Insect-plant interactions: The evolution of component communities

Because plant resistance to different herbivores seems generally not to be genetically highly correlated, selection by herbivores for plant resistance traits and for investment in such traits is likely to be strongly influenced by the species composition of a plant species' associated community of enemies. We summarize evidence that the host associations of specialized herbivorous insects are often phylogenetically very conservative, and include an analysis of host associations of eastern North American leaf beetles (Chrysomelidae). The great majority of these feed on the same plant families as their congeners in other biogeographic regions. The phylogenetic evidence for conservatism is complemented by a survey of several species of Ophraella (Chrysomelidae) for genetic variation in feeding responses to and survival on host plants of congeric species. In about half the cases, no genetic variation was discerned. Genetic variation was displayed most often in responses to plants closely related to the species' natural hosts. Biases in patterns of genetic variation may therefore underlie the phylogenetic conservatism of host use. Long-lasting associations of plants with specialized herbivores may provide opportunity for coevolution.