Abstract
BackgroundThe cotton bollworm (Helicoverpa armigera) is one of cotton’s most destructive insect pests in terms of yield and quality. Since 1997, China has grown commercially available transgenic Bacillus thuringiensis (Bt) cotton. We aimed to investigate the variation in resistance of transgenic Bt cotton varieties to cotton bollworm in North China.MethodsPopulations of cotton bollworm were monitored from 2008 to 2015 in environments where Bt cotton was planted adjacent to other non-Bt crops. The study included 197 Bt cotton varieties planted in 42 counties/locations in three provinces (Hebei, Shandong and Henan) of North China, which were evaluated through field investigations, bioassays, and enzyme-linked immunosorbent assays (ELISA).ResultsThe average number of cotton bollworms never exceeded the action threshold (10 larvae per 100 cotton plants), however, their number reached 19.55 per 100 cotton plants in 2011. The ratios of damaged plants to total Bt cotton stem-tips, buds, and bolls was low except in 2010, when the ratios reached 1.82%, 2.09%, and 10.63%, respectively. The results of bioassay showed that the corrected mortality were higher at the second generation cotton bollworm stage than the third and fourth germination stages. Totally, Bt protein content declined sharply at the seedling stage from 2008 to 2015.ConclusionsThis study indicated that almost all Bt cotton varieties were capable to effectively control the populations of cotton bollworm in North China.
Highlights
The cotton bollworm (Helicoverpa armigera) is one of cotton’s most destructive insect pests in terms of yield and quality
We investigated three sites forming a triangle for each Bacillus thuringiensis (Bt) cotton variety
The results showed that the number of cotton bollworm larvae peaked in 2011, the only year in which the average number of cotton bollworm larvae per 100 plants exceeded the action threshold of 10 larvae at the second cotton bollworm generation stage
Summary
The cotton bollworm (Helicoverpa armigera) is one of cotton’s most destructive insect pests in terms of yield and quality. We aimed to investigate the variation in resistance of transgenic Bt cotton varieties to cotton bollworm in North China. The cotton bollworm, Helicoverpa armigera Hübner, is one of cotton’s most destructive insect pests. In the 1990s, both cotton yield and quality were severely affected by cotton bollworm outbreaks in major cotton production provinces of China. Since 1997, China has grown commercially available transgenic Bacillus thuringiensis (Bt) cotton. As the plantation areas for Bt cotton have expanded, cotton bollworms have become increasingly resistant to Bt insecticidal proteins, prompting researchers to conduct investigations (Liu et al 2010; Zhang et al 2011). Bt-resistant cotton bollworm strains have been reported to have 28,93.3-fold higher resistance than susceptible strains when fed Bt toxins in the laboratory (Liang et al 2008)
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