Odour-mediated nectar foraging in the silver Y moth, Autographa gamma

Abstract: It is well established that floral odours play a significant role in the nectar foraging behaviour in Lepidoptera and other insect orders. Floral odour may elicit searching, alighting and feeding behaviours alone or in concert with visual stimuli. The goal of the present project was to investigate attractiveness of different species of flowers to the silver Y moth, to identify constituents of volatile floral components responsible for this attraction, and to study how they are processed in the peripheral nervous system. Moth's foraging as well as mate-finding behaviour is altered by the risk of bat predation. Thus I also studied if males and females take different risks when preyed upon, and if male risk taking depends on the nature of stimuli. Attractivity of six flower species differed in the flight tunnel assay. This difference can be explained by a difference in the emission rate of volatiles, by difference in innate preferences for specific compounds or by a combination of both factors. Gas chromatographic–electroantennographic analysis demonstrated the absence of a common volatile compound present in flowers of different plants visited by A. gamma. Forty-four electrophysiologically active compounds were identified. Employing the single sensillum recording method I found that these compounds are detected with high selectivity and sensitivity by the olfactory receptor neurones (ORNs) of the moth. Eleven ORN types were identified. ORNs responding to lilac aldehydes, cinnamyl alcohol, a-farnesene and cis-trans-nepetalactone were the most abundant. A flight tunnel assay revealed that lilac aldehyde(s) are the major attractive compound(s) responsible for the attraction of moths to the flowers of an orchid Platanthera bifolia. To test attractivity of extracts, blends and individual compounds an ultrasonic sprayer was used for release of stimuli. Noctuid moths are able to hear the ultrasound emitted by the sprayer that affects their behaviour. The sprayer was improved to eliminate the negative sound effect by introducing a new piezo ceramic transducer able to generate 300 kHz frequency sound that is beyond the hearing threshold of the moth. Males did not take a higher risk under the simulated bat predation than females; neither male risk taking was dependent on whether they were stimulated by floral odour or a pheromone.