Adaptive Potential of Fall Armyworm (Lepidoptera: Noctuidae) Limits Bt Trait Durability in Brazil

The fall armyworm, Spodoptera frugiperda (J.E. Smith 1797) (Lepidoptera: Noctuidae), is the most important corn pest in South America. Larvae feed mostly on leaves, but also ears when population densities are high. This pest has been historically controlled with insecticide applications, but many cases of resistance have limited their efficacy. Transgenic corn varieties expressing Bacillus thuringiensis proteins (Bt corn) have been a widely adopted alternative to insecticides and, in the past 8 yr, have been the primary technology for fall armyworm control in Brazil. Because transgenic varieties require 10-15 yr to be developed and fall armyworm has quickly evolved resistance to most commercially released Bt corn hybrids, strategies for Bt trait durability are paramount. Most of the Bt corn hybrids lost their ability to control fall armyworm in just 3 yr after their release in Brazil. Here we summarize what is known about Bt resistance in fall armyworm in Brazil, a phenomenon perhaps never seen before in any part of the world. Furthermore, we suggest that the interactions between management practices adopted (or not adopted, e.g., refuge compliance) to delay the evolution of resistance and the ecological and evolutionary characteristics of fall armyworm are driving the rapid evolution of resistance to Bt corn in Brazil. As newer products emerge in the market, careful consideration will be needed to maximize trait durability.