Fitness costs of Cry1F resistance in fall armyworm, Spodoptera frugiperda

Transgenic corn (Zea maize) expressing Cry1F protein from Bacillus thuringiensis Berliner (Bt) has been registered for Spodoptera frugiperda (J. E. Smith) control since 2003. However, unexpected damage to Cry1F corn was reported in 2006 in Puerto Rico, and Cry1F resistance in S. frugiperda was documented. The study of fitness costs associated with resistance to Bt toxins is important in understanding resistance evolution and for evaluating resistance management practices to mitigate resistance to transgenic corn. Currently, no studies have addressed the existence and dominance of fitness costs associated with Cry1F resistance in S. frugiperda. The objective of this study was to determine if resistance to Cry1F is associated to fitness costs in S. frugiperda. Comparisons of life-history traits and population growth rates of homozygous susceptible, heterozygous and homozygous resistant genotypes were used to determine the existence of fitness costs associated with resistance. Major fitness costs were not apparent in either heterozygote or homozygous resistant insects. The lack of strong fitness costs may affect the frequency of resistant alleles and the persistence of resistance in field populations in the absence of selection (e.g. Puerto Rico).