Crop Location by Oilseed Rape Pests and Host Location by Their Parasitoids

Abstract

The behavioural ecology associated with location of the oilseed rape crop by its major coleopteran and dipteran pests and by their key hymenopterous parasitoids is reviewed. Results of studies investigating their responses to odour and colour cues from the crop, using olfactometers, wind tunnels, baited and/or coloured traps, and different plant lines, are presented. Host plant volatiles, particularly the isothiocyanates, carried downwind from the crop, and the colours yellow and green are important cues for orientation; odour cues can induce responses to colour cues. Species differ in the subset of cues they use and responses can vary with sex, age, generation, nutritional status, previous experience and time since last oviposition. Evidence suggests that odour-mediated upwind anemotaxis is used by the pests to locate the crop and their host plant, as well as by their parasitoids to locate the crop, the habitat of their host larvae, from a distance, while visual cues are important for orientation at closer range. Once the crop is located, pests use taste and tactile cues from the oilseed rape plant to accept or reject it while parasitoids use host-derived cues to locate their hosts. The implications for integrated pest management and conservation biocontrol are discussed.