Fitness Costs Associated with Spinetoram Resistance in Spodoptera Frugiperda is Driven by Host Plants

Insecticide resistance is usually associated with fitness costs. The magnitude of the fitness costs is affected by environmental and ecological factors. Here, we explored how host plants could affect fitness costs associated with insecticide resistance. Initially, spinetoram-resistant and susceptible strains of Spodoptera frugiperda were selected using a F-2 screen from a population collected in Sao Desiderio, Bahia State, Brazil. In addition to the RR and SS strains, fitness costs were also assessed for a heterozygous strain (RS). Life-history traits were evaluated to estimate population growth parameters of each strain feeding on corn, soybean, and cotton plants. The relative fitness of the RR strain was 1.06 higher compared to the SS strain on corn plants, while in soybean and cotton plants these values were 0.84 and 0.67 lower, respectively. The relative fitness of the RS strain was similar to the SS strain regardless of the host plant, suggesting a recessive fitness cost. No differences were found between the strains fed on corn plants. The larval development time was greater for the RR strain fed on soybean and cotton plants compared to the RS and SS strains. Low survival rate and fecundity of the RR strain were found when larvae fed on soybean and cotton plants. The results of this study showed that fitness costs of spinetoram resistance in S. frugiperda depend on the host plants that S. frugiperda larvae fed on. Such information can be used to design resistance management strategies considering the host plants of the agricultural landscape.