HortFACT
Identification
Typhlodromus pyri, which has no standard common name as yet, is a predatory mite. The adult female is just under 0.4 mm long, ovoid, and somewhat pear-shaped, with the posterior end broad and rounded. The male is less common than the female, and is narrower, shorter, and more flattened dorsoventrally. The female is pale creamish-white and the male browner. After it has fed on red mites, the adult acquires a reddish H-shaped pattern visible through the body surface.
The 0.2-mm-long eggs are translucent white and ovoid. They are laid mainly among leaf hairs beside the midrib and main veins of host-plant leaves.
A six-legged larva hatches from the egg. It soon moults into the protonymph stage, which in turn changes into the deutonymph. These nymphs are eight-legged, and resemble adults except in being smaller.
T. pyri is of similar size to its commonest prey, European red mite, but very different in appearance. Although very similar to related predatory mites, it can be readily distinguished from other common species with a microscope or a good hand lens. A large, hard plate bearing setae (hairs) can be seen on the upper surface of the adults. The arrangement of setae and their relative lengths distinguish one species from another; T. pyri has only short setae.
Host plants
T. pyri is found on a wide range of plants, but lives mainly on deciduous trees and shrubs. It is particularly common on fruit trees (apple, cherry, peach, pear, and plum), on trees of European origin (elm, hazel, lime, maple, and willow), garden shrubs, and such plants as raspberry and blackberry.
Feeding habits
Although largely a predator, T. pyri also consumes pollen, fungal tissue, and honeydew. It preys mainly on other species of mite, taking the active stages (but not the eggs) of European red mite, Bryobia species, various rust mites, and other pests such as two-spotted mite. Cannibalism occurs when other food sources are absent.
Distribution
T. pyri originated in northern Europe, and is now common in North America and many other regions with a temperate climate. It occurs throughout New Zealand.
Pesticide - resistant strains
Earlier studies in Europe showed T. pyri to be very susceptible to many of the chemicals used in orchards for pest and disease control, and therefore it was rarely found in heavily sprayed orchards. In New Zealand within the past 10 years it has been found in increasing numbers where regular spray programmes of chemicals such as azinphos-methyl have been used. It was first found in the Nelson area, and then in Marlborough and Hawke's Bay The levels of resistance of orchard strains of the mite to these pesticides are now known to be high, and these strains are being used increasingly by orchardists in integrated mite control. Their predation on European red mite can reduce the number of miticide applications needed to maintain acceptable control of the pest.
Resistant strains of other predatory species, similar in appearance to T. pyri, are being imported into New Zealand, and may be encountered in orchards.
Life cycle
| Egg |  |
| Larvae | |
| Nymph | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
In October the overwintered females are found on the blossom and young leaves of apple trees, where they feed on both pollen and young stages of European red mite which have just hatched from winter eggs. Later they are found on the underside of leaves, usually alongside the midrib and main veins. Having mated at the end of the previous summer, they begin laying eggs soon after they start feeding. The rate depends on temperature, and is rarely more than one egg per day in October and November. After only a few days the six-legged larva hatches from the egg. The first-generation adults (male and female) develop from late November and early December. Second generation adults appear in early January, and a third generation in February. More generations can be produced if food supplies, host-plant leaf condition, and weather are favourable. These later generations overlap.
In late February and March an increasing proportion of females become dormant, which is obvious in that they cease to feed or lay eggs. These females are mated and prepare to overwinter. They remain dorsoventrally flattened, become slightly brownish, and frequently aggregate in groups of 20 or more along a leaf midrib. They tend to stay on the leaves almost until leaf-fall, but eventually they move back on to the branches and trunks, where they hibernate in loose bark and crevices. On young orchard trees with smooth bark they may seek shelter in tree-ties or stakes. Winter mortality of dormant females is usually very high.
ELSIE COLLYER