Field Development of Resistance to Bacillus thuringiensis in Diamondback Moth (Lepidoptera: Plutellidae)

Abstract

Foliar applications of commercial formulations of the insecticidal spore-crystal protein complex of Bacillus thuringiensis subsp. kUTstaki caused development of resistance in field populations of a major lepidopteran pest of vegetables, diamondback moth, Plutella xylostella (L.). Laboratory bioassays of larvae showed that the LC"" and LC for a field population of diamondback moth treated repeatedly with B. thuTingiensis were 25 to 33 times greater than the respective LC",,'sand LC's for two susceptible laboratory colonies. Mortality at the field rate of B. thuTingiensis was 34-35% in two resistant populations compared with 90-100% in two susceptible laboratory colonies. The results suggest that the potential for resistance development in pest populations is an important consideration for deployment of B. thuTingiensis toxin genes in genetically-engineered crop plants and use of B. thuringiensis in related tactics.