In agricultural settings, examples of effective control strategies using repellent chemicals in integrated pest management (IPM) are relatively scarce compared to those using attractants. This may be partly due to a poor understanding of how repellents affect insect behavior once they are deployed. Here we attempt to identify potential hallmarks of repellent stimuli that are robust enough for practical use in the field. We explore the literature for success stories using repellents in IPM and we investigate the mechanisms of repellency for two chemical oviposition deterrents for controlling Drosophila suzukii Matsumura, a serious pest of small fruit crops. Drosophila suzukii causes injury by laying her eggs in ripening fruit and resulting larvae make fruit unmarketable. In caged choice tests, reduced oviposition was observed in red raspberry fruit treated with volatile 1-octen-3-ol and geosmin at two initial concentrations (10% and 1%) compared to untreated controls. We used video monitoring to observe fly behavior in these caged choice tests and investigate the mode of action for deterrence through the entire behavioral repertoire leading to oviposition. We observed fewer visitors and more time elapsed before flies first landed on 1-octen-3-ol-treated fruits than control fruits and concluded that this odor primarily inhibits behaviors that occur before D. suzukii comes in contact with a potential oviposition substrate (precontact). We observed some qualitative differences in precontact behavior of flies around geosmin-treated fruits; however, we concluded that this odor primarily inhibits behaviors that occur after D. suzukii comes in contact with treated fruits (postcontact). Field trials found reduced oviposition in red raspberry treated with 1-octen-3-ol and a combination of 1-octen-3-ol and geosmin, but no effect of geosmin alone. Recommendations for further study of repellents for practical use in the field are discussed.
Adult spotted lanternflies, Lycorma delicatula, launch themselves into the wind from elevated locations such as trees, lamp posts, and buildings. Individuals fly in short, successive bouts along descending trajectories of between 10 and 50 m before landing, crawling upward on a new structure, and again launching upwind. The possible physiological limits to the durations of flight-bouts, if not constrained by their poor ability to generate lift, however, remain unknown. In this study, we observed the behavior of tethered spotted lanternflies known to be prone to flight-dispersing, and recorded the number and durations of their successive flight bouts. Additionally, we recorded the flight distances and durations of similar spotted lanternflies in the field that had spontaneously taken flight or had been manually launched. We found that tethered females can perform >20 successive bouts with only 1 min between bouts when flight durations were limited to 20 s/bout. Bouts averaged 97.9 ± 11.4 s when bout durations were unlimited, with some females flying bouts lasting >400 s. Females could quickly advance upwind a distance >3000 m if the bouts of~100 s each were performed in quick succession in the field. However, adults spontaneously taking flight in the field flew for an average of only~13 s and traveled an average of 29 m before landing on the ground or on nearby objects. This information is important to determine how far a locally dispersing adult can fly before finding a suitable host to finish feeding and attain reproductive maturity.
The use of sensory information to control behavior usually involves the integration of sensory input from different modalities. This integration is affected by behavioral states and experience, and it is also sensitive to the spatiotemporal patterns of stimulation and other general contextual cues. Following the finding that hawkmoths can use relative humidity (RH) as a proxy for nectar content during close-range foraging, we evaluate here whether RH could be used during locomotive flight under two simulated contexts in a wind tunnel: (1) dispersion and (2) search phase of the foraging behavior. Flying moths showed a bias towards air with a higher RH in a context devoid of foraging stimuli, but the addition of visual and olfactory floral stimuli elicited foraging responses that overrode the behavioral effects of RH. We discuss the results in relation to the putative adaptive value of the context-dependent use of sensory information.
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