Olfactory Cues From Host- and Non-host Plant Odor Influence the Behavioral Responses of Adult Drosophila suzukii (Diptera: Drosophilidae) to Visual Cues.

While trapping methods for Drosophila suzukii Matsumura (Diptera: Drosophilidae) have typically relied on fermentation volatiles alone or in association with a visual stimulus, the relative contribution of visual and olfactory stimuli to the food- and host-seeking behavior of D. suzukii is poorly understood. This study quantified the type of response exhibited by male and female D. suzukii to color and the effects that volatiles (fermentation, fresh fruit, and leaf) exert on the outcome. Seven-, four- and two-choice assays were used to quantify interactions between visual and olfactory cues. When no volatiles were present in a seven-choice assay, D. suzukii preferred red, black, and green pigments. Black and red were preferred when yeast odors were present, and black alone was the most attractive color when blueberry odor was present. A strawberry leaf terpenoid, ß-cyclocitral, seemed to have overridden the flies' response to color. In four-choice assays, blueberry odor was more likely to interact synergistically with color than yeast or ß-cyclocitral. This study demonstrates that D. suzukii modulates the response to multimodal sensory modalities (vision and olfaction) depending, to some extent, on the type of olfactory stimuli. Our findings also provide insight into the relative importance of vision as a function of odor quality in this invasive species.

Electrophysiological and Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) Towards the Leaf Volatile ß-cyclocitral and Selected Fruit-Ripening Volatiles.

The spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is attracted to numerous volatile organic compounds (VOCs) emitted from several ripening, small fruit crops. However, the strawberry leaf terpenoid, ß-cyclocitral, is reportedly very attractive to D. suzukii (but not to all Drosophila spp.). This suggests that leaf and fruit VOCs may be critical sources needed to further develop a more species-specific D. suzukii monitoring lure, or semiochemically based attract-and-kill systems. This study investigated the electrophysiological responses of male and female D. suzukii towards selected host fruit-ripening VOCs and ß-cyclocitral, along with behavioral responses toward combined fruit VOCs with ß-cyclocitral. Electroantennogram (EAG) results revealed a positive dose-response, for both sexes, as concentrations increased for all VOCs tested. For ß-cyclocitral, hexyl acetate and methyl butyrate, the mean male EAG responses were significantly greater than the female responses at lower doses. In caged behavioral bioassays, only in the ß-cyclocitral treatments were the mean number of flies captured (sexes combined) significantly greater than that captured in solvent (mineral oil) controls. Our study has demonstrated that while single fruit-based VOCs alone are not enough to cause a strong behavioral attraction by both male and female D. suzukii, the addition of ß-cyclocitral did produce a significant attraction response from both sexes. In both bioassays, males had higher responses to ß-cyclocitral than females, which suggest a greater sensitivity to this compound. Further studies are needed to ascertain the role ß-cyclocitral may play in the development of a more species-specific D. suzukii monitoring lure.

ß-cyclocitral synergizes the response of adult Drosophila suzukii (Diptera: Drosophilidae) to fruit juices and isoamyl acetate in a sex-dependent manner.

Semiochemicals play a pivotal role in the location, evaluation, and utilization of hosts by herbivorous insects. Mixtures of host plant-derived compounds are often required to elicit appropriate levels of response to olfactory stimuli. In multiple-choice bioassays, we characterized the response of adult Drosophila suzukii to foliage- and fruit-based synthetic compounds tested alone and in association with grape and tart cherry juices, and assessed whether synergistic interactions among olfactory stimuli are involved in the olfactory-driven behavior of D. suzukii. Our results established (1) significant attraction of females (but not males) to ß-cyclocitral and isoamyl acetate when tested singly, (2) the presence of a synergistic interaction between ß-cyclocitral and cherry juice only for females, and (3) the presence of a synergistic interaction between ß-cyclocitral and isoamyl acetate but only in the case of males. Our findings increase our understanding of male and female D. suzukii olfactory responses to synthetic compounds and fruit juices as sources of attractants. Combinations of foliage- and fruit-based compounds may be needed to increase SWD attraction.

Inverse resource allocation between vision and olfaction across the genus Drosophila.

Divergent populations across different environments are exposed to critical sensory information related to locating a host or mate, as well as avoiding predators and pathogens. These sensory signals generate evolutionary changes in neuroanatomy and behavior; however, few studies have investigated patterns of neural architecture that occur between sensory systems, or that occur within large groups of closely-related organisms. Here we examine 62 species within the genus Drosophila and describe an inverse resource allocation between vision and olfaction, which we consistently observe at the periphery, within the brain, as well as during larval development. This sensory variation was noted across the entire genus and appears to represent repeated, independent evolutionary events, where one sensory modality is consistently selected for at the expense of the other. Moreover, we provide evidence of a developmental genetic constraint through the sharing of a single larval structure, the eye-antennal imaginal disc. In addition, we examine the ecological implications of visual or olfactory bias, including the potential impact on host-navigation and courtship.

Behavioral Responses of Hunting Billbug (Coleoptera: Curculionidae) Towards Odors From Different Turfgrass Species and Adult Conspecifics.

A series of bioassays involving a four-choice olfactometer were conducted to assess the behavioral responsiveness of adult hunting billbugs (Sphenophorus venatus vestitus Chittenden) towards odors emanating from samples of three different turfgrasses: tall fescue (Festuca arundinacea Schreb. (Poales: Poaceae)), Kentucky bluegrass (Poa pratensis L. (Poales: Poaceae)), and zoysiagrass (Zoysia japonica Steud. (Poales: Poaceae)). When exposed to the three turf species simultaneously, the majority of billbugs preferred the zoysiagrass treatment over the tall fescue and Kentucky bluegrass treatments. When billbugs of both sexes were added to the three turf treatments, their presence with the turf did not enhance the released billbugs preference towards any of the treatments. Without the presence of turf, the released female billbugs were strongly attracted towards the male-only billbug treatment; however, a similar phenomenon was not observed for males. When a single turf type and/or mixed-sex adult billbugs were presented, treatments that contained the turf, especially zoysiagrass and tall fescue, strongly attracted the released billbugs compared with treatments that contained billbugs only. In the final bioassay experiment when billbugs were exposed to treatments of zoysiagrass and zoysiagrass + billbugs (with either sex), the released billbugs showed a significant preference towards the zoysiagrass + male billbugs treatment. Collectively, this series of experiments demonstrated the hunting billbugs preference to all three turf species tested, and their attraction to male conspecifics. This overall study was the first to investigate some basic aspects of the chemical ecology of the hunting billbug; specifically, the role turfgrass and adult billbug volatiles might have in billbug orientation and host selection.

Exposure to methoxyfenozide-treated surfaces reduces the responsiveness of adult male codling moth (Lepidoptera: Tortricidae) to codlemone and pear ester lures in a wind tunnel.

The responsiveness of male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide, toward lures loaded with the synthetic sex pheromone codlemone and/or the pear ester kairomone were investigated in wind tunnel experiments. Five different kinds of commercially available codling moth monitoring lures (obtained from Tr6c6 Inc., Adair, OK) were used in the bioassay: Pherocon CM Standard lure (loaded with 1 mg of codlemone), Pherocon CM Long-Life L2 (loaded with 3.5 mg of codlemone), Pherocon CM 10X (loaded with 10 mg of codlemone), Pherocon CM-DA Combo (loaded with 3.0 mg of codlemone and 3.0 mg of pear ester), and Pherocon DA (loaded with 3.0 mg of pear ester). Results from the study revealed that male codling moth exposed to surfaces treated with methoxyfenozide and the surfactant exhibited a significant decline in responsiveness toward lures loaded with either codlemone or pear ester. The full impact of how this negative effect might alter current moth monitoring procedures in orchards receiving ecdysone agonist sprays requires further investigation.

Assessment of methoxyfenozide exposure on the sexual attractiveness and responsiveness of adult codling moth, Cydia pomonella L., in small orchard blocks.

BACKGROUND: The sexual attractiveness of female and the responsiveness of male codling moth, Cydia pomonella L., exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide were investigated in small orchard block experiments. The main purpose of the study was to determine whether the reported sublethal effects of methoxyfenozide affecting moth behavior also occur under field conditions. RESULTS: Data from the first experiment showed that in some trials untreated females were significantly more attractive to wild males than methoxyfenozide-treated females. The second experiment revealed that some released methoxyfenozide-treated males were not as responsive to calling females as untreated males, and that some untreated females were more attractive to males than methoxyfenozide-treated females. The third experiment revealed that wild males exposed to treated tree surfaces were significantly less responsive to traps than were wild males exposed to untreated trees. However, there were no significant differences in mean recaptures of released males between the untreated and treated orchard blocks. CONCLUSION: Exposure of adult C. pomonella to methoxyfenozide-treated surfaces resulted in a negative impact on male responsiveness to calling females and synthetic pheromone lures. However, the level of impact on the sexual attractiveness of treated females did not appear to be as explicit.

Sublethal exposure to methoxyfenozide-treated surfaces reduces the attractiveness and responsiveness in adult oriental fruit moth (Lepidoptera: Tortricidae).

The chemical communication (female attractiveness and male responsiveness) of adult oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide for 48 h were investigated in two laboratory wind tunnel assays. The recapture assay examined the ability of treated males to orient to a single cage of treated females, and the data gathered were mean percentage of males recaptured per treatment. The male sexual behavior assay examined some specific orientation behaviors (associated with sexual excitability) of treated males when they were given a choice of two competing pheromone sources (cages of treated females), and the data gathered were mean time males spent in upwind plume orientations and at source contact (female cage) per treatment. Data from the recapture assay suggests that exposure to methoxyfenozide impacts male responsiveness more than female attractiveness. In contrast, data from the sexual behavior assay strongly revealed that exposure to methoxyfenozide-treated surfaces does negatively impact both the ability of calling females to attract males and of aroused males to display sustained upwind flight behavior and time spent at the female cages.

Effects of methoxyfenozide-treated surfaces on the attractiveness and responsiveness of adult codling moth (Lepidoptera: Tortricidae).

The attractiveness and responsiveness of adult codling moth, Cydia pomonella (L.), exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide was investigated in wind tunnel and orientation tube assays. When males were exposed to either water- or surfactant-treated surfaces for 48 h, and regardless of what treatment surfaces the females had been exposed to, the mean percent recaptures of such treated males in the wind tunnel assay were sometimes significantly greater than the recaptures of males that had been exposed to methoxyfenozide. Similarly, in the orientation tube assay, males exposed to methoxyfenozide-treated surfaces almost always had significantly lower mean levels of individuals exhibiting sexual excitability and the mean distances traveled upwind, regardless of female exposures. The two assays demonstrated that male codling moths exposed to methoxyfenozide-treated surfaces were not as responsive to calling females (treated and nontreated) as were the nontreated males. Conversely, females exposed to methoxyfenozide-treated surfaces were just as attractive to nontreated males as were nontreated females. It appears that a male's ability to respond to a calling female is more negatively affected by the ecdysone agonist than a female's ability to call and attract males.