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A mutation in chitin synthase I associated with etoxazole resistance in the citrus red mite Panonychus citri (Acari: Tetranychidae) and its uneven geographic distribution in Japan.

BACKGROUND
High-levels of etoxazole resistance have not yet been frequently reported in Panonychus citri. Although a highly resistant strain was discovered in 2014, etoxazole resistance has not become a significant problem in areas of citrus production in Japan. A target site mutation in chitin synthase 1 (CHS1), I1017F, is a major etoxazole-resistance factor in Tetranychus urticae. To investigate the mechanisms of etoxazole resistance and the dispersal of resistance-genes, we analyzed target-site mutations in a highly resistant strain and their geographic distribution in Japan.


RESULTS
High-level etoxazole resistance was completely recessive. The I1017F mutation was detected in CHS1 of the highly resistant strain, and its frequency was correlated with the hatchability of eggs treated with etoxazole. Sequencing and variant frequency analyses of local populations by qPCR revealed that I1017F is restricted to the Ariake Sea area of Kyushu Island. Although a new nonsynonymous substitution, S1016L, accompanied by I1017F was found in CHS1 of the highly resistant strain, CRISPR/Cas9 engineering of flies showed that S1016L had no effect on the etoxazole resistance conferred by I1017F.


CONCLUSION
I1017F is a major target site mutation that confers high-level etoxazole resistance on P. citri. Dispersion of I1017F was possibly suppressed as a result of the completely recessive inheritance of resistance together with low gene flow between local populations. This article is protected by copyright. All rights reserved.