Résumé
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.