Spatial distribution of Aphis gossypii (Glover) (Hemiptera, Aphididae) and Bemisia tabaci (Gennadius) biotype B (Hemiptera, Aleyrodidae) on Bt and non-Bt cotton

Spatial distribution of Aphis gossypii (Glover) (Hemiptera, Aphididae) and Bemisia tabaci (Gennadius) biotype B (Hemiptera, Aleyrodidae) on Bt and non-Bt cotton. The study of spatial distribution of the adults of Bemisia tabaci and the colonies of Aphis gossypii on Bland non-Bt cotton crop is fundamental for improving the sampling techniques and revealing differences in the behavior of non-target species between both cultivars. So, this experiment aimed to investigate the spatial distribution pattern of those species on the conventional non-Bt cotton crop, compared to the B! cultivar. The samplings took place in two areas of 5.000 m(2) each, where it was done 14 evaluations counting adults of white-flies and colonies of aphids. The aggregation indexes (variance/mean rate, index of Morisita and Exponent k of the Negative Binomial Distribution) were calculated and accomplished the fitness tests of the individuals' numeric classes found and expected to the theoretical distributions of frequency (Poisson, Negative Binomial and Positive Binomial). Those analyses showed that in both cultivars, the spatial distribution of B. tabaci fitted to negative binomial distribution throughout the study period, indicating that the transgenic cultivar did not influence the pattern of aggregate distribution of this insect. With respect to the analysis for A. gossypii, the aggregation indexes showed aggregated distribution in both cultivars, but the distributions of frequency pointed to the occurrence of aggregate distribution only on conventional cotton, since there was no adjustment to the data on Bt crop. This indicates that Bt cotton has altered the aphids normal pattern of dispersion in the crop.