Low risk of resistance evolution of Spodoptera frugiperda to chlorfenapyr in Brazil.
Insecticide resistance is serious problem for Spodoptera frugiperda (Lepidoptera: Noctuidae). Due to intense selection pressure, the evolution of S. frugiperda resistance to major insecticides groups and Bt proteins has already been documented. Therefore, studies to preserve the lifetime of insecticides with unique modes of action such as chlorfenapyr are important in insect resistance management programs. For implementing a proactive resistance management program of S. frugiperda to chlorfenapyr, studies were conducted with field populations collected from major corn-growing regions in Brazil from 2016 to 2018. We aimed to (i) characterize and monitor the susceptibility of field populations, (ii) estimate the frequency of resistance alleles and (iii) evaluate cross-resistance patterns between insecticides and Bt-resistant strains of S. frugiperda to chlorfenapyr. Baseline susceptibility of field population showed a LC50 ranged from 18.3 to 25.1 µg ml-1. The survival rate at the diagnostic concentration ranged from 0 to 8.4%. Using the F2 screen method, the overall estimated resistance allele frequency was 0.0003. No cross-resistance was observed between chlorfenapyr and other insecticides and Bt proteins. Results demonstrated a high susceptibility, low frequency of resistance alleles and lack of cross-resistance. Thus, we concluded there is a low risk of resistance evolution of S. frugiperda to chlorfenapyr in Brazil using the current pest management strategies.