Frequency of alleles conferring resistance to a Bacillus thuringiensis toxin in a Philippine population of Scirpophaga incertulas (Lepidoptera : Pyralidae)

Using the F-2 screen methodology, we estimated the frequency of alleles con ferring resistance to the CrylAb toxin of Bacillus thuringiensis Berliner i n a Philippine population of the stem borer Scirpophaga incertulas (Walker) . Evaluation of >450 isofemale lines for survival of F-2 larvae on crylAb p lants did not detect the presence of an allele conferring a high level of r esistance. The frequency of such an allele in the sampled population was co nservatively estimated to be <3.6 X 10(-3) with 95% confidence and a detect ion probability of 94%. However, there was evidence of the presence of alle les conferring partial resistance to CrylAb. The frequency of alleles for p artial resistance was estimated as 4.8 X 10(-3) with a 95% CI between 1.3 X 10(-3) and 1.04 X 10(-2) and a detection probability of 94%. Our results s uggest that the frequency of alleles conferring resistance to CrylAb in the population of S. incertulas sampled is not too high to preclude successful implementation of the high dose/refuge resistance management strategy.