Susceptibility monitoring and comparative gene expression of susceptible and resistant strains of Spodoptera frugiperda to lambda‐cyhalothrin and chlorpyrifos

BACKGROUND Spodoptera frugiperda (J. E. Smith) is a widespread agricultural pest with several records of resistance to different insecticides and Bt proteins, including the neurotoxic insecticides chlorpyrifos (organophosphate) and lambda‐cyhalothrin (pyrethroid). Here, we (i) characterized and monitored the susceptibility of field populations of S. frugiperda to chlorpyrifos (194 populations) and lambda‐cyhalothrin (197 populations) collected from major maize‐growing regions of Brazil from 2003 to 2016, and (ii) compared gene expression levels of laboratory‐selected, chlorpyrifos‐ and lambda‐cyhalothrin‐resistant strains to a susceptible reference strain (Sf‐ss) of S. frugiperda. RESULTS The susceptibility monitoring detected average survival ranging from 29.3% to 36.0% for chlorpyrifos, and 23.1% to 68.0% for lambda‐cyhalothrin. The resistance ratio of the chlorpyrifos‐resistant strain (Clo‐rr) was 25.4‐fold and of the lambda‐cyhalothrin‐resistant strain (Lam‐rr) was 21.5‐fold. We identified 1098 differentially expressed genes (DEGs) between Clo‐rr and Sf‐ss, and 303 DEGs between Lam‐rr and Sf‐ss. Functional analyses of the DEGs revealed the up‐regulation of several detoxification enzymes, mainly cytochrome P450 belonging to CYP3 and CYP6 clans. Genes associated with regulatory processes, such as the forkhead box class O (FoxO) transcription factor were also up‐regulated. Variant analysis of target‐site mutations for both pesticides identified the A201S and F290V mutations in acetylcholinesterase‐1, both occurring in heterozigosis in the Clo‐rr S. frugiperda strain. CONCLUSION Our data show that the overexpression of the enzymatic detoxification machinery is the main difference to explain the resistance of Clo‐rr and Lam‐rr strains of S. frugiperda to chlorpyrifos and lambda‐cyhalothrin, although a target‐site mutation also contributes to the Clo‐rr resistance to chlorpyrifos. © 2023 Society of Chemical Industry. Resistance of S. frugiperda to lambda‐cyhalothrin occurs due to an elevation of the detoxification process by an increased expression of CYP3 and CYP6 genes. The mechanism of resistance to chlorpyrifos involves the up‐regulation of several detoxification enzymes and the protective oxidative response through up‐regulation of AKH and FoxO.