Fruit IPM Fact Sheet Van Buren MSUE Home
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Fruit IPM Fact Sheet
Van Buren MSUE Home
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Scientific Name- Tetranychus urticae (Koch)
Family-Tetranychidae
Reference: Common Tree Fruit Pests, Angus Howitt, 1993,
NCR 63 - Michigan State University
The Two-spotted Spider Mite is present worldwide. It feeds on a wide range of both wild and cultivated plants.
Life Stages
Egg: The spherical eggs are clear and watery when first deposited and become opaque and glassy as incubation progresses. Just before hatching, they become a pale straw color. The red eye spots of the embryo are plainly visible at this time.
Larva: The newly hatched larva is round, about the size of the egg, and has six legs. At this time it is colorless, except for the eyes, which are carmine. Feeding begins at once and the color changes to pale green, brownish green or very dark green, and two black spots appear, one one each side of the eye spot.
Protonymph: The protonymph is larger and more oval in outline than the larva and has four pairs of legs. The ground color is pale green to dark green, sometimes brownish green. The two spots are larger and more pronounced than in the larva.
Deutonymph: The ground color of the deutonymph is generally some shade of green. It apparently is influenced by the mite's food. The spots are larger and more distinct. Males are readily distinguished from females in this stage by their smaller bodies, pointed abdomens and small spots.
Adult: The male is much smaller and more active than the female. The male's body is narrow and the abdomen is distinctly pointed. The color is pale yellow, pale to dark green, brownish or at times faintly orange. An inconspicuous dark area is generally present on each side, and other dark areas are frequently seen along the middle. The body of the female is oval, about 0.42 mm long and about 0.27 mm wide. The color of females varies from light yellow or straw color to green, brown, black and various shades of orange. Newly emerged females have two large black spots, one on each side just behind the eye spot. After feeding takes place, black splotches show up in irregular patterns in other parts of the body.
Host Range
This mite attacks many species of wild and cultivated plants in many parts of the world. Deciduous fruit tree hosts are apple, pear, peach, nectarine, plum, apricot and cherry.
Injury or Damage
The injury the two-spotted mite causes is similar to that caused by the European red mite. Bronzing, however, is more gray, and there is much more webbing with two-spotted spider mites than with similar populations of European red mites.
Factors Affecting Abundance
The two-spotted mite has a wide range of host plants, a high biotic potential -- producing multiple generations in a season -- and a considerable propensity for developing resistance to miticides. Drought conditions will cause the mites to migrate from grasses to nearby orchard fruit trees.
Life History
Full-grown female mites and some immature overwinter under bark scales on the trunk of the tree or among fallen leaves and in other protected places on the ground. With the arrival of warm weather in the spring, these mites leave their places of hibernation and start wandering about looking for food plants. Almost all of the those on the tree trunk crawl down the trunk to the ground, where they feed on weeds and grasses. The first eggs can usually be found around the pink stage. In warm weather, these hatch in five to eight days. A complete generation from egg to adult may require no more than three weeks. Five to nine generations occur in the orchard each season, depending on the weather.
In mid- or late summer, when drought and other factors cause poor food conditions among weeds and grasses, mites move from the old host up the tree trunks or to low-hanging apple branches in contact with the ground vegetation. Low-hanging branches that touch grass or weeds are usually attacked first; then mites spread upward and into the interior of the tree. Once established, the population may develop into a serious infestation and cause injury. Injury to the leaves resembles that of the European red mite, except that a more grayish cast is prevalent. As indicated previously, these mites also spin a fine silken web over many infested leaves.
In the fall, the adults leave the trees and hibernate among weeks or leaves or in the soil, although some may overwinter on the trees.
Monitoring
Begin checking in early summer and continue until fall. Select 10 leaves from the lower shoots and water sprouts along the trunk from each of 10 trees in an orchard. If the ground cover touches the lower limbs, pick an additional 100 leaves from the limbs touching the weeds. Treatment is recommended if the counts average six or more two-spotted mites per leaf and the predators average less than one per leaf.
Control
Control these mites with summer applications of miticides.
