Abstract
The development of resistance to a new acaricide, etoxazole, was found in populations of the two-spotted spider mite, Tetranychus urticae, collected from apple orchards in Soma-Mura village, Aomori Prefecture. Laboratory tests showed that a few mite populations of the 30 populations collected from an approximately 7×5 km area were insensitive to the acaricide, even though they have never been exposed to this acaricide. We selected a resistant and a susceptible strain from an insensitive population through selection and reciprocal selection by etoxazole. The resistance ratio calculated from the LC50s of the resistant and susceptible strain was more than 20,000. Crossing tests between the two strains indicated that the resistance to etoxazole was under control of a completely recessive single gene.
