Host specificity assessments of Cotesia plutellae, a parasitoid of diamondback moth

Cotesia plutellae is being assessed as a potential biological control agent for introduction against Plutella xylostella in New Zealand. As the literature on C. plutellae provided variable assessments of its host specificity, further information was collected from the laboratory and field. Our field assessments in Fiji indicated that this parasitoid did not attack other Lepidoptera in or around vegetable brassica crops. Laboratory tests on a colony of C. plutellae in South Australia, including simple no-choice experiments and flight tunnel choice tests, showed that the parasitoid could choose to oviposit in other Lepidoptera and that successful development rarely occurred. In New Zealand, similar laboratory tests of C. plutellae collected from Fiji revealed that it was capable of ovipositing and developing in seven other species of Lepidoptera. Host suitability was assessed by comparing the ability of the parasitoid to develop in P. xylostella and other species. Host acceptability was compared by assessing the flight of adults to test larvae on their host plants, and by comparing oviposition preferences. These experiments suggested that C. plutellae may parasitise Lepidoptera other than P. xylostella in New Zealand and indicate that further assessments are required to determine its potential impact in the field.