Monitoring cotton bollworm resistance to Cry1Ac in two counties of northern China during 2009-2013.

Abstract

Transgenic cotton that expresses a gene derived from the bacterium Bacillus thuringiensis (Bt) has been deployed for combating cotton bollworm in China since 1997. As a follow-up on research started in 2002, the quantitative shifts in larval Cry1Ac resistance of field Helicoverpa armigera populations were monitored from 2009-2013 using bioassays of isofemale lines. A total of 2837 lines from Xiajin and 2055 lines from Anci were screened for growth rate on normal artificial diet and on a diet containing 1.0 µg mL(-1) of Cry1A(c) toxin. In 2009-2013, the mean relative average development rates (RADRs) of H. armigera larvae in the Xiajin population were 0.62, 0.59, 0.59, 0.58 and 0.62 respectively, and in the Anci population 0.54, 0.58, 0.60, 0.53 and 0.62 respectively. Compared with previous results in 2002, there was an increase in the RADR of H. armigera during 2009-2013, with ratios of 1.53-1.63 and 1.77-2.07 in the respective Xiajin and Anci populations, suggesting that resistance to Cry1Ac has increased in H. armigera populations in northern China.