Field monitoring of Helicoverpa armigera (Lepidoptera: Noctuidae) Cry1Ac insecticidal protein resistance in China (2005-2017): Bt resistance monitoring of Helicoverpa armigera

BACKGROUND: Bt cotton expressing Cry1Ac can efficiently control Helicoverpa armigera, but field‐evolved Bt resistance reduces its efficacy. Susceptibility of H. armigera field populations to Cry1Ac protein has been monitored since Bt cotton was commercialized in 1997 in China. Here we report the results of our continued monitoring from 2005 to 2017 to provide important guidelines for sustainably growing cotton. RESULTS: From 13 provinces and regions, 221 populations were sampled and measured. IC₅₀ values (concentration producing 50% inhibition of larval development to third instar) among different strains ranged from 0.004 to 0.212 µg mL⁻¹, the percentage survival at a diagnostic concentration (IC₉₉, 1.0 µg mL⁻¹) (SUR) ranged from 0% to 22.2%, and the percentage of field populations yielding survivors at diagnostic concentration (PSD) increased from 0 in 2006 and 2007 to 80% in 2015. CONCLUSIONS: Compared to resistance level from 1998 to 2004 and the geographic baseline in different places of China in 1997, Bt resistance of H. armigera field populations to Cry1Ac protein has increased significantly, but failure of Bt cotton has not yet been detected. © 2018 Society of Chemical Industry