Although most monitoring of pest resistance to widely cultivated transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) relies on bioassays, DNA screening for alleles associated with resistance has some advantages, particularly for rare, recessively inherited resistance. In China's Yangtze River Valley, where farmers first planted transgenic cotton producing Bt toxin Cry1Ac in 2000, bioassays have been used to monitor the recessive resistance of pink bollworm (Pectinophora gossypiella). Previous bioassay results show a small but significant increase in resistance to Cry1Ac during 2008–2010, followed by a significant decrease in resistance during 2011–2015 associated with extensive planting of second‐generation hybrid cotton seeds that boosted the percentage of non‐Bt cotton. Here we screened DNA from 19 748 pink bollworm collected during 2012–2015 from the Yangtze River Valley for seven alleles associated with resistance to Cry1Ac. These alleles were previously identified from lab‐selected strains; three from the U.S. and four from China.
The most common resistance allele was first identified from the U.S. and accounted for over 71% of all resistance alleles detected. Resistance was rare, with the total frequency of the seven resistance alleles showing a significant, 2.3‐fold decrease from 0.0105 (95% CI: 0.0084–0.0132) in 2012 to 0.0046 (0.0031–0.0067) in 2015.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.