COMPARATIVE EFFECT OF TEMPERATURE AND TIME ON ACTIVITY OF DIPEL 2X AND MVP PREPARATIONS OF BACILLUS-THURINGIENSIS SUBSP KURSTAKI ON DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE)

Bioassays with MVP, a genetically engineered form of a toxin of Bacill us thuringiensis susp. kurstaki, demonstrated that a plateau in concen tration response depended on the temperature and time when mortality w as assessed. The presence of a plateau did not indicate resistance in diamondback moth, Plutella xylostella (L.). Comparisons of LC(50)s at 25 degrees indicated that MVP acted more slowly than a conventional B. thuringiensis subsp. kurstaki formulation (Dipel 2X). However, LT(50) s of the preparations at a given concentration did not vary substantia lly. AT 28 degrees C, responses were approximately equal over time. To avoid artifacts in analyses of concentration-response data, we recomm end that bioassays be designed carefully to account for subtle differe nces in the behavior of genetically engineered versus conventional pre parations of B. thuringiensis.