Levels and genetics of organophosphate resistance in Italian and Oregon biotypes of Amblyseius andersoni (Acari : phytoseiidae)

Strains of the predaceous phytoseiid mite Amblyseius andersoni Chant from Verona, Italy, and the Willamette Valley, Oreg., were compared for their susceptibility to several insecticides used on western Oregon fruit crops. The Italian race showed 80-100-fold higher resistance to azinphosmethyl, diazinon, malathion, phosalone, and carbaryl. Endosulfan was slightly toxic to both races at field rates, whereas fenvalerate was highly toxic. Genetic analysis by bioassay of reciprocal F sub(1) hybrids revealed that azinphosmethyl resistance is a semidominant polygenic trait. Differences between reciprocal F sub(1) crosses demonstrated maternal influences which increased variation in response to azinphosmethyl in progeny of females from Oregon. Prospects for establishing the Italian race in western Oregon and stability in managing resistance are discussed.