Three-trophic-level interactions among cruciferous plants, one of their major herbivores, the diamondback moth Pluetella xylostella and its major parasitoid Diadegma insulare will be studied. Sex ratios and population sizes of both the moth and the parasitoid are correlated with differences in food plants; and the trophic levels are likely to have major effects on the regulation of population size and the dynamics of interactions between these insect species and other components of the community. The variations in the sex ratios of the herbivore and its parasitoid, using both wild and cultivated crucifers will be explored. Selection of species from both wild and cultivated habitats will allow the scanning of a large array of plant properties, from individual variation in such factors as nitrogen, defensive chemistry and morphology, up to population variation in patch size and density. The primary goal of the research is to identify factors affecting both moth and wasp sex ratios within population and community contexts. The secondary goal is to compare these interactions on wild vs. cultivated crucifers. Together, these different systems cover an array of community situations from the high density, agricultural environments in which population interactions and sex ratio variation are usually studied, to the low density, patchy communities in which these interactions and insect behaviors probably evolved.
