Plasticity of male response to sex pheromone depends on physiological state in a long-lived moth

Plasticity of response to sexual signals is predicted to occur in long-lived animals that have periods of reproductive inactivity. Response should be adaptive to avoid wasted energy mate searching when conditions are unfavourable. Here we test that male response to female-produced sex pheromone in a long-lived moth species, Caloptilia fraxinella, is plastic and depends on male physiological state. Electrophysiological and behavioural studies indicated that the sex pheromone is composed of two compounds: (Z)-11-hexadecenal and (Z)-11-hexadecen-1-ol. Experiments were conducted to examine how males that differed in physiological state responded to signals of varying quality and quantity produced by manipulating synthetic pheromone blends. Reproductively active males had a lower pheromone response threshold and showed an upper threshold compared to males in reproductive diapause, which responded only to high pheromone doses with no upper threshold. The nature of pheromone response also varied depending on the male's physiological state. Reproductively active males showed a more narrowly tuned response than males in diapause. However, reproductively active males did not discriminate among pheromones with (Z)-11-hexadecenal and 1–50% of (Z)-11-hexadecen-1-ol. Males in diapause were not attracted to pheromone composed of (Z)-11-hexadecenal and 1% (Z)-11-hexadecen-1-ol, showing reduced signal perception in moths in diapause. Taken together, these results indicate that male C. fraxinella pheromone response is plastic with respect to threshold and specificity and depends on physiological state of the responder.