Not my host? Does phylogenetic distance influence repulsion for the specialist swede midge (Contarinia nasturtii)?

Swede midge, Contarinia nasturtii (Diptera: Cecidomyiidae) is a recent invader in North America, which is beginning to cause devastating losses to brassica crops in the Northeastern United States and much of Canada. While systemic insecticides are recommended for conventional management, there are limited pest control options for organic growers. As specialist insect herbivores, C. nasturtii adults are likely to be specifically attracted to chemical cues emitted by brassica plants. However, this may mean that chemical cues from non-host plants induce a repellent response. Given that specialist insects tend to be attracted to closely related species, we hypothesized that a repellent effect may be correlated to phylogenetic distance, with distantly related genera being more repellent. We investigated if extracts of essential oils from more closely and more distantly related aromatic plants differ in their ability to repel swede midge from brassica plants. Our results on host specificity and repellency can provide insight on how agroecosystems can be designed to reduce pest attack.