Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/2/2009
Publication Date: 1/5/2009
Citation: Zhu, Y., Liu, F., Xu, Z., Huang, F., Wu, X., Abel, C.A., Shen, J. 2009. Monitoring of resistance development to Bt cotton in field populations of Helicoverpa armigera (Lepidoptera: noctuidae). National Cotton Council Beltwide Cotton Conference. Proceeding of Beltwide Cotton Conference 674-680, CD-ROM. January 5-8, 2009. San Antonia, TX. http://www.cotton.org/beltwide/preceedings/2005-2011/index.htm Interpretive Summary: The old world bollworm is a serious pest on cotton in Southeast Asia and Australia. To ensure the durability of Bt cotton technology as an effective pest management tool, resistance monitoring is essential to provide information on early changes in resistance allele frequency in field populations. Results from this study suggested that the bollworm in northern China has potential to develop resistance to Bt cotton. Nine-year field monitoring revealed a potential risk of extensive plating of single Bt (Cry1Ac) protein-expressing cotton. Unlike the Bt-cotton in US, which expresses dual or multiple Bt proteins (Cry1Ac and Cry2Ab for Bollgard II), the single Bt protein-producing cotton in China might allow target insects to adapt and evolve resistance faster than multi-Bt toxin-producing cotton. Although the bollworm in China is a different species from the bollworm and budworm in the United States, the information generated from this study can serve as a model for studying and managing potential Bt resistance development in the United States.
Technical Abstract: Evolution of resistance threatens the continuing success of transgenic crops expressing insecticidal proteins. One of the key factors for a successful resistance management is the timely implementation of monitoring program to detect early changes of resistance frequency in field populations and implementation of resistance management tactics. F1 and F2 screens, designed for accurately detecting rare resistance alleles, were used to estimate the frequencies of alleles conferring resistance to the Cry1Ac-expressing cotton in a field population of Helicoverpa armigera, which is closely related to the cotton bollworm and tobacco budworm in US. The potential mechanism for Bt resistance in H. armigera was associated with modified Bt receptor encoded by disrupted or truncated cadherin genes (Xu et al. 2005: Appl Environ Microbiol 71:948-954; Yang et al. 2007: Appl Environ Microbiol 73:6939-6944) in the Bt-resistant strains. By using the F2 and F1 screening procedures, the resistance allele frequency in field population of H. armigera collected during 2007 in China was estimated to be 0.075 (95% CI: 0.053 - 0.100), which was 12-times greater than that estimated 9 years ago. This study provided valuable information for understanding field-evolved resistance in H. armigera after several years of intensive planting of Bt cotton expressing Cry1Ac. Our results also suggested that proactive tactics must be adopted to prevent further increase of resistance gene frequency.