Multitrophic interactions and the diamondback moth: implications for pest management

There is a scarcity of studies concerning Plutella xylostella L. dealing with either interactions between partial plant resistance and insecticides or multitrophic interactions (with or without insecticides). Such studies are vital to allow improved understanding of possible interactions in IPM programmes and may help both to develop approaches which enhance cultural and biological controls and minimise insecticide use. Laboratory studies showing the relationship between different degrees of partial plant resistance to P. xylostella (in various Brassica oleracea var. capitata L. and B. pekinensis (Lour.) Rupr. cultivars), leaf biomass consumption, leaf surface area damage and residual toxicity of two selective insecticides are presented and reasons for consistent relationships between various factors are discussed. Insecticide toxicity to P. xylostella larvae on plants with partial plant resistance is shown to be less compared with insecticides applied to either more or less resistant plants. Tritrophic laboratory and field studies in Malaysia show that larvae of P. xylostella on different host plant species and cultivars may experience different and sometimes contrasting rates of relative survival and parasitism by the key endolarval hymenopteran parasitoids, Diadegma semiclausum Hellén and Cotesia plutellae Kurdj. Finally, the value of multitrophic studies is discussed and their potential for stimulating novel strategies is considered.