WESTERN FLOWER THRIPS 
Female
western flower thrips are small, slender, winged insects which are amber
or yellowish-brown to dark brown in color. The wings have microscopic fringes
of setae. Females are about 1/16 long.
Males are similar to females but smaller and always light yellow. Western
flower thrips eggs are delicate, cylindrical, slightly kidney shaped, smooth
and translucent white.
First stage larvae are very tiny,
almost worm-like insects that are translucent white.
Second stage larvae are also translucent white, but are similar to the adult in size and shape. Both instars have red eyes. Prepupae are similar to second stage larvae except that the wing buds are externally visible. Pupae have longer wing buds and the antennae are folded back over the head.
In
flowers, thrips feed on pollen and on the petals. Feeding on the petals
causes pale spots and necrotic patches so that infested blossoms age prematurely.
Feeding on young foliage by this pest results in distorted growth as the
leaf tissue expands. Damaged leaves may be puckered and twisted. Feeding
on expanded tissue forms pale spots as the thrips slash the surface of
the leaf and suck out the contents of the cells beneath.
The western flower thrips is now the most damaging insect pest of greenhouse
floral crops in the United Stated. Females insert eggs into succulent host
plant tissue. Soon, tiny first stage larvae
hatch that molt into second stage larvae. These soon molt into a prepupal
stage that sometimes drops to the soil. Prepupae do not feed although they
can crawl about. In a few days, the prepupae molt into the pupal
stage and within a few more days, new adults emerge from the pupal stage.
At 86 degrees F, development takes 13 days, and the adults live about 28
days and lay an average of 44 eggs. Larvae of the western flower thrips
can become infected with tomato spotted wilt virus or impatiens necrotic
spot virus by feeding on an infected plant for only 30 minutes. After a
latent
period of 3 to 18 days, these thrips can then infect new plants after
feeding only 5 to 15 minutes. Only larvae can become infected by these
viruses, but adults do most transmission of the disease. Western flower
thrips are attracted to flowers of ornamental plants, although they breed
readily on the foliage of chrysanthemum, gloxinia, tomato, vegetables,
and grasses.
Conserve® seems to be the most effective chemical registered for western flower thrips. Avid® also has good activity and Orthene®, sumithrin, and Thiodan® sprays reportedly gave good control. Pedestal is labeled for thrips in the greenhouse. Some flower growers report adding sugar at 1 pound per 100 gallons of spray mixture enhances thrips control. Our demonstrations have not corroborated the effectiveness of sugar in drawing the thrips out of deep crevices to areas of higher pesticide concentration. If sugar is used, the highly refined table sugar will not damage plants at 1 pound per 100 gallons whereas brown sugar may cause some damage. When treating for thrips, it is better to use normal rates and treat more often than to use heavy rates and treat less often. In order to impede the onset of resistance to insecticides, it is recommended that growers use a variety of insecticides rather than using only one pesticides time after time. The latest and more complete set of pesticide choices can be found in the North Carolina Agricultural Chemicals Manual under "thrips". Unfortunately, control of the western flower thrips is likely to be difficult and costly in the foreseeable future.
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.
Interesting Links:
WFT
Biocontrol in Greenhouses
OHP's
Information note on WFT management in Greenhouses
Published by 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.
© 2001 NC Cooperative Extension Service
Web page last reviewed January, 2008 by the webperson