Twospotted Spider Mite

This species has two dark spots, composed of food content, showing through the transparent body wall. The abdomen is oval and sparsely covered with spines. 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 usually more active than the female. The female is more robust than the male and is more oval in shape. Color of the female can vary; typically, it is a pale leaf-green, but it can also be tinged with yellow, brown, and sometimes orange.

All stages of the twospotted spider mite overwinter in protected places on the tree, such as the navel of navel oranges, under the button, and where fruit touch. If the weather is mild, mites continue to feed and reproduce during winter. Activity increases in late spring and peaks in summer. Spider mites first appear on the underside of leaves and when numbers increase, they can also be found on the upper side of leaves and on fruit. They cover leaves and fruit with conspicuous webbing.

Eggs are spherical and translucent when first laid, becoming opaque before hatching. Immature mites molt three times before becoming adults; under ideal conditions, a generation can be completed in 7 days.

As a result of their small size and habit of feeding on the underside of foliage, this species may go undetected until a population has caused serious damage to a tree. Light infestations result in yellow or brown spots between leaf veins. Clusters of dried, brown leaves and profuse webbing indicate a heavy infestation, which if compounded by water stress, could result in leaf and fruit drop.

The twospotted spider mite is an occasional pest on citrus, particularly in the San Joaquin Valley. Its damage potential varies from year to year and is related to water stress and heat. Monitor for twospotted spider mite year round and spray with the most selective miticide to preserve natural enemies.

A number of predators provide substantial control of twospotted spider mites. These include the sixspotted thrips, Scolothrips sexmaculatus, the spider mite destroyer, Stethorus picipes, minute pirate bugs, Orius spp., and the beneficial mite, Euseius tularensis.

Adequate irrigation will reduce the damage from spider mite feeding.

Use cultural and biological controls and certain petroleum oil sprays (such as PureSpray Green NR 440) on organically managed citrus.

Miticides available for controlling twospotted spider mite in bearing orchards include abamectin (Agri-Mek, etc.), acequinocyl (Kanemite), fenbutatin oxide (Vendex), fenpyroximate (Fujimite), hexythiazox (Onager), oil, pyridaben (Nexter), and spirodiclofen (Envidor); in nonbearing orchards, bifenazate (Acramite) can be used.

Of these miticides, some are more selective than others. Acequinocyl, bifenazate, fenbutatin oxide, and oil cause the least harm to natural enemies, including predatory mites, but they also provide a shorter period of control of pest mites. Etoxazole, hexythiazox, pyridaben, and spirodiclofen are of intermediate selectivity because they harm both pest mites and predatory mites for up to 6 weeks but cause minimal harm to beneficial insects such as lacewings, lady beetles, and Aphytis melinus, which help control caterpillars, scale, thrips, and other pests.

In the San Joaquin Valley, check for twospotted mites when you monitor citrus red mite in late winter and early spring. Continue monitoring twospotted mite occasionally during summer and more closely in late summer and fall. Look for yellow-brown spots on foliage, particularly in the last growth flush, indicating feeding by twospotted spider mites. High numbers of mites in summer and fall may require miticide applications, but thresholds have not been established.

• Photos of twospotted spider mite