Efficiency of Bt cotton cultivars without control of different stages of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a pest that can be highly destructive to cotton, Gossypium hirsutum. Transgenic plants technology have increasingly been used as a means of control. In this context, the aim of this study was to evaluate the mortality of 1st and 3rd instar larvae of S. frugiperda fed with leaves and flower buds from two Bt cotton cultivars (Cry1Ab+Cry2Ae and Cry1Ac+Cry2Ab2). Plant parts were collected in the field to provide to the larvae. The leaves were exposed to the 1st and 3rd instar larvae (10 replications of three larvae each) and the flower buds to the 3rd instar larvae (4 replications of five larvae each), which were kept in a climate-controlled room (25 ± 2 °C, 75 ± 10% RH, and 12:12 h photoperiod). The trials were carried out in a completely randomized design (CRD). Mortality was analyzed at 72, 96, and 120 hours after supplying the plant parts. There was no significant difference in the mortality of 1st and 3rd instar larvae between the Bt cultivars when the plant parts were supplied. A 46% reduction was observed in the mortality of 3rd instar larvae compared to the 1st instar larvae exposed to the leaves. The 3rd instar larvae fed with leaves of Bt cultivars and fed with the reproductive structures of the plant did not differ from each other regarding mortality. Thus, the Bt cotton cultivars evaluated caused mortality of 1st instar S. frugiperda larvae. Therefore, there is a need to adopt complementary tools such as biological control, for example, to control caterpillars in more advanced stages which may remain in these areas planted with Bt crops.