Tree Fruit Research & Extension Center

Orchard Pest Management Online

 

Twospotted spider mite


Tetranychus urticae Koch
(Acari: Tetranychidae)

-- Elizabeth H. Beers and Stanley C. Hoyt
  (originally published 1993)

Gallery

The twospotted spider mite is probably one of the most polyphagous arthropods that feeds on tree fruits. It is distributed worldwide and is an economic pest of many crops. It is in the same family as the European red mite and McDaniel spider mite but is more closely related in feeding habits and life cycle to the latter.

 
Hosts

Its innumerable hosts include many weeds, field crops, ornamental and house plants, vegetables, forage crops, small fruits and tree fruits. Among the tree fruits, apple, pear, peach, nectarine, apricot, cherry (sweet and sour), plum, and prune are suitable hosts. High mite populations encountered on pear are likely to be either twospotted or McDaniel spider mite. Twospotted spider mite used to be rare on apple, but has become more common in recent years, greatly surpassing McDaniel spider mite as a problem.

 
Life stages

Twospotted spider mite larva and egg (E. Beers)

Egg: The egg is spherical and about 1/150 inch (0.14 mm) in diameter. When first deposited, the egg is translucent, taking on the greenish tinge of the leaf where it is laid. It becomes more opaque as it matures, finally turning a pale yellow. The red eyespots of the embryo are visible just prior to hatch.

Immatures: The larva is round, about the same size as the egg, and has three pairs of legs. Initially it also is translucent (except the red eyespots), but once it begins feeding, it turns pale green to straw color, and the characteristic black spots begin to form on the dorsum (back). The protonymph is larger and more oval, and has four pairs of legs, as do all succeeding stages. The two dorsal spots are more pronounced, and the green color is slightly deeper. The deutonymph is slightly larger than the preceding stage, and males can be distinguished

Twospotted spider mite adult females (E. Beers)

from females at this stage by the smaller size and more pointed abdomen. Each immature stage goes through three phases: active feeding, a quiescent period, and a molt. The integument (the outer covering of the body) may take on a silvery appearance in the quiescent stage as it separates from the skin below in preparation for the molt.

Adult: The adult male is smaller than the female and is characterized by its distinctly pointed abdomen. It sometimes has an orange or brown tinge and is more active than the female. The female is about 1/60 inch (0.42 mm) and more robust than the male and is more oval in shape. Color of the female can also vary. Typically, it is a pale leaf-green, but it can be tinged with yellow, brown and orange. As the name implies, there are generally two distinct spots on the front half of the dorsum behind the eyes. These spots are caused by pigments in the digestive tract which is why the size, distinctness, and pattern of spots can vary considerably among individuals or at different times during the life span of a single individual. Overwintering females are usually a distinct solid orange, and the spots disappear. During this stage, they can only be distinguished from McDaniel mite by slide mounting and examining the integument of the dorsum for a diamond-shaped section of striations.

 
Life History

The twospotted spider mite overwinters as orange colored adult females in the duff at the base of trees and in sheltered sites beneath bark scales. Only females are known to overwinter. They emerge from their overwintering sites about the half-inch green stage of apple development. As these mites begin feeding, they gradually lose their orange color and gain their normal greenish hue and dorsal spots. After about 2 to 5 days, egg laying begins, primarily on the underside of newly expanded leaves, and later on the fruitlets. Overwintering females lay an average of 39 eggs over a life span of 23 days, considerably fewer than the summer forms. These eggs may take up to 3 weeks to hatch, depending on temperature. From this point onwards, generations begin to overlap. Summer-form females can lay about 100 eggs over a period of 30 days. Egg hatch takes only one or two days during the warm part of the summer, and the entire generation time (oviposition to adult) may take only 10 days. When leaf quality begins to decline (e.g., from excessive mite feeding), or when cooler temperatures and shorter day lengths occur during the fall, the orange overwintering forms are again produced.

 
Damage, Biological Control, and Management

see sections under European red mite.

 
Monitoring

 
Gallery

Photo Gallery

 

Orchard Pest Management, is copyrighted by the Washington State Fruit Commission. Soft cover copies are available for purchase.
Tree Fruit Research & Extension Center , 1100 N Western Ave, Washington State University, Wenatchee WA 98801, 509-663-8181, Contact Us