Impact of Bollgard® genetically modified cotton on the biodiversity of arthropods under practical field conditions in Brazil

Using cotton cultivars that express a gene of the Bacillus thuringiensis (Bt) bacterium producing a protein (Cry1Ac) with an insecticide effect on the Lepidoptera pests has made it possible to reduce the number of insecticide applications during the crop cycle. Thus, the objective was to determine, in the field during the 2006/2007 harvest in Dourados/MS, Brazil, the impact of the transgenic cultivar (NuOpal®) by comparison with the isogenic, non-transgenic cultivar (DeltaOpal®) on target pests, nontarget pests and natural enemies using two sampling methods (beatsheet and whole plant observation) under conventional growing conditions, with both varieties cultivated in a system incorporating the application of insecticides for non-target pests that reached the recommended threshold level for integrated pest management. It was verified that the average number of target pest specimens for both sampling methods was significantly lower in Bt-cotton than in non-Bt-cotton. However, the average number of non-target pest specimens and natural enemies presented no significant differences between the cultivars for both sampling methods assessed. The diversity of non-target pests characterized by the Shannon-Wiener index presented a significant difference between Bt-cotton and non-Bt-cotton for the whole plant sampling method, whereas for naturally occurring enemies, no difference was revealed using this sampling method.Key words: Bt-cotton, non-target effect, diversity index, side-effect, risk assessment, cotton production, Brazil

Arthropods biodiversity index in Bollgard (R) cotton (CRy1Ac) in Brazil

Shannon-Wiener's diversity index (SWI) was used under untreated conditions of a cotton field during the 2006/2007 crop season in the Cerrado region, Brazil. Comparison was carried out between the transgenic NuOpal (R) (BollgarD (R))(Cry1Ac) and the non-transgenic isogenic variety DeltaOpal (R). SWI was calculated for target pests, non-target herbivores and predators groups. Two sampling methods were used: whole plant observation and beat sheet. As expected, the mean number of target pests, especially Pectinophora gossypiella (Saund) and Alabama argillacea (Hubner), was significantly smaller in Bt cotton. In the whole plant method sampling the SWI for non-tar- get herbivores was significantly higher in Bt-cotton. The mean number of Anthonomus grandis (Boh) and Edessa meditabunda (Fabr) adults were significantly higher in NuOpaP with the whole plant sampling method. However, such differences were not observed with the beat sheet method. For the natural enemies, SWI and mean number of larvae and adults of the dominant predators did not show any significant difference between Bt and non-Bt cotton. These results confirm the conservation of some tritrophic interactions inside the Bt (untreated) cotton and contributes to a better sustainable management of nontarget pests by enhancement of their natural biological control