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 ev idence for resistance to selective insecticides (Bacillus thuringiensi s-based products and abamectin), and the urgent need for resistance ma nagement strategies is discussed. Field studies on parasitism of P. xy lostella on two host plant species (Brassica oleracea var. capitata an d 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, Pl utella xylostella outbreaks occurred most commonly on B. pekinensis, a crop which appeared less attractive to D. semiclausum (in terms of se arching efficiency, the superior endolarval parasitoid) than to Cotesi a plutellae. The possible involvement of induction and genetic (co-evo lutionary) mechanisms in the observed species-specific differences is discussed together with suggestions for research which may assist in t he long-term management of P. xylostella.