The Biological Activity of an <i>Sf</i>MNPV-Based Biopesticide on a Resistant Strain of <i>Spodoptera frugiperda</i> Developing on Transgenic Corn Expressing Cry1A.105 + Cry2Ab2 + Cry1F Insecticidal Protein

Insecticides based on baculoviruses have become an alternative for pest control in different agricultural crops. The aim of this study was to assess the biological activity of the bioinsecticide Cartugen^™ (<i>Sf</i>MNPV: Baculoviridae: Alphabaculovirus) on larvae of <i>Spodoptera frugiperda</i> J. E. Smith (Lepidoptera: Noctuidae) resistant to Bt corn expressing the insecticidal proteins Cry1A.105+Cry2Ab2+Cry1F. In addition, we assessed the efficiency of <i>Sf</i>MNPV on <i>S. frugiperda</i> control in the field from natural infestation of the pest during two agricultural seasons. The results showed that no larvae survived 10 days after being inoculated with Bt and non-Bt corn leaves contaminated with 1.50 × 10¹⁰ occlusion bodies (OBs)/L (equivalent to the recommended dose of the product). However, when using doses equivalent to 50% (7.50 × 10⁹ OBs/L) and 25% (3.75 × 10⁹ OBs/L), the larval mortality ranged from 21.12% to 46.55%, respectively. Although larvae resistant to the Cry1A.105+Cry2Ab2+Cry1F proteins, when exposed to 50% of the <i>Sf</i>MNPV dose (7.50 × 10⁹ OBs/L), showed reductions in larval weight (52 to 67% reduction), pupal weight (32 to 59% reduction), and total fecundity (67 to 86% reduction) compared to the control. Furthermore, doses above 25% (3.75 × 10⁹ OBs/L⁻¹) caused a population decrease in the growth of the species in both Bt and non-Bt corn according to the fertility life table. In the field, at 7 and 10 DAA (days after application), corn plants sprayed with <i>Sf</i>MNPV (1.50 × 10¹⁰ OBs/L) showed reductions in leaf damage according to the Davis scale. However, from 14 to 21 DAA, there was an increase in leaf damage in corn leaves from both treatments, with or without the application of <i>Sf</i>MNPV. This shows that <i>Sf</i>MNPV may be an important strategy in the integrated management and resistance management of <i>S. frugiperda</i>.