Associative learning and memory through metamorphosis in Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Learning of chemical stimuli by insects can occur during the larval or adult life stage, resulting in changes in the imago chemotaxic behaviour. There is little information on learning in Tortricidae, and associative learning through metamorphosis is unknown in this group. Here, we evaluate the influence of olfactory aversive learning in Grapholita molesta (Busck) (Lepidoptera: Tortricidae) during the immature stage and determine if memory persists after metamorphosis. Larvae (10–12 days old) were conditioned to associate the odour of ethyl acetate with pulses of aversive electric shock. Insects were exposed to air, to the ethyl acetate odour, and to shock, in isolation or combination. After conditioning, both larvae and adults were tested in a two-choice olfactometer. Larvae exposed only to air or ethyl acetate increased legibility. Larvae trained with ethyl acetate and shock simultaneously exhibited significant avoidance to ethyl acetate. Avoidance was still present for at least 72 hours after metamorphosis. Thus, G. molesta has the ability to associate an odour to an aversive stimulus precociously, and this association is maintained through metamorphosis and persists into adulthood.