Nonassociative learning in the heliolithine moth

Abstract

Heliolithine moth larvae are serious agricultural pests causing hundreds of millions of dollars in agricultural damage annually. Mating disruption, a behavioral method of control of adult male sexual response to female pheromones, has been successfully administered in the field for many years, yet the underlying mechanisms that account for mating disruption are poorly understood. Habituation, a form of nonassociative learning, has been implicated as one possible mechanism that effects male moth behavior during the application of mating disruption strategies. To substantiate the claim that habituation can play a role in mating disruption, data were collected on five of habituation's classic characteristics: (1) The existence of a negatively accelerated relationship between trials and response strength; (2) Spontaneous recovery of response strength; (3) A long-term reduction in male moth pheromonal response strength; (4) More rapid reduction of response strength and greater spontaneous recovery of response with less intense stimuli; (5) Learning associated with a highly specific stimuli will not generalize to exceedingly dissimilar stimuli. Results of this study clearly indicate that all five characteristics related to habituation were present. Specifically, males, repeatedly exposed to pheromones of conspecifics, display a decrease in response strength. Response reduction and spontaneous recovery were both found to be greater with less complex stimuli. Long-term habituation was successfully demonstrated for up to 96 hours post habituation training. Most importantly, it was found that males, habituated to one blend, demonstrated little habituation when exposed to a second blend. Additionally, it was found that a substantial amount of individual differences in responsiveness to habituation training exists between males of this species. The findings of this study indicate two major points. First, habituation can be used as part of an effective integrated pest control strategy. However, because there is a substantial amount of individual differences in habituation susceptibility, some male moths may experience greater reproductive success. Further, because the males did not generalize habituation across the two stimuli presented in this study, there is concern that if all known pheromone components of this species are not used in field applications, males will habituate to the applied pheromone but not individual females.