Karla M. Addesso

Pepper Weevil Attraction to Volatiles from Host and Nonhost Plants

ABSTRACT The location of wild and cultivated host plants by pepper weevil (Anthonomus eugenii Cano) may be aided by visual cues, the male-produced aggregation pheromone, herbivore-induced, or constitutive host plant volatiles. The attractiveness of constitutive plant volatiles to pioneer weevils is important in understanding, and perhaps controlling, dispersal of this insect between wild and cultivated hosts. Ten-day-old male and 2- and 10-day-old female weevils were tested in short-range Y-tube assays. Ten-day-old male and female weevils were attracted to the volatiles released by whole plants of three known oviposition hosts, ‘Jalapeno’ pepper, American black nightshade, and eggplant, as well as tomato, a congener, which supports feeding but not oviposition. Two-day-old females were attracted to all plants tested, including lima bean, an unrelated, nonhost plant. Fruit volatiles from all three hosts and flower volatiles from nightshade and eggplant were also attractive. In choice tests, weevils showed different preferences for the oviposition hosts, depending on age and sex. Upwind response of 10-day-old male and female weevils to host plant volatiles was also tested in long-range wind tunnel assays. Weevils responded to pepper, nightshade, and eggplant volatiles by moving upwind. There was no difference in the observed upwind response of the weevils to the three host plants under no-choice conditions. Reproductively mature pepper weevils can detect, orient to, and discriminate between the volatile plumes of host plants in the absence of visual cues, conspecific feeding damage, or the presence of their aggregation pheromone.

Attraction of pepper weevil to volatiles from damaged pepper plants

Pioneer herbivorous insects may find their host plants through a combination of visual and constitutive host‐plant volatile cues, but once a site has been colonized, feeding damage changes the quantity and quality of plant volatiles released, potentially altering the behavior of conspecifics who detect them. Previous work on the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), demonstrated that this insect can detect and orient to constitutive host plant volatiles released from pepper [Capsicum annuum L. (Solanaceae)]. Here we investigated the response of the weevil to whole plants and headspace collections of plants damaged by conspecifics. Mated weevils preferred damaged flowering as well as damaged fruiting plants over undamaged plants in a Y‐tube olfactometer. They also preferred volatiles from flowering and fruiting plants with actively feeding weevils over plants with old feeding damage. Both sexes preferred volatiles from fruiting plants with actively feeding weevils over flowering plants with actively feeding weevils. Females preferred plants with 48 h of prior feeding damage over plants subjected to weevil feeding for only 1 h, whereas males showed no preference. When attraction to male‐ and female‐inflicted feeding damage was compared in the Y‐tube, males and females showed no significant preference. Wind tunnel plant assays and four‐choice olfactometer assays using headspace volatiles confirmed the attraction of weevils to active feeding damage on fruiting plants. In a final four‐choice olfactometer assay using headspace collections, we tested the attraction of mated males and virgin and mated females to male and female feeding damage. In these headspace volatile assays, mated females again showed no preference for male feeding; however, virgin females and males preferred the headspace volatiles of plants fed on by males, which contained the male aggregation pheromone in addition to plant volatiles. The potential for using plant volatile lures to improve pepper weevil monitoring and management is discussed.

Conophthorin enhances the electroantennogram and field behavioural response of Xylosandrus germanus (Coleoptera: Curculionidae) to ethanol

Ethanol acts as an attractant that aids Xylosandrus germanus (Blandford) in locating living but weakened hosts. Electroantennogram (EAG) and field trapping experiments were conducted with conophthorin and other selected semiochemicals that function as important olfactory cues for various ambrosia beetles to characterize their effect on the attraction of X. germanus to ethanol and to assess whether EAG responses provide an indication of behavioural activity. Thus, semiochemicals hypothesized to enhance (i.e. conophthorin), reduce (i.e. terpinolene, verbenone) or have a negligible (i.e. lineatin, sulcatol, retusol) effect on the attraction of X. germanus to ethanol were selected for comparative purposes. Ethanol plus conophthorin elicited larger EAG amplitudes than binary (1 : 1) mixtures of ethanol plus the remaining semiochemicals at dilutions of 0.001%, 0.01% and 1% per compound. Conophthorin also enhanced the attraction of X. germanus, Euwallacea validus (Eichhoff) and Cyclorhipidion pelliculosum (Eichhoff) to ethanol under field conditions. By contrast, terpinolene and verbenone reduced the attraction of X. germanus and other ambrosia beetles to ethanol. Semiochemicals that enhance (i.e. conophthorin) or reduce (i.e. terpinolene, verbenone) attraction by X. germanus may improve monitoring and/or management tactics. These results also suggest that EAG responses can indicate field behavioural activity and be useful for screening attractants for X. germanus.

Host-marking by female pepper weevils, Anthonomus eugenii

Pepper weevils, Anthonomus eugenii Cano (Coleoptera: Curculionidae), feed and oviposit in flower buds and small fruits of plants in the genus Capsicum, as well as several species of Solanum (Solanaceae). Females chew a small hole into the fruit, deposit a single egg within the cavity, and seal the hole with a clear anal secretion that hardens into an ‘oviposition plug’. Female oviposition behavior was studied in a series of small‐arena bioassays to determine whether previous oviposition in Jalapeño pepper fruit deterred subsequent oviposition and to determine what specific cues from an infested fruit influence female behavior. In choice and no‐choice tests, females preferred clean fruit to fruit that had received four eggs 24 h previously (i.e., infested fruit), whether the fruit was infested with conspecific eggs or their own eggs. Further bioassays demonstrated that the presence of female frass, or oviposition plugs alone, in the absence of eggs or any fruit damage, was sufficient to deter oviposition. In addition, females given the choice between an infested fruit with the oviposition plug removed or an unaltered infested fruit preferred the fruit with no plugs, even when eggs, frass, and feeding damage were still present. To determine whether females would avoid infested peppers under more natural conditions, we quantified oviposition on infested and uninfested sentinel pepper fruit within individually caged plants and on clean and infested plants caged together. Females consistently laid more eggs on clean fruit than on infested fruits and moved within and among pepper plants to search for more acceptable oviposition sites. We conclude that oviposition plugs, along with contaminated female, but not male, frass contain a deterrent that, in the absence of any other cue, is enough to alert a female that a patch is occupied.

Context-dependent female mate preferences in leaf-footed cactus bugs

Female mate preferences can shape sexual selection and evolution. Thus, it is important to understand the factors that affect mating decisions. Here, we examine context-dependent mate preferences in the leaf-footed cactus bug, Narnia femorata Stal (Hemiptera: Coreidae), a species that experiences distinct seasonal changes and spatial variation in the quality of their food, cactus. Previous work has shown that cactus with fruit is a superior resource for these insects, however they must sometimes develop, mate, and reproduce without cactus fruit. We reared males on Opuntia humifusa (Raf.) (Cactaceae) cactus pads with and without cactus fruit. We found that females preferred the odour of males that had developed on cactus fruit over males that developed only on cactus pads. However, the current cactus context also affected female preference. Females were more likely to choose males that developed with cactus fruit when cactus fruit was currently available. Our results suggest that natural fluctuations in resource availability during development and adulthood may result in fluctuations in the strength of sexual selection via female mate choice.

Aggregation Behavior of the Southern Chinch Bug (Hemiptera: Blissidae)

ABSTRACT The southern chinch bug, Blissus insuhris Barber, forms dense, multigenerational aggregations in St. Augustinegrass lawns leading to grass death from sap feeding. We conducted laboratory bioassays to better understand the signals responsible for the formation and maintenance of southern chinch bug aggregations. In small arena assays, chinch bugs demonstrated a stronger aggregation response over time and aggregated more often on or beneath St. Augustinegrass leaf blades than on or under artificial leaf-like shelters constructed from white or green paper. In Y-tube olfactometer assays, bugs of different age and sex were attracted to volatiles from mixed-sex chinch bug aggregations and showed particular attraction to groups of adult female chinch bugs. Adult males and nymphs were also attracted to adult males. Nymphs were attracted to nymphs and were also more attracted to aggregation volatiles when they could see bugs in the arm of the Y-tube. Adult males were more attracted to short-winged than long-winged adults, while females and nymphs demonstrated no preference. All bugs were attracted to St. Augustinegrass volatiles when presented alone, but only males preferred the odor of grass over odor released from a chinch bug mixed-sex aggregation. When presented with a choice of grass and grass + aggregation volatiles, males preferred the combined treatment. The results of these assays suggest that a complex combination of life stage, sex, as well as plant and insect-derived signals influence chinch bug aggregation behavior.

Efficacy of Nootka Oil as a Biopesticide for Management of Imported Fire Ants (Hymenoptera: Formicidae)

Abstract Recent concerns regarding the impact of traditional synthetic pesticides on nontarget organisms have generated demand for alternative products with lower environmental impact. This demand has led to increasing focus on plant essential oils as sources of new biopesticides. In this study, we demonstrate that the essential oil of the Alaskan yellow cedar, Cupressus nootkatensis (D. Don) Spach, has activity against hybrid imported fire ant workers, Solenopsis invicta Buren × Solenopsis richteri Forel. In digging assays, ants were repelled by nootka oil and digging continued to be suppressed by nearly 50% in nootka oil-treated sand aged 6 mo in the laboratory. Higher worker mortality was also observed in contact and fumigation assays compared to control checks. In a field drench test, mortality of mounds treated with nootka oil lagged behind mounds treated with bifenthrin treatment for 7 wk, but both nootka oil and bifenthrin had higher mortality than the untreated check at the end of the 12-wk evaluation period. In a band application evaluation, nootka oil plots maintained a 90–95% reduction in fire ant mounds from the 2nd to 17th wk, when new mounds began to intrude on the field plots. The quarantine-approved bifenthrin band treatment maintained 100% control from the 2nd to 24th wk. Although the formulation tested here did not perform to Federal Imported Fire Ant Quarantine standards, other formulations may enable this product to reach 100% control. In addition, nootka oil could be beneficial in situations where ant suppression rather than complete quarantine elimination is the management goal.

Trapping Social Wasps (Hymenoptera: Vespidae) in Nurseries with Acetic Acid and Isobutanol

Abstract European hornet, Vespa crabro L., damages bark of nursery trees, and most vespid species can be a sting hazard to nursery personnel when nests are disturbed. We tested acetic acid and isobutanol lures in traps for V. crabro spring queens to determine the seasonality of vespid captures and compare the efficacy of patterns of trap placement in Tennessee nurseries. Forty traps in transects from nursery tree blocks into the forest captured 547 vespid queens during 2001 and 2002. These were 78.8% Vespula maculifrons (Buysson), 6.9% Vespula squamosa (Drury), 6.8% V. crabro, 4.8% Dolichovespula maculata (L.), 2.6% Vespula flavopilosa Jacobson, and 0.2% Vespula vidua (Saussure). Total worker and male wasp captures in these traps were 2525 and 28, respectively. Polistes spp. (n = 416) were also trapped. Peak queen trap catch was in April for V. crabro and V. maculifrons and in May for other Vespula. Numbers of worker wasps captured were greater within nursery blocks or at field-forest edges compared with within forest, except D. maculata. Numbers of V. maculifrons, V. squamosa, and D. maculata queens trapped were greater in blocks in some years. The study demonstrated a strong response of V. crabro and several Vespula spp. to the lure, showed spring queen captures of V. crabro and other wasps, and indicated that trapping of the majority of vespid species was most effective at locations outside of the forest. The trapping of queens indicates some potential for reducing colony founding by queen removal in spring.

Novel Aspects of Drosophila suzukii (Diptera: Drosophilidae) Biology and an Improved Method for Culturing this Invasive Species with a Modified D. melanogaster Diet

Abstract Drosophila suzukii (Matsumara) (Diptera: Drosophilidae), the spotted wing drosophila, is a global pest of soft fruits now rearable on a standard D. melanogaster (Meigen) diet containing the flys own natural food: soft-skinned berries. The techniques tested here can save 40% of cultures from microbial contamination that develops after combining artificial food sources (e.g., standard drosophila media) with unsterilized host plant material (berries). A suitable ratio for mixing dietary ingredients for a vial or test-tube rearing system includes, by weight, 1 part berry tissue for oviposition, 1.5 parts dry diet media for carbohydrate, 7 parts clean water for moisture, and ∼5 grains (0.8 mg) of dry yeast for protein. One or two blackberry or blueberry fruits used by spotted wing drosophila as edible oviposition substrates doubled and tripled pupal and adult production in standard 68 mL culturing vials. To prevent mold from spoiling the diet, the exocarp of berries was sterilized in an 80 or 90% ethanol bath at room temperature for ∼5 min, followed by a thorough rinsing with deionized water to remove residual alcohol, which can be acutely toxic to D. suzukii, a highly ethanol-intolerant species. Sterilized fruit and a larger fly population in vials disrupted the growth of microbial biofilms capable of suffocating adults. Identical body size in reared adults and locally caught wild flies of D. suzukii substantiates nutritional similarity between the fruit-media-based diet and the flys own natural food (i.e., whole berries). Triethylamine (50%), a common fly anesthetic, was acutely toxic to D. suzukii adults but not to D. melanogaster adults.

Survey for Spotted-Wing Drosophila (Diptera: Drosophilidae) in the Five-County Nursery Production Region of Middle Tennessee, USA

Abstract Through global trade, spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), a native of Southeast Asia, has spread to at least 3 other continents since 2008. Initial reports of the fly in new regions often are associated with damage in agriculture fields, but the fly may be present in the landscape for years before populations reach a level at which they become a pest in fruit production. In 2012, spotted wing drosophila was reported in blueberry fields in eastern Tennessee, USA, for the first time. In order to determine whether the fly was established in middle Tennessee, we conducted landscape surveys over 2 yr in the middle of the states ornamental nursery industry where many fruit and ornamental hosts of the fly are grown. Red and yellow colored traps baited with yeast solution were placed in 17 locations of the 5-county nursery production region of middle Tennessee. Traps were monitored weekly for 8 wk in 2013 and 9 wk in 2014. Flies were caught at all 17 locations in 2013 and 16 of 17 locations in 2014. First activity was delayed 3 wk and total captures were 77% lower in 2014 relative to the previous year, likely due to high mortality of overwintering flies resulting from unusually cold winter temperatures in the region. No statistical differences were detected between trap colors in the landscape or between total captures of each sex, despite a trend for more female than male captures by the end of the season. Beginning Feb 2014, we also sampled weekly from a single yellow monitoring trap suspended within a plot of mixed-species dogwood trees (Cornus spp.; Caryophyllales: Cornaceae) for nearly 1 yr. Adult D. suzukii consistently were caught from late Jul until mid-Dec when the first frost occurred. Our surveys confirm that spotted wing drosophila is well established in the middle Tennessee nursery production region, despite no concurrent reports of damage by local small-fruit producers in the region.