Acaricides are a diverse group of chemicals with excellent efficacy primarily on mite and tick species. The mode of action of acaricides is often less understood in comparison to insecticides. Spider mites are probably the most problematic mite pest species in plant production, as they are extremely polyphagous and have a tendency to develop resistance extremely fast. Recently, the genome of the two-spotted spider mite Tetranychus urticae was sequenced. Based on the availability of the small genome (90 Mb), we developed a population, multi-generational bulk segregant analysis (BSA) mapping method to uncover resistance mutations. When target-site resistance is the main resistance mechanism, this technique also potentially elucidates the molecular targets of acaricides. Etoxazole represents one of the several compound classes that act as potent chitin biosynthesis inhibitors and are of great agricultural importance for the control of arthropod populations. Using a BSA approach, we identified a non-synonymous variant in the major T. urticae chitin synthase enzyme that confers target-site resistance to etoxazole, suggesting a direct interaction between etoxazole and chitin synthase. Identification of the target-site of a chitin synthase inhibitor is important to exploit chemical structures fully. Intriguingly, the nature of the CHS1 mutation underlying resistance is potentially informative as to why the exact mode of action of arthropod chitin biosynthesis inhibitors have remained elusive for decades: the target site mutation suggests that inhibition acts on a non-catalytic (but essential) function of CHS1 complexes. Next to etoxazole, we have performed BSA analysis to uncover resistance mutations in strains resistant to a number of chemicals, and we will present the initial but exciting results.

Using genomic tools to determine the mode of action of acaricides: The tale of chitin synthesis inhibitors in <i>Tetranychus urticae</i>

246th National Meeting (2013)

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Using genomic tools to determine the mode of action of acaricides: The tale of chitin synthesis inhibitors in Tetranychus urticae