State-Dependent Plasticity in Response to Host-Plant Volatiles in a Long-Lived Moth, Caloptilia fraxinella (Lepidoptera: Gracillariidae)

Volatile chemicals produced by plants mediate host location, mate-finding and oviposition behavior in insects. State-dependent response to plant cues allows for timing of foraging, mating and oviposition on ephemeral host plants or plant parts. Caloptilia fraxinella is a herbivorous specialist on the foliage of ash trees (Fraxinus). Adults are long-lived and undergo a nine-month reproductive diapause over the fall and winter. Mating and oviposition occur in the spring when volatile chemicals released by ash leaves mediate host location. This study tested the plasticity of olfactory response of C. fraxinella to host plant volatiles using both electroantennogram and behavioral bioassays. The effect of moth physiological state on olfactory response was tested on male and female moths in different nutritional, mating, and diapause states. Antennal responses to host plant volatiles were plastic and depended on moth physiological state, and were highest when moths were reproductively active and would be seeking oviposition hosts. Moth sex and nutritional status also impacted antennal response to host plant volatiles. Oriented flight of females to ash seedlings varied with physiological state and nutritional status, with fed, reproductively active females having the highest response. Physiological state impacted oriented flight of males to female-produced sex pheromone signals whether or not a host plant was present, and there was no increase in behavioral response to sex pheromone in the presence of an ash host.