Effect of patch heterogeneity on oviposition in two lepidopteran Brassica pests

Abstract: The plant family of Brassicaceae is widespread around the world and many members of the family are important food and oil-seed crops. There are many insect pests specialized on brassicaceous crops and interactions between crop and pest are well studied. Many studies concern Brassicas as hosts in mixed cropping systems with non-host species but very few use a mix of host-plants. Intercropping or mixed cropping can be seen as a way to manipulate patch heterogeneity. In this project I investigate if patch heterogeneity on a small scale has an effect on the egg distribution of two Brassica pests; one butterfly, Pieris brassicae (Lepidoptera: Pieridae) and one moth, Plutella xylostella (Lepidoptera: Plutellidae). Three Brassica oleracea genotypes were used; cabbage (B. oleracea subs. capitata, cv. Consul), cauliflower (B. oleracea subs. botrytis, cv. Nautilus) and broccoli (B. oleracea subs. cymosa, cv. Marathon). Experiments were carried out in cages and turntable using two arrangements; complex (all three genotypes in every patch) and simple (every patch consisting of one genotype). Results differed between species. P. brassicae responded significantly to arrangement. Eggs numbers differed much more between genotypes in the complex patches than in the simple patches. P. xylostella on the other hand were not significantly affected by the arrangement. The two species differ in the way they find their host plants and how they utilize a patch of host plants once found, these differences may explain their different response to small scale patch heterogeneity.