Field development of resistance to Bacillus thuringiensis in diamondback moth (Lepidoptera: Plutellidae)

Foliar applications of commercial formulations of the insecticidal spore-crystal protein complex of Bacillus thuringiensis subsp. kurstaki 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 LC50 and LC95 for a field population of diamondback moth treated repeatedly with B. thuringiensis were 25 to 33 times greater than the respective LC50's and LC95's for two susceptible laboratory colonies. Mortality at the field rate of B. thuringiensis 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. thuringiensis toxin genes in genetically-engineered crop plants and use of B. thuringiensis in related tactics