Resistance of Spodoptera frugiperda (Lepidoptera: Noctuidae) to spinetoram: inheritance and cross-resistance to spinosad.

Background: The use of spinosyn insecticides is one of the major control strategies of the fall armyworm, Spodoptera frugiperda (J. E. Smith) in Brazil. In this study, we selected a spinetoram-resistant strain from a field-population of S. frugiperda to characterize the inheritance of the resistance and cross-resistance relationship between spinosyn insecticides.

Results: The values of LC (95% CI) obtained from concentration-response bioassays were 0.63 (0.55-0.73) μg spinetoram mL for the susceptible strain (SUS), and 1170.96 (1041.61-1323.89) μg spinetoram mL for the strain resistant to spinetoram (SPT-R). These values resulted in a resistance ratio of 1844-fold. The SPT-R strain showed cross-resistance with spinosad (resistance ratio = 1196-fold). The reciprocal crosses showed LC values of 3.91 (2.97-5.84) and 5.37 (4.52-6.52) μg spinetoram mL , suggesting that the resistance of S. frugiperda to spinetoram is autosomal and incompletely recessive. The backcrosses of the F progeny with the SPT-R strain suggest a resistance with polygenic effect. Estimates of the effective number of loci with equal contributions to the resistance effect were from 1.18 to 1.76, suggesting that resistance to spinetoram is associated with a few genes.

Conclusion: The inheritance pattern of resistance of S. frugiperda to spinetoram was characterized as autosomal, incompletely recessive and polygenic. Cross-resistance between spinosyns was confirmed in S. frugiperda. The importance of this information for implementing insect resistance management strategies is discussed in this paper. © 2020 Society of Chemical Industry.