Common Name: Spider mite
Scientific Name: Tetranynchus urticae Koch
Description: Adult mites are small, 1/32 inch (0.4 mm) or less. Body is globular, yellowish to greenish and is often marked with darker spots on the back. The body has eight legs. The mites spin protective webs of silk over infested plant surfaces.
There are many other spider mites common in Texas, the southern red mite, Oligonychus ilicus (McGregor) is similar to the twospotted spider mite. Another important plant feeding mite group is the false spider mites (Tenuipalpidae).
Life Cycle: Outdoors, twospotted spider mites may overwinter as adults or continue to breed on host plants in mild winters or indoors. Adults lay clear to yellowish spherical eggs, often suspended in a fine web of silk on the undersides of host plant leaves. Spotless, clear greenish to brownish six legged nymphal stages hatch from eggs and develop into 8 legged nymphs as they molt two more times. Adult male and female mites mate soon after emerging from the last nymphal stage. Generation from egg to adult occurs in 5 to 20 days, depending upon temperature. Many generations can occur per year. When heavily infested host plants decline, the mites spin silk threads and use these strands to passively “fly” or “balloon” in wind to disperse.
Habitat, Food Source(s), Damage: Mouthparts (chelicerae) appear as tiny microscopic toothpick-like structures with which they can pierce plant cells. Mites pierce clusters of surface (epidermal) cells and use their other mouthparts (palpi) to suck out the contents (mesophyll). Damaged clusters of cells appear as yellow (chlorotic) yellow and later, bronzish (necrotic) stipples on the leaves. On light to moderately infested leaves, stipples are concentrated around the leave’s midrib and larger veins. Leaves on more heavily injured plants can become yellowed, bronze and fall off.
Pests of many (over 180) agronomic and horticultural crops including soybeans, cotton, small grains, vegetables and ornamental plants. They also thrive on some weed species (chickweed, pokeweed, wild mustard) and blackberries. All stages occur primarily on the undersides of leaves.
Pest Status: Plant feeder, causes stippling or bronzing of leaves.
Literature: Carter et al. 1982; Drees 1994.