by Helmut Riedl and Brian A. Croft, originally published 1993
Typhlodromus pyri is a predatory mite found in fruit growing regions throughout the world, including Europe, North America and New Zealand. It preys on the apple rust mite, European red mite and twospotted spider mite.
T. pyri closely resembles T. occidentalis, but there are important differences between the two. For example, T. pyri is a more effective predator in cool, humid conditions, whereas T. occidentalis increases most rapidly and is most effective in dry, hot climates. The two can work well together. T. pyri is effective at the start and end of the season when the weather is cooler and prey densities are low, and T. occidentalis works best during midseason when prey are abundant.
In the arid areas of eastern Oregon and Washington, T. occidentalis is the predominant of the two predatory mites. In the more humid growing areas of western Oregon and Washington, T. pyri is the more prevalent. T. pyri is also found in British Columbia.
Both predatory mites have become resistant to a range of agricultural pesticides, including organophosphate insecticides, which has led to their successful use in tree fruit IPM programs. A strain of T. pyri that is resistant to pyrethroids has been patented in New Zealand.
Unlike T. occidentalis, which is an obligate predator of mites, T. pyri feeds on pollen as well as pest mites. T. pyri prefers to prey on European red mite, whereas T. occidentalis prefers McDaniel or twospotted spider mite.
T. pyri is the most important predatory mite on blackberries in western Oregon and Washington. It also inhabits fruit trees, many rosaceous plants and occasionally hops.
T. pyri looks very similar to T. occidentalis. Adults are difficult to distinguish without a microscope or 30-power lens. The main difference is that T. occidentalis has long setae, or hairs, on its back. The setae on T. pyri are much shorter and less conspicuous.
Adults overwinter in diapause and emerge in early April. Female T. pyri tend to begin laying eggs earlier than T. occidentalis, perhaps because they are better adapted to cool temperatures and will feed on other foods when prey is scarce. During the summer, several generations develop, and the population is usually made up of equal numbers of adults, nymphs and eggs.
T. pyri females lay eggs for about 2 to 3 weeks longer than T. occidentalis in the fall. T. pyri numbers may increase with the onset of cool weather, whereas T. occidentalis populations tend to decline. T. pyri adults are active until October. Winter mortality can be high.
Examine the undersurface of leaves where mites are likely to be. Use a leaf-brushing machine to count both pests and predatory mites. Repeat samples at intervals to monitor changes in their relative abundance. Though T. pyri numbers may not be high in midsummer, it can be an effective predator towards the end of the season when the weather cools off and T. occidentalis numbers begin to wane.
Research shows that T. pyri requires a ratio of about 1 predator per leaf (all life stages) to about 5 to 10 European red mites per leaf before biological control can be highly successful. This is a higher predator ratio than required for T. occidentalis.
T. pyri is less inclined than T. occidentalis to emigrate to other leaves, trees or habitats in search of prey. For this reason, it can take several years for the mite to move into an orchard from nearby habitat.
To introduce it to an orchard, bring in water sprouts or clippings from trees where the mite is known to occur. Because T. pyri does not move very much, populations outside orchards may not have built up resistance to pesticides like those inside orchards. Although T. pyri is unlikely to thrive in very dry conditions, it may be able to survive in orchards in arid areas that have overtree irrigation systems.