Parasitism of Plutella xylostella (Lepidoptera, Plutellidae): Field and laboratory observations

Abstract

Investigations carried out at Alice and its rural environs in the Eastern Cape province of South Africa, showed that parasitoids affecting the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) were Cotesia plutellae, Apanteles eriophyes, Diadegma sp., Diadromus collaris, Oomyzus sokolowskii and Hokeria sp. Cotesia plutellae was active all year round and accounted for 30-50% parasitism of P. xylostella. Field experiments using three cabbage cultivars, grown under pesticide-free conditions, indicated that C. plutellae achieved rates of parasitism as high as 90-95% for at least eight months of the year. In winter and early spring parasitism by C. plutellae was less than 30% in the field. This level of parasitism coincided with rising pest density resulting in a pest increase in early spring when C. plutellae appeared unable to control the high pest numbers. Towards the latter part of spring and early summer, C. plutellae parasitism and that of the other parasitoids increased. The possibility of using indigenous parasitoids especially C. plutellae in the management of P. xylostella in this area requires further investigation.