Insectary Rearing and Initial Testing in Canada of an Organophosphate/Pyrethroid-Resistant Strain of the Predator Mite Typhlodromus pyri (Acari: Phytoseiidae) from New Zealand

A strain of Typhlodromus pyri Scheuten resistant to pyrethroids and to several organophosphate insecticides was imported into Nova Scotia, Canada, from New Zealand in 1988. T. pyri reared on potted apple trees treated with dilute cypermethrin in outdoor insectaries remained at densities >1 per leaf throughout the summers of 1988–1994 and were able to suppress European red mite, Panonychus ulmi (Koch), and twospotted spider mite, Tetranychus urticae Koch. Leaf disk bioassays in 1988 indicated that native T. pyri from an orchard regularly sprayed with several organophosphates had low mortality when exposed to azinphosmethyl, malathion, and phosmet. However, the New Zealand strain had significantly lower mortality and less repellancy than did native T. pyri when exposed to the pyrethroid insecticide cypermethrin or the organophosphate azinphosmethyl. In an orchard trial, the New Zealand strain colonized trees and exerted effective control of P. ulmi and apple rust mite, Aculus schlechtendali (Nalepa), despite minimum winter temperatures of −20 to −22°C from 1988 to 1992 and −30°C in 1993. In late August 1988, New Zealand T. pyri were placed on trees that were treated with cyperemethrin in 1988, 1989, and 1991. Maximum densities of motile P. ulmi decreased from 32 per leaf in 1988 to 10 in 1989 and to <1 per leaf in 1990 and 1991. By August 1990 the T. pyri had dispersed at least 3 rows north from the release row. Slide dip bioassays indicated that T. pyri on the release trees had higher survival of cypermethrin than did T. pyri from control trees 10 rows to the north in the same orchard, suggesting the former were the New Zealand Strain (pyrethroid resistant) and the latter were native (pyrethroid susceptible). Evidence of retention of pyrethroid resistance was seen in a 2nd orchard trial. Cypermethrin was applied in mid-May 1992 to eliminate native T. pyri . New Zealand T. pyri released in late May and early July colonized the release trees, dispersed to other trees in the same rows, and suppressed P. ulmi and A. schlechtendali despite pyrethroid residues on all trees. Suppression of phytophagous mites continued in 1993 despite application of dilute cypermethrin in May of that year.