The role of plant genotype, environment and gender in resistance to a specialist chrysomelid herbivore.

Patchiness in herbivore attack is a well-documented phenomenon. When neighboring plants suffer vastly different levels of attack, then one suspects genotypic differences among plants to be the underlying mechanism. In this study, I use common garden experiments in two natural, but divergent, habitats at the Cedar Creek Natural History Area in central Minnesota to determine the role of plant genotype, environment and gender in plant resistance to a specialist herbivore. Resistance was measured by larval survivorship and weight. Eight clones ofRhus glabra were selected and 12 equal-aged ramets were dug up and planted in two gardens (each garden received 6 ramets per clone). First instarBlepharida rhois (Coleoptera: Chrysomelidae) larvae of known parentage were transferred to ramets and censused every other day. At the end of the experiment, larvae were collected and weighed. Analysis of variance was used to determine the importance of plant genotype, environment and gender on larval mortality and weight. The experiment was repeated in its entirety one month later. Both plant genotype and environment significantly affected larval survivorship in the first run of the experiment. No interactions were significant. Results from the second run indicated marginally significant genotype and environment main effects, and a genotype by environment interaction in larval survivorship. There was a significant genotype by environment interaction in larval weight on the same run. In neither run did clone gender have significant affects on resistance.