Field risk assessments of transgenic Bt-Cry1Ab rice and its residues on aboveground nontarget arthropod community in postharvest seasons

Abstract Risk assessments and ecological effects of transgenic rice expressing lepidoptera-active Cry proteins from Bacillus thuringiensis (Bt) on nontarget arthropods have primarily focused on rice plant during cropping seasons, whereas few studies have investigated the effects in postharvest seasons. Harvested rice fields provide critical overwintering habitat for arthropods in the rice planting areas of southern China with warm and humid climate, which is vital for natural control of rice arthropod pests.During 2006-08, field studies were conducted at two locations in Chongqing to investigate the effects of transgenic Cry1Ab rice and its residues on the guild dominance, family composition, individuals of each guild, and community indices (Shannon-Weaver diversity and dominance concentration indexes) of aboveground nontarget arthropods in two postharvest seasons. Pitfall traps were used to sample arthropods in non-Bt and Bt rice fields. Aboveground arthropods in rice fields during the postharvest seasons were abundant, while community densities varied significantly between the two locations/seasons. A total of 52,386 individual insects and spiders, representing 93 families, were captured during the two postharvest seasons from non-Bt and Bt rice fields. Predominance of the captures was detritivores, which accounted for 91.9% of the total captures. Other arthropods sampled included predators (4.2%), herbivores (3.2%), and parasitoids (0.7%). In general, there were no significant differences between the non-Bt and Bt rice plots in all arthropod community-specific parameters analyzed. The similarity of arthropod communities in the non-Bt and Bt rice plots was apparently high, suggesting no adverse impact of the Bt rice and its residues on aboveground arthropod community in rice fields during postharvest seasons. The results of this study provide additional evidence that Bt rice has no significantly negative impact on nontarget arthropod community in the Chinese rice ecosystems. Keywords Bt rice; nontarget effects; aboveground arthropod; postharvest season