Diversity, Composition and Population Dynamics of Arthropods in the Genetically Modified Soybeans Roundup Ready® RR1 (GT 40-3-2) and Intacta RR2 PRO® (MON87701 x MON89788)

Knowledge of insect diversity is essential for ecological studies and pest management. The aim of this study was to study the occurrence, abundance of target and non-target pests in genetically modified insect resistant (Bt) and glyphosate-tolerant soybeans (RR1 and RR2), with and without the application of insecticides. Experiments were carried out in the agricultural year of 2011/2012 in four municipalities in the State of Mato Grosso do Sul. The treatments were- 1 - Roundup Ready® RR1 soybeans without insecticide application; 2 - Roundup Ready® RR1 soybeans with application whenever the control level was reached; 3 - Intacta RR2 PRO® soybeans without insecticide application; and 4 - Intacta RR2 PRO® soybeans with application whenever the control level was reached. The evaluations were initiated soon after emergence of the plants at weekly intervals. In order to obtain representative gradients of species composition, we used the method of ordering by non-metric multidimensional scaling (NMDS) and the Bray-Curtis dissimilarity index. Insects of the order Lepidoptera presented 7547 specimens, composing more than 70% of the insect community. The orders Coleoptera and Hemiptera also stood out, consisting of 2066 and 331 insects, respectively. Most of the samples were recorded in stages V8 to R2 for defoliating caterpillars and between R5.2 and R6 for the phytophagous stink bug complex. The Bt technology significantly reduced the target insect pests and favored populations of natural enemies. The treatments with insecticide application resulted in reduction of arthropods collected and changes in population outbreaks when compared to areas without spraying.