Monitoring of Bacillus thuringiensis Cry1Ac Resistance in Helicoverpa armigera (Hübner) (Noctuidae: Lepidoptera)

Laboratory selection pressure of Bacillus thuringiensis Cry1Ac toxin against a selected strain of cotton bollworm (Helicoverpa armigera) increased the resistance to the toxin 83-fold. Sequence tagged microsatellite (STMS) markers were employed to genetically map the gene(s) for resistance to the Bacillus thuringiensis toxin. Out of the 43 STMS markers used, Ha 34 was found to be polymorphic between the two parental types and two bulks. Single factor analysis of variance using the marker locus genotypic class mean body weight values revealed strong linkage between the marker and trait (P ≤ 0.0001). The resistant parent had two fragments while the susceptible had one fragment. The sequences of the resistant and susceptible samples with Ha 34 marker were done. The data showed that the lower band of resistant sample gave 479 bases and was submitted to the GenBank with Accession No. AJ875063. On the other hand, the susceptible sample contained 491 bases and its sequence was submitted to the GenBank with Accession No. AJ875064. This is the first molecular mapping of Cry1Ac resistance in the insect under study. This in turn will facilitate assessment, monitoring, and management of resistance in pest populations, and increase our understanding of Bt Cry1Ac resistance