Synthetic or biological insecticide performance on Bt corn to control Spodoptera frugiperda

Abstract

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) is the main defoliating pest of corn ( Zea mays L.) in Brazil. Corn expressing proteins of Bacillus thuringiensis (Bt) associated with synthetic insecticides is common to manage FAW. However, FAW evolved field resistance to several insecticides and Bt proteins. In this sense, biological insecticides based on Baculovirus spodoptera have become a valuable alternative to control FAW. Our goal was to evaluate the control efficacy of FAW with either biological or synthetic insecticides on Bt corn hybrids. Managing FAW in early-planted non-Bt (Pioneer 30F53R) and Bt corn (Pioneer 32R22YHR, DKB 290, Morgan 20A78,) both required up to 4 or 5 synthetic insecticide applications to manage FAW. Late planted Bt corn required 3 to 7 insecticide applications, depending on the insecticide used, while non-Bt corn required 5 to 7 sprays. Independently of planting date, those corn expressing Vip proteins (Brevant 2401, Pioneer 30F53VYHR) did not require any insecticide spray. The application of insecticides is needed to increase the control of FAW in corn hybrids expressing only Cry toxins. Exalt was the best insecticide to manage FAW in early and late planted corn. Despite treatment with biologicals, damage by FAW remained high and likely contributed to a lower yield in comparison to traditional chemical control. Synthetic insecticides had higher efficacy to manage FAW in early and late-planted corn. The application of biologicals to manage FAW should be further investigated in combination with time and spray technology to improve IPM and IRM.

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