Parasitism of Nyctemera amica (White) (Lepidoptera: Arctiidae) and Plutella xylostella (L.) (Lepidoptera: Plutellidae) by Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae)

The parasitoid, Cotesia plutellae, is used as a biological control agent for diamondback moth, Plutella xylostella, in many countries and has been evaluated as a candidate for release in New Zealand. C. plutellae was originally released in Australia in 1951, but is rarely found. A glasshouse host specificity trial was conducted in Australia to assess whether C. plutellae would parasitise Nyctemera amica, magpie moth, on the noxious weed ragwort (Senecio jacobæa L.) in the presence of P. xylostella on cabbage. Although P. xylostella was expected to be the preferred host of C. plutellae, a greater proportion of the N. amica larvae was parasitised. It is likely, therefore, that C. plutellae would parasitise N. amica on ragwort in the vicinity of Brassica plants in the field. The closely related moth, Nyctemera annulata (Boisduval), is valued as a native species in New Zealand and significant parasitism of this insect would not be acceptable. The proposal to release C. plutellae will not be pursued until further information on host specificity is obtained.