Toxicological and molecular profiling of insecticide resistance in a Brazilian strain of fall armyworm resistant to Bt Cry1 proteins

Abstract

Background Spodoptera frugiperda, fall armyworm (FAW) is the major pest of maize in Brazil and has readily acquired field resistance to a broad range of synthetic insecticides and to Bacillus thuringiensis (Bt) insecticidal proteins expressed in important crops. This study aims to understand patterns of cross‐resistance in FAW by investigating the toxicological profile of a Bt‐resistant Brazilian strain (Sf_Des) in comparison to a Bt‐susceptible strain (Sf_Bra). Results Laboratory bioassays with 15 active substances of nine mode of action classes revealed that Sf_Des has a medium level of resistance to deltamethrin and chlorpyrifos. Very high cross‐resistance was observed among Cry1 toxins, but high susceptibility against Vip3A. Strain Sf_Des exhibited – depending on the substrate – up to 19‐fold increased cytochrome P450 activity in comparison to Sf_Bra. RNA‐Seq data support a major role of P450 enzymes in the detoxification of insecticides because we detected 85 P450 transcripts upregulated in Sf_Des. Quantitative reverse transcription polymerase chain reaction (RT‐qPCR) analysis confirmed that CYP9A‐like and CYP6B39 are significantly upregulated (>200‐fold) in Sf_Des in comparison to Sf_Bra strain. No target‐site mutation linked to pyrethroid resistance was detected, but mutations in the AChE linked to organophosphate resistance were observed in Sf_Des. A Gene Ontology (GO) analysis of differentially expressed genes (DEG) categorized most of them into the biological process category, involved in oxidation–reduction and metabolic processes. Conclusion Our results indicate that multiple/cross‐resistance mechanisms may have developed in the Sf_Des strain to conventional insecticides and Bt insecticidal proteins. The systematic toxicological analysis presented will help to guide recommendations for an efficient resistance management. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

ABC transporter mutations in Cry1F‐resistant fall armyworm (Spodoptera frugiperda) do not result in altered susceptibility to selected small molecule pesticides

“…This observation is also in agreement with recent reports of multiple resistance mechanisms in Cry1F‐resistant S. frugiperda from Brazil that are cross‐resistant to conventional insecticides 31 . Taken together with our results, these observations show that resistance to small molecule pesticides in S. frugiperda from Puerto Rico 14 and Brazil 31 are independent from SfABCC2 alleles yielding resistance to Cry1F.…”

“…These results are in agreement with ABCC2 knockout experiments in H. armigera 17 and clearly support that truncation of SfABCC2 in Cry1F‐resistant S. frugiperda does not result in altered susceptibility to the tested small molecule pesticides. This observation is also in agreement with recent reports of multiple resistance mechanisms in Cry1F‐resistant S. frugiperda from Brazil that are cross‐resistant to conventional insecticides 31 . Taken together with our results, these observations show that resistance to small molecule pesticides in S. frugiperda from Puerto Rico 14 and Brazil 31 are independent from SfABCC2 alleles yielding resistance to Cry1F.…”

Resistance in the Genus Spodoptera: Key Insect Detoxification Genes

“…In a recent study, a Brazilian population of S. frugiperda resistant to Bacillus thuringiensis (Bt) Cry1 toxins was tested against 15 insecticide molecules with different modes of action. In addition to resistance to Bt toxins, the Sf-Des strain had showed 14-and eight-fold resistance to deltamethrin and chlorpyrifos, respectively [40]. P450 activity was increased in the Sf-Des strain compared to the susceptible Bt strain.…”

Deltamethrin-Mediated Effects on Locomotion, Respiration, Feeding, and Histological Changes in the Midgut of Spodoptera frugiperda Caterpillars

“…Thus, the long-term effects of insecticides are poorly understood [ 33 ]. Deltamethrin has broad action of and toxicity against arthropods [ 34 ], being the major insecticide used to control maize pests such as S. frugiperda [ 35 , 36 ]. In this research, the action of deltamethrin on S. frugiperda survivorship, locomotion, respiration, feeding, and histotoxicity in the midgut were assessed.…”