INTERRELATIONSHIP OF BACILLUS-THURINGIENSIS BERLINER TO THE DIAMONDBACK MOTH (LEPIDOPTERA, NOCTUIDAE) AND ITS PRIMARY PARASITOID, DIADEGMA INSULARE (HYMENOPTERA, ICHNEUMONIDAE)

The interrelationship of Bacillus thuringiensis Berliner var. Kurstaki to the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutell idae), and its primary parasitoid, Diadegma insulare Cress. (Hymenopte ra: Ichneumonidae), was investigated using laboratory colonies of the insects. The differential response of third-instar diamondback moth, p arasitized and unparasitized, to B. thuringiensis (Bt), and the abilit y of D. insulare to oviposit in Bt-stressed hosts were determined. No significant difference (P > 0.05) was found between the mean mortality of parasitized and unparasitized larvae at each of three concentratio ns (154, 334, and 2,237 IU/ml) of Bt endotoxin. The three concentratio ns were equivalent to the LC(30), LC(50), and LC(90) of Bt potency bas ed on preliminary tests. Parallel line assay analysis, however, reveal ed that the Linear dose-response regressions of parasitized and unpara sitized larvae were highly significant (P = 0.0001). The LC(50)s of pa rasitized versus unparasitized larvae were 373 and 175 IU/ml Bt endoto xin, respectively, indicating that parasitized larvae were less suscep tible to Bt. Female D. insulare oviposited in Bt-stressed hosts. The p ercentage of D. insulare females emerging from Bt-treated larvae (41.4 %) was not significantly different from that of untreated larvae (32.0 %).