Inheritance of Resistance to <i>Bacillus thuringiensis</i> Toxin Cry1Ac in a Cry1S1000 Strain of <i>Plutella xylostella</i> (Lepidoptera: Plutellidae)

Understanding the genetic basis of pest resistance to Bacillus thuringiensis (Bt) (Berliner) (Bacillales: Bacillaceae) toxins is important for optimizing integrated pest management (IPM). In this study, we characterized a strain (Cry1S1000) of Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) highly resistant to Bt using genetic crosses and dose-response bioassays. This strain exhibited >13,333-fold resistance to Cry1Ac toxin, which was conferred by a single autosomal locus and inherited in a completely recessive manner. Cross-resistance profiling revealed high-level resistance to Cry1Aa (>115-fold) and Cry1Ab (491-fold), but only minimal resistance to Cry1C (5-fold). These findings elucidate the evolution and mechanisms of Bt resistance in P. xylostella and provide a foundation for developing targeted resistance management tactics to sustain Bt efficacy.