Environmental Entomology (2000) 29, 683-689

Debra L. Moreau, John Michael Hardman and Olga Kukal (2000)
Supercooling capacity and survival of low temperatures by a pyrethroid-resistant strain of Typhlodromus pyri (Acari: Phytoseiidae)
Environmental Entomology 29 (4), 683-689
Abstract: An organophosphate/pyrethroid resistant strain of the phytoseiid mite Typhlodromus pyri Scheuten was imported from New Zealand in 1988 for use in biological control of European red mite, Panonychus ulmi (Koch), and apple rust mite, Aculus schlechtendali (Nalepa), in Nova Scotia. To better understand the overwintering strategy of T. pyri and the likelihood the New Zealand strain would withstand winter conditions in Canada, we measured supercooling points and mortality of diapausing females held at subzero temperatures. Mites in quartz crucibles were placed in the liquid nitrogen-cooled stage of a cryostage microscope, and temperature was lowered 1°C/min until the mites froze, as indicated by an instantaneous darkening of their body contents. Supercooling points of the New Zealand strain averaged -18.2°C for July to September, were -23.2°C in October, and averaged -28.2°C in the colder months from November to March. The mean supercooling points for December 1994 did not differ from the mean for the native Nova Scotian strain. However, the mean supercooling point of the New Zealand strain for March 1995 was higher than the means for the native strain and for a T. pyri strain that was imported from Geneva, NY. New Zealand strain T. pyri taken from cloth bands affixed to orchard trees were placed on apple leaves in plastic vials and exposed to low temperatures for various periods of exposure. At -5°C, mortality at 24 h was less for mites collected in February than for those collected in November (6% versus 44%) but at -10°C trends were similar, reaching 100% by 24 h in both trials. For the February trial, a logistic function with a coefficient for the product of time and temperature explained 61% of the variation in mortality. If these results are applied to populations in Nova Scotian orchards, where winter temperatures of -10°C are common, one would predict complete annihilation of the New Zealand strain. However, populations of the New Zealand strain, first released in orchards in 1988, have survived every winter since that date and have proven effective in biological control of European red mite and apple rust mite. Possible reasons for survival and increase of populations of this exotic strain of T. pyri, despite apparent susceptibility to cold-induced mortality, are discussed.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): John Michael Hardman

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
environment/habitat manipulation
resistance to pesticides

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
Typhlodromus pyri (predator)			Canada (east)
Typhlodromus pyri (predator)			New Zealand