Issue 3, May 7, 2012

Eastern Flower Thrips

Large numbers of eastern flower thrips, Frankliniella tritici, are present in central Illinois. This insect primarily overwinters in the southern U.S. and typically migrates into Illinois in the spring. They are major pests of greenhouses and outdoor flowers. These thrips cause severe distortion of the berries of strawberry. They are attracted to yellow, blue, and white sticky traps, so greenhouse growers should monitor their traps for an influx of thrips through the vents. Thrips is both singular and plural, as is sheep and shrimp.

Eastern flower thrips are small, very slender, tan insects. Adults are about three mm long, less than one-eighth inch with dark, feather-like wings; nymphs are smaller and yellowish. Thrips have rasping-sucking mouthparts. When they feed, they scrape away the surface cells of leaves and flower petals, then suck up the cell contents. Damage appears as whitish streaks which turn brownish as the injured cells die. They also feed on pollen in the flower anthers, breaking up the pollen packets, resulting in pollen that is easily seen scattered on the petals.

Thrips hide in tight locations such as at the bases of leaves and petals and in leaf and flower buds. Pulling back the leaves or petals disturbs the thrips, causing them to crawl upward on the leaves or petals where they are easily seen, despite their small size.

Thrips on mum.

Thrips damage on azalea.

Thrips probe anything while searching for food. When numerous, they will fly onto people and probe them to determine whether they are edible. These bites are easily felt, but are not particularly painful. However, they are at least distractive and at most upsetting when numerous bites are occurring. High numbers of thrips are typically localized and can be avoided if the job at hand allows moving to a different location away from the thrips.

Minute pirate bugs, also known as insidious plant bugs, feed on thrips and are associated with the high thrips influx that is currently being seen. Minute pirate bugs are also small, being about one-eighth inch long. They are black and white, somewhat triangular in shape, and flat on the back. They will also bite people, but these predators have more substantial piercing mouthparts. Their bites feel like a small pinch, being much more noticeable than a thrips bite.

Pirate bug adults.

Thrips secretive nature makes them more difficult to control. Although some insecticides labeled for thrips are systemic, control can be difficult to achieve. Control is improved by removing the leaf and flower buds before spraying as well as thorough application to leaf axils using higher pressure. Outdoors, remove blossoms before spraying to reduce impact to pollinators.

Effective insecticides include spinosad (Conserve), abamectin (Avid), novaluron (Pedestal), bifenthrin (Talstar), tau-fluvalinate (Mavrik), pyrethrins (Pyreth-lt), azadirachtin (Azatin), acephate (Orthene), and chlorpyrifos (DuraGard). Two applications are typically necessary seven to ten days apart to provide control. In extended control situations, rotate between insecticide chemistries to avoid insecticide resistance. In that case, do not rotate between the pyrethroids, bifenthrin, tau-fluvalinate, and pyrethrins, or the organophosphates, acephate and chlorpyrifos. (Phil Nixon)

Phil Nixon

Return to table of contents