Western Flower Thrips
- Many field crops, such as alfalfa and cotton
- Many weeds
Thrips are a group of tiny, elongated, and fringe-winged insects that are commonly found in flowers of most plants. Many feed on plant tissues as well as pollen. They feed by a “punch and suck” method, whereby they push their mouth cone into plant tissue or pollen, and then suck the contents through their straw-like stylets. A few species of thrips are now worldwide pests, and one of these is the western flower thrips (Frankliniella occidentalis). In this region, western flower thrips damages not only apples but also many horticultural and field crops, such as tomatoes and cotton. Even though western flower thrips can transmit plant viruses to some crops, apples are not affected.
Adult western flower thrips can be distinguished from other insects by their fringed wings, their tubular body shape and color. Females are about 1/25 of an inch long and have many color forms. These vary from pale yellow thorax and abdomen to yellow thorax and dark abdomen to very dark color throughout their body. In higher elevations, females are black. Wings are fringed on the margins and are clear to yellow in color. Males are smaller than females (about 2/3 the female length) and are light yellow throughout their body. Wings are clear and yellow like those of the female.
Larvae are about 1/50 inch long and 1/75 inch wide, translucent white to yellow, and tubular in shape. They can be mistaken for leafhopper and Campylomma nymphs, which are about the same size and color. However, thrips larvae are more elongated and worm-like.
- Oviposition scars that can enlarge into extended halos or "pansy spots" with a central spot of russet on apples.
- White net-like blemishes and silvering on nectarine fruits
- Deformed strawberry fruits
- Thrips scarring on plum and grape fruits
- formetanate hydrochloride (Carzol) - minimize bee hazard by spraying before bees are placed in the orchard; apply late evening or at night if fruit trees are blooming
- spinosad (Success, EntrustO)H
OOrganic (OMRI-approved) products available.
HHomeowner products available.
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There are a number of predators and parasites that attack western flower thrip. One naturally occurring predator is the minute pirate bug (Orius spp.), a small black and white-colored bug with piercing-sucking mouthparts, that can kill thrips larvae and adults. Immature Orius nymphs, that are orange-colored and have a pungent odor, are also effective predators. Banded wing thrips are also good predators. As the name suggests the wings of these thrips have dark and light bands, and can be easily distinguished from the western flower thrips. Predaceous mites can be purchased and released to kill thrips. However, these will attack only larval thrips and therefore are not effective for preventing the damage caused by the ovipositing female. Only those biological controls that target the adult female have any chance of reducing damage, and they must respond quickly when adult female thrips first move into the blossoms.