Local outbreak risk for the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae), is forecast with a trapping survey conducted every spring throughout the southeastern United States. Traps baited with pine odors and components of the D. frontalis aggregation pheromone are used to obtain abundance estimates of both this species and its clerid predator Thanasimus dubius (F.) (Coleoptera: Cleridae); these data are entered into a predictive model that estimates outbreak risk. An attractant synergist for D. frontalis, endo-brevicomin, has recently been included in the survey lure, but it can have the unintended effect of attracting nontarget species Hylesinus pruinosus Eichhoff (Coleoptera: Curculionidae: Scolytinae) and Enoclerus nigripes (Say) (Coleoptera: Cleridae) which, due to their sometimes large numbers and general similarity in appearance to the target species, could complicate sorting and counting of trap catches. Analysis of bycatch data from a previously-published, 31-mo trapping study in Mississippi indicated that displacement of the endo-brevicomin releaser 6 m from the trap largely eliminated catches of the nontarget species H. pruinosus and E. nigripes while not reducing catches of the target species D. frontalis and T. dubius. Our analysis demonstrates that interspecific differences in spatial responses to attractive semiochemicals can be used to improve insect trap selectivity. Both nontarget beetle species were captured in highest numbers during late winter/early spring, coinciding with the D. frontalis survey. Key words: Hylesinus pruinosus, Enoclerus nigripes, Dendroctonus frontalis, Thanasimus dubius, bycatch The southern pine beetle, Dendroctonus frontalis Zimmermann the abundance of infestations which may require control during the (Coleoptera: Curculionidae) is a native pest species that causes sig- following summer (Billings and Upton 2010, Billings 2011). Until nificant economic losses to pine forests in the southeastern United this year (2017), traps have been baited with an aggregation pher- States (Price et al. 1998). Adult D. frontalis use an aggregation pher- omone component (frontalin) and host volatiles (pine turpentine omone to organize mass attacks that can overwhelm the defenses or a mixture of alpha- and beta-pinene); this combination attracts of healthy host trees (Sullivan 2011). They then feed and repro- both D. frontalis and a major predator, Thanasimus dubius (F.) duce in the phloem of the host which inevitably dies as a result of (Coleoptera: Cleridae). The numbers of D. frontalis, as well as the colonization. Beetles disperse in the spring and, when population proportion of T. dubius trapped, are entered into a model used to densities are sufficient, may initiate localized infestations or ‘spots’ predict population levels and infestation trends later in the year that consist of patches of adjacent, infested trees. Infestations may (Billings 2011). The ability to predict the severity of an outbreak grow through the spring and summer, but this growth may be sup- months in advance allows forest pest managers to more effectively pressed through felling of infested and adjacent trees (Billings 2011). plan for spot detection and suppression activities. D. frontalis outbreaks occur periodically and may last for several The male-produced pheromone component endo-brevicomin is years (Turchin et al. 1991, Birt 2011). a potent synergist of the combination of frontalin and host com- Outbreaks may not be apparent until summer when flagging pounds in attracting D. frontalis to traps located outside of beetle of foliage of killed trees becomes visible (Billings and Kibbe 1978). infestations (Sullivan et al. 2007). Furthermore, the degree of catch Therefore, every spring a network of traps is established through- enhancement is similar or increased when an endo-brevicomin lure is out the southeastern United States to detect whether outbreak-level displaced a few meters from (as opposed to being placed directly on) populations of D. frontalis exist and to make forecasts regarding a trap baited with the other lure components (Moreno et al. 2008, Published by Oxford University Press on behalf of Entomological Society of America 2017. This work is written by (a) US Government employee(s) and is in the public domain in the US. This Open Access article contains public sector information licensed under the Open Government Licence v2.0 (http://www.nationalarchives.gov.uk/doc/ open-government-licence/version/2/). Downloaded from https://academic.oup.com/jinsectscience/article-abstract/18/1/3/4781596 by Ed 'DeepDyve' Gillespie user on 16 March 2018 2 Journal of Insect Science, 2017, Vol. 18, No. 1 Sullivan and Mori 2009). The capacity of endo-brevicomin to act species relative to the target species with which they might poten- as an attractive synergist for D. frontalis has led to the decision to tially be confused (i.e., the ratio H. pruinosus to D. frontalis, and include it in the lure combination used for the annual spring survey E. nigripes to T. dubius). Two data subsets were created for H. pru- of D. frontalis (John T. Nowak, personal communication). inosus and E. nigripes, respectively, from the 31 mo of trapping, by A sympatric species of D. frontalis, the ash bark beetle, Hylesinus including only groups of three consecutive collections (i.e., approx. pruinosus Eichhoff (Coleoptera: Curculionidae: Scolytinae), 6 wk; one complete lure rotation) during which at least one individ- employs (+)-endo-brevicomin as an aggregation pheromone com- ual was trapped; periods in which no or merely sporadic H. pruino- ponent and is strongly attracted to lures with either racemic or sus or E. nigripes catch occurred were considered irrelevant to our (+)-endo-brevicomin (Shepherd et al. 2010). Similarly, the sym- question of interest. Catches were then averaged within treatment patric bark beetle predator Enoclerus nigripes (Say) (Coleoptera: and trap to obtain six averages (one per trap) for each treatment. Cleridae) is attracted to endo-brevicomin, presumably utilizing this Mean catches per trap per day were cube root transformed to meet compound as a host-location kairomone. Neither species appears to assumptions of normality and homoscedasticity prior to analyses. be attracted significantly to frontalin and host odors (authors’ un- The ratios of E. nigripes to T. dubius and H. pruinosus to D. fron- published data). These nontarget species superficially resemble D. talis were calculated for each trap from the untransformed catches frontalis and T. dubius, respectively, and their presence could con- and were log transformed. Transformed mean catches for each spe- found the identification and counting of beetles in survey samples. cies and ratios between species were analyzed for treatment effects Such confusion is more likely if the personnel sorting samples are with ANOVAs using model factors treatment and trap within group not thoroughly trained/experienced or a microscope is not available (PROCGLM, SAS 9.4). We calculated all pairwise comparisons of to them. Bycatches of H. pruinosus and E. nigripes might occur if treatment means for each species and nontarget/target species ratios endo-brevicomin is included in the D. frontalis survey lure, and there using LSD with Bonferroni correction (α = 0.05). are clear benefits in adjusting procedures to reduce bycatches if it can be done without reducing lure efficacy for target species. A pre- Results vious study conducted by the authors (Sullivan et al. 2016) exam- ined the response of D. frontalis and T. dubius to traps baited with Both H. pruinosus and E. nigripes were trapped predominantly in the endo-brevicomin devices positioned either on or 6 m distant from spring with very few caught during the other seasons (Fig. 1). When monitoring traps during a 31 mo. interval. In the present study, we data were limited to collections from 6-wk intervals in which at least examined catch data for H. pruinosus and E. nigripes from the pre- one nontarget beetle was caught, treatment differences were signifi- vious study to determine if displacement of the endo-brevicomin lure cant for D. frontalis (F = 79.5; df = 2,10; P < 0.0001), H. pruinosus might have benefits in reducing the proportion of these nontarget (F = 38.1; df = 2,10; P < 0.0001), and E. nigripes (F = 30.8; df = 2,10; species in survey traps. P < 0.0001). For both nontarget species, catches were significantly higher in traps with endo-brevicomin attached directly to them rather than displaced 6 m away, while the reverse was observed for D. fronta- Materials and Methods lis (Table 1). Treatment differences were significant for both the ratios of H. pruinosus to D. frontalis (F = 101.8; df = 2,10; P < 0.0001), Detailed methods for the trapping experiment are given in Sullivan and E. nigripes to T. dubius (F = 42.1; df = 2,10; P < 0.0001). Both et al. (2016) and are summarized here. Six 12-unit Lindgren multi- ratios were significantly higher (P < 0.001) for collections from traps ple-funnel traps were spaced 450–720 m apart within mixed pine/ with the endo-brevicomin device attached directly to them compared hardwood forests in the Homochitto National Forest, Mississippi to those from traps with the endo-brevicomin device positioned 6 (within 5 km of W91.200, N31.419). Traps were suspended from m away (Table 1). Highest ratio of H. pruinosus to D. frontalis in metal standards with their collection cups approximately 1 m any single trap was 37.1:1 (3,633 H. pruinosus and 98 D. frontalis; above the ground. Each trap was baited with devices releasing fron- recorded in late March/early April 2010); the highest recorded ratio of talin (>95% purity, racemic; release rate = 1–5 mg/d) and alpha- E. nigripes to T. dubius was 1.2:1 (117 E. nigripes and 98 T. dubius; pinene (>95% purity, 25% (+)-enantiomer; release rate = 1–5 g/d), recorded in late February 2011). Both of these extremes were recorded both from Synergy Semiochemicals, Vancouver, British Columbia, from traps on which the endo-brevicomin lure was attached directly. Canada. A third lure (racemic endo-brevicomin; >95% purity; re- lease rate = 0.25–1.5 mg/d; Synergy Semiochemicals) was either ab- sent, placed directly on the trap, or positioned 6 m east of the trap Discussion at 1.5 m height. Release rates of each lure were measured gravi- metrically in a fume hood at room temperature (20–24°C) prior to Undesired bycatches of two potentially confounding species were initial deployment and after removal from the trap. We observed reduced to low numbers by removing one lure component a few meters a substantial decrease in release over the lifetime of each lure, and from the trap. Changing the placement of an olfactory lure relative to this is reflected in the ranges of release rates reported above. Traps the trap appears to be a novel method for minimizing bycatches while were grouped into two lines of three traps, then one of each of the maintaining levels of target species catches. Other methods have been three treatments were assigned randomly to each trap of the group. identified for reducing catches of nontarget species for the purpose Treatments were then rotated (by movement of endo-brevicomin of improving sorting efficiency or protecting beneficial insects. These lure) continuously through the three positions of each group; treat- include altering the types or enantiomeric blends of chemicals used ments were reassigned at the time of catch collection. Collections (Raffa and Klepzig 1989, Aukema et al. 2000, Panzavolta et al. 2014), were made approximately biweekly between 6 February 2009 and and altering the design of traps (e.g., adding a mesh screen to prevent 6 September 2011. All D. frontalis, T. dubius, H. pruinosus, and entry) to restrict the size of insects that can enter (Ross and Daterman E. nigripes were sorted and counted. 1998, Martín et al. 2013). Use of specific trap colors has been shown We analyzed these data to determine whether displacement of effective in lowering natural enemy and pollinator trap catches (Weber the endo-brevicomin lure significantly altered the ratios of bycatch et al. 2005, Mori and Evenden 2013, Spears et al. 2016). Downloaded from https://academic.oup.com/jinsectscience/article-abstract/18/1/3/4781596 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Journal of Insect Science, 2017, Vol. 18, No. 1 3 Fig. 1. Catches of clerid predator Enoclerus nigripes and ash bark beetle Hylesinus pruinosus in multiple funnel traps during 31 mo of trapping in the Homochitto National Forest, Mississippi. Traps were baited with frontalin, alpha-pinene, and a device releasing endo-brevicomin that was located either on the trap or 6 m away. Lure treatments were exchanged among traps so that approximately every 6 wk the treatments were rotated through every trap position. Hence, to balance site effects for trap, mean values shown are the average catches over 6 wk (i.e., a complete rotation). The higher catches of these two species in traps to which the endo-brevicomin device was attached directly contrasts with the response of southern pine beetle, Dendroctonus frontalis and its clerid predator, Thanasimus dubius, caught in the same traps (Sullivan et al. 2016). These latter species either did not discriminate (T. dubius) or showed a preference for traps with displaced endo-brevicomin (D. frontalis), which is a potent attractant synergist for D. frontalis. Table 1. Mean (±SE) catch per day and ratios of catches of target and nontarget species in traps baited with attractive lures for D. frontalis over a 31-mo interval endo-Brevicomin lure status Species Category Absent On trap 6 m away E. nigripes Nontarget 0.003 ± 0.002a 0.462 ± 0.170b 0.014 ± 0.007a T. dubius Target 2.980 ± 0.340a 2.971 ± 0.358a 3.265 ± 0.511a E. nigripes/T. dubius 0.001 ± 0.001a 0.185 ± 0.082b 0.004 ± 0.002a H. pruinosus Nontarget 0.006 ± 0.003a 9.708 ± 3.843b 0.317 ± 0.120a D. frontalis Target 0.893 ± 0.141a 3.257 ± 0.236b 14.867 ± 2.616c H. pruinosus/D. frontalis 0.009 ± 0.004a 2.957 ± 1.157b 0.022 ± 0.007a Mean catch of each of six traps (n = 6) including averaged catches only from 6-wk intervals in which at least one individual of the nontarget species was trapped (see text). Means associated with the same letter were not significantly different within species or species combination (α = 0.05; LSD with Bonferroni correction). It is possible that lowering the release rate of the endo-brevi- For both H. pruinosus and E. nigripes, annual flight peaked in comin device placed directly on the trap would likewise have late winter through early spring (February through April) and over- reduced the proportion of the bycatch species. An endo-brevicomin lapped with the springtime burst of flight activity of both D. fronta- dose-response study (with endo-brevicomin devices located on the lis (February through June) and T. dubius (February through April) traps and trapping methodology otherwise similar to the present (Sullivan et al. 2016). The period of H. pruinosus and E. nigripes study; Sullivan 2016, authors’ unpublished data) suggested that peak flight also coincides with the period when traps for the an- slightly lowering the release rate of endo-brevicomin from than that nual D. frontalis forecasting survey are deployed (the 4 wk follow- used in the present study might significantly increase D. frontalis ing bloom of dogwood, Cornus florida L., and, in a recently revised and decrease H. pruinosus catches. However, in this aforementioned protocol, the bloom of eastern redbud, Cercis canadensis L.; John study, at the most attractive release rate of endo-brevicomin for T. Nowak, personal communication). D. frontalis (approximately 0.16 mg/d), the ratio of trapped H. pru- endo-Brevicomin is an attractant synergist for D. frontalis that inosus to D. frontalis was still nearly 1:1. This suggests that lure rate is unusual in its capacity to enhance attraction of this species to adjustment could not duplicate the bycatch reduction effects of lure sources of attractive lure components (frontalin and host odors) over displacement. a radius of at least tens of meters while simultaneously having no Downloaded from https://academic.oup.com/jinsectscience/article-abstract/18/1/3/4781596 by Ed 'DeepDyve' Gillespie user on 16 March 2018 4 Journal of Insect Science, 2017, Vol. 18, No. 1 tendency to increase attraction to its own point of release (Sullivan Mori, B. A., and M. L. Evenden. 2013. Factors affecting pheromone-baited trap capture of male Coleophora deauratella, an invasive pest of clover in and Mori 2009). Thus, it is not necessary for the compound to be Canada. J. Econ. Entomol. 106: 844–854. released from an attractant-baited trap for D. frontalis catches to be Panzavolta, T., M. Bracalini, L. Bonuomo, F. Croci, and R. Tiberi. 2014. Field enhanced. However, removal of the endo-brevicomin device from the response of non-target beetles to Ips sexdentatus aggregation pheromone trap greatly reduced catches of H. pruinosus and E. nigripes, suggest- and pine volatiles. J. Appl. Entomol. 138: 586–599. ing that these species orient close to the source of endo-brevicomin Price, T. S., C. Doggett, J. M. Pye, and B. Smith. 1998. A history of southern which is for them an attractant rather than a synergist (Shepherd pine beetle outbreaks in the southeastern United States. Georgia Forestry et al. 2010). Simultaneously, T. dubius does not show behavioral Commission, Macon, GA. responses to endo-brevicomin (Salom et al. 1992, Sullivan et al. Raffa, K. F., and K. D. Klepzig. 1989. Chiral escape of bark beetles from pred- 2016), and therefore its placement is irrelevant to this species. Our ators responding to a bark beetle pheromone. Oecologia 80: 566–569. study demonstrates that interspecific differences in spatial behavior Ross, D. W., and G. E. Daterman. 1998. Pheromone-baited traps for Dendroctonus pseudotsugae (Coleoptera: Scolytidae): influence of selected to attractive semiochemicals among insect species can be exploited release rates and trap designs. J. Econ. Entomol. 91: 500–506. in order enhance the targeting of particular species. Salom, S. M., R. F. Billings, W. W. Upton, M. J. Dalusky, D. M. Grosman, T. L. Payne, C. W. Berisford, and T. N. Shaver. 1992. Effect of verbenone enantiomers and racemic endo-brevicomin on response of Dendroctonus Acknowledgments frontalis (Coleoptera: Scolytidae) to attractant-baited traps. Can. J. For. We wish to thank Cavell Brownie, NC State University (retired), for help Res. 22: 925–931. with statistical analyses; Lee Dunnam and other Homochitto National Forest SAS Institute. 2013. SAS 9.4. SAS Institute, Cary, NC. personnel for providing research sites; and JoAnne Barrett, Zach Oliver and Shepherd, W. P., B. T. Sullivan, B. M. Hoosier, J. P. Barrett, and T. A. Bauman. Chris Young for technical help in field and lab. Drs. Alex Mangini and Rabiu 2010. Characterization of an aggregation pheromone in Hylesinus pruinosus Olatinwo, USDA Forest Service, reviewed an earlier version of this article. (Coleoptera: Curculionidae: Scolytinae). Environ. Entomol. 39: 633–641. Funding was provided by USDA Forest Service Southern Research Station Spears, L. R., C. Looney, H. Ikerd, J. B. Koch, T. Griswold, J. P. Strange, and R. RWU-4552. A. Ramirez. 2016. Pheromone lure and trap color affects bycatch in agri- cultural landscapes of Utah. Environ. Entomol. 45: 1009–1016. Sullivan, B. T. 2011. Southern pine beetle behavior and semiochemistry, pp. References Cited 25–50. In R. N. Coulson and K. D. Klepzig (eds.), The southern pine beetle Aukema, B. H., D. L. Dahlsten, and K. F. Raffa. 2000. Exploiting behavioral II. USDA Forest Service Southern Research Station Gen. Tech. Rep. 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