In natural plant populations there is often considerable genetic variation in the expression of a range of phenotypic traits. Wild cabbage (Brassica oleracea) plants are native to the coastlines of France and Great Britain. In southern England, previous work has shown there to be profound differences in qualitative and quantitative aspects of secondary (= defence) chemistry in shoots of wild cabbage plants growing only a few kilometres from one another. Using 5 populations of B. oleracea from Dorset, this project will explore the effects of differences in primary (nutrients) and secondary (glucosinolates) metabolites, as well as on morphological traits, on interactions between above-ground (AG) and below-ground (BG) chains involving herbivores and parasitoids. The cabbage populations were selected on the basis of known differences in secondary chemistry and other morphological traits. In naturally occurring populations of B. oleracea in Dorset, U.K., insect communities colonizing shoots and roots will be monitored over the summer months. The development of insects will be compared in controlled laboratory experiments on plants with and without root or shoot herbivores. The insects will include AG herbivores from two feeding guilds (phloem versus tissue feeder) and their respective parasitoids. The BG system will consist of a chewing root herbivore and its parasitoid. Additionally, the effects of multiple AG herbivory on the BG trophic chain will be tested. The main objective of this project is to study the effect of population variation in plant chemistry and morphological traits in wild cabbage on AB-BG insect interactions.