Efeitos de biotecnologias de milho (Zea mays L.) Na estrutura de comunidades de artrópodes

Abstract

The area planted with transgenics has increased exponentially, which makes transgenics the most adopted agricultural technology in modern history. However, Bt crops may have direct and indirect effects under non-target organisms. The overall objective of this work was to evaluate four maize cultivars, one conventional and three transgenic (Bt) and their effects on target and non-target organisms. Four different fields were evaluated with the following commercial cultivars of GM maize: EXP3320YG (Monsanto, USA) expressing Cry1Ab, MG600PW (Monsanto, USA and Dow Agrosciences, USA) expressing Cry1A.105+Cry2Ab2+Cry1F both conferring resistance to Lepidoptera Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) with early cycle; and AG9030VTpro3 (Monsanto, USA) expressing Cry1A.105+Cry2Ab2+Cry3Bb1 conferring resistance to Lepidoptera S. frugiperda, Helicoverpa zea (Bodie, 1850) (Lepidoptera: Noctuidae) and Coleoptera Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) super-precocious. We also evaluated a fourth field with the conventional cultivar SW5560 (without expression of the transgenic protein), which has an early cycle. In each of the four fields were sampled 50 plants (sample units) with weekly frequency, totaling 15 evaluations. The visual record of the number of arthropod specimens was performed. Visual notes were assigned following a scale ranging from 0 to 9 by Davis & Williams (1989) to verify the intensity of foliar damage caused by S. frugiperda and the size of caterpillars and S. frugiperda postures were also evaluated visually in each of the areas. The Shannon-Wiener and Simpson indices, which compare species diversity in different environments, indicated that the cultivar MG600PW showed a greater diversity of non-target insects than the others, while EXP3320YG resulted in low diversity throughout the crop cycle. The cultivar EXP3320YG showed the highest damage, while the cultivars MG600PW and AG9030VTpro3 showed the lowest damage. The cultivar EXP3320YG showed the highest number of herbivores (651) and the lowest number of predators (51), and the cultivar MG600PW presented the lowest number of herbivores (211) and the highest number of predators (161). The results showed that the evaluated cultivars presented differences in relation to the attack of S. frugiperda, and the cultivar EXP3320YG presented the highest damages, demonstrating that this pest acquired resistance to Cry1Ab toxin.