FLOWER THRIPS

Steven Frank, Extension Entomologist

General Information

Female flower thrips are yellowish-brown to amber with an orange thorax and barely visible to the eye (1/16 inch). Males are slightly smaller and paler than females. The most notable character are the fringe or feather-like wings.

The flower thrips' delicate egg is inserted completely into the plant tissue. The egg is cylindrical and kidney-shaped, with a smooth pale or yellow surface. Immature thrips are yellow and resemble adults except for lack of wings. Prepupae are pale and have wing buds and antennae which are to the side or front of the head. Pupae are also pale and have longer wing buds and antennae which bend back over the head.

Biology

Flower thrips have been collected from 29 plant orders including various berries, cotton, day lilies, field crops, forage crops, grass flowers, legumes, peonies, privet, rose, trees, truck crops, and vines. They seem to prefer grasses and yellow or pale blossoms. Roses are most susceptible in June.

Flower thrips feed by piercing the leaf or petal surface and drawing sap>from injured cells. Only the epidermis and relatively few mesophyll cells are affected. On ornamental plants, this damage is restricted to the flowers. For example, rose blossoms turn brown and buds open only partially. The petals, distorted with brown edges, seem to stick together.

First described in 1855 in New York, flower thrips are one of the most numerous insect pests of ornamental crops. During warm periods, swarms of these tiny orange insects often fly in late afternoon. Thrips bite people, causing a minor, but noticeable stinging sensation. Their large numbers account for considerable and rapid damage to flowers, especially those with pale petals. Yet thrips contribute to pollination of some crops, an unexpected benefit!

Flower thrips are generally found at the base of the flower petals. They reproduce throughout the year in North Carolina, with the majority of their 12 to 15 generations occurring in the warmer months. Newly emerged females begin to lay eggs within 1 to 4 days in summer and within 10 to 35 days in winter, reproduction being much faster in warmer weather. In summer, it takes about 11 days to reach the adult stage. Flower thrips pass through egg, 2 larval, prepupal, pupal and adult stages. The eggs are inserted into flower or leaf tissue, and the prepupal and pupal stages are spent in the soil. During summer, flower thrips may live 26 days, though overwintering thrips may live all winter. Flower thrips can overwinter as far north as North Dakota in grass clumps and other sheltered refuges.

The past few years we have seen a lot of damage by flower thrips on knockout roses in nurseries. They have proven a formidable enemy and the best control will come with early identification of the problem. Flower thrips are smaller than western flower thrips and can be beaten from plants into a tray or onto a clipboard. They cause characteristic deformation and discoloration of foliage on roses and other plants.

Control

Control of flower thrips is difficult because of constant migration from weeds, grass, flowers and trees. Shortly after elimination, new thrips often migrate back onto plants. On roses, old blossoms should be destroyed and applications of pesticides made at close intervals, especially in late May and June.  Control, mow or reduce weeds and/or grasses in the vicinity all season long. Monitor population with yellow sticky cards.

For a key to thrips identification see: http://ipm.ncsu.edu/AG136/thrips.html

The following pesticides give adequate control of flower thrips on a short-term basis.

Active ingredient	Trade name	Thrips stage affected	Signal word	IRAC MOA group	Compatible with beneficials
abamectin	Avid	L, A	Caution	6	Yes
*acephate	Orthene	L, A	Caution	1B	No
acetamiprid	TriStar	L, A	Caution	4A	Yes
*azadirachtin	Azatin	L	Caution	18B	Yes
*bifenthrin	Talstar	L, A	Caution	3	No
cyfluthrin	Decathlon	L, A	Caution	3	No
fenpropathrin	Tame	L, A	Caution	3	No
*horticultural oil	many	L, A	Warning	-	Yes
kinoprene	Enstar II	L	Warning	7A	Yes
novaluron	Pedestal	L	Caution	15	Yes
*spinosad	Conserve	L, A	Caution	5	Yes

* Suitable for home use or some consumer products available with identical active ingredient.

Other Resources

• Back to Insect Notes
• Horticulture Information Leaflets(HILs)
• Plant Disease Notes
• North Carolina Agricultural Chemicals Manual
• North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Web page last reviewed January, 2011 by the webperson.