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Thrips (Thysanoptera)
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Tiny, feather-winged insects -
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Summary:
Thrips are tiny insects, most feed on leaves
but some species are predators. Leaf-feeding
causes very distinctive silvery patches on the
injured leaf. 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.)
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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
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western
flower thrips (highly magnified) with
wings folded along the back; the large green
tube-like structure is a leaf vein
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Vectors of plant disease
Some plant-feeding thrips
transmit an important plant virus. The virus,
called tomato spotted wilt virus or impatiens
necrotic spot virus, 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 virus is present.
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.
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Use row covers &
screen vents
Row covers (see Related
Articles 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
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 (see Insect & Spider
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.
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Use insecticidal soap
Insecticidal soap
(see Related Articles 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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Mission: To
provide accurate, up-to-date and unbiased information
for solving common insect and mite problems around
your home, business and landscape using least-toxic
methods.
Jack DeAngelis,
Ph.D.
Please see the Disclaimer statements as
well.
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