84, df = 7, P < 0.001). The Solo pitfall cup, the Solo pitfall cup modified with wire mesh to exclude large bycatch, and the yellow pan trap all successfully captured PLW (Fig. 9). The remaining traps captured few PLW. There was no effect of trap position in the field on the capture of PLW as traps placed on the edge of the field captured a similar number of PLW as those placed on a parallel transect 25 m into the field (χ2 = 0.063, df = 1, P = 0.802). A low number of PLW were captured in the trap type experiment in 2015 (n = 5) that precluded statistical analysis. Fig. 8. View largeDownload slide Box plot of PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 8 August to 6 September 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Trap capture of PLW in the Solo cup pitfall trap was greater than in all other trap types tested. Fig. 8. View largeDownload slide Box plot of PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 8 August to 6 September 2013. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Trap capture of PLW in the Solo cup pitfall trap was greater than in all other trap types tested. Fig. 9. View largeDownload slide Box plot PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 7 August to 15 September, 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Fig. 9. View largeDownload slide Box plot PLW captured in different trap types baited with 21 mg of PLW aggregation pheromone released from a 250 µl Eppendorf tube from 7 August to 15 September, 2014. The midline indicates the median and the bottom and top of the box represent the 25th and 75th percentiles, respectively. Vertical lines extending from the box (whiskers) represent the maximum and minimum values. Bars marked with different letters indicate significantly different PLW captures (P < 0.05). Discussion Semiochemical Lures: Dose and Release Device After comparing various doses and combinations of the PLW pheromone and host plant volatiles, the best lure tested was 21 mg of PLW pheromone, 4-methyl-3,5-heptanedione, in a 250 μl Eppendorf tube. A combined lure of 21 mg of PLW pheromone in a 250 μl Eppendorf tube with host volatile lures (21 mg of (Z)-3-hexenyl acetate in a 250 μl Eppendorf tube, 34 mg of (Z)-3-hexenol in a 250 μl Eppendorf tube, and three 250 μl Eppendorf tubes, each with 50 mg of linalool) was at least equally as attractive and sometimes more attractive than the pheromone lure alone. The added efficacy of the combined lure over the pheromone lure alone was not consistent enough to justify future effort and expense of inclusion of the host plant volatiles as part of a semiochemical lure. Evaluation of various ground-based and aerial insect traps found that the most successful trap type is a wet pitfall trap, which is easily constructed from Solo cups, Choroplast, and nails. Semiochemical-baited traps successfully attracted and retained PLW adults in both the spring and fall, corroborating the findings of Evenden et al. (2016). Capture of PLW in baited traps in the fall allows assessment of pre-overwintering populations that could assist producers in planning pest management tactics including whether to plant insecticide-treated pea seed the following spring. Trap capture in semiochemical-baited traps can vary with semiochemical dose (Byers 2013) because the active space of the signal changes with dose (Byers 2008) causing the signal to be variably sensed by insects in space (Dolzer et al. 2003). The insect may also show plasticity in response to signals released from lures containing different pheromone doses (Roelofs 1978). PLWs, however, did not respond differently to the two pheromone doses tested in the semiochemical-baited traps tested in 2013 and 2014. Because PLW captures were similar between both release devices and doses of pheromone tested, the best lure would be the least expensive to produce: 21 mg of pheromone in a 250 μl Eppendorf tube. Blight et al. (1984) found that more PLW were captured in traps baited with a 21 mg pheromone dose released from a polythene vial as compared to a 5 mg dose. PLW in the current study did not respond differently to the different pheromone doses used to bait traps. The release rate of 0.3 mg/day of pheromone from the 21 mg dose in a 250 μl Eppendorf tube (Table 3) is similar to the stable attractive release rate tested in a small plot push-pull study of PLW in the United Kingdom (Smart et al. 1994). Response to a broad range of semiochemical doses may relate to the aggregating mating behavior of PLW, as aggregations may vary from a few to a few thousand males and females. It would therefore be adaptive for PLW to respond to a wide range of pheromone release rates. Similarly, attraction of plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) weevils to trap trees at the perimeter of apple orchards was not enhanced by a 5-fold increase in pheromone dose (Leskey et al. 2014). The red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) exhibits a dose-dependent response to male-produced aggregation pheromone at low release rates, but this relationship breaks down at high release rates (Vacas et al. 2013). If the pheromone signal increases with weevil aggregation size, enhanced response to high release rates would be advantageous only to a certain point, depending on the optimal aggregation size. This may be similar to the behavior of granary weevils, Sitophilus granaries L. (Coleoptera: Curculionidae) that are attracted to low concentrations but arrested to high concentrations of aggregation pheromone (Plarre 1994). Electrophysiological responses of antennae of male and female Sitona discoideus Gyllenhål to pheromone presented at medium (100 µg) and high (1,000 µg) doses was significantly greater than that to low doses (0.1–10 µg) (Unelius et al. 2013) suggesting that Sitona weevils are capable of processing strong pheromone signals. Future studies which test a broader range of PLW pheromone release rates should be conducted to determine if PLW behavioral response is dose-dependent at lower release rates or if high doses repel or arrest PLW. In this study, PLW response to pheromone was enhanced by the presence of host plant volatiles in three of the four trapping periods. Blight et al. (1984) and Evenden et al. (2016) also found that PLW response to pheromone was sometimes synergized by the presence of host plant volatiles. Both doses of host plant volatile lures tested here were not attractive alone. This is in contrast to laboratory studies that showed PLW orient to plant volatile compounds in an olfactometer assay (Landon et al. 1997) and could suggest that natural host cues are masking the host plant volatile lures in our experiments. Similarly, Anthonomus rubi Herbst (Coleoptera: Curculionidae), is weakly attracted to traps baited with pheromone, exhibits a synergistic response to traps baited with pheromone and host plant volatiles, but does not respond to traps baited with host plant volatiles alone (Wibe et al. 2014). Response by the cotton boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), to pheromone is enhanced by host plant volatiles (Dickens 1989). A synergistic effect of host plant volatiles with pheromone would be expected to occur if calling or mating behavior occurs in association with the host plant (Landolt 1997). The PLW orient to reproductive host plants prior to mating and producing eggs (Vankosky et al. 2009) and males release pheromone while feeding on the host plant (Blight et al. 1984). PLWs consistently respond to pheromone lures in both the spring and fall. Host plant volatiles enhance response to pheromone, primarily in the fall which may be due to a scarcity of host plants at this time of year that makes the semiochemical signal from the trap more apparent. In the fall, PLW may also be better tuned to respond to host plant cues as they need to find plants after the fall migration away from pea fields to feed before overwintering (Jackson 1920, Landon et al.1997). The olfactory response of other insects can be influenced by background volatiles. A volatile compound released by strawberry flowers enhances the response of A. rubi to its aggregation pheromone throughout the growing season (Wibe et al. 2014) when the plants in the background are both in vegetative and flowering states. Despite the presence of olfactory neurons sensitive to the strawberry leaf volatile (-)-germacrene D on the antennae of A. rubi, this compound did not synergize weevil response to pheromone traps positioned in strawberry fields (Wibe et al. 2014). During the spring trapping period, the pea crop is green and edible to PLW (Jackson 1920, Landon et al. 1995). As pea plants enter the flowering or bud stages, relative emission of (Z)-3-hexenol and (Z)-3-hexenyl acetate decreases compared to other volatiles (Thöming et al. 2014). By the fall, PLW are not attracted to desiccated pea plants (Landon et al. 1995) but likely still use host volatiles in the fall to orient to plants after migration for feeding before overwintering. In the current study, the sex ratio of weevils captured in semiochemical-baited traps did not vary statistically among the various semiochemical-baited traps. The sex ratio within individual trap treatments, however, sometimes varied from an expected 1:1 ratio and this difference was dependent on the season of trapping. PLW captures in spring 2014 were predominantly male-biased. In fall 2014, traps captured weevils in even sex ratios except for those baited with a high release rate of host plant volatiles in which capture was female-biased. This may be because female PLW need to feed before overwintering to maximize egg production (Schotzko and O’Keeffe 1986). Blight et al. 1984) also reported male-biased captures of PLW in semiochemical-baited traps in the spring. Interestingly, Evenden et al. (2016) reported female-biased PLW captures in semiochemical-baited traps in the spring and an even number of males and females in the fall. Both male-biased and female-biased PLW captures in semiochemical-baited traps were also reported to vary by crop (Nielsen and Jensen 1993). It is also possible that PLW sex ratios vary with population density, if sex-specific costs and benefits change with density, as occurs in other insects such as the sandfly, Lutzomyia longipalpis, França (Diptera: Phlebotominae) (Jones and Quinnell 2002). Laboratory feeding experiments by Schotzko and O’Keeffe (1988) found that female PLW have greater longevity than male PLW when maintained in single reproductive pairs, but male and female PLW have similar longevity when maintained in groups of 13 reproductive pairs, indicating that PLW density may affect PLW mortality in a sex-specific way. This is supported in our study by the finding of relatively even sex ratios of newly eclosed weevils in the fall but uneven sex ratios in the spring when mortality agents have had more time to act. Future studies should determine if PLW sex ratios in pea fields are density dependent and if PLW sex ratios in semiochemical traps mirror PLW sex ratios in surrounding crops. Future studies should investigate state-specific plasticity of PLW response to semiochemicals. Our trap catch data illustrate that some PLW that overwinter remain active throughout the following season and are sensitive to semiochemical cues as they are captured in semiochemical-baited traps the following fall. Similarly, weevils from the spring and summer generation of A. rubi responded to semiochemical-baited traps in northern Europe (Wibe et al. 2014). In general, more overwintered male PLW were captured in traps the following fall than overwintered females. Landon et al. (1995) tested the response of male and female PLW to pea volatiles in the laboratory at various times of year and found that weevil response was decreased only in the winter and there was no effect of PLW sex on response to plant volatiles. The closely related clover root weevil, Sitona lepidus Gyllenhål (Park et al. 2013) and S. discoideus (Unelius et al. 2013) exhibit sexual dimorphism in the expression of olfactory receptor neurons. Sitona discoideus also exhibits sexual dimorphism in electrophysiological response to the various enatiomers of their pheromone 5-hydroxy-4-methyl-3-heptanone (Unelius et al. 2013). The pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), exhibits sexual dimorphism in response to semiochemicals as male response to pheromone is synergized with the addition of host plant volatiles, but female response to pheromone is not (Muniz-Merino et al. 2014). Both sexes of PLW respond to pheromone in spring and fall in our trapping studies and those of Evenden et al. (2016), but little is known about the effect of season or sex on the neurophysiological response to pheromone. The semiochemical traps tested here were specific for PLW. A few specimens of the sweetclover weevil, Sitona cylindricollis were captured in 2014. The aggregation pheromone of S. cylindricollis likely overlaps slightly with that of the PLW and other Sitona species. Tóth et al. (1998) captured multiple Sitona species in traps baited with 4-methyl-3,5-heptanedione in Hungary. Information on the specific aggregation pheromone identity of various Sitona species is limited, but S. discoideus utilizes a two-component blend: 4-methyl-3,5-heptanedione and (4S,5S)-5-hydroxy-4-methyl-3-heptanone as an aggregation pheromone (Unelius et al. 2013). Sitona lepidus also uses these components in its aggregation pheromone but only males are responsive to 4-methyl-3,5-heptanedione (Park et al. 2013). Sitona weevils utilize legumes as host plants (Jackson 1920) and it is likely that there is overlap in attractive host plant volatiles. Besides PLW, the Sitona species present in the Prairie Provinces are S. cylindricollis, S. flavescens, S. hispidulus, S. lineellus, and S. californius (Bright 1994) and their chemical ecology is virtually unknown. Knowledge on the chemical ecology of the non-Sitona weevil bycatch is also limited. Non-Sitona bycatch included weevils in Hypera, Ceutorhynchus, Otiorhynchus, and Perapion. These weevils may also have similar pheromones to the PLW. The alfalfa weevil, Hypera postica (Gyllenhål), was captured in significant numbers in traps targeting PLW in the Pacific Northwest, United States (Quinn et al. 1999). Nontarget weevil species might also be attracted to the host plant volatiles used to bait the traps tested here. For example, Otiorhynchus sulcatus is responsive to linalool and (Z)-3-hexenol (van Tol and Visser 2002). Despite some non-PLW bycatch, the overall specificity of these semiochemical-baited traps is high. Trap Type The pitfall trap was the most successful trap type tested for attraction and retention of PLW in the fall trapping period across three field seasons. As we conducted the trap type test in the fall, when less than 10% of newly emerged adults are estimated to leave the crop by flight (Hamon et al. 1987) it is not surprising that a ground-based trap was most effective. The pitfall trap constructed from Solo cups consistently captured the most PLW, but it is not the most user-friendly trap. The addition of a ring of wire mesh around the pitfall cup does not hinder PLW captures and may successfully exclude some of the large bycatch, such as small mammals, amphibians, or large carabid beetles, captured in this study. Vertebrates are common bycatch in pitfall traps, and there can be a trade-off between the utilization of pitfall traps for insect monitoring and the loss of vertebrates and arthropod predators, such as carabids (Thompson and Thompson 2008). Lemieux and Lindgren (1999) found that the addition of a lid to open-top pitfall traps reduced vertebrate bycatch. By similarly reducing the entrance size, the addition of mesh to covered pitfall traps is expected to also reduce vertebrate bycatch, although this was not statistically tested in this study. The Vernon pitfall trap is expected to be a suitable trap for capturing PLW. Unfortunately, an overall low number of PLW were captured in the 2015 trapping experiment, and we were unable to demonstrate that the Vernon pitfall trap successfully captures PLW in the field. Similar to the pitfall trap modified with mesh, the Vernon pitfall trap includes pegs that limit the entrance size. The Vernon pitfall trap warrants further testing for PLW in the future. The Vernon pitfall traps tested here were brown, but yellow or green traps are also available and may be more visually attractive to PLW (Reddy et al. 2011). Yellow pan traps also successfully attracted and retained PLW in similar numbers to the two pitfall traps tested in 2014. Yellow pan traps are used in canola fields in the Prairie Provinces to monitor the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) (Fox and Dosdall 2003, Blake et al. 2010) and Delia spp. (Diptera: Anthomyiidae) (Broatch and Vernon 1997). Yellow pan traps positioned in pea fields in this study, however, were more susceptible than pitfall traps to evaporation of propylene glycol and unintended bycatch. The remaining traps tested did not successfully capture PLW in the fall trapping period and should not be adopted as traps for a semiochemical-based monitoring system. Traps placed above the ground may be more successful in the spring trapping period as weevils fly to locate pea crops in the spring and then disperse throughout the field by walking (Hamon et al. 1987). Unitraps placed 1 m above the ground did not capture PLW in the fall and also had a high level of hymenopteran bycatch as previously reported in other systems (Mori and Evenden 2013) that could result in removal of pollinators from the cropping area. The various yellow sticky card traps tested in our study rarely captured PLW and were difficult to handle. In contrast, unbaited sticky traps captured PLW during peak flight in the spring in studies in Europe (Fisher and O’Keeffe 1979, Nielsen and Jensen 1993). Semiochemical-baited Legget cone traps have been used to monitor PLW during the spring migration in Europe (Blight et al.1984, Blight and Wadhams 1987, Nielsen and Jensen 1993, Smart et al. 1994), but were unsuccessful in the spring in the Prairie Provinces (Evenden et al. 2016). Legget traps and other hand-constructed cone traps were also unsuccessful in the current study, even when modified to prevent escape. Future experiments testing semiochemical-baited trap types should assess aerial traps against ground-based traps during the spring migration but focus on pitfall traps during the fall trapping period. The Solo pitfall trap is inexpensive and easy to make, but the Vernon pitfall trap is likely as effective and more user-friendly. The experiments reported here support the potential for semiochemical-based monitoring of PLW in the Canadian Prairie Provinces. All of our experiments were performed in Alberta, where the PLW is established but similar results are expected in the other Prairie Provinces. These experiments have identified 21 mg of 4-methyl-3,5-heptanedione released from a 250 μl Eppendorf tube as a reliable lure. The addition of host plant volatiles (21 mg of (Z)-3-hexenyl acetate in a 250 μl tube + 34 mg of (Z)-3-hexenol in a 250 μl Eppendorf tube, and three 250 μl tubes, each with 50 mg of linalool) sometimes enhanced PLW captures in pheromone-based traps, especially in the fall. The next step in the development of this semiochemical-based trapping system is to identify if PLW captures in traps are related to PLW populations or to PLW-induced damage in the field. This system will be especially useful for pulse producers if a predictive model for PLW activity can be developed. A predictive model based on fall trap captures would be particularly useful for Canadian pea producers, as it would allow producers to make informed decisions on the use of insecticide-treated pea seed. Acknowledgments The authors thank Shelley Barkley and Scott Meers, Alberta Agriculture and Forestry, for assistance with site location and establishment. Lawrence Vanderark and J.-P. Lafontaine of Scotts Canada for synthesis, formulation, and release rate measurements of the semiochemicals used in this study. Danielle Hoefele, Dylan Sjølie, and other members of the Evenden and Cárcamo labs assisted with trap collection and the sorting and identification of trap capture. The study was funded by the Agriculture Crop Industry Development Fund, the Alberta Pulse Growers Commission, and the Western Grain Research Foundation in grant #2013F175R to M.L. Evenden (PI) and H.A. Cárcamo (Collaborator, Agriculture and Agri-Food Canada). The University of Alberta, Department of Biological Sciences, partially supported A. St. Onge through Graduate Student Teaching Assistant stipends. References Cited Alberta Agriculture and Forestry. 2017. Historical Pea Leaf Weevil Forecast Maps. http://www1.agric.gov.ab.ca/$Department/deptdocs.nsf/all/prm15622 (Accessed 1 August 2017). Blake A. J. Dosdall L. M., and Keddie B. A.. 2010. 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