INHERITANCE OF RESISTANCE TO A BACILLUS-THURINGIENSIS TOXIN IN A FIELD POPULATION OF DIAMONDBACK MOTH (PLUTELLA-XYLOSTELLA)

Inheritance of resistance to the Bacillus thuringiensis Berl. CryIA(b) crystal protein was studied in Plutella xylostella L. (diamondback moth). A field population 50-fold more resistant to CryIA(b) than a control susceptible strain was used. Dose-mortality curves of the resistant population, the susceptible strain and the F1 from the two reciprocal crosses were compared. Resistance transmission to the F1 was dependent on the sex of the resistant progenitor. Sex ratio of the survivors to high doses of CryIA(b) in the F1 of the two reciprocal crosses did not corroborate the preliminary hypothesis of resistance being due to a recessive sex-linked allele. Since, in a previous work, the loss of CryIA(b) binding capacity of resistant insects had been demonstrated, binding to midgut tissue sections from F1 individuals was also analysed. The presence of binding in all of the F1 preparations showed that, at least, a recessive autosomal allele was responsible for the loss of binding capacity in the resistant population.