| Abstract: | The genetic inheritance of resistance to a commercial formulation of Bacillus thuringiensis subsp. kurstaki was examined in a Trichoplusia ni colony initiated from a resistant population present in a commercial vegetable greenhouse in British Columbia, Canada. Progeny of F1 reciprocal crosses and backcrosses between F1 larvae and resistant (PR) and susceptible (PS) populations were assayed at different B. thuringiensis subsp. kurstaki concentrations. The responses of progeny of reciprocal F1 crosses were identical, indicating that the resistant trait was autosomal. The 50% lethal concentration for the F1 larvae was slightly higher than that for PS, suggesting that resistance is partially recessive. The responses of both backcross progeny (F1 × PR, F1 × PS) did not correspond to predictions from a single-locus model. The inclusion of a nonhomozygous resistant parental line in the monogenic model significantly increased the correspondence between the expected and observed results for the F1 × PR backcross but decreased the correspondence with the F1 × PS backcross results. This finding suggests that resistance to B. thuringiensis subsp. kurstaki in this T. ni population is due to more than one gene. |
