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In northern China, wheat aphids are widespread and pose serious threats to wheat crop yields. As parasitoids are important parasitic natural enemies of wheat aphids, their interactions with wheat aphids have received much attention. Traditional methods commonly cannot provide clear evidence of trophic links between primary parasitoids and hyperparasitoids or multiparasitism. To overcome this problem, we developed a molecular approach including three multiplex PCRs and five singleplex PCRs. With this approach, four wheat aphid species, four primary parasitoid species and eight to nine hyperparasitoid species were detected from aphid samples, which covered all the primary parasitoids and 94.8-98.1% of the hyperparasitoids found in wheat fields of northern China. The trophic interactions between aphids and primary parasitoids and between primary parasitoids and hyperparasitoids were determined, and a quantitative tri-trophic food web was established through molecular detection. The proportion of hyperparasitized samples was 53.36%, and multiparasitism was very common in the hyperparasitoid trophic interactions (22.02%). These results indicate that this approach is effective for revealing the complex wheat aphid-parasitoid-hyperparasitoid networks in northern China. [ABSTRACT FROM AUTHOR]

Transgenic cotton that has been engineered to produce insecticidal toxins from Bacillus thuringiensis (Bt) and so to resist the pest cotton bollworm (Helicoverpa armigera) has been widely planted in Asia. Analysis of the population dynamics of H. armigera from 1992 to 2007 in China indicated that a marked decrease in regional outbreaks of this pest in multiple crops was associated with the planting of Bt cotton. The study area included six provinces in northern China with an annual total of 3 million hectares of cotton and 22 million hectares of other crops (corn, peanuts, soybeans, and vegetables) grown by more than 10 million resource-poor farmers. Our data suggest that Bt cotton not only controls H. armigera on transgenic cotton designed to resist this pest but also may reduce its presence on other host crops and may decrease the need for insecticide sprays in general. [ABSTRACT FROM AUTHOR]