ADAPTIVE GENETIC - STRUCTURE IN PHYTOPHAGOUS INSECT POPULATIONS

Genetic variation in insect populations is frequently structured into discrete groups, or demes, that form in response to stochastic forces or natural selection. Because host-plant populations are often highly heterogeneous, phytophagous insects may form demes that are adapted to the unique traits of individual plants. Recent field experiments indi cate that selection pressures imposed by host-plants can promote rapid adaptive evolution in natural insect populations at very fine spatial scales. Adaptive deme formation may be more common among endophagous insects, which feed and reside within plant tissue, than for externall y feeding insects, because internal feeders experience stronger plant- mediated selection pressures.