Survival and nutritional indexes of Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) maintained in Bt maize for five generations
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The selection pressure generated by the incorrect use of Bt maize might result in Spodoptera frugiperda individuals resistant to the toxins synthesized by the plant. In this study was evaluated the nutritional parameters of Spodoptera frugiperda submitted to the maize that synthesize the toxins Cry1F, Cry1A105-Cry2Ab2 and Vip3Aa20, during five subsequent generations of selection pressure. The caterpillars were submitted to the treatments: Non-Bt maize (CONV), Cry1F (Bt1), Cry1A105/Cry2Ab (Bt2) and Vip3Aa20 (VIP1, VIP2 and VIP3) and exposed for a period of four days in each cycle, for five successive generations. The larval survival of S. frugiperda was evaluated in five generations. The consumed leaf area was quantified in the second generation and the nutritional indexes in the latter ones. The results indicate that caterpillars of S. frugiperda from VIPs lineage presented the lowest percentage of survival, with a high Metabolic Cost and a considerable efficiency reduction in the conversion of the digested and ingested food. The lineage maintained in VIP2 showed the lowest leaf consumption (83.13%). However, the action of Vip3Aa20 toxin on S. frugiperda resulted in a higher Metabolic Cost in reduction of leaf area consumption. However, from the third generation on there is a survival of insects exposed to Bt toxins, suggesting the surviving potential of this species in Bt maize subjected to continuous exposure to this technology.