Foraging and mate-finding in the silver Y moth, Autographa gamma (Lepidoptera : Noctuidae) under the risk of predation

Animal foraging and reproductive behaviour is influenced by other simultaneous demands such as predator avoidance. The trade-offs between these demands may depend on sex or mating experience. This study demonstrates that the olfactory-mediated foraging and mate-seeking behaviours in the silver Y moths, Autographa gamma, are affected by auditory cues mimicking their bat predators. Both males and females changed their foraging behaviour under simulated predation risk. Fewer moths reached the odour source following sound stimulation and the time to find the odour source increased by up to 250%. However. there were no significant differences between male and female ability to reach the plant odour source or the duration of the flight towards the source when stimulated with ultrasound. Hence females are not more cautious than males when observed in the same behavioural context. Risk-taking in males was independent of whether they were flying toward a flower odour or sex pheromones having equal attractive value. This indicates that the trade-off between olfactory and acoustic cues is independent the type of odour. Mated females were not as strongly affected by sound as non-mated, indicating that flower odours have a higher adaptive value for mated females, suggesting that some processes following mating experience influence the trade-off between flower odours and simulated bat sounds

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

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

Quantitative analysis of the effects of ultrasound from an odor sprayer on moth flight behavior

A piezoelectric sprayer was recently developed for precision release of odor stimuli in olfactory research. The device replaces conventional dispensers used to release semiochemicals in studies of moth flight toward odor sources. However, the device generates high-frequency sounds in the range that some moths can hear. Ultrasound from the standard set-up sprayer had a considerable impact on flight behavior of the silver Y moth, Autographa gamma, tested in a flight tunnel. It was affected at all behavioral stages when the dispenser was driven at 120 kHz. Only 5% of the moths reached the source when exposed to 120-kHz sound from the dispenser compared to 65% in the control group without sound. The proportion taking flight was also reduced. Hearing threshold curves obtained electrophysiologically revealed that moths were sensitive to the frequency range at which the sprayer was operated and that sound intensity from the sprayer was up to 40 dB above the moths' electrophysiological hearing threshold. The audiogram for A. gamma was similar to audiograms obtained for other noctuids. Hearing sensitivity was highest at around 15 kHz, where the threshold was 35 dB SPL (sound pressure level). The threshold increased with frequency up to 94 dB SPL at 160 kHz. We improved the sprayer to operate at 300 kHz, which is beyond the hearing ability of most insects with ears. At this high frequency, the moths' sensitivity to ultrasound is reduced considerably, and we did not observe any effect on flight behavior compared to a control group without sound. Accordingly, this new piezoelectric sprayer can be used with ultrasound-sensitive insects and insensitive insects alike

Volatiles from flowers of Platanthera bifolia (Orchidaceae) attractive to the silver Y moth, Autographa gamma (Lepidoptera : Noctuidae)

We examined the attractiveness of a natural headspace sample of [i]Platanthera bifolia[/i blossoms, synthetic blends and Single compounds to the silver Y moth, Autographa gamma, in a flight tunnel. The synthetic blend consisted of previously identified electrophysiologically active compounds from P. bifolia: benzyl benzoate, benzyl salicylate, cinnamyl alcohol, lilac aldehydes, methyl benzoate and methyl salicylate. This blend had a similar attractivity as the natural headspace sample. Subtraction of lilac aldehydes significantly decreased attractiveness of the synthetic blend. When a mixture of lilac aldehydes was tested alone. it showed attractiveness similar to that of the synthetic blend. One or a mixture of lilac aldehydes accounts for the attraction of moths to P. bifolia. All other Compounds elicited significantly lower responses. Results are discussed in relation to the pollination biology of P. bifolia