Mite Midges / Home and Landscape / UC Statewide IPM Program (UC IPM)

Hosts or Prey

Plant-feeding spider mites (family Tetranychidae)

Identification

Adults are delicate flies with long slender antennae and legs. At rest the wings are commonly held above the body, angled and separated and antennae are curled backwards over the body. The body is grayish, light brown, orangish, or pink. The body (excluding antennae) and wings are each 1/25 to 1/12 inch (1–2 mm) long.

Eggs are oblong to slightly curved. They are yellowish, about 1/100 inch (0.3 mm) long, and easily overlooked.

Larvae occur in colonies of spider mites. They are slow-moving, maggotlike, and 1/12 inch (2 mm) or less in length. The elongate body tapers toward the head. Young larvae are commonly yellow. Coloration of older larvae varies with their prey, and is a mix of colors that can include brown, gray, orange, red, yellow, or white.

Pupa are found on leaves or in litter or topsoil. They occur in a flattened, roundish, whitish cocoon about 1/12 inch (2 mm) in diameter.

Lookalikes

Mite midge adults resemble those of fungus gnats, Bradysia species (Sciaridae), but can be distinguished by wing venation. Bradysia species have a distinct, forked (Y-shaped) vein near the apex (tip) of each wing. Predaceous midges have a faint, forked vein in the posterior (outer) portion of wings. Both species can occur together, such as when plants are grown in containers or greenhouses where spider mites and the root-feeding larvae of fungus gnats are common.

Larvae of mite midges resemble those of various other species of Cecidomyiidae. However, Feltiella larvae are unique for having a short, hemispherical head and long antennae that are apparent under magnification.

The circular, flattened cocoon resembles that of dustywings and both predators can occur together. In comparison with dustywings, the Feltiella cocoon is smaller, one-third or less the diameter of dustywing cocoons. Mite midge cocoons occur only in colonies of mites, commonly next to a leaf vein and among the silk webbing and empty skins of killed spider mites; dustywing cocoons are somewhat oblong and can occur on bark or foliage and among various prey types in addition to mites.

Life Cycle

Mite midges develop through 4 life stages: egg, larva, pupa, and adult. After hatching, the slow-moving larvae develop through 3, increasingly larger instars. Larvae suck the body contents of prey and prefer to feed on mite eggs and nymphs. Each midge larva consumes up to several dozen mite eggs per day, or about 200 to 300 mite eggs while feeding for 1 to 2 weeks before pupating.

After adult emergence and mating, each female lays about 2 or 3 eggs per day, about 30 eggs total during a lifespan of 1 to 2 weeks. Eggs are laid singly among spider mites, commonly on the underside of leaves near or on silken webbing.

Mite midges have several generations per year. Egg to adult development time is about 2 to 5 weeks, when temperatures, respectively, are warm versus cool. Females stop laying eggs when day length is short. Overwintering is as mature larvae (prepupae) in cocoons. In climate-controlled greenhouses where plants are grown with supplemental lighting, mite midges may reproduce and feed throughout the year if mites are present.

Habitat

Feltiella larvae feed almost exclusively on spider mite eggs, immatures, and adults. More than one species of Feltiella can be found within the same mite colony. Mite midges in California occur mostly in coastal locations and greenhouses, in crops such as artichoke, avocado, citrus, and strawberry and on mite-infested garden and landscape plants.

Where humidity is relatively high, midge adults and larvae live longer, larvae consume more mites, and pupal mortality is lower. Where relative humidity is low for an extended period, mite midges can be uncommon because females' egg laying is greatly reduced and few larvae or pupae survive to maturity. Optimal conditions for Feltiella are 68° to 81°F and relative humidity greater than 60%, although larvae can tolerate a wider range of conditions.

Commercial Availability

Mite midges are commercially available and released for biological control of spider mites in commercial greenhouses and nurseries. A general recommendation is weekly releases of one midge per 10 ft sq of low-growing plants and a minimum of 4 weekly introductions in infested spots.

To increase the effectiveness of resident natural enemies and any that are released

Avoid the use of broad-spectrum and persistent insecticides and miticides (acaricides).
Control ants and dust.
Grow flowering plants that provide nectar and pollen for adults (insectary plants).

See Natural Enemy Releases for Biological Control of Crop Pests, Protecting Natural Enemies and Pollinators, and Vendors of Beneficial Organisms in North America for more information.

Species

The Cecidomyiidae tribe Lestodiplosini is comprised entirely of natural enemies. Of at least nine Feltiella species known in the world, at least Feltiella acarisuga, F. occidentalis, and F. pini occur in California. What in California was previously identified as Feltiella acarivora is now known to be F. occidentalis. Feltiella acarivora occurs from at least Australia to Japan and is commercially produced. It may have been introduced in California.

The family is commonly named gall midges because many species of Cecidomyiidae as larvae feed inside plant tissue, causing distorted foliage and shoot growth. The family includes the honeylocust pod gall midge, Monterey pine midge, and rose midge. The aphid midge, Aphidoletes aphidimyza, is an important predator of aphids.