Activity, selection response and molecular mode of action of the isoxazoline afoxolaner in Tetranychus urticae

Abstract

BACKGROUND Afoxolaner is a novel representative of the isoxazolines, a class of ectoparasiticides which has been commercialized for the control of tick and flea infestations in dogs. In this study, the biological efficacy of afoxolaner against the two‐spotted spider mite Tetranychus urticae was evaluated. Furthermore, as isoxazolines are known inhibitors of γ‐aminobutyric acid‐gated chloride channels (GABACls), the molecular mode of action of afoxolaner on T. urticae GABACls (TuRdls) was studied using functional expression in Xenopus oocytes followed by two‐electrode voltage‐clamp (TEVC) electrophysiology, and results were compared with inhibition by fluralaner, fipronil and endosulfan. To examine the influence of known GABACl resistance mutations, H301A, I305T and A350T substitutions in TuRdl1 and a S301A substitution in TuRdl2 were introduced. RESULTS Bioasassays revealed excellent efficacy of afoxolaner against all developmental stages and no cross‐resistance was found in a panel of strains resistant to most currently used acaricides. Laboratory selection over a period of 3 years did not result in resistance. TEVC revealed clear antagonistic activity of afoxolaner and fluralaner for all homomeric TuRdl1/2/3 channels. The introduction of single, double or triple mutations to TuRdl1 and TuRdl2 did not lower channel sensitivity. By contrast, both endosulfan and fipronil had minimal antagonistic activities against TuRdl1/2/3, and channels carrying single mutations, whereas the sensitivity of double and triple TuRdl1 mutants was significantly increased. CONCLUSIONS Our results demonstrate that afoxolaner is a potent antagonist of GABACls of T. urticae and has a powerful mode of action to control spider mites. © 2022 Society of Chemical Industry.

Intraspecific diversity in the mechanisms underlying abamectin resistance in a cosmopolitan pest

“…While a plethora of mechanisms underlying abamectin resistance has been identified in arthropod and non-arthropod taxa, high abamectin resistance levels could, in most cases, not be attributed to one single mechanism (Choi et al, 2017;Dermauw et al, 2012;Ghosh et al, 2012;Khan et al, 2020;Kwon et al, 2010;Mermans et al, 2017;Riga et al, 2014;Xue et al, 2020Xue et al, , 2021. Mutations in genes encoding subunits of the glutamate-gated chloride channel (TuGluCl1 and TuGluCl3) are major factors contributing to abamectin resistance in T. urticae (Dermauw et al, 2012;Kwon et al, 2010;Mermans et al, 2017;Xue et al, 2020). However, introgression experiments of single target-site mutations have revealed that they do not confer a strong resistance phenotype without additive or synergistic effects of other resistance factors.…”

“…Multiple resistance mechanisms to abamectin have been described, including target-site insensitivity and oxidative metabolism, suggesting a complex genetic basis of abamectin resistance (Kwon et al, 2010;Mermans et al, 2017;Riga et al, 2014;Wang et al, 2017;Xue et al, 2020Xue et al, , 2021. Abamectin is an allosteric modulator that targets cys-loop ligand-gated ion channels in invertebrates, of which glutamate-gated chloride channels (GluCl) are the main target site in arthropods and nematodes (Clark et al, 1995;Dent et al, 2000;Ludmerer et al, 2002;Mermans et al, 2017;Sparks et al, 2021). Mutations in GluCl genes associated with resistance to avermectins have been identified in Caenorhabditis elegans, Drosophila melanogaster, Plutella xylostella and T. urticae, and in some cases, these mutations have been functionally validated using different approaches, including two-electrode voltage-clamp electrophysiology, the creation of near-isogenic lines and classic backcrossing experiments with F2 screens (Choi et al, 2017;Dent et al, 2000;Dermauw et al, 2012;Ghosh et al, 2012;Hibbs & Gouaux, 2011;Kwon et al, 2010;Mermans et al, 2017;Riga et al, 2017;Wang et al, 2016Wang et al, , 2017Xue et al, 2021).…”

Nitrile Oxide, Alkenes, Dipolar Cycloaddition, Isomerization and Metathesis Involved in the Syntheses of 2-Isoxazolines

“…Afoxolaner is a novel representative of the isoxazolines, a class of ectoparasiticides commercialized for controlling tick and flea infestations in dogs. Furthermore, as isoxazolines are known inhibitors of γ-aminobutyric-acid-gated chloride channels (GABACls), the molecular mode of action of afoxolaner on T. urticae GABACls (TuRdls) was examined [ 360 ]. One part of the book from 2018 entitled “Isoxazolines: Preeminent Ectoparasiticides of the Early Twenty-first Century” is dedicated to isoxazolines as certain drugs [ 361 ], and antitubercular and antibacterial activities of isoxazolines derived from natural products were described by Anuchit Phanumartwiwath et al [ 362 ].…”

Design, Synthesis, Insecticidal Activity, and SAR of Aryl Isoxazoline Derivatives Containing Pyrazole-5-carboxamide Motif

“…Among them, the GABA-gated chloride channel allosteric modulators are new integrated pest management tools, , including isoxazoline insecticides and meta-diamide insecticides, which were in group 30 by the Insecticide Resistance Action Committee (IRAC) . So far, many isoxazoline insecticides have been discovered, such as fluralaner, fluxametamide, afoxolaner, isocycloseram, sarolaner, and lotilaner . These isoxazoline insecticides had similar structures and mode of action, which not only prevent and control some pests resistant to insecticides but also have excellent effects on a variety of parasites.…”