Effect of dose and trap type on captures of striped and spotted cucumber beetles using synthetic vittatalactone.

Striped cucumber beetle, Acalymma vittatum (F.) and spotted cucumber beetle (Diabrotica undecimpunctata howardi Barber) are key pests of cucurbits. Pesticide applications directed against cucumber beetles can jeopardize bee pollination which is essential to crop yield. Alternative selective tactics, including behavioral control for managing cucumber beetles, are needed in order to improve pest management. The striped cucumber beetle pheromone vittatalactone is attractive to both male and female adults, and also to spotted cucumber beetles. We tested the response of both species to different doses of synthetic vittatalactone, and to different trap types, in field trapping experiments in Maryland. Both species showed strong dose-response in May-June and October 2020. Among 12 trap types tested during a 2-wk experiment in June, using 1 mg mixed vittatalactone, sticky panel traps caught the most of each species, with vittatalactone-baited traps exceeding unbaited traps by >8 fold for striped and >2 fold for spotted, and with significant response to yellow versus clear color absent in striped, but strong in spotted. Among nonsticky traps, those with yellow or yellow-green exceeded those without these colors for both beetle species, and a ground-placed boll weevil trap captured the most striped cucumber beetles. Bucket-style traps caught excessive nontarget bumblebees (Bombus spp.) if yellow, and a few beetles, if all green. Results allow field monitoring with a choice of sticky or nonsticky traps and suggested lure loading of 1 mg mixed vittatalactone, containing ~90 µg active isomer. These findings contribute to the development of multispecies behavioral monitoring and control as a component of cucurbit IPM.

Vittatalactone is the Male-Produced Aggregation Pheromone of the Western Striped Cucumber Beetle, Acalymma trivittatum.

We found that vittatalactone, specifically (3R,4R)-3-methyl-4-[(1S,3S,5S)-1,3,5,7-tetramethyloctyl]oxetan-2-one, is the male-produced aggregation pheromone of the western striped cucumber beetle, Acalymma trivittatum (Mannerheim), as was previously shown for the striped cucumber beetle, Acalymma vittatum (F.) (Coleoptera: Chrysomelidae). A synthetic mixture containing 9% of the authentic natural pheromone, is attractive to both sexes of both species in the field, as demonstrated by trapping using baited and unbaited sticky panels in California and earlier in Maryland. Females of both species do not produce detectable vittatalactone. This finding expands the usefulness of the synthetic vittatalactone mixture for pest management throughout the range of both A. vittatum and A. trivittatum. Development of vittatalactone time-release formulations combined with cucurbitacin feeding stimulants offer the potential for selective and environmentally-friendly cucurbit pest management tactics.

Both the Squash Bug Anasa tristis and Horned Squash Bug Anasa armigera (Hemiptera: Coreidae) are Attracted to Vittatalactone, the Aggregation Pheromone of Striped Cucumber Beetle.

Vittatalactone, the aggregation pheromone of the striped cucumber beetle, Acalymma vittatum (F.) (Coleoptera: Chrysomelidae), is attractive to two species of squash bugs (Hemiptera: Coreidae), the squash bug Anasa tristis (DeGeer) and horned squash bug Anasa armigera (Say). In field trapping experiments in Maryland and Virginia, clear sticky traps baited with 1 mg of a synthetic 8-isomer mix of vittatalactone captured ~9× more of female A. tristis and of both sexes of A. armigera, whereas male A. tristis were not significantly attracted, compared to unbaited traps. A. armigera showed a distinct dose-response to vittatalactone lure loading in the late season, and this species was more attracted than A. tristis, based on comparison to captures from underneath wooden boards emplaced in adjacent fields. Results suggest that vittatalactone could be a 'keystone semiochemical' in colonization of cucurbit hosts by specialist herbivores, and may offer the opportunity for multi-species behavioral control as a component of integrated pest management in cucurbit crops.

Host Finding Behavior of the Parasitoid Hadronotus pennsylvanicus (Hymenoptera: Scelionidae) for Egg Masses of the Squash Bugs Anasa tristis and Anasa armigera (Hemiptera: Coreidae) in Squash and Cucumber Fields.

Parasitoid foraging behavior is affected by habitat and host plant differences. Egg parasitoids also use a combination of oviposition-induced and host-derived cues to find host eggs. This study compared parasitism by Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) on two squash bug species, Anasa tristis (DeGeer) and Anasa armigera Say (Hemiptera: Coreidae), by placing sentinel squash and cucumber plants with egg masses of either of the two squash bug species in squash and cucumber fields in a 3-way factorial design. Host density of wild A. tristis egg masses in squash fields may have influenced parasitoid foraging behavior on sentinel plants. In the 3-way factorial design, parasitism was higher on sentinel squash plants and in squash fields overall. However, parasitism on A. armigera egg masses was highest on sentinel cucumber plants in squash fields and parasitism on A. tristis egg masses was higher on sentinel squash plants in either squash or cucumber fields and lowest on sentinel cucumber plants in cucumber fields. Results suggest that parasitoids were able to specifically orient to the combination of host plant and host cues associated with A. tristis egg masses on sentinel squash plants, but that they were more responsive to plant-induced cues associated with cucumber when searching for A. armigera egg masses. Parasitoids appear to utilize different combinations of host plant and host cues when searching for eggs of the two squash bug species.

Trapping of Crucifer-Feeding Flea Beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) With Pheromones and Plant Kairomones.

Flea beetles (Coleoptera: Chrysomelidae) of the genus Phyllotreta are major pests of cole crops, canola, and related crops in the mustard family (Brassicaceae). Adults may damage seedlings or larger crop plants, impairing crop growth, rendering crops unmarketable, or killing seedlings outright. The two major North American crucifer pest species, Phyllotreta striolata (F.) and Phyllotreta cruciferae (Goeze), have male-produced pheromones attractive to both female and male adults. We tested the racemic synthetic pheromones, himachaladiene and hydroxyhimachalanone, as well as the host-plant-produced allyl isothiocyanate, alone and in combination, with experimental trapping in Maryland, Virginia, and North Dakota, using clear and yellow sticky traps and the ground-based 'rocket' trap (modified from boll weevil trap). Phyllotreta striolata was consistently attracted to the hydroxyketone, and captures were often enhanced by allyl isothiocyanate (AITC), but its response to pheromones, AITC, and trap color were variable from state to state. Phyllotreta cruciferae was strongly attracted to AITC, but its response to pheromone components varied by state, and this species was found rarely at the Maryland site. Phyllotreta bipustulata (F.) was attracted to the diene component, a new finding for this species. Several other genera of flea beetles were captured, some showing response to the semiochemicals and/or color. Results will be helpful in monitoring and possibly population suppression; however, further research is necessary to develop more efficient syntheses, optimal lure loadings, combinations, and controlled release methods.

Both male- and female-produced pheromones influence Colorado potato beetle movement in the field.

BACKGROUND: Colorado potato beetle [Leptinotarsa decemlineata (Say); Coleoptera: Chrysomelidae] is a widespread key pest of potatoes and other solanaceous crops of the temperate Northern Hemisphere. Its evolution of multiple pesticide resistance is a continuing threat if chemical control is relied upon for pest management. An integrated approach including semiochemicals and other non-pesticidal tactics is essential to sustainable management. In addition to the known volatile aggregation pheromone produced by male adult beetles that is attractive to both females and males, there is a yet-unidentified female-produced sex pheromone. Using caged 'bait plants' in the field in Maryland, USA, we tested the attraction of male and female beetles to groups of male-only, female-only, larvae, and uninfested bait plants. RESULTS: Results of five field experiments demonstrate that the female-produced sex pheromone is attractive to male beetles, whereas the male-produced pheromone is attractive to both females and males. Male attraction increased with higher densities of females on bait plants, but female attraction did not change with female density on bait plants. CONCLUSION: This is the first study to demonstrate male attraction to the female sex pheromone in the field, and to our knowledge, the first to demonstrate a beetle species using bidirectional communication between males and females. Use of semiochemicals for monitoring and management of Colorado potato beetle should consider male-, female-, as well as plant-produced volatiles as important tools for pest manipulation in potato integrated pest management. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

A sensory bias overrides learned preferences of bumblebees for honest signals in Mimulus guttatus.

Insect pollinators readily learn olfactory cues, and this is expected to select for 'honest signals' that provide reliable information about floral rewards. However, plants might alternatively produce signals that exploit pollinators' sensory biases, thereby relaxing selection for signal honesty. We examined the innate and learned preferences of Bombus impatiens for Mimulus guttatus floral scent phenotypes corresponding to different levels of pollen rewards in the presence and absence of the innately attractive floral volatile compound ß-trans-bergamotene. Bees learned to prefer honest signals after foraging on live M. guttatus flowers, but only exhibited this preference when presented floral scent phenotypes that did not include ß-trans-bergamotene. Our results suggest that a sensory bias for ß-trans-bergamotene overrides the ability of B. impatiens to use honest signals when foraging on M. guttatus. This may represent a deceptive pollination strategy that allows plants to minimize investment in costly rewards without incurring reduced rates of pollinator visitation.

Trap Cropping Harlequin Bug: Distance of Separation Influences Female Movement and Oviposition.

To evaluate perimeter trap crops for management of harlequin bug, Murgantia histrionica (Hahn), we undertook greenhouse and field experiments with mustard greens as trap crop for a collard cash crop. We confirmed that harlequin bugs prefer to immigrate to and reside on mustard. Females, however, in greenhouse cage experiments, 'commuted' to collards to lay their eggs. In separate spring and fall field plantings, using replicated 12 m by 12 m collard plots in 1-ha fields, we tested mustard planted as an adjacent perimeter trap crop, or a perimeter trap crop separated by 2 unplanted rows (2.3 m), or with no trap crop. Adults accumulated on the spring mustard crop but overall numbers remained low, with all collards sustaining <1% leaves damaged. In the fall, the separation of 2.3 m reduced oviposition on collards fourfold, and feeding damage approximately 2.5-fold, compared to collards with an adjacent trap crop. Fall control plots with no border trap crop showed even lower foliar damage; likely result of preferential immigration of harlequin bugs to mustard at the field scale, resulting in fewer bugs near the control treatment plots. Thus, the spatial arrangement of the mustard trap crop, and its separation from the cash crop, influences pest abundance and damage. A separated mustard border can reduce bug movement including female commuting and egg-laying, thus better protecting the collard cash crop. Future research should address reduction in area of trap crops, deployment of semiochemicals, and possible changes in timing, to promote trap cropping that is practical for grower implementation.

Transcriptome Sequencing of the Striped Cucumber Beetle, Acalymma vittatum (F.), Reveals Numerous Sex-Specific Transcripts and Xenobiotic Detoxification Genes.

Acalymma vittatum (F.), the striped cucumber beetle, is an important pest of cucurbit crops in the contintental United States, damaging plants through both direct feeding and vectoring of a bacterial wilt pathogen. Besides providing basic biological knowledge, biosequence data for A. vittatum would be useful towards the development of molecular biopesticides to complement existing population control methods. However, no such datasets currently exist. In this study, three biological replicates apiece of male and female adult insects were sequenced and assembled into a set of 630,139 transcripts (of which 232,899 exhibited hits to one or more sequences in NCBI NR). Quantitative analyses identified 2898 genes differentially expressed across the male-female divide, and qualitative analyses characterized the insect's resistome, comprising the glutathione S-transferase, carboxylesterase, and cytochrome P450 monooxygenase families of xenobiotic detoxification genes. In summary, these data provide useful insights into genes associated with sex differentiation and this beetle's innate genetic capacity to develop resistance to synthetic pesticides; furthermore, these genes may serve as useful targets for potential use in molecular-based biocontrol technologies.

Use of Chemical and Nonchemical Methods for the Control of Varroa destructor (Acari: Varroidae) and Associated Winter Colony Losses in U.S. Beekeeping Operations.

The parasitic mite Varroa destructor (Acari: Varroidae) is a major cause of overwintering honey bee (Apis mellifera) colony losses in the United States, suggesting that beekeepers must control Varroa populations to maintain viable colonies. Beekeepers have access to several chemical varroacides and nonchemical practices to control Varroa populations. However, no studies have examined large-scale patterns in Varroa control methods in the United States. Here we used responses from 4 yr of annual surveys of beekeepers representing all regions and operation sizes across the United States to investigate use of Varroa control methods and winter colony losses associated with use of different methods. We focused on seven varroacide products (amitraz, coumaphos, fluvalinate, hop oil, oxalic acid, formic acid, and thymol) and six nonchemical practices (drone brood removal, small-cell comb, screened bottom boards, powdered sugar, mite-resistant bees, and splitting colonies) suggested to aid in Varroa control. We found that nearly all large-scale beekeepers used at least one varroacide, whereas small-scale beekeepers were more likely to use only nonchemical practices or not use any Varroa control. Use of varroacides was consistently associated with the lowest winter losses, with amitraz being associated with lower losses than any other varroacide product. Among nonchemical practices, splitting colonies was associated with the lowest winter losses, although losses associated with sole use of nonchemical practices were high overall. Our results suggest potential control methods that are effective or preferred by beekeepers and should therefore inform experiments that directly test the efficacy of different control methods. This will allow beekeepers to incorporate Varroa control methods into management plans that improve the overwintering success of their colonies.

Variation in reward quality and pollinator attraction: the consumer does not always get it right.

Nearly all bees rely on pollen as the sole protein source for the development of their larvae. The central importance of pollen for the bee life cycle should exert strong selection on their ability to locate the most rewarding sources of pollen. Despite this importance, very few studies have examined the influence of intraspecific variation in pollen rewards on the foraging decisions of bees. Previous studies have demonstrated that inbreeding reduces viability and hence protein content in Mimulus guttatus (seep monkeyflower) pollen and that bees strongly discriminate against inbred in favour of outbred plants. We examined whether variation in pollen viability could explain this preference using a series of choice tests with living plants, artificial plants and olfactometer tests using the bumble bee Bombus impatiens. We found that B. impatiens preferred to visit artificial plants provisioned with fertile anthers over those provisioned with sterile anthers. They also preferred fertile anthers when provided only olfactory cues. These bumble bees were unable to discriminate among live plants from subpopulations differing dramatically in pollen viability, however. They preferred outbred plants even when those plants were from subpopulations with pollen viability as low as the inbred populations. Their preference for outbred plants was evident even when only olfactory cues were available. Our data showed that bumble bees are able to differentiate between anthers that provide higher rewards when cues are isolated from the rest of the flower. When confronted with cues from the entire flower, their choices are independent of the quality of the pollen reward, suggesting that they are responding more strongly to cues unassociated with rewards than to those correlated with rewards. If so, this suggests that a sensory bias or some level of deception may be involved with advertisement to pollinators in M. guttatus.