The question of whether local adaptation by leaf feeding herbivores occurs at the small scale of individual plant genotypes and how recombination and the introduction of new alleles through sexual reproduction affect local adaptation by both plant and insect will be examined. The host plant, Erigeron glaucus, is a long-lived, mat forming plant that produces both apomictic seeds and outcrossed seeds. The herbivore, a thrips Apterothrips secticornis, goes through many generations each year and produces offspring either asexually or sexually. The mode of reproduction (sexual vs. asexual) of both the plant and the herbivore can be experimentally manipulated. Previous work showed that population growth of thrips was very strongly affected by host plant variation. Conversely, preliminary evidence indicates that thrips can reduce seed production of their hosts. To determine if thrips show local adaptation to individual hosts, the population growth of genetic lines derived from thrips on five different host clones will be compared. If adaptation to individual clones has taken place, then thrips from each clone may be expected to perform best on the clone from which their ancestors were taken. A preliminary run of this experiment suggested that thrips have adapted to individual plants. If thrips have adapted to host genetic lines, can hosts escape their parasites by reproducing sexually? This question will be answered by comparing the population growth of thrips on plants that were produced apomictically versus those that were produced by outcrossing. Similarly, the role of mode of reproduction, in the success of thrips on host plant lines by using parthenogenetically-produced or sexually-produced thrips progeny will be examined.
