Sobrevivência de espécies de Spodoptera (Lepidoptera: Noctuidae) em soja expressando Cry1A.105, Cry2Ab2 E Cry1Ac e suscetibilidade a inseticidas

Abstract

In recent seasons, an increase in infestations of species of the genus Spodoptera (Lepidoptera: Noctuidae) was reported in soybean expressing the Cry1Ac insecticidal protein in Brazil. On this basis, the objective of this study was to evaluate the survival of Spodoptera cosmioides (Walker, 1898), Spodoptera eridania (Stoll, 1782), Spodoptera albula (Walker, 1857) e Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae) on MON 87751 × MON 87708 × MON 87701 × MON 89788 soybean, which expresses Cry1A.105, Cry2Ab2 and Cry1Ac, MON 87701 × MON 89788 soybean containing Cry1Ac and non-Bt soybean and the susceptibility to flubendiamide and thiodicarb. Initially, neonates of Spodoptera species were fed on Bt and non-Bt soybean leaves for 10 days. Then, surviving larvae were separated by instar (L1, L2 or L3) and transferred to the soybean leaves on which they developed but treated with the field dose of flubendiamide (70 mL/ha), thiodicarb (400 g/ha) or 50% of these doses. The mortality of S. cosmioides, S. eridania and S. albula on soybean leaves expressing Cry1A.105, Cry2Ab2 and Cry1Ac was >81% at 10 days, with no insects developing to adulthood. In contrast, S. frugiperda showed <60% mortality, with some larvae developing to adult stage. In the same period, on Cry1Ac soybean and non-Bt soybean, the mortality of S. frugiperda was <25%. L1, L2 and L3 larvae of S. cosmioides, S. eridania and S. albula showed >83% mortality when exposed to Bt and non-Bt soybean leaves treated with both doses of flubendiamide or thiodicarb, with no insects developing until adult stage. In contrast, only L1, L2 and L3 larvae of S. frugiperda fed on Cry1Ac and non-Bt soybean treated with 50% of the field dose of previous insecticides produced adults. However, S. frugiperda larvae that developed on Cry1Ac and non-Bt soybean treated with the half dose of flubendiamide or thiodicarb showed prolonged immature stage and females lower fecundity. Therefore, it may be concluded that: (i) MON 87701 × MON 89788 × MON 87751 × MON 87708 soybean, which expresses Cry1A.105, Cry2Ab2 and Cry1Ac insecticidal proteins, was effective at protecting soybean against S. cosmioides, S. eridania and S. albula; (ii) this Bt soybean had some minimal lethality against S. frugiperda; (iii) MON 87701 × MON 89788 soybean, which expresses Cry1Ac insecticidal protein, showed poor lethality against all Spodoptera species evaluated; (iv) flubendiamide and thiodicarb were effective in controlling Spodoptera species that survived on Bt or non-Bt soybean; and (v) surviving larvae developing on Cry1Ac or nonBt soybean treated with flubendiamide or thiodicarb had prolonged immature stage and females lower fecundity. In summary, the integration of control tactics would provide an effective management of Spodoptera species on soybean fields in Brazil and other South America countries.