Characterization of Indoxacarb Resistance in the Fall Armyworm: Selection, Inheritance, Cross-Resistance, Possible Biochemical Mechanisms, and Fitness Costs

Simple Summary The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a voracious insect pest native to the Western Hemisphere, particularly in South America. The polyphagous fall armyworm feeds on more than 350 plants in such families, including Poaceae, Asteraceae, and Fabaceae. Transgenic plants that express Bacillus thuringiensis proteins (Bt plants) and synthetic insecticides are the main tactics to control Spodoptera frugiperda, although widespread usage of synthetic chemicals has resulted in the emergence of resistance. We assessed cross-resistance, resistance mechanism, and fitness costs based on the life history traits of Spodoptera frugiperda. Results indicated that after 24 generations of selection, the resistance to indoxacarb was increased by 472.67-fold as compared to the Ind-UNSEL. Significantly longer developmental time of larvae extended pupal duration, shorter adult longevity, and lower fecundity were observed in Ind-SEL as compared with the Ind-UNSEL population. Butoxide synergist increased susceptibility to indoxacarb, indicating that P450 enzymes may be involved in indoxacarb resistance. Therefore, it is crucial that we comprehend how insecticides work and how resistance develops in order to develop techniques for managing resistance. These data are valuable to understand the indoxacarb resistance mechanism and provides vital information for scientific-based guidance of pest management decisions. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a voracious insect pest that is difficult to control due to resistance to insecticides and Bt proteins. We assessed cross-resistance, resistance mechanism, and fitness costs based on the life history traits of S. frugiperda. We established an S. frugiperda strain selected for resistance to indoxacarb (Ind-SEL) from a field-collected population and an unselected strain, Ind-UNSEL. Results indicated that after 24 generations of selection, the resistance to indoxacarb was increased by 472.67-fold as compared to the Ind-UNSEL. There was high cross-resistance to deltamethrin (31.23-fold) with very low or negligible cross-resistance to chlorantraniliprole, emamectin benzoate, and/or methoxyfenozide in the Ind-SEL population. Butoxide synergist increased susceptibility to indoxacarb, indicating that P450 enzymes may be involved in indoxacarb resistance. Significantly longer developmental time of larvae extended pupal duration, shorter adult longevity, and lower fecundity were observed in Ind-SEL as compared with the Ind-UNSEL population. The Net reproductive rate (R-0) was the only growth parameter that differs between crosses of Ind-SEL male x Ind-UNSEL female (176 +/- 46) and Ind-SEL female x Ind-UNSEL male (328 +/- 57). On the other hand, all population growth parameters differ between Ind-SEL and Ind-UNSEL strains. Our work contributes to the growing body of research that demonstrates the importance of strain genetics in fitness cost experiments and helps resistance management programs make decisions.

Automated summary

This study assessed the resistance and fitness costs of the fall armyworm to the insecticide indoxacarb. After 24 generations of selection, the resistance to indoxacarb significantly increased, accompanied by longer developmental time, shorter adult longevity, and lower fecundity. The study also suggested the involvement of P450 enzymes in indoxacarb resistance. These findings provide valuable insights into the resistance mechanism of the fall armyworm and guidance for pest management decisions.