Frequency of Bt resistance genes in Helicoverpa armigera populations from the Yellow River cotton‐farming region of China

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Abstract
Bt cotton has been widely planted in the Yellow River valley of China since 1998. Anci County in Hebei Province and Xiajin County in Shandong Province are two areas where almost 100% of the cotton grown produces Cry1A(c) toxin. These areas were therefore selected for analysis of the frequency of genes coding for resistance to Cry1A(c) in field populations of the bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). In 2002, adult females were collected using light traps. Females were caged individually and were allowed to lay eggs. At hatch, 25–35 larvae from each female were screened for growth rate on normal artificial diet, and on diet containing 1.0 µg of Cry1A(c) toxin per ml of diet. This growth rate bioassay was designed to detect non‐recessive resistance genes in heterozygous genotypes and to detect recessive resistance genes only when present in a homozygous resistant genotype. The bioassay detected one resistant individual out of 234 screened in Anci and one resistant individual out of 420 in Xiajin. These results suggest that a conservative estimate of the resistance gene frequency is 0.00107 in the Anci population, and 0.00059 in the Xiajin population. Our results indicate that minor resistance genes or less dominant genes for resistance may occur at higher frequencies, especially in the Xiajin population.