Thrips (Thysanoptera)

- Tiny, feather-winged plant-feeding insects -

Summary: Thrips are tiny insects, most feed on leaves but some species are predators. Thrips feeding causes very distinctive silvery patches on injured leafs. Thrips can be important pests in greenhouses because of the feeding injury as well as for a serious plant disease they can spread. Thrips, both plant-feeding and predatory species, also occasionally bite people. The bites are harmless but annoying.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

What are thrips?

Thrips* are tiny (1-2 mm) insects with thin, feathery wings. Most thrips feed on plants but some species are predatory on other small arthopods. Thrips feeding injury often appears as sunken, silvery patches on leaf surfaces.

Plant-feeding thrips develop from eggs through several immature stages to a pupal stage then emerge as adults. Eggs are laid in leaf tissue, larvae feed on leaves and the pupal stage often occurs off the plant in soil. There are multiple generations of thrips each year so populations can build rapidly to damaging levels. The generation time from egg to egg can be as little as two weeks.

* Thrips is always plural, one thrips or many thrips. Common misspelling: thrip

western flower thrips

western flower thrips (highly magnified) with wings folded along the back; the large green tube-like structure is a leaf vein

Vectors of plant disease

Some plant-feeding thrips transmit an important plant virus (in the same way that mosquitoes can transmit certain human diseases while feeding on us). The virus in this case is called tomato spotted wilt virus (TSWV) or impatiens necrotic spot virus and it is lethal to a wide range of ornamental and garden plants. Commercial growers, therefore, often have zero tolerance for thrips in their greenhouses if the TSWV virus is present in the greenhouse.

Tiny slivers that bite!

Many people complain about tiny slivers that bite during summer months that can often be traced to thrips. Even plant-feeding thips can bite resulting in a mild but annoying pinch. These bites are not dangerous in any way and thrips do not normally occur indoors.

Use row covers & screen vents in greenhouses

Row covers (see article below) can be used to protect individual plants and trays of seedlings from thrips, spider mites and aphids. Place row covers loosely and use a lightweight material. Since thrips usually enter greenhouses through open vents, commercial greenhouse growers now use fine mesh screens over vent openings. Screening vents, however, will slow air flow so additional vent area may be needed.

Use yellow/blue sticky traps to monitor thrips activity

Some greenhouse growers prefer blue sticky traps for monitoring thrips activity but studies have shown that blue traps are only slightly more effective than the standard yellow sticky traps and the yellow traps are much easier to find. Use a minimum of 1-2 traps per 1000 square feet of greenhouse. Check traps every 2 or 3 days. Traps will capture winged aphids, fungus gnats, thrips and whiteflies.

Use insecticidal soap

Insecticidal soap as low toxicity control (see article below) is a very effective and low toxicity treatment for larval and adult thrips. Apply soap sprays whenever sticky traps capture adult thrips. Complete coverage is key to success. Apply soap 3 times at 3-4 day interval in order to control all stages. Since thrips pupate in the soil there will always be a portion of the population that is not susceptible to these leaf sprays.

Using Row Covers to Protect Greenhouse Plants

Using Insecticidal Soap for Aphids and Spider Mites

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