SKALS, N.*; Lund University, Sweden: Sex or Death: The Sensory Conflict Between Mate Attraction and Predator Avoidance in Moths

In many situations animals will receive simultaneously information from different sensory modalities. Moths are distinguished for their abilities to evade echolocating insectivorous bats and for their skilled mate location by pheromone detection. The relatively simple system in moths where the predator signal arrives through one channel (the ears) and the sexual signal arrives through another (the antennae) might serve as a model system for studying how two orthogonal modalities influence each other. We used an integrative approach between chemical ecology and bioacoustics to study the behaviour of male Spodoptera littoralis moths when they are simultaneously exposed to sex pheromones and synthetic bat cries. The reaction to acoustic predator cues in male moths decreased by more than 40 dB when they were attracted to female sex pheromones. Hence their detection range of approaching bats is considerably reduced. Our data suggest that male moths take higher predation risk when pheromone quality and/or quantity increases, and that their decision is based on a trade-off between the relative intensity and quality perceived by the two sensory modalities. Similar experiments with young and old non-mated male moths showed that young males responded more often to bat sounds than old males, suggesting that old non-mated male moths take higher predation risk when searching for potential mates than young ones. Our findings show that behavioural thresholds estimated under unimodal conditions in the lab may be far from the relevant thresholds in the animal�s habitat. A simple method to study the trade-off between acoustic and chemical stimuli in the moth, as presented here, offers an interesting model for studies on how dynamic integration of bimodal sensory information is processed by the CNS.