Inheritance of Bacillus thuringiensis Cry1C resistance in Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae)

A field strain of Spodoptera littoralis Biosduval was selected against Cry1C toxin derived from Bacillus thuringiensis entomocidus for 10 subsequent generations under laboratory conditions. Selection pressure resulted in a 29-fold resistance ratio compared with the susceptible strain. Inheritance of Cry1C resistance was partially dominant and autosomal on the basis of bioassay response to Cry1C toxin in a reciprocal cross between male and/or female F1. Consistent with earlier findings, resistance was recessive at high concentrations of Cry1C toxin. However, the dominance of resistance increased as the concentration of Cry1C decreased. Analysis of survival and growth of progeny from a backcross (F1 × resistance strain) suggested that resistance was controlled by either a single or a few loci in cotton leafworm.