Laboratory odour-specificity testing of Cotesia urabae to assess potential risks to non-target species

Abstract

The larval parasitoid Cotesia urabae Austin and Allen (Hymenoptera: Braconidae) is known to be attracted to odours of its target host Uraba lugens Walker (Lepidoptera: Nolidae), host plant (Eucalyptus species), and target plant-host complex. Cotesia urabae females were tested in both a Y-tube and four-arm olfactometer to further investigate these attractions as well as their attraction to three non-target Lepidoptera (two in the family Erebidae and one in the family Geometridae), and their corresponding host plants and plant-host complexes. In a Y-tube olfactometer, wasps were attracted to the odours of the non-target Erebidae larvae when tested on their own and when feeding on their host plants, but not to their non-target host plants alone, suggesting some rare circumstances in the field these non-targets could be attacked by C. urabae. The multiple-comparison bioassay conducted in a four-arm olfactometer indicates that target plant-host complex odours invariably produced the strongest attraction compared with any other of the non-target plant-host complex odours tested. Cotesia urabae females that were given prior exposure and the opportunity to oviposit within either non-target species were not subsequently more attracted to the Erebidae odours, suggesting that associative learning is unlikely to increase non-target attack. Such olfactometer assays could be a very useful addition to the host specificity testing methods able to be conducted within quarantine facilities, prior to the release of candidate biological control agents. We urge other biocontrol scientists to undertake similar assays to assist with non-target risk assessments.