Bt resistance alleles in field populations of pink bollworm from China: Similarities with the United States and decreased frequency from 2012 to 2015

Authors: WANG, JINTAO - Huazhong Agricultural University; XU, DONG - Hubei Academy Of Agricultural Sciences; WANG, LING - Hubei Academy Of Agricultural Sciences; CONG, SHENGBO - Hubei Academy Of Agricultural Sciences; WAN, PENG - Hubei Academy Of Agricultural Sciences; LEI, CHAOLIANG - Huazhong Agricultural University; Fabrick, Jeffrey; LI, XIANCHUN - University Of Arizona; TABASHNIK, BRUCE - University Of Arizona; WU, KONGMING - Chinese Academy Of Agricultural Sciences

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2019
Publication Date: 1/13/2020
Citation: Wang, J., Xu, D., Wang, L., Cong, S., Wan, P., Lei, C., Fabrick, J.A., Li, X., Tabashnik, B.E., Wu, K. 2020. Bt resistance alleles in field populations of pink bollworm from China: Similarities with the United States and decreased frequency from 2012 to 2015. Pest Management Science. 76(2):527-533. https://doi.org/10.1002/ps.5541.
DOI: https://doi.org/10.1002/ps.5541

Interpretive Summary: Cotton genetically engineered to produce Bacillus thuringiensis (Bt) insecticidal proteins are used widely to control important insect pests, including the pink bollworm (Pectinophora gossypiella). However, pest resistance to these Bt proteins can rapidly erode the benefits of such transgenic crops. In order to maintain the efficacy of Bt crops, it is critical to monitor populations for changes in pest susceptibility. Today, most monitoring of pest resistance to Bt crops relies on diet bioassays, which involves testing live insects on diet prepared in the laboratory and containing the Bt protein(s) of interest. However, the use of modern molecular DNA screening for resistance has some advantages over diet bioassays, especially for rare, recessive traits. Here, an ARS scientist at Maricopa, AZ and collaborators screened DNA from 19,748 pink bollworm collected during 2012-2015 from the Yangtze River Valley in China for seven known mutations associated with pink bollworm resistance to the Bt toxin, Cry1Ac. These mutations were previously identified from lab-selected strains; three from the U.S. and four from China. Our results show that the most common mutation was first identified from the U.S. and accounted for over 71% of all resistance mutations detected. Resistance in China was rare, with the total frequency of all seven mutations showing a significant 2.3-fold decrease from 2012-2015. The DNA screening data confirm previous results from bioassays showing pink bollworm resistance to Cry1Ac remained rare in the Yangtze River Valley of China from 2012-2015 and the prevalence in China of the resistance allele from the U.S. implies a shared genetic basis of resistance, which could facilitate world-wide molecular monitoring of pink bollworm Bt resistance.

Technical Abstract: 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. The DNA screening data confirm results from bioassays showing pink bollworm resistance to Cry1Ac remained rare in the Yangtze River Valley from 2012-2015. The prevalence in China of the resistance allele from the U.S. implies a shared genetic basis of resistance that could facilitate molecular monitoring of resistance