Field-based studies with the diamondback moth tritrophic system in Cameron Highlands of Malaysia: Implications for pest management

A brief chronological history of the management of Plutella xylotsella L. in the Cameron Highlands to date is presented: including recent evidence for resistance to selective insecticides (Bacillus thuringiensis-based products and abamectin), and the urgent need for resistance management strategies is discussed. Field studies on parasitism of P. xylostella on two host plant species (Brassica oleracea var. capitata and B. pekinensis) by three key parasitoids (Diadegma semiclausum Hellen, Diadromus collaris Gravenhorst and Cotesia plutellae Kurdjumov) are described and show distinct species-specific trends. In particular, Plutella xylostella outbreaks occurred most commonly on B. pekinensis, a crop which appeared less attractive to D. semiclausum (in terms of searching efficiency, the superior endolarval parasitoid) than to Cotesia plutellae. The possible involvement of induction and genetic (co-evolutionary) mechanisms in the observed species-specific differences is discussed together with suggestions for research which may assist in the long-term management of P. xylostella.