TY - JOUR
AU - McCreary,, Cara
AB - Abstract The pepper weevil, Anthonomus eugenii Cano, is an economically important pest of field and greenhouse pepper crops in North America. In this study, a series of insecticides covering a broad-spectrum of insecticidal modes of action were assessed for their potential in managing the pepper weevil under laboratory and greenhouse conditions. To accomplish this, laboratory mini-spray tower and greenhouse cage trials were conducted that evaluated the efficacy of 16 conventional, reduced-risk, and microbial insecticides. In laboratory trials, adult weevils were sprayed with insecticides, placed on treated leaves within a cup cage, and were monitored for their survival over 10 d. Of the 16 insecticides tested, 8 provided greater than 60% weevil control, a threshold considered necessary for including products in further greenhouse testing. In greenhouse trials, adult weevil mortality, bud and foliar damage, bud and fruit abortion, and subsequent weevil offspring emergence were measured following each of three weekly insecticide applications. The most efficacious insecticides included kaolin clay and mineral oil, which performed as well as the thiamethoxam-positive control, and incurred 70 and 55% of adult weevil mortality, respectively. Additionally, kaolin clay and mineral oil reduced offspring weevil emergence by 59 and 54%, respectively, compared with untreated controls. Despite the clear challenge that controlling this pest represents, this study has identified useful new tools for the integrated management of the pepper weevil, which may accelerate the rate at which these become available for use in greenhouse and field pepper production. management, microbial, insecticide, reduced risk Throughout North and Central America, the cultivation of pepper crops belonging to the genus Capsicum is an important component of agricultural productivity. Originating from the Neotropics (Wien 1997), Capsicum pepper production is widespread in countries such as Mexico, where over 3.29 million tons of fresh chillies, bell peppers, and other cultivars are produced on over 160,000 ha of land (2017 data FAOSTAT 2019). Recently, pepper production has expanded throughout the globe, including in the United States and Canada where over a million tons of pepper are produced annually (Statistics Canada 2016, FAOSTAT 2019). Today, pepper crops are grown not only in fields but also increasingly in greenhouse environments. Commercial greenhouse production is now extensive in certain regions of Spain, the Netherlands, Israel, Mexico, Canada, and the United States (Jovicich et al. 2005). This new way of growing pepper fruits is driven primarily by an increasing consumer appetite for large, high-quality bell peppers, and as a way to prolong the growing season in temperate areas of the globe (Lin and Saltveit 2012). Furthermore, growing indeterminate cultivars on a vertical scale in greenhouses also makes it possible to significantly increase the duration and output of crop production. Thus, while many greenhouse pepper producing countries account for less than 1% of the global production area, the quantity of pepper production per acre far exceeds that which is possible through field cultivation (Correll and Thornsbury 2013). One of the major factors which threatens productivity of large-scale global pepper production is infestation by the pepper weevil, Anthonomus eugenii Cano. The pepper weevil, which also shares its Neotropical origins with Capsicum plant species, is a pest capable of causing total yield loss when its population densities are high in pepper crops (Clausen 1978). Today, this weevil is found throughout many pepper growing regions of Mexico and occurs periodically in the Northern Hemisphere. It is seasonally present in field crops of the southern United States, with irregular occurrences in more northerly regions such as New Jersey (Ingerson-Mahar et al. 2015). It is also occasionally present in Canada, with infestations documented from British Columbia in 1992 (Costello and Gillespie 1993) and again in Ontario in 2016 (Labbé et al. 2018). Furthermore, the pepper weevil has sporadically made its way to other parts of the globe, including Italy and the Netherlands (van der Gaag and Loomans 2013, Speranza et al. 2014), and poses a threat to other major pepper producing regions of the world including in Asia, Europe, and Africa (FAOSTAT 2019). Thus, the losses attributed to pepper weevil infestations, and the continued risk this pest represents on a global scale, highlight the importance of identifying effective management tools for use in both greenhouse and field pepper crop production. Currently, the combined use of chemical insecticides, intensive crop scouting, and cultural management are recognized as the main tools available to pepper growers for managing pepper weevil populations. However, even in early accounts of pepper weevil management, it was clear that pepper weevil populations are difficult to control using chemical insecticides alone (Elmore and Campbell 1954). This can be attributed in part to the concealed biology of this pest species, whereby all immature life stages of the pepper weevil occur within the confines of the pepper buds and fruits, where they are protected from insecticidal sprays. In addition, the presence of alternate solanaceous weedy or crop plants around fields or greenhouses can represent an important source of re-infestation. Thus, while the adults are exposed, the continuous and asynchronous emergence of new weevil offspring from pepper fruits and buds, as well as the movement of weevils from surrounding solanaceous hosts, mean that frequent applications of insecticides are required to significantly reduce weevil numbers. Another factor affecting the sustainable control of the pepper weevil is the development of insecticide resistance. In their native range, populations of the pepper weevil have been shown to display strong resistance to multiple insecticides, including methomyl, oxamyl, methamidophos, endosulfan, cyfluthrin, and azinphos-methyl (Servin-Villegas et al. 2008). Furthermore, in many countries of the world, insecticides such as the neonicotinoids are gradually being phased-out, leaving growers with fewer tools available for the management of this pest. Consequently, growers currently have a limited number of validated and registered insecticides available to manage the pepper weevil. Another necessary consideration is the nontarget effects insecticides may have on beneficial arthropod communities in greenhouse environments, including biological control agents used to manage other pests and bees employed for crop pollination. Due to the combined concerns over the development of insecticide resistance, the undesired effects insecticides may have on beneficial arthropod communities, and limited registered insecticides, there is a clear interest by growers to evaluate novel, reduced-risk microbial and conventional insecticides for pepper weevil management in protected environments. Until now, the systematic assessment of insecticides which meet the unique needs of greenhouse pepper producers had yet to be completed. This work aimed to address the current need for new insecticides for pepper weevil management in both greenhouse and field environments. We performed laboratory bioassays to compare the efficacy of 16 different insecticides, including several microbial and reduced-risk agents, an insect growth regulator and a ryanoid class agent with a relatively new mode of action, on adult pepper weevil mortality. Following these bioassays, the most effective agents were assessed for their impact on pepper weevil populations on pepper plants in greenhouse cage trials. Unique to this study was our assessment of how each insecticide affected variables including weevil egg laying, the incidence of offspring emergence, and the proportion of fruit aborted from plants in each treatment. These assessments not only contributed to identifying good pepper weevil control agents but also provide an in-depth account of how different insecticide types can impact both pepper weevil population dynamics and potential crop yield. Together, these details can contribute to effective and sustainable integrated pest management of the pepper weevil on both greenhouse and field pepper crops. Materials and Methods Pepper Weevil Colonies Anthonomus eugenii used in this study originated from an on-site colony maintained at the Harrow Research and Development Centre, Agriculture and Agri-food Canada, Harrow, Ontario. A secondary colony, established from this same source but maintained at the University of Guelph, Ontario, was also used to complete assessment of Bacillus thuringiensis subsp. galleriae str. SDS-502 in greenhouse trials. Adults and immature weevils from these sources were reared in controlled environment cabinets (CONVIRON A-1000) maintained at 29°C oviposition and 27°C, respectively. Cabinet temperatures were chosen to optimize oviposition by adults and percent hatch of immatures, when rearing on whole peppers (Toapanta et al. 2005). Cabinets were maintained at 60% relative humidity and a photoperiod of 14:10 (L:D) h. All rearing containers were maintained twice a week. Adults were provided greenhouse sweet bell pepper (c.v. Felicitas and Fascinato) and jalapeño (Capsicum annuum Group) fruits for oviposition, as well as leaves, water wicks, and a 10% honey wick as sources of food and water. Evaluation of Residual and Direct Toxicity Laboratory efficacy trials were conducted at the Harrow Research and Development Centre, Harrow, Ontario, in 2018 and 2019. For these trials, each of 16 conventional, reduced-risk, and biopesticide treatments were applied both as a leaf dip and sprayed directly onto the surface of adult pepper weevils to test the combined effect of residual and direct contact activity. Clear cup cages were created to hold pesticide-treated leaves and weevils by nesting a 60-ml clear plastic portion cup (Dart Conex Complements, Merchants Paper Company, Windsor, Ontario, Canada) inside a 266-ml clear plastic cup (Dart, Merchants Paper Company; Gillespie et al. 2012). A water reservoir was created at the base of the cup cage by filling it with 38 ml of distilled water, into which the leaf petiole was positioned, which maintained leaf freshness for 10-d post-dip application. To dip leaves, the ~6.5-cm wide leaves of bell pepper, Capsicum annuum, were lowered into 180 ml of prepared insecticide solution for ~5 s. Leaf petioles were then individually wrapped with cotton batting and secured into the clear cup cage. Leaves were left to dry in these containers for 2 h in a fume hood prior to the addition of product-treated weevils and microperforated plastic lids. Evaluation of Direct Toxicity Adult pepper weevils were treated with formulated insecticides using a custom-made mini spray tower, consisting of a 7.5-cm-diameter and 24-cm-long metal cylinder of approximately one-ninth the scale of a Potter spray tower (Potter 1952, Telfer 2017). The spray tower used a Paasche VL airbrush (Paasche Airbrush Company, Chicago, IL), fitted with a 0.5-mm needle (Paasche, VLT-1, Chicago, IL), connected to an airbrush compressor (LS-186S Pro Air, China). The cylinder and airbrush were set to fixed positions on a retort stand ensuring consistent product delivery between treatments and trials. The airbrush was set to 5 cm within the top of the metal spray cylinder, a position which optimized the distribution of spray product onto the basal application surface. Prior to pesticide application, 15- to 28-d-old pepper weevils were removed from the colony and aspirated into groups of 10. Pepper weevils were anesthetized via CO2 exposure for 5 s before being transferred to a 30-ml portion cup (Dart, Conex cup 650–1330, Merchants Papers) lined with filter paper (Whatman, Z240567, Sigma–Aldrich, Oakville, Ontario, Canada). The portion cup containing the weevils was attached to the base of the tower using an 8-cm wide plastic cup lid (Dart, Conex cup lid, Merchants Papers). All insecticides were mixed with sterilized distilled water on the day of application. Insecticide treatments were tested at low (1/2× label), label, and high (2× label) rates (Table 1). The label rate used to test the efficacy of each insecticide for pepper weevil control was based on the recommended rates (RR) available from labels for each insecticide. The laboratory experiments were divided into four trials, to accommodate the large number of weevils needed for each. For each insecticide testing trial, 1× label rate thiamethoxam was applied as a positive control and distilled water as a negative control. If the published label rate was given as a range, the middle of the range was chosen for evaluation in this study. Table 1. Percent pepper weevil control (mean ± SEM) after 10 d following direct cuticular spray and foliar exposure to one of 16 insecticide treatments within four laboratory bioassay trials Trial Active ingredient Trade name IRAC groupa Rateb Percent control (mean ± SEM)c 1 Bacillus thuringiensis subsp. aizawai str. ABTS-1857 Xentari DF (WP) 11A 1.75 × 107 Lat/ml 4.10 ± 3.69ab 3.5 × 107 Lat/ml 5.00 ± 5.00ab 7.0 × 107 Lat/ml 5.28 ± 4.87ab Bacillus thuringiensis subsp. galleriae str. SDS-502 BeetleGone 11 6.4 × 107 cfu/ml 2.41 ± 1.57a 1.3 × 107 cfu/ml 48.06 ± 12.49b 2.6 × 108 cfu/ml 43.33 ± 16.36ab Metarhizium anisopliae str. F52 Met52 EC UNF 2.5 × 106 cfu/ml 40.19 ± 3.15abc 5.0 × 106 cfu/ml 71.67 ± 0.00c 1.0 × 1067 cfu/ml 43.33 ± 42.50abc 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 95.28 ± 4.72c 2 Bacillus thuringiensis subsp. tenebrionis str. NB176 Novodor 11A 3.3 × 105 LTU/ml 3.33 ± 3.33a 6.7 × 105 LTU/ml 0.00 ± 0.00a 1.3 × 106 LTU/ml 0.00 ± 0.00a Beauveria bassiana str. ANT-03 (F1) BioCeres UNF 2.0 × 107 conidia/ml 6.67 ± 0.00a 4.0 × 107 conidia/ml 15.00 ± 15.00ab 8.0 × 107 conidia/ml 35.83 ± 5.83b Beauveria bassiana str. PPRI5339, 8% Velifer UNF 3.6 × 109 conidia/ml 30.00 ± 0.00bc 7.2 × 109 conidia/ml 83.03 ± 6.36c 1.4 × 1010 conidia/ml 100.00 ± 0.00c Beauveria bassiana str. GHA Botanigard ES UNF 2.8 × 107 conidia/ml 100.00 ± 0.00c 5.5 × 107 conidia/ml 100.00 ± 0.00c 1.1 × 108 conidia/ml 100.00 ± 0.00c 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 100.00 ± 0.00c 3 Lecanicillium muscarium Mycotal UNF 5.0 × 106 conidia/ml 13.51 ± 6.24a 1.0 × 107 conidia/ml 9.01 ± 7.70a 2.0 × 107 conidia/ml 35.14 ± 10.81abc Beauveria bassiana str. R444 Bb-Protec WP UNF 1.0 × 106 conidia/ml 16.22 ± 14.89a 2.0 × 106 conidia/ml 49.55 ± 19.07abc 4.0 × 106 conidia/ml 53.15 ± 9.53abc Kaolin clay, 95% Surround WP n/a 17,813 ppm 31.53 ± 9.53abc 35,625 ppm 38.74 ± 14.41abc 71,250 ppm 85.59 ± 3.60c Mineral oil, 98% PureSpray GREEN n/a 12,250 ppm 56.76 ± 21.62bc 24,500 ppm 78.38 ± 0.00c 49,000 ppm 74.77 ± 3.60bc Beauveria bassiana str. ANT-03 (F2) BioCeres UNF 2002 ppm 78.38 ± 6.24c 4005 ppm 78.38 ± 6.24c 8009 ppm 89.19 ± 6.24c 4 10% Novaluron Rimon 0.83 EC 15 89 ppm 18.01 ± 6.02a 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 85.82 ± 3.27b 10.2% Cyantraniliprole Exirel 28 418 ppm 93.10 ± 3.45bc 25% Spinetoram Delegate WG 5 28 ppm 100.00 ± 0.00c Trial Active ingredient Trade name IRAC groupa Rateb Percent control (mean ± SEM)c 1 Bacillus thuringiensis subsp. aizawai str. ABTS-1857 Xentari DF (WP) 11A 1.75 × 107 Lat/ml 4.10 ± 3.69ab 3.5 × 107 Lat/ml 5.00 ± 5.00ab 7.0 × 107 Lat/ml 5.28 ± 4.87ab Bacillus thuringiensis subsp. galleriae str. SDS-502 BeetleGone 11 6.4 × 107 cfu/ml 2.41 ± 1.57a 1.3 × 107 cfu/ml 48.06 ± 12.49b 2.6 × 108 cfu/ml 43.33 ± 16.36ab Metarhizium anisopliae str. F52 Met52 EC UNF 2.5 × 106 cfu/ml 40.19 ± 3.15abc 5.0 × 106 cfu/ml 71.67 ± 0.00c 1.0 × 1067 cfu/ml 43.33 ± 42.50abc 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 95.28 ± 4.72c 2 Bacillus thuringiensis subsp. tenebrionis str. NB176 Novodor 11A 3.3 × 105 LTU/ml 3.33 ± 3.33a 6.7 × 105 LTU/ml 0.00 ± 0.00a 1.3 × 106 LTU/ml 0.00 ± 0.00a Beauveria bassiana str. ANT-03 (F1) BioCeres UNF 2.0 × 107 conidia/ml 6.67 ± 0.00a 4.0 × 107 conidia/ml 15.00 ± 15.00ab 8.0 × 107 conidia/ml 35.83 ± 5.83b Beauveria bassiana str. PPRI5339, 8% Velifer UNF 3.6 × 109 conidia/ml 30.00 ± 0.00bc 7.2 × 109 conidia/ml 83.03 ± 6.36c 1.4 × 1010 conidia/ml 100.00 ± 0.00c Beauveria bassiana str. GHA Botanigard ES UNF 2.8 × 107 conidia/ml 100.00 ± 0.00c 5.5 × 107 conidia/ml 100.00 ± 0.00c 1.1 × 108 conidia/ml 100.00 ± 0.00c 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 100.00 ± 0.00c 3 Lecanicillium muscarium Mycotal UNF 5.0 × 106 conidia/ml 13.51 ± 6.24a 1.0 × 107 conidia/ml 9.01 ± 7.70a 2.0 × 107 conidia/ml 35.14 ± 10.81abc Beauveria bassiana str. R444 Bb-Protec WP UNF 1.0 × 106 conidia/ml 16.22 ± 14.89a 2.0 × 106 conidia/ml 49.55 ± 19.07abc 4.0 × 106 conidia/ml 53.15 ± 9.53abc Kaolin clay, 95% Surround WP n/a 17,813 ppm 31.53 ± 9.53abc 35,625 ppm 38.74 ± 14.41abc 71,250 ppm 85.59 ± 3.60c Mineral oil, 98% PureSpray GREEN n/a 12,250 ppm 56.76 ± 21.62bc 24,500 ppm 78.38 ± 0.00c 49,000 ppm 74.77 ± 3.60bc Beauveria bassiana str. ANT-03 (F2) BioCeres UNF 2002 ppm 78.38 ± 6.24c 4005 ppm 78.38 ± 6.24c 8009 ppm 89.19 ± 6.24c 4 10% Novaluron Rimon 0.83 EC 15 89 ppm 18.01 ± 6.02a 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 85.82 ± 3.27b 10.2% Cyantraniliprole Exirel 28 418 ppm 93.10 ± 3.45bc 25% Spinetoram Delegate WG 5 28 ppm 100.00 ± 0.00c Each trial included different insecticides at various dosage rates, as well as a thiamethoxam-positive control and a water negative control. Letters following percent control values indicate the presence of significant differences in Abbott’s corrected proportion weevil control for each insecticide as determined through ANOVA at P < 0.05. aModes of action derived from https://www.irac-online.org/modes-of-action/ bRate units include colony forming units (cfu), conidia per mL in spray solution, Leptinotarsa units (LTU) or Lepidopteran active toxins (Lat) for biologicals, or as parts per million (ppm). cPercent control data presented are Abbott’s corrected (Abbott, 1925). Numbers followed by same letters are not statistically different (Tukey’s HSD, α = 0.05). Open in new tab Table 1. Percent pepper weevil control (mean ± SEM) after 10 d following direct cuticular spray and foliar exposure to one of 16 insecticide treatments within four laboratory bioassay trials Trial Active ingredient Trade name IRAC groupa Rateb Percent control (mean ± SEM)c 1 Bacillus thuringiensis subsp. aizawai str. ABTS-1857 Xentari DF (WP) 11A 1.75 × 107 Lat/ml 4.10 ± 3.69ab 3.5 × 107 Lat/ml 5.00 ± 5.00ab 7.0 × 107 Lat/ml 5.28 ± 4.87ab Bacillus thuringiensis subsp. galleriae str. SDS-502 BeetleGone 11 6.4 × 107 cfu/ml 2.41 ± 1.57a 1.3 × 107 cfu/ml 48.06 ± 12.49b 2.6 × 108 cfu/ml 43.33 ± 16.36ab Metarhizium anisopliae str. F52 Met52 EC UNF 2.5 × 106 cfu/ml 40.19 ± 3.15abc 5.0 × 106 cfu/ml 71.67 ± 0.00c 1.0 × 1067 cfu/ml 43.33 ± 42.50abc 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 95.28 ± 4.72c 2 Bacillus thuringiensis subsp. tenebrionis str. NB176 Novodor 11A 3.3 × 105 LTU/ml 3.33 ± 3.33a 6.7 × 105 LTU/ml 0.00 ± 0.00a 1.3 × 106 LTU/ml 0.00 ± 0.00a Beauveria bassiana str. ANT-03 (F1) BioCeres UNF 2.0 × 107 conidia/ml 6.67 ± 0.00a 4.0 × 107 conidia/ml 15.00 ± 15.00ab 8.0 × 107 conidia/ml 35.83 ± 5.83b Beauveria bassiana str. PPRI5339, 8% Velifer UNF 3.6 × 109 conidia/ml 30.00 ± 0.00bc 7.2 × 109 conidia/ml 83.03 ± 6.36c 1.4 × 1010 conidia/ml 100.00 ± 0.00c Beauveria bassiana str. GHA Botanigard ES UNF 2.8 × 107 conidia/ml 100.00 ± 0.00c 5.5 × 107 conidia/ml 100.00 ± 0.00c 1.1 × 108 conidia/ml 100.00 ± 0.00c 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 100.00 ± 0.00c 3 Lecanicillium muscarium Mycotal UNF 5.0 × 106 conidia/ml 13.51 ± 6.24a 1.0 × 107 conidia/ml 9.01 ± 7.70a 2.0 × 107 conidia/ml 35.14 ± 10.81abc Beauveria bassiana str. R444 Bb-Protec WP UNF 1.0 × 106 conidia/ml 16.22 ± 14.89a 2.0 × 106 conidia/ml 49.55 ± 19.07abc 4.0 × 106 conidia/ml 53.15 ± 9.53abc Kaolin clay, 95% Surround WP n/a 17,813 ppm 31.53 ± 9.53abc 35,625 ppm 38.74 ± 14.41abc 71,250 ppm 85.59 ± 3.60c Mineral oil, 98% PureSpray GREEN n/a 12,250 ppm 56.76 ± 21.62bc 24,500 ppm 78.38 ± 0.00c 49,000 ppm 74.77 ± 3.60bc Beauveria bassiana str. ANT-03 (F2) BioCeres UNF 2002 ppm 78.38 ± 6.24c 4005 ppm 78.38 ± 6.24c 8009 ppm 89.19 ± 6.24c 4 10% Novaluron Rimon 0.83 EC 15 89 ppm 18.01 ± 6.02a 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 85.82 ± 3.27b 10.2% Cyantraniliprole Exirel 28 418 ppm 93.10 ± 3.45bc 25% Spinetoram Delegate WG 5 28 ppm 100.00 ± 0.00c Trial Active ingredient Trade name IRAC groupa Rateb Percent control (mean ± SEM)c 1 Bacillus thuringiensis subsp. aizawai str. ABTS-1857 Xentari DF (WP) 11A 1.75 × 107 Lat/ml 4.10 ± 3.69ab 3.5 × 107 Lat/ml 5.00 ± 5.00ab 7.0 × 107 Lat/ml 5.28 ± 4.87ab Bacillus thuringiensis subsp. galleriae str. SDS-502 BeetleGone 11 6.4 × 107 cfu/ml 2.41 ± 1.57a 1.3 × 107 cfu/ml 48.06 ± 12.49b 2.6 × 108 cfu/ml 43.33 ± 16.36ab Metarhizium anisopliae str. F52 Met52 EC UNF 2.5 × 106 cfu/ml 40.19 ± 3.15abc 5.0 × 106 cfu/ml 71.67 ± 0.00c 1.0 × 1067 cfu/ml 43.33 ± 42.50abc 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 95.28 ± 4.72c 2 Bacillus thuringiensis subsp. tenebrionis str. NB176 Novodor 11A 3.3 × 105 LTU/ml 3.33 ± 3.33a 6.7 × 105 LTU/ml 0.00 ± 0.00a 1.3 × 106 LTU/ml 0.00 ± 0.00a Beauveria bassiana str. ANT-03 (F1) BioCeres UNF 2.0 × 107 conidia/ml 6.67 ± 0.00a 4.0 × 107 conidia/ml 15.00 ± 15.00ab 8.0 × 107 conidia/ml 35.83 ± 5.83b Beauveria bassiana str. PPRI5339, 8% Velifer UNF 3.6 × 109 conidia/ml 30.00 ± 0.00bc 7.2 × 109 conidia/ml 83.03 ± 6.36c 1.4 × 1010 conidia/ml 100.00 ± 0.00c Beauveria bassiana str. GHA Botanigard ES UNF 2.8 × 107 conidia/ml 100.00 ± 0.00c 5.5 × 107 conidia/ml 100.00 ± 0.00c 1.1 × 108 conidia/ml 100.00 ± 0.00c 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 100.00 ± 0.00c 3 Lecanicillium muscarium Mycotal UNF 5.0 × 106 conidia/ml 13.51 ± 6.24a 1.0 × 107 conidia/ml 9.01 ± 7.70a 2.0 × 107 conidia/ml 35.14 ± 10.81abc Beauveria bassiana str. R444 Bb-Protec WP UNF 1.0 × 106 conidia/ml 16.22 ± 14.89a 2.0 × 106 conidia/ml 49.55 ± 19.07abc 4.0 × 106 conidia/ml 53.15 ± 9.53abc Kaolin clay, 95% Surround WP n/a 17,813 ppm 31.53 ± 9.53abc 35,625 ppm 38.74 ± 14.41abc 71,250 ppm 85.59 ± 3.60c Mineral oil, 98% PureSpray GREEN n/a 12,250 ppm 56.76 ± 21.62bc 24,500 ppm 78.38 ± 0.00c 49,000 ppm 74.77 ± 3.60bc Beauveria bassiana str. ANT-03 (F2) BioCeres UNF 2002 ppm 78.38 ± 6.24c 4005 ppm 78.38 ± 6.24c 8009 ppm 89.19 ± 6.24c 4 10% Novaluron Rimon 0.83 EC 15 89 ppm 18.01 ± 6.02a 25% Thiamethoxam Flagship 25 WG 4A 35 ppm 85.82 ± 3.27b 10.2% Cyantraniliprole Exirel 28 418 ppm 93.10 ± 3.45bc 25% Spinetoram Delegate WG 5 28 ppm 100.00 ± 0.00c Each trial included different insecticides at various dosage rates, as well as a thiamethoxam-positive control and a water negative control. Letters following percent control values indicate the presence of significant differences in Abbott’s corrected proportion weevil control for each insecticide as determined through ANOVA at P < 0.05. aModes of action derived from https://www.irac-online.org/modes-of-action/ bRate units include colony forming units (cfu), conidia per mL in spray solution, Leptinotarsa units (LTU) or Lepidopteran active toxins (Lat) for biologicals, or as parts per million (ppm). cPercent control data presented are Abbott’s corrected (Abbott, 1925). Numbers followed by same letters are not statistically different (Tukey’s HSD, α = 0.05). Open in new tab For direct insect exposure, a 1-ml volume of pesticide was pipetted into the air brush sprayer reservoir via a plastic tube attached to the reservoir opening. The airbrush sprayed the solution at 20 PSI until it entirely left the reservoir (with ~0.2 ml adhering to the weevils). Following each treatment, pepper weevils were transferred to plastic cups containing the dipped leaf, which were then covered with a venting microperforated plastic, held in place by an elastic band. Each treatment and application rate had three replicates of 10 pepper weevils. Following completion of spray treatments, all cups were held in a controlled environment cabinet maintained at a constant 25°C, a photoperiod of 16:8 (L:D) h, and 50% RH. Pepper weevil mortality was recorded daily for 10 d. Insects that failed to move when touched with a dissection probe were counted as dead. Leaf feeding was monitored daily so that leaves with heavy feeding could be replaced as needed with leaves treated with the same insecticide and dose rate applied on the initial insecticide application date. Four separate trials, each evaluating different pesticides, were conducted over time so as not to deplete the pepper weevil colony (Table 1). Greenhouse Efficacy Trials Greenhouse insecticide efficacy trials were conducted starting in April 2019 at the Harrow Research and Development Centre, Harrow, Ontario. Trials were conducted in two research greenhouses of 7.4 m in width and 12.5 m in length, which were ventilated by exterior fans and ceiling vent controlled by Argus climate control systems (Argus, Surrey, British Columbia, Canada). To replicate typical commercial greenhouse growing conditions during trials, two naturally lit greenhouses were set at 24°C (venting at 26°C and above) during the day, 18°C (venting at 20°C and above) during the night and a 50% RH. Over the course of these 22-d trials, the average temperature and RH values achieved were of 22.93 ± 0.08°C and 45.53 ± 0.29% RH in one experimental greenhouse and 24.65 ± 0.09°C and 39.78 ± 0.24% RH in the second. Treatments within each of the greenhouses were arranged in a randomized complete block with three replicates of each treatment present in each of the two trial greenhouses, for a total of six replicates per treatment. Experimental units consisted of individual 47.5 × 47.5 × 93-cm cages (Bugdorm 2400, MegaView Science Co., Ltd., Taiwan) positioned on six greenhouse benches, each containing two 12-wk-old pepper plants (cv. Felicitas) transplanted onto rockwool slabs. Plants were irrigated twice a day with a standard pepper nutrient solution and pruned to two stems (OMAFRA 2010). All plants contained a mixture of buds, flowers, and fruit. On the first insecticide application date, plants in cages were first infested with ten 7- to 28-d-old adult pepper weevils. Just prior to the application of insecticide suspensions, tanks were mixed to ensure an even insecticide application in every treatment cage. Insecticides were applied at label rate using a CO2 pressurized backpack sprayer calibrated to deliver 0.52 liter/min of solution at 276 kPa through a hollow cone spray tip nozzle (TXVS-8 ConeJet VisiFlo TeeJet, R & D Sprayers, Opelousas, LA) fitted with a 50-mesh strainer (TeeJet 55215–50, R & D Sprayers), except for the kaolin clay treatment, in which a 50-mesh slotted strainer (4514-0 TeeJet, R & D Sprayers) was used to prevent clogging the spray tip. Each insecticide treatment was applied three times at 7-d intervals. On each of these dates, plants were sprayed for 7 s each to achieve complete coverage. Three untreated control cages were also included in each of the two trial greenhouses. In order to include the assessment of Bacillus thuringiensis subsp. galleriae strain SDS-502 within this study, a treatment which only narrowly achieved weevil suppression in laboratory assays, weevils from the second laboratory colony source at the University of Guelph (Guelph, Ontario, Canada) were used. To account for any variability in effect that this colony source had on weevil survival, a second set of control treatment cages was also included in these analyses, which were infested with weevils from the University of Guelph colony. Assessments following each of the three weekly insecticide treatments were performed 2 and 6 DAA (days after application). On these six assessment dates, plants within cages were carefully examined to evaluate the numbers of live and dead weevils, damaged and undamaged flowers, damaged and undamaged buds, damaged and undamaged fruit, aborted flowers, buds and fruits, and percentage of defoliation were quantified. Following the sixth and final assessment date, all fruits and buds from each cage were counted, placed within a micro perforated bag, and monitored twice a week for over 3 wk for the emergence of offspring pepper weevil adults resulting from oviposition by primary test subject weevils. After the last on-plant assessment, all plant material was bagged, frozen for 2 wk to eliminate any possible pepper weevils, and destroyed according to federal law. Statistical Analyses Laboratory trials Ten days following the application of each product in laboratory bioassay trials, data for percent weevil control was calculated using Abbott’s formula (Abbott 1925). To account for the diversity of treatments assessed in each of the four laboratory trials, the effects of insecticide treatments on percent weevil control were analyzed separately for each trial, through analysis of variance (ANOVA) using PROC GLM in SAS where treatment was modeled as a fixed effect and replicate as a random effect (SAS v. 9.3 SAS Institute 2011, Cary, NC). Mean separation was performed through Tukey’s HSD at P < 0.05. Data were assessed for normality, as well as for homogeneity of variance, which was verified by graphical visualization of residuals against predicted values. Greenhouse trials The effects of insecticide treatments, time, greenhouse, and their interactions on the cumulative average number of dead weevils per cage, the number of injured and aborted fruits, as well as the number of offspring weevils, were initially compared through repeated measures ANOVAs using PROC MIXED in SAS (v. 9.3 SAS Institute 2011). However, due to the lack of an interaction between time and treatment, cumulative data for adult weevil mortality as well as offspring emergence were instead analyzed at the trial endpoint through ANOVA using PROC MIXED in SAS (v. 9.3 SAS Institute 2011). In these analyses, treatment was modeled as a fixed effect, while greenhouse, repetition, and their interactions were modeled as random effects. Data were verified for normality, as well as for homogeneity of variance, which was confirmed by graphical visualization of residuals against predicted values. Differences in mean weevil morality among treatments were identified through Tukey’s HSD at P < 0.05. Differences in offspring weevil emergence among treatments were separated using Dunnett’s multiple comparison procedure at P < 0.05. Due to the absence of a treatment effect on percent fruit injury and abortion, analyses for these variables are not reported. Results Laboratory Insecticide Testing Trials In each of the four insecticide testing trials performed in this study, treatment was found to be a significant factor (P ≤ 0.0002) and specifically indicated for each trial result section below). Of the 16 insecticides assessed in laboratory bioassays, 9 achieved at least 60% pepper weevil control by 10 DAA, which we selected as a minimum control level required to qualify agents for further greenhouse testing. Among insecticides treatments tested in the first of laboratory bioassay trial (F = 8.59; df = 9, 2; P = 0.0002), the thiamethoxam-positive control and Metarhizium anisopliae strain F52 applied at the recommended label rates performed significantly better than other treatments (P < 0.05). Despite this finding, M. anisopliae strain F52 was not included in the greenhouse component of this study because it was no longer commercially available when greenhouse cage trials commenced. Bacillus thuringiensis subspecies galleriae strain SDS-502 also performed better than Bacillus thuringiensis subsp. aizawai strain ABTS-1857 (P < 0.05; Table 1). In the second laboratory insecticide testing trial, multiple treatments differed significantly in percent pepper weevil control (F = 106.92; df = 12, 2; P < 0.0001). Beauveria bassiana strain GHA was highly effective against pepper weevil at all application rates 10 DAA, followed closely by Beauveria bassiana strain PPRI5339, when these were applied at the recommended label rates (Table 1). Suppression by these insecticides was also statistically equivalent to that provided by the thiamethoxam control (P < 0.05). In contrast, when applied at the label rate, neither Bacillus thuringiensis subsp. tenebrionis strain NB176 nor a preliminary formulation of Beauveria bassiana strain ANT-03 (F1) surpassed the 60% minimum level of pepper weevil suppression to pursue further testing. When applied at their respective label rates, these two insecticides also incurred significantly lower mortality of pepper weevil adults relative to B. bassiana strains GHA and PPRI5339 (P < 0.05). However, an improved formulation of B. bassiana strain ANT-03 (F2) was subsequently provided by suppliers for testing in the third laboratory bioassays trial. In the third laboratory trial (F = 6.31; df = 15, 2; P < 0.0001), mineral oil was found to provide effective mortality of pepper weevil adults at each of the three rates tested (Table 1). Kaolin clay also provided equivalent pepper weevil mortality relative to the thiamethoxam-positive control (as was the 2× label rate of kaolin clay, 95%). In contrast, the entomopathogenic fungi Lecanicillium muscarium and Beauveria bassiana strain R444 were the least effective insecticidal agents tested in this trial and did not meet the minimum 60% mortality threshold required to be included in further greenhouse insecticide testing. In the fourth laboratory trial, four conventional insecticides at their recommended label rates were assessed, which were found to differ significantly in their resulting control of pepper weevil (F = 173.20; df = 3, 2; P < 0.0001). Of these, both cyantraniliprole and spinetoram incurred levels of pepper weevil mortality that were at least as high or greater than the thiamethoxam-positive control (P < 0.05; Table 1). In contrast, novaluron did not effectively control pepper weevils relative to any of the other conventional insecticides tested in this trial (Table 1). Both cyantraniliprole and novaluron are already registered for control of pepper weevil on greenhouse and field pepper crops and were not included in subsequent greenhouse insecticide testing trials. Insecticide Efficacy in Greenhouse Cage Trials Overall, the insecticide treatments assessed in greenhouse cage trials had significant effects on both adult weevil mortality as well as on offspring weevil emergence (Table 2), but not on fruit or bud damage nor on fruit or bud abortion. Table 2. Parameter estimates for the effects of insecticide treatments, greenhouse, and their interaction on adult Anthonomus eugenii mortality and offspring emergence in greenhouse cage trials Factor . Covariance parameter . Estimate . Z-value . PR > Z . Weevil mortality Greenhouse 0 . . Rep 0 . . Rep (greenhouse) 8.24E-18 . . Residual 0.821 . . Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 3.84 0.0012 Offspring weevil emergence Covariance parameter Estimate Z-value PR > Z Greenhouse 0 . . Rep 0.0055 0.0083 0.2560 Rep(greenhouse) . . . Trt*rep(greenhouse) . . . Residual 0.5709 4.90 <0.0001 Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 4.15 0.0006 Factor . Covariance parameter . Estimate . Z-value . PR > Z . Weevil mortality Greenhouse 0 . . Rep 0 . . Rep (greenhouse) 8.24E-18 . . Residual 0.821 . . Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 3.84 0.0012 Offspring weevil emergence Covariance parameter Estimate Z-value PR > Z Greenhouse 0 . . Rep 0.0055 0.0083 0.2560 Rep(greenhouse) . . . Trt*rep(greenhouse) . . . Residual 0.5709 4.90 <0.0001 Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 4.15 0.0006 ndf, numerator degrees of freedom; ddf, denominator degrees of freedom. Open in new tab Table 2. Parameter estimates for the effects of insecticide treatments, greenhouse, and their interaction on adult Anthonomus eugenii mortality and offspring emergence in greenhouse cage trials Factor . Covariance parameter . Estimate . Z-value . PR > Z . Weevil mortality Greenhouse 0 . . Rep 0 . . Rep (greenhouse) 8.24E-18 . . Residual 0.821 . . Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 3.84 0.0012 Offspring weevil emergence Covariance parameter Estimate Z-value PR > Z Greenhouse 0 . . Rep 0.0055 0.0083 0.2560 Rep(greenhouse) . . . Trt*rep(greenhouse) . . . Residual 0.5709 4.90 <0.0001 Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 4.15 0.0006 Factor . Covariance parameter . Estimate . Z-value . PR > Z . Weevil mortality Greenhouse 0 . . Rep 0 . . Rep (greenhouse) 8.24E-18 . . Residual 0.821 . . Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 3.84 0.0012 Offspring weevil emergence Covariance parameter Estimate Z-value PR > Z Greenhouse 0 . . Rep 0.0055 0.0083 0.2560 Rep(greenhouse) . . . Trt*rep(greenhouse) . . . Residual 0.5709 4.90 <0.0001 Fixed effects ndf/ddf F-value Pr > F Treatment 9/45 4.15 0.0006 ndf, numerator degrees of freedom; ddf, denominator degrees of freedom. Open in new tab Direct pepper weevil adult mortality In greenhouse cage trials, weevils treated with kaolin clay incurred the greatest level of adult pepper weevil mortality among all insecticides tested, equivalent to a mean of 76.6 ± 1.4%, following three foliar insecticide applications (Fig. 1). This was a significantly better reduction in adult weevil numbers relative to some insecticides tested, with the exception of thiamethoxam, which incurred 61.6 ± 0.6%, weevil mortality (P = 0.952), mineral oil which killed 55.0 ± 8.4% of weevils (P = 0.699), Beauveria bassiana strains GHA and ANT-03, which incurred 43 ± 4.9% (P = 0.991) and 43.3 ± 7.1% weevil mortality (P = 0.150), respectively, as well as to B. thuringiensis strain SDS-502 which accounted for 41.7 ± 6.0% weevil mortality (P = 0.110). In addition to kaolin clay, mineral oil also incurred significantly greater levels of weevil mortality relative to the control (P = 0.039), with more than double the number of weevils having died in this treatment relative to the untreated control (21.7 ± 0.60%). Finally, while other insecticide treatments tested including B. bassiana strains ANT-03, GHA, PRI15339, B. thuringiensis strain SDS-502 and spinetoram incurred some degree of adult pepper weevil mortality, these levels were not significantly different relative to the untreated control (Fig. 1). Fig. 1. Open in new tabDownload slide Pepper weevil mortality over time following application of each of eight insecticides, or untreated controls, to plants within small cage greenhouse trials. Dotted vertical lines represent times at which each of three insecticide applications were made onto caged plants, following an initial release of adult weevils on 9 April 2019. Significant differences (at P < 0.05) by Tukey’s HSD were indicated by different letters within the figure legend. Fig. 1. Open in new tabDownload slide Pepper weevil mortality over time following application of each of eight insecticides, or untreated controls, to plants within small cage greenhouse trials. Dotted vertical lines represent times at which each of three insecticide applications were made onto caged plants, following an initial release of adult weevils on 9 April 2019. Significant differences (at P < 0.05) by Tukey’s HSD were indicated by different letters within the figure legend. Fruit damage and abortion Other measures of insecticide efficacy include reductions in the quantities of fruit damaged and aborted by pepper weevil in treatment cages. Overall, no significant difference existed among levels of fruit abortion or fruit injury between treatments (Fig. 2). However, it is notable that the lowest level of fruit abortion observed in this trial (18.3 ± 7.0%) was observed within the kaolin clay treatment, which also incurred the greatest level of adult pepper weevil mortality relative to most other insecticide treatments assessed (Figs. 1 and 2). In contrast, the highest level of fruit abortion was observed in untreated control cages (86.5 ± 27.4%). Despite this possible trend for reduced fruit abortion with increased weevil mortality, the highest percentage of fruit damage incurred in this trial was observed in kaolin clay treatment cages (86.4 ± 11.8 %), and the lowest in untreated control cages (46.0 ± 13.9%). This suggests there may be an inverse relationship between the incidence of fruit abortion and the percent fruit damage. Despite fruit injury, it was observed that a large proportion of fruit continued to develop into fully mature peppers. Fig. 2. Open in new tabDownload slide Summary of percentage of fruit damage and abortion observed for pepper weevil infested plants in all insecticide treated cages. Fig. 2. Open in new tabDownload slide Summary of percentage of fruit damage and abortion observed for pepper weevil infested plants in all insecticide treated cages. While the spinetoram treatment did not incur a significant increase in adult weevil mortality relative to the control, there was a numerically lower rate of fruit abortion of 36.1 ± 3.51% in this treatment, which was 50.5% lower relative to the untreated control (Fig. 2). In addition to this, both microbial insecticides B. bassiana strains ANT-03 and PPRI5339 had numerically lower percentages of fruit abortion of 47.4 ± 13.0 and 36.8 ± 9.3% relative to the untreated control. While counts for bud injury and abortion were collected at each of six sample time points over the course of this trial, no significant difference was found among any of these, even by trial end (P = 0.442). Despite this, a numerically lower mean number of aborted buds were counted from the spinetoram (17.83 ± 4.18), kaolin clay (19.17 ± 3.43), and thiamethoxam (21.0 ± 3.54) treatment cages, whereas the Guelph pepper weevil control had the greatest level of fruit abortion (32.83 ± 4.97). Weevil offspring emergence The number of viable offspring that initial pepper weevils produced, either over the course of these trials or thereafter, differed significantly among treatments (P < 0.0001; Fig. 3). Comparing treatments for differences in weevil emergence levels relative to their control showed that only the kaolin clay (P = 0.0204) and mineral oil (P = 0.0267) had significantly fewer offspring weevils emerged relative to the untreated control. Overall, weevil emergence was numerically highest for peppers collected from B. bassiana strain PPRI5339 treatment cages, with an observed cage average of 153 ± 11.18 weevils for this treatment, compared with nearly half or 88.7 ± 14.7 weevil offspring observed from control untreated cages (Fig. 3). Fig. 3. Open in new tabDownload slide Cumulative number of pepper weevil offspring emergence from insecticide treatment cages following the end of greenhouse cage trials. Treatments different from the control by Dunnett’s test are indicated by an asterisk above columns. Fig. 3. Open in new tabDownload slide Cumulative number of pepper weevil offspring emergence from insecticide treatment cages following the end of greenhouse cage trials. Treatments different from the control by Dunnett’s test are indicated by an asterisk above columns. Discussion Achieving effective management of the pepper weevil is problematic. In this study, most insecticides assessed were only partially efficacious for controlling pepper weevil adults within the greenhouse environment and often remaining adults continued to reproduce, amounting to as many as 157 weevil offspring among only two pepper plants, as was observed in Beauveria bassiana strain PPRI5339 treatment cages. These results exacerbate pre-existing difficulties of managing immature life stages that occur within the protected confines of the pepper fruit, thereby sheltering them from insecticides and natural enemies. Thus, it is not surprising that management of this pest continues to represent a seasonally recurring challenge across many parts of North America. These results also highlight the importance of integrating multiple management tools and strategies to achieve year-round control of this pest. With this, it remains vital to identify effective insecticides for long-term management of pepper weevil. Impact of microbial insecticides for the control of pepper weevil Through laboratory bioassays and greenhouse trials, this study explored the efficacy of multiple conventional, reduced-risk, and microbial insecticides for suppression of pepper weevil. With respect to entomopathogenic fungi assessed in this study, three strains of Beauveria bassiana (ANT-03, GHA and PPRI5339), and Metarhizium anisopliae strain F52 all provided over 80% adult pepper weevil control in laboratory bioassays, which contrasted with an overall low efficacy obtained for B. bassiana strain R444. Similar variation in efficacy of different strains of B. bassiana for the control of the strawberry clipper weevil, Anthonomus signatus (Say) have previously been reported, with mortality ranging from 23 to 100% among 16 isolates (Sabbahi et al. 2008). Entomopathogenic fungal strains may vary in virulence due to several factors including the quantity and types of mycotoxins produced by individual strains (Leland et al. 2005). In the greenhouse, the efficacy of entomopathogens that successfully reduced adult weevil populations in the laboratory was lower than expected. One possible explanation is the spatial complexity in greenhouse environments, which facilitates weevil avoidance to pesticide exposure. As observed in this study, pepper weevil adults nestle their bodies among the high-density plant bud and fruit structures, which are difficult to reach with spray equipment. With minimal to no direct contact between the pathogen and the insect cuticle, it is more likely for weevils to survive with little impact on their populations. Thus, of all insecticides tested in these greenhouse trials, it is not surprising that survival of adult weevils was followed by high rates of offspring emergence. Entomopathogens also need to grow and develop within the host for several days before insect mortality occurs, thereby delaying the impact of microbial insecticides as observed in this study. Last, the infestation level of 10 weevils per cage for cages containing two 12-wk-old pepper plants, is critically high and the tolerance for pepper weevil populations in a commercial crop is very low. For instance, the action threshold for pepper weevil on field bell pepper crops is one pepper weevil adult per 100 terminal fruiting buds (Riley et al. 1992). Thus, testing lower weevil population densities may have incurred greater insecticide efficacy with these same insecticide treatments; however, both space and time limitations made testing such lower densities unfeasible. From a management perspective however, these reduced-risk and microbial insecticides should include early applications to much lower pepper weevil densities, which would most likely result in a greater level of pest control overall. In contrast to the broad host-range of entomopathogenic fungi, prior research done on Bacillus thuringiensis entomopathogenic bacteria suggests that certain strains of this species might be more effective for the control of specific orders of insects, such as the Coleoptera, relative to others (reviewed by Martins et al. 2007). For instance, B. thuringiensis subspecies tenebrionis and israelensis produce a number of Cry proteins which are associated with control of the cotton boll weevil, Anthonomus grandis (Martins et al. 2007). Additionally, B. thuringiensis subspecies galleriae strain SDS-502 was found to be very toxic to both the cupreous chafer, Anomala cuprea (Coleoptera: Scarabaeidae) (Asano et al. 2003) as well as to the rice water weevil, Lissorhoptrus oryzophilus Kushel (Aghaee and Godfrey 2015). It is perhaps not surprising then that in this study, B. thuringiensis subspecies galleriae strain SDS-502 did achieve at least 60% weevil mortality in laboratory trials. Unexpectedly, B. thuringiensis subspecies tenebrionis, with known activity against the Coleoptera, did not perform well in laboratory bioassays. Furthermore, the galleriae strain tested in greenhouse efficacy trials also did not significantly improve weevil mortality relative to the untreated control. This suggests that these microbes may not be specific enough to pepper weevil, or as previously documented, may function through other mechanisms not evaluated in this study, such as by reducing plant feeding or fecundity (Ignoffo and Gregory 1972, Smirnoff 1983). Another factor which may also influence the efficacy of Bacillus thuringiensis includes the development of resistance over time. For example, Colorado potato beetle, Leptinotarsa decemlineata (Say) readily develops resistance to B. thuringiensis strain tenebrionis after repeated exposure (Whalon et al. 1993). Other subspecies of B. thuringiensis including aizawai, strain ABTS-1857, had minimal toxicity for neonate larvae of the cotton boll weevil, Anthonomus grandis, which may be attributed either to resistance or to lack of agent specificity (Pérez et al. 2017), and may also explain why this agent did not effectively control pepper weevil in laboratory trials of this study. Together these factors may represent important determinants of microbial efficacy and suggests that there is an ongoing need to evaluate new, more potent microbial agents for pepper weevil management. Evaluation of reduced-risk agents In both laboratory and greenhouse trials, reduced-risk agents including kaolin clay and mineral oil demonstrated efficacy for the suppression of pepper weevil. Unlike conventional pesticides which rely on the molecular inhibition of neuro-receptor proteins, these agents act on a more physical level by forming a barrier on plant parts and serving as an irritant to exposed insects. Mineral oils can also physically coat insects at various life stages where they reduce survivorship, lower rates of oviposition and interfere with insect development (Messina and Renwick 1983). While both insecticides leave some residue on plant and fruit surfaces that would necessitate washing fruit prior to marketing, the significantly better performance of insecticides such as kaolin clay relative to many others tested in this study indicate their considerable value to growers. Furthermore, these insecticides have the potential to be useful after the last greenhouse harvest and cleanout when they may minimize the risk of pest carryover to a new cropping cycle. Conventional agents With respect to conventional insecticides assessed in this study, the neonicotinoid thiamethoxam and the anthranilic diamide cyantraniliprole were the most effective agents tested. This agrees with prior findings showing that these agents are effective for the control of pepper weevil, though thiamethoxam was found to be more efficacious overall (Caballero et al. 2015). In contrast, while spinetoram demonstrated efficacy in laboratory trials, results from greenhouse trials were more variable and suggest that this product of fermentation would not necessarily constitute a more effective agent over thiamethoxam, as has previously been suggested (Seal et al. 2016). As conventional agents, these pesticides can disrupt established greenhouse biological control programs that target other pests, and would be most useful at the crop clean-up stage. Overall, the results from these trials indicate that insecticides may be less effective against pepper weevil. Products besides kaolin clay and thiamethoxam did not meet a minimum threshold of 60% pepper weevil control. The large size of the adult pepper weevil, its ability to conceal itself from insecticides, and the weevil’s hard protective exoskeleton might together serve to protect weevils to the point that insecticide efficacy is overall reduced in this species. In summary, this assessment of insecticides belonging to a broad spectrum of functional activities provides new knowledge that helps identify those with the greatest potential to reduce pepper weevil adult and offspring populations. This study also serves as an important step toward prioritizing effective insecticides as candidates for registration or label expansion for the management of the pepper weevil in North America. Furthermore, measuring weevil offspring can be another effective way to identify agents that are acting rapidly on pepper weevils at a population level. This will contribute to establishing the best tools and practices to apply for achieving year-round management on both continuously growing greenhouse pepper crops, as well as minimize crop losses by this challenging pest species on a year-round basis both in the greenhouse as well as in fields. 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TI - Assessing New Tools for Management of the Pepper Weevil (Coleoptera: Curculionidae) in Greenhouse and Field Pepper Crops
JO - Journal of Economic Entomology
DO - 10.1093/jee/toaa092
DA - 2020-08-13
UR - https://www.deepdyve.com/lp/oxford-university-press/assessing-new-tools-for-management-of-the-pepper-weevil-coleoptera-b01CyKULAG
SP - 1903
EP - 1912
VL - 113
IS - 4
DP - DeepDyve
ER -