Intraspecies mixture exerted contrasting effects on nontarget arthropods of Bacillus thuringiensis cotton in northern China

Row-intercropping is a type of multiple cropping with two or more crops grown simultaneously in alternate rows in the same area. It is a traditional agronomic practice and is still prevalent in modern Chinese agricultural ecosystems. Many studies have proposed that intercropping at the crop species level can significantly contribute to pest management when properly managed. However, the performance of intercropping at the plant genotype level is still largely unknown. A multiyear field experiment was conducted to examine the effects of intraspecies Bacillus thuringiensis (Bt)/non-Bt crop mixture on nontarget arthropods. Densities of dominant pests and predators were assessed via direct visual observations. Cotton aphid population levels in monoculture Bt cotton fields were greater than that observed in non-Bt cotton, whereas the row-mixture planting of Bt and non-Bt suppressed the abundance of cotton aphids compared with that in monoculture of either genotype. Investigations also demonstrated that the intraspecies row-mixture increased whitefly abundance compared with monoculture of either genotype. However, the mixture exerted neutral effects on population sizes of mirid bugs and predators. These results suggest that crop cultivation management is insufficient to control secondary pests of Bt cotton, and thus multiple pest suppression strategies are warranted