Differences in learning and memory of host plant features between specialist and generalist phytophagous insects

Abstract

Insects are able to learn from experience acquired in their natal habitat, thereby obtaining adaptive advantages. However, the acquisition of new information could involve defects in retrieving previously learned information (i.e. forgetting), a process known as retroactive interference, which diminishes learning capacities. In this study, we evaluated the learning capacity and the impact of retroactive interference during host searching by ecological specialist and generalist phytophagous insects. We examined whether the generalist aphid, Myzus persicae s. str., and the tobacco-specialized subspecies, Myzus persicae nicotianae differ in (1) learning capacity, or (2) retroactive interference during host selection, and (3) whether the learning-associated foraging gene (for) is differentially expressed. Differences in learning capacity and retroactive interference were assessed in bioassays using rearing hosts and alternative hosts followed by choices between or transferences to rearing or alternative hosts. During the pre-alighting phase of host searching, the generalist aphid showed attraction to the alternative host after 12 h of experience, while the specialist showed no attraction to the alternative host regardless of the amount of time on the plant. The retroactive interference experiments showed that when aphids were exposed to an alternative host for different periods, odour attraction to the rearing host persisted in the generalist after 72 h of experience on the alternative host, whereas in the specialist the attraction to the rearing host was lost after 12 h of experience on the alternative host. During the post-alighting phase of host searching, both taxa performed better on their rearing hosts, but in the specialist aphid, a short period on the alternative host reversed this behaviour. In addition, the specialist showed lower levels of gene for expression, which could be associated with the differences in learning performance. Herein we present further evidence of differences in learning capacities between a specialist and a generalist aphid, which may influence the process of host searching and evolution of ecological specialization.