INSECT-PLANT INTERACTIONS - THE EVOLUTION OF COMPONENT COMMUNITIES

Because plant resistance to different herbivores seems generally not t o be genetically highly correlated, selection by herbivores for plant resistance traits and for investment in such traits is likely to be st rongly influenced by the species composition of a plant species' assoc iated community of enemies. We summarize evidence that the host associ ations of specialized herbivorous insects are often phylogenetically v ery conservative, and include an analysis of host associations of east ern North American leaf beetles (Chrysomelidae). The great majority of these feed on the same plant families as their congeners in other bio geographic regions. The phylogenetic evidence for conservatism is comp lemented by a survey of several species of Ophraella (Chrysomelidae) f or genetic variation in feeding responses to and survival on host plan ts 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 pa tterns of genetic variation may therefore underlie the phylogenetic co nservatism of host use. Long-lasting associations of plants with speci alized herbivores may provide opportunity for coevolution.