THRIPS

General Description

Thrips are very small, elongate, cylindrical, gregarious insects ranging from 1/25 to 1/8 inch in length. The nymph are frequently pale yellow and highly active. The antennae and legs are relatively short. Adults are usually black or yellow-brown, but may have red, black or white markings and often jump when disturbed. They may have wings or may be wingless. If wings are present, they are long, narrow and fringed with hairs. For this reason, thrips are commonly referred to as fringed-winged insects.

Important Species

There are 264 species of thrips in the U.S. and Canada that feed on plants. Many other species are predaceous. The most common plant-feeding thrips on woody plants in Florida are:
banded greenhouse thripsHercinothrips femoralis
Cuban laurel thripsGynaikothrips ficorum
flower thripsFrankliniella tritici
greenhouse thripsHeliothrips haemorrhoidalis
redbanded thripsSelenothrips rubrocinctus

Biology

Thrips undergo gradual metamorphosis. A general thrips life cycle is as follows. Female thrips deposit eggs in slits made in the leaf tissue by their sharp ovipositors. Each female lays 25 to 50 eggs which hatch (in two to seven days) into active nymphs. Immature thrips resemble adults, but the immatures lack wings and are lightly colored. These two nymphal stages are followed by two resting stages: the prepupa and pupa. The resting stages can be found either on the host or in the soil below the host. Under favorable conditions, the developmental period from egg to adult ranges from 11 days to three weeks depending on the species, hence, a population may increase quite rapidly. Parthenogenesis occurs in many species. When male thrips are present, they are usually smaller than the females.

Host Plants

Thrips attack an extremely wide variety of woody plants including azalea, ardisia, dogwood, gardenia, hibiscus, magnolia, maple, palm and viburnum.

Seasonal Abundance

Thrips occur throughout the growing season.

Damage

Thrips feed on the foliage and flowers, as well as young tissues in shoot apexes where the leaves are expanding. They puncture the plant cells with their rasping-sucking mouthparts and withdraw cell sap. Feeding activities produce bleached, silvered or deformed leaves and necrotic spots or blotches on flower petals. Eventually the damaged foliage becomes papery, wilts and drops prematurely. Thrips produce large quantities of a varnish-like excrement which collects on leaves, creating an unsightly appearance.

Sampling

To aid in detecting thrips, place a sheet of white typing paper beneath the leaves or flowers and shake the plant. The thrips will fall onto the paper and can be more easily observed and identified than when on the plant. Also look for the small spots of varnish-like excrement on the leaves. If plants are flowering, be sure to inspect the flower parts for thrips presence.

Since thrips are so small, use a 10 to 15-power magnifying glass. Blue-colored sticky traps have been developed for monitoring thrips and are available commercially. They appear to be somewhat more effective than yellow traps.

Biological Control

The predatory mites, Neoseiulus mackanziei and Amblyseius cucumeris look promising for thrips control. They also prey on spider mites if sufficient thrips are not present. Green lacewing larvae, damsel bugs and pirate bugs are also predators of thrips as well as many other pests of plants.

Cultural Control

The use of blue or yellow sticky traps give an indication of the current pest population level and enables better timing of an insecticide application. Since thrips may come in large flights over an extended period of time, insecticides which give good initial results but have a short residual effect are generally inadequate for control of thrips infestations. Systemics are highly effective and provide long-term control. Select insecticides that have the least effect upon other non-target orgamisms.

Chemical Control

For the most current insecticide recommendations to control these pests, please contact the local county office of the Cooperative Extension Service. If you have access to the World Wide Web you can consult the University of Florida's Insect Management Guide at:

http://edis.ifas.ufl.edu/TOPIC_GUIDE_Insect_Management_Guide

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