Response of Slugs to Unacceptable Food Items

Abstract

(1) Recent studies in plant-herbivore coevolution have concentrated on adaptations that have allowed herbivores to overcome plant defences and suggest that generalist herbivores evolve an ability to tolerate unacceptable plants in their habitat. (2) This study was designed to test the hypothesis that relatively unacceptable plants will be more acceptable to generalist herbivores (slugs) from the same habitat than to slugs from other populations that are not normally exposed to these plants. (3) Two slug species that occur in both waste-sites and woodland were selected for feeding trials with one relatively unacceptable plant species from each habitat. (4) The hypothesis was not supported. In fact, the unacceptable plants were initially fed on more by the slugs not usually exposed to them. (5) However, the 'naive' slugs showed a reduced amount of feeding on the unacceptable plants in a second feeding trial, suggesting that they learned to avoid these plants. (6) These two aspects of feeding behaviour, namely extensive feeding on a novel food and learning to avoid unacceptable food items, probably allow the tracking of new potential foods in a changing habitat while reducing the time spent in unnecessary feeding on unacceptable food items. The importance of these factors is discussed in relation to the climatic and energetic constraints on slug activity.