Genetic analysis and molecular detection of resistance to chlorpyrifos mediated by the A216S substitution in acetylcholinesterase‐1 in the plant bug Apolygus lucorum

The green plant bug Apolygus lucorum is a major pest of Bacillus thuringiensis cotton in China. Previously, we reported that chlorpyrifos resistance in a laboratory‐selected strain of A. lucorum (BZ‐R) is associated with the homozygosis of an allele in the ace‐1 gene encoding an alanine to serine substitution at position 216 of acetylcholinesterase‐1. Here we describe the results of crosses between the resistant BZ‐R strain (41‐fold to chlorpyrifos) and the unselected susceptible BZ‐S strain homozygous for the wild type alanine allele at position 216. Resistance to chlorpyrifos was inherited as a semi‐dominant trait mainly controlled by a single autosomal gene and co‐segregates strongly but not completely with the serine substitution in ace‐1. Synergism bioassays and enzyme assays showed that minor contributions to resistance are also made by enhanced cytochrome P450 and carboxylesterase activities. A survey of 25 field populations from five Chinese provinces showed strong positive correlations between 50% lethal concentration against chlorpyrifos and S216 allele and genotype frequencies, although the most tolerant populations still only show 40%–50% S216 allele frequencies. The results above provide important information for designing effective resistance monitoring and management strategies for A. lucorum in China.