Phenotypic plasticity in a willow leaf beetle depends on host plant species: release and recognition of beetle odors.

Aggregation behavior of herbivorous insects is mediated by a wide range of biotic and abiotic factors. It has been suggested that aggregation behavior of the blue willow leaf beetle Phratora vulgatissima is mediated by both host plant odor and by odor released by the beetles. Previous studies show that the beetles respond to plant odors according to their prior host plant experiences. Here, we analyzed the effect of the host plant species on odor released and perceived by adult P. vulgatissima. The major difference between the odor of beetles feeding on salicin-rich and salicin-poor host plants was the presence of salicylaldehyde in the odor of the former, where both males and females released this compound. Electrophysiological studies showed that the intensity of responses to single components of odor released by beetles was sex specific and dependent on the host plant species with which the beetles were fed. Finally, behavioral studies revealed that males feeding on salicin-rich willows were attracted by salicylaldehyde, whereas females did not respond behaviorally to this compound, despite showing clear antennal responses to it. Finally, the ecological relevance of the influence of a host plant species on the plasticity of beetle odor chemistry, perception, and behavior is discussed.