Crop dominance exerts specific effects on foliage-dwelling arthropods in Bacillus thuringiensis cotton

Shifts in crop composition in an agro-ecosystem may have profound effects on plant-associated arthropods. The widespread adoption of transgenic insect-resistant cotton expressing insecticidal toxins Cry1A from Bacillus thuringiensis (Bt) has caused a dramatic shift in agricultural landscapes over the last 15years, thus raising concerns about the potential impacts of Bt crops on nontarget organisms worldwide. The potential effect of crop composition shift as a result of the increasing acreage of Bt cotton on an arthropod community was assessed at three levels (0%, 75% and 100%) of Bt dominance in a 2-year field trial in northern China. Three findings confirmed that the arthropod assemblage of a certain field was influenced by crop composition and its developmental stage: (i) the proportion of Bt cotton in the crop mixture consistently affected the abundance of pests, natural enemies and total arthropods; (ii) bootstrap methods demonstrated significant effects of Bt cotton on species richness, diversity and evenness; and (iii) non-metric multidimensional scaling analysis showed that the arthropod community of a certain agricultural ecosystem varied with crop composition and plant developmental stage. The findings of the present study may have significant implications for cotton pest management with respect to transgenic Bt cotton, highlighting the potential of conservation biological control via the combination of an appropriate crop genetic ratio and timely chemical control