The relative contribution of target-site mutations in complex acaricide resistant phenotypes as assessed by marker assisted backcrossing in Tetranychus urticae

Maria Riga,Stavrini Papadaki,John Vontas,Sabina Bajda,Thomas Van Leeuwen,Wannes Dermauw,Maria Palzewicz,Christos Themistokleous

doi:10.1038/s41598-017-09054-y

Abstract

The mechanisms underlying insecticide and acaricide resistance in insects and mites are often complex, including additive effects of target-site insensitivity, increased metabolism and transport. The extent to which target-site resistance mutations contribute to the resistance phenotype is, however, not well studied. Here, we used marker-assisted backcrossing to create 30 congenic lines carrying nine mutations (alone, or in combination in a few cases) associated with resistance to avermectins, pyrethroids, mite growth inhibitors and mitochondrial complex III inhibitors (QoI) in a polyphagous arthropod pest, the spider mite Tetranychus urticae. Toxicity tests revealed that mutations in the voltage-gated sodium channel, chitin synthase 1 and cytochrome b confer high levels of resistance and, when fixed in a population, these mutations alone can result in field failure of acaricide treatment. In contrast, although we confirmed the implication of mutations in glutamate-gated chloride channels in abamectin and milbemectin insensitivity, these mutations do not lead to the high resistance levels that are often reported in abamectin resistant strains of T. urticae. Overall, this study functionally validates reported target-site resistance mutations in T. urticae, by uncoupling them from additional mechanisms, allowing to finally investigate the strength of the conferred phenotype in vivo.

Highlights

Insecticide resistance is a major threat for the chemical control of insects and mites in public health and agriculture
The majority of studies that look into epistatic interactions and/or resistance levels confirmed by a single genetic factor, are sometimes difficult to interpret if resistance alleles are not investigated in a common genetic background[9, 12,13,14,15]
We investigated the relative contribution of nine known target-site mutations conferring resistance to abamectin, pyrethroids, bifenazate and mite growth inhibitors

Summary

Introduction

Insecticide resistance is a major threat for the chemical control of insects and mites in public health and agriculture. The relative importance and strength of target-site mutations is often hard to assess by merely associating a phenotype with mutation frequency in field populations, where prolonged selection may have led to the accumulation of additional resistance mechanisms. Inhibitor-protein interactions are quantified via enzymatic reactions or ligand binding assays such as voltage-clamp electrophysiology They provide strong evidence of the effect of a mutation on the affinity for the compound to the target-site, they are less suitable to assess the relative phenotypic consequences in vivo[18, 19]. Several target-site mutations have been uncovered and were associated with acaricide resistance in populations of T. urticae, recently summarized in Van Leeuwen and Dermauw[4]. We investigated the relative contribution of nine known target-site mutations conferring resistance to abamectin, pyrethroids, bifenazate and mite growth inhibitors. When a combination of mutations in homologous genes was reported, the phenotypic levels of resistance were examined for both the single mutations, as well as their combination

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Conclusion