1 University of Auckland
Olfaction is acknowledged as the primary mechanism used by parasitic wasps to detect and locate a number of resources (e.g. a food source, hosts, mates), where they make use of chemical cues to orient first towards a host habitat and secondly towards their host. Cotesia urabae is solitary larval endoparasitoid that was introduced into New Zealand as a biological control against the gum leaf skeletoniser, Uraba lugens. A series of bioassays using Y-shaped and four-arm olfactometers were conducted to investigate the response of C. urabae to volatiles emitted by its host-plant, host, host by-products and male and female conspecifics. In a Y-tube olfactometer, males exhibited a significant positive response only to conspecific females. Mated females exhibited a significant positive response to E. fastigata leaves, E. fastigata leaves with feeding damage caused by U. lugens larvae, U. lugens larvae, U. lugens larvae feeding on E. fastigata leaves, but not to U. lugens frass on its own nor conspecific males. The multiple comparison bioassay conducted in a four-arm olfactometer clearly shows that C. urabae females were significantly more attracted to U. lugens host larvae feeding on E. fastigata leaves than any other of the odours tested. This study made it clear that C. urabae respond only to chemical cues with a high reliability of what they are searching for, for males it is a female, for females it is cues closely associated with their target host. Frass is not a chemical cue used by foraging C. urabae females as it is generally shed from the plant, and therefore does not reliably indicate the presence of host larvae.