Resistance allele frequencies of Chilo suppressalis populations to Cry1Ab in Chongqing

Transgenic rice expressing Bacillus thuringiensis (Bt) insecticidal toxins for insect resistance represent a novel method of controlling Chilo suppressalis; however, potential resistance of pests to Bt toxins is a key factor restricting sustainable application of transgenic Bt crops. Here, we assessed the initial risk of resistance to transgenic Bt rice in local C. suppressalis populations in the municipality of Chongqing in China by testing their sensitivities to Bt proteins and determining resistance allele frequencies. Toxicity testing showed that sensitivity of C. suppressalis populations to Bt toxins (Cry1Ab and Cry1Ac) varied across geographical areas (LC₅₀ ranges, 1.39–7.14 and 3.02–8.81 mg/L, respectively), with sensitivity of the Fengjie population to Cry1Ab 5.13-fold that of the Nanchuan population. F₂ screening showed that resistance allele frequencies to Cry1Ab in C. suppressalis larvae, pupae, and adults in Chongqing were 0.0048, 0.0050, and 0.0053 during 1999–2021, respectively. After 20 generations of resistance selection using Cry1Ab, the resistance level of the C. suppressalis population was 15.67-fold that of the initial population. These results demonstrate the presence of Bt protein-resistant C. suppressalis individuals, and a risk of producing resistant C. suppressalis populations, in the field in Chongqing, China.