Fine-scale adaptation of herbivorous thrips to individual host plants

Abstract

Short-lived sedentary herbivores that feed on long-lived plants can complete hundreds or thousands of generations on a single host genotype. Insects are known to adapt rapidly to changes in the resistance characteristics of their host plants1 and new plant cultivars bred for resistance to specific pests 'lose' their resistance within a few years due to evolution of the pests. These observations led to the proposal that natural populations of scale insects become differentiated into small demes, each specialized on an individual pine tree2. This hypothesis predicts that a herbivore found on and hence adapted to, host individual A should have a higher fitness than should insects from other unrelated conspecific host individuals, when both are reared on host A. Testing this hypothesis by measuring the population growth of thrips (Apterothrips secticornis Trybom, Thysanoptera: Thripidae) on individual clones of their host (Erigeron glaucus Ker., Compositae), I found that their growth was greater on cuttings of their native plant clone than on other clones. This was not the result of environmental conditions experienced by insects or their hosts, but rather, of genetic adaptation and is the first demonstration of fine-scale adaptation of a herbivore to individual clones of its host plant. © 1989 Nature Publishing Group.