Kearney Agricultural Research and Extension Center
University of California
Kearney Agricultural Research and Extension Center

Western flower thrips

Western flower thrip
Western flower thrip
Western flower thrips (Frankliniella occidentalis) are minute insects, about 0.03 inch long, with two pairs of fringed wings. The adult has three color forms that vary in abundance depending on the time of year. There is a pale form that is white and yellow, except for slight brown spots or blemishes on the top of the abdomen; an intermediate color form with an orange thorax and brown abdomen; and a dark form that is dark brown. The intermediate form is present throughout the year, but in spring the dark form predominates while the pale form is most abundant at other times throughout the year.

First instar nymphs are opaque or light yellow, turning to golden yellow after the first molt. The nymphal stage lasts from 5 to 20 days.

Western flower thrips overwinter as adults in weeds, grasses, alfalfa, and other hosts, either in the orchard floor or nearby. In early spring, if overwintering sites are disturbed or dry up, thrips migrate to flowering trees and plants and deposit eggs in the tender portions of the host plant, e.g. shoots, buds, and flower parts. The peak infestation is usually reached in May or June.

(Description from UC Pest Management Guidelines)

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