Penetration of 32P-dimethoate into organophosphate resistant and susceptible citrus red mite, Panonychus citri McGregor (Acarina : Tetranychidae)

The penetration of dimethoate into the mite body was investigated as part of a broad study attempting to clarify the mechanism of dimethoate resistance in the citrus red mite, Panonycus citri McGREGOR. Although there was no apparent difference in dimethoate penetration between the resistant and susceptible strains by topical application with a micrometer syringe without distinction of the solvents for dimethoate, an interstrain difference in penetration was observed by a spraying method. Sixty-two and 64% of sprayed dose penetrated the cuticle into the mite body of the susceptible strains, Wakayama and Ogi, while only 44 and 15% of sprayed dose penetrated into the body of the resistant strains, Shuku and Shizuoka, by the 9 th hour following application. The difference in penetration rate of dimethoate is considered to be one of the factors involved in the mechanism of dimethoate resistance in the citrus red mites.