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Western Flower Thrips (WFT) - Frankliniella occidentalis Pergande   Jack T. Reed, Mississippi State
University, Helen Atthowe Missoula County Extension
www.ipmimages.org
 HOSTS: Many kinds of
flowers and vegetable crops.
DESCRIPTION: Adults
are tiny (1/8 inch), winged and pale yellow-brown in color. Nymphs are
whitish, 1/8 inch and resemble elongated aphids. The distinguishing
signs of thrips are tiny black dots (frass) associated with leaf
damage. Leaves have white flecks that look like the chlorophyll has
been sucked out. LIFE
CYCLE: It is
unclear whether WFT are able to overwinter outdoors in Montana.
Researchers in Southern Ontario report that WFT do not overwinter
outdoors there. However WFT reportedly overwinters outdoors in
Pennsylvania. Thrips pupate in growing media, leaf litter, and/or
flowers. Adults emerge and lay eggs in leaves or flowers. Optimum
temperatures are 80 - 85° F. At these temperatures, development
from egg to adult can take 1-2 weeks (generally it is 2-3 weeks). Larva
feed on leaves and flowers. WFT has large reproductive power; adult
females can lay between 150 - 300 eggs during their 30 - 45 day life.
WFT have been implicated in the mechanical transmission of fungal
pathogens (Fusarium and Botrytis) and virus in greenhouse crops.
Greenhouse sanitation with a summer fallow period of 4 - 5 days at
105° F. and 10% relative humidity is recommended to kill all stages
of WFT. CONTROLS:Mechanical: Use yellow or blue sticky traps to monitor thrips populations. Biological: In indoor, greenhouse, or very high humidity outdoor situations, Beauveria bassiana (BotaniGard and Naturalis-O) can be used. Beauveria is usually ineffective at relative humidities below 50% and efficacy increases with increasing humidity. In one greenhouse test, Beauveria (esp. the oil formulation) killed up to 82% of thrips on rose foliage at 79° F. and 75% relative humidity. Beauveria works more slowly than insecticides so should not be relied on if thrip populations are already high. Good foliage coverage is essential. In a California study on roses, thrips were controlled with weekly Beauveria applications. In greenhouse studies, flower thrips at low population levels were controlled by release of a phytoseiid mite, Neoseiulus cucumeris. This predaceous mite works best at 54-86° F. and 70-80% humidity. Good establishment can take one month, so mite release is required prior to thrips establishment. Botanical: Spinosad (Conserve) insecticide performed best against western flower thrips in a study on Chrysanthemum. |
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