Frequencies of the M918I mutation in the sodium channel of the diamondback moth in China, Thailand and Japan and its association with pyrethroid resistance

In addition to the allele frequencies of the L1014F and T929I mutations which are involved in nerve-insensitive resistance to a pyrethroid, those of the M918I mutation were examined using field strains obtained in China, Thailand, and Japan during 2009–2011. Results show that the resistance allele frequencies at the L1014F site were 89–100%, 97–100% and 65–85%, respectively, for strains in China, Thailand, and Japan. The respective allele frequencies at the T929I site were 86–100%, 70–97% and 58–84% for Chinese, Thai, and Japanese strains. With low frequencies up to 27%, M918I was found in Japan and China, but not in Thailand. The strain homozygous for the M918I and L1014F mutations was established and its resistance level to a pyrethroid was examined. The strain lacks a portion of the sodium channel gene corresponding to the 3′ portion of exon 18a, intron 18, and the 5′ portion of exon 18b. Nevertheless, the strain showed a similar level of resistance to that which was homozygous for the T929I and L1014F mutations.

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► We examine frequencies of L1014F, T929I and M918I in three Asian countries.
► Frequencies of L1014F and T929I are respectively 65–100% and 58–100%.
► M918I is found with low frequencies up to 27%.
► Insects with M918I are found in Japan and China, but not in Thailand.
► Insects with M918I show a high level of pyrethroid resistance.