INTEGRATED CONTROL OF APPLE PESTS IN NEW-ZEALAND .7. AZINPHOSMETHYL RESISTANCE IN STRAINS OF TYPHLODROMUS-PYRI FROM NELSON

The mite T. 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. Azinphos-methyl had been used extensively on these properties for some years for codling moth and leafroller moth control, and suggestions of field resistance to azinphos-methyl by T. pyri were confirmed in laboratory tests. Detailed toxicological examination of T. pyri from 4 properties established LC50 values for 3 strains considerably higher than previously determined values from Nelson orchards (1971). LC50 values ranged from 0.08% to 0.30% a.i. [active ingredient] azinphos-methyl. The LC50 for the Appleby-R strain previously tested in 1971 increased from 0.07%-0.30% from 1972-1976. 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 azinphos-methyl, the most resistant strain having the longest history of exposure to azinphos-methyl. The implications of this relationship for integrated mite control are discussed.