CHARACTERISTIC OF PARASITISM OF DIAMONDBACK MOTH BY 2 LARVAL PARASITES

Laboratory and greenhouse studies were conducted to investigate the suitability of 2 hymenopterous parasites, Diadegma eucerophaga Horstmann and Apanteles plutellae Kurdjumov for introduction to control diamonback moth (DBM), Plutella xylostella (L.), a destructive pest of crucifers in tropical to subtropical Southeast Asia. Parasitism by D. eucerophaga was high at temperature range of 15-degrees-C to 25-degrees-C and that of A. plutellae, at 20-degrees-C to 35-degrees-C. Both parasites were active in searching for host and oviposited only during photophase. No parasitism was observed during darkness. Whereas A. plutellae could parasitize all instars of DBM larvae, D. eucerophaga parasitized only the first 3 instars and failed to parasitize the 4th. Parasitism by D. eucerophaga was greater when DBM larvae were feeding on common cabbage (Brassica oleracea var. capitata L.), than on cauliflower (B. oleracea var. italica L.), broccoli (B. oleracea var. botrytis L.) or Chinese cabbage [Brassica campestris L. ssp. pekinensis (Lour) Olsson]. A. plutellae parasitism was greater when DBM larvae were feeding on Chinese cabbage than on common cabbage, cauliflower or broccoli. Storage of pupae at 0-degrees-C and 4-degrees-C to 6-degrees-C for up to 2 weeks reduced emergence of D. eucerophaga adults more than that of A. plutellae. A non-selective insecticide, deltamethrin, was toxic to adults of both parasites but selective ones such as Bacillus thuringiensis, teflubenzuron, and pirimicarb were not. Pupae were more tolerant than adults to insecticides. The insecticide-resistant Luchu strain and susceptible laboratory strain of DBM suffered an equal level of parasitism by both parasites.