Effects of host plant growth form on dropping behaviour in leaf beetles

Abstract

Many leaf-eating insects drop from their host plants to escape predators. However, they must return to the leaves of the host plant after dropping, which represents a cost associated with this behaviour. In woody plants, the positioning of leaves is generally higher than that of herbaceous plants, which suggests that dropping from woody plants might be costlier for leaf-eating insects than dropping from herbaceous plants. Therefore, we predicted that dropping behaviour would be observed less frequently in insects that feed on woody plant leaves than in those that feed on herbaceous plant leaves. To test this prediction, we investigated dropping behaviour experimentally in larvae (23 species) and adults (112 species) of leaf beetles (Coleoptera: Chrysomelidae) on their host plants (86 species of 44 families) in field conditions. Larvae on woody plants exhibited dropping behaviour less frequently than those on herbaceous plants. However, this pattern was not detected in adults. Thus, host plant growth form might affect the evolution of dropping behaviour in leaf beetle larvae, but not in winged adults, perhaps owing to their higher mobility.