Fitness costs of Vip3A resistance in Spodoptera frugiperda on different hosts

BACKGROUND: Fall armyworm, Spodoptera frugiperda, is a major target pest of the Vip3A protein. The fitness of Bacillus thuringiensis (Bt)-resistant insects on refuges is an important factor in determining the speed of resistance development. Fitness costs associated with Bt resistance can vary among host plants. Here, we provide the first experimental evaluation of the interactions between non-Bt hosts and fitness costs of Vip3A resistance in S. frugiperda. RESULTS: Laboratory bioassays showed that survivorship, pupal weight, sex ratio, developmental time, fecundity, net reproductive rate, and intrinsic rate were not different among Vip3A-resistant (RR), -susceptible (SS) and -heterozygous (R _♂ S _♀ and R _♀ S _♂ ) strains of S. frugiperda on non-Bt corn, non-Bt cotton, and non-Bt diet. R _♂ S _♀ and R _♀ S _♂ also showed no differences on sorghum relative to SS. However, compared to SS, RR on sorghum showed significant reduction in pupal weight, and took longer time to develop to pupa and adult. CONCLUSION: These findings suggest that recessive fitness costs of reduced pupal weight and growth rate were detected at the individual level in the Vip3A resistant populations of S. frugiperda on sorghum. However, at the population level in terms of net reproductive rate and intrinsic rate, fitness costs of Vip3A resistance was not evident in S. frugiperda.