VII. Azinphosmethyl resistance in strains of Typhlodromus pyri from Nelson

Abstract

The mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae), a predator of European red mite Panonychus ulmi (Koch), was detected in 16 of 22 surveyed apple orchards (1975) in Nelson, New Zealand. Azinphosmethyl had been used extensively on these properties for some years for codling moth and leafroller moth control, and suggestions of field tesistance to azinphosmethyl by T. pyri were confirmed in laboratory tests. Detailed toxicological examination of T. pyri from four properties established LC₅₀ values for three strains considerably higher than previously determined values from Nelson orchards (1971). LC₅₀ values ranged from 0.08% to 0.30% a.i. azinphosmethyl. The LC₅₀ for the Appleby-R strain previously tested in 1971 increased from 0.07% to 0.30% from 1972 to 1976. the slopes of the dosage-mortality lines were similar for all strains. Integrated control of European red mite using T. pyri appears feasible at the detected levels of resistance. LC₅₀ values increased curvilinearly in response to continuing exposure to azinphosmethyl, the most resistant strain having the longest history of exposure to azinphosmethyl. The implications of this relationship for integrated mite control are discussed.