Wednesday, December 3, 2008

Inviting Thrips Indoors

As the cooler weather approaches, we will begin to move our potted plants indoors. One insect that may go undetected are western flower thrips. These insects are very tiny (almost microscopic) but can be a nuisance since their mouthparts are able to penetrate into human skin, causing a prickly sensation.

Female thrips lay eggs inside plant leaf tissue, using a serrated ovipositor to cut through the plant tissue. This allows the eggs and larvae to be well protected from insecticides and natural enemies. The immature thrips will feed on the plant tissue until it falls to the ground to pupate. Thrips undergo a prepupal and pupal stage before becoming an adult.
Thrips have rasping-sucking mouthparts that allow them to cut open epidermal cells to release the cell contents that are then ingested. This causes the cells to collapse due to absence of its contents. Their feeding also causes discoloration and deformities of leaves and petals.
As thrips feed, they inject salvia into the plant tissue which allows viruses to be transmitted, such as Tomato Spot Wilt Virus and Impatiens Necrotic Spot Virus.

Some Control Options:

Cultural Control Tactics:

1) Dispose of weeds, trash or debris to reduce the thrips population, since these areas may serve as overwintering sites for thrips.
2) Avoid planting thrips susceptible plants in areas close to wheat or rye fields. Wheat and rye are both good overwintering sites for some thrips species that can move over to feed on landscape plants.
3) Discard infested plant materials to avoid infesting other plants.

Biological Control Tactics:

Some natural enemies of thrips include the adult minute pirate bug (Orius sp.), which attacks both immature and adult thrips; Neoseiulus spp. predatory mites, which attacks the first instar thrips and the soil-dwelling predacious mite, Hypoaspsis spp., which attacks the prepupal and pupal stages of thrips in the soil. Also Beauveria bassiana, a fungus, is sold in biopesticide products and is effective at controlling thrips.

Some Chemical Control Tactics:

Some chemical control options include products containing abamectin,, chlorfenapyr, chlorpyrifos, dimethoate, fenoxycarb, methiocarb, novaluron, pyridalyl, and spinosad applied as foliar sprays or systemic products containing such chemicals as imidacloprid or acephate.

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