Inheritance of Cry1Ac resistance and associated biological traits in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The analysis of reciprocal genetic crosses between resistant Helicoverpa armigera strain (BH-R) (227.9-fold) with susceptible Vadodara (VA-S) strain showed dominance (h) of 0.65–0.89 and degree of dominance (D) of 0.299–0.782 suggesting Cry1Ac resistance as a semi-dominant trait. The D and h values of F1 hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F2 crosses, backcrosses of F1 hybrid with resistant BH-R parent did not differ significantly in respect of mortality response with resistant parent except for backcross with female BH-R and male of F1 (BH-R × VA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F1 crosses, backcrosses and F2 crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 μg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F2 crosses, Cry1Ac resistance favored emergence of more females than males on untreated diet. The normal larval period and the body weight (normal larval growth) were the dominant traits associated with susceptible strain as contrast to longer larval period and the lower body weight (slow growth) associated with resistance trait. Further, inheritance of larval period in F2 and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.