A flavin-dependent monooxgenase confers resistance to chlorantraniliprole in the diamondback moth, Plutella xylostella

Abstract

The diamondback moth, Plutella xylostella, is a damaging pest of cruciferous crops, and has evolved resistance to many of the insecticides used for control, including members of the diamide class. Previous work on the molecular basis of resistance to diamides has documented mutations in the target-site, the ryanodine receptor, in resistant populations of P. xylostella worldwide. In contrast the role of metabolic resistance to this insecticide class is significantly less clear. Here we show that overexpression of a flavin-dependent monooxgenase (FMO) confers resistance to the diamide chlorantraniliprole in P. xylostella. Transcriptome profiling of diamide resistant strains, with and without target-site resistance, revealed constitutive over-expression of several transcripts encoding detoxification enzymes compared to susceptible strains. Two of these, CYP6BG1, and PxFMO2 were particularly highly overexpressed (33,000 and 14,700-fold, respectively) in a resistant strain (HAW) lacking target-site resistance. After 17 generations without diamide selection the resistance of the HAW strain fell by 52-fold and the expression of PxFMO2 by > 1300-fold, however, the expression of CYP6BG1 declined by only 3-fold. Generation of transgenic Drosophila melanogaster expressing these genes demonstrated that PxFMO2, but not CYP6BG1, confers resistance in vivo. Overexpression of PxFMO2 in the HAW strain is associated with mutations, including a putative transposable element insertion, in the promoter of this gene. These enhance the expression of a reporter gene when expressed in a lepidopteran cell line suggesting they are, at least in part, responsible for the overexpression of PxFMO2 in the resistant strain. Our results provide new evidence that insect FMOs can be recruited to provide resistance to synthetic insecticides.

Comparative transcriptomics indicates endogenous differences in detoxification capacity after formic acid treatment between honey bees and varroa mites

“…A number of structurally different compounds containing a “soft nucleophile” (usually nitrogen or sulphur) that have access to the peroxyflavin intermediate are considered as potential substrates 79 , 80 . The detoxification mechanisms have been associated with the development of resistance to certain chemical pesticides including pyrethroids, pyrrolizidine alkaloids and diamides 81 – 83 . Both structural and physiological properties of the FMO enzyme family are still relatively unknown, except for functions in xenobiotic metabolism.…”

Increased Responses of Phenoloxidase in Chlorantraniliprole Resistance of Plutella xylostella (Lepidoptera: Plutellidae)

“…Chlorantraniliprole and other diamide insecticides have unique mechanisms and demonstrate good control of Lepidoptera pests ( Zhang et al 2014 ; Xu et al 2016 , 2017 ; He et al 2019 ), such as in DBM management ( Nauen and Steinbach 2016 ). However, the resistance of DBM to this class of insecticides has become increasingly serious ( Steinbach et al 2015 ; Liu et al 2015a , b ; Mallott et al 2019 ). This poses a challenge for the integrated management of DBM on vegetables.…”

Fly-Tox: A panel of transgenic flies expressing pest and pollinator cytochrome P450s

“…We have also previously created and performed bioassays with a transgenic fly line expressing this P450 which is included in the Fly-Tox panel. However, in our prior study this line showed no tolerance to chlorantraniliprole in the standard adult bioassay (see methods), indeed it was significantly more susceptible to this insecticide when compared to the control line lacking the transgene ( Mallott et al, 2019 ). Thus, detection of a resistance phenotype using this line with this compound may require larval bioassays to be performed.…”

“…Both RNAi knockdown and transgenic expression in D. melanogaster have provided support for a causal role of this P450 in resistance ( Li et al, 2018 ). However, in a following study, transgenic expression in Drosophila failed to confer resistance to chlorantraniliprole, with transgenic flies significantly more sensitive to this compound than a control line lacking the transgene ( Mallott et al, 2019 ). One possible explanation for this discrepancy may be differences in the bioassay methodology employed in the two studies with the former using a larval assay and the latter testing adults.…”