A slender insect under 2 mm that feeds inside flowers, buds and shoot tips, leaving silvery scars flecked with black specks, streaked petals and distorted growth. It also spreads tomato spotted wilt and impatiens necrotic spot viruses, which can kill young plants.
Adult Frankliniella occidentalis among the stamens of an open flower. Photo: pending.
Adults are under 2 mm, slender, with two pairs of narrow fringed wings folded along the back. Colour varies widely — light, yellow with a dark band, or dark brown — and UC IPM notes that dark forms dominate outdoors in winter and spring, pale forms in summer and autumn, and all year in heated greenhouses with supplemental light. Larvae are wingless, white at first, then yellow to orange.
It hides in flowers, unopened buds, shoot tips and folded tissue, so you usually see the damage before the insect. Shake or tap flowers over white paper; thrips run rather than hop. What that tells you has limits: thrips can be named to species reliably only by an expert with a microscope, and many thrips in flowers are harmless pollen feeders — so thrips in the blooms are not, on their own, proof of this species or of a problem.
Thrips puncture surface cells and suck them empty, so the damage is scarring rather than wilting. Because they feed inside buds and on unexpanded tissue, injury often shows only as the tissue grows, and by then the thrips may have moved on (UC IPM). Spider mites and some true bugs stipple leaves too; webbing points to mites, black varnish-like specks to thrips.
Eggs go inside plant tissue, the larvae feed alongside the adults, and the prepupa and pupa drop into the soil or compost — so much of the population is where sprays do not reach. UC IPM gives about 11 days from egg to adult at 25–31 °C and 44 days at 10–16 °C. A UK study estimated at most three to five outdoor generations a year in the West Midlands, and the RHS notes that thrips in glasshouses may go on breeding all year.
UF/IFAS records hosts in 65 plant families, and UC IPM notes it feeds on pollen in the flowers of virtually any broadleaved plant; thrips that feed this widely move into gardens as nearby weeds and grassland dry out in spring and summer. Being listed as a host does not always mean the thrips can breed on that plant. Each crop hub below carries the seasonal calendar and starter beneficial program for that setting.
UC IPM's greenhouse figure, for western flower and greenhouse thrips counted together on sticky cards; most effective insecticides need two applications 5–7 days apart. In gardens UC says thrips damage does not usually warrant insecticides, and large trap catches do not necessarily mean control is needed.
Blue sticky cards catch the most western flower thrips; UC IPM still recommends yellow for greenhouses because they also catch other pests and are easier to count on. Hang cards vertically with the lower third below the top of the canopy and raise them as the crop grows — UC suggests at least one card per 10,000 sq ft (about 930 m²) in crops other than roses. Cards show trends, not damage, so tap flowers over white paper as well. The RHS suggests blue cards under glass and indoors, but not outdoors, where they trap too many other insects.
Every thrips predator works on stages you cannot see, so releases go in early, before damage shows. Amblyseius cucumeris and A. swirskii eat young larvae, not adults; sources disagree on the best temperature for cucumeris (Koppert 15–25 °C, UConn 75–85 °F, Cornell 25–35 °C) and it needs humidity above about 65–70%, while swirskii needs warmth — Koppert says it is not effective below 18 °C. Orius bugs are the key natural enemy in UF/IFAS work on pepper. Stratiolaelaps works underneath, on pupae in the compost. UC IPM is blunt about gardens: there is little research on releases there, and bought predators are unlikely to give satisfactory control.
Exclusion and hygiene do most of the work under glass, because thrips arrive on plants and through vents and then hide from sprays. Outdoors, UC IPM says damage rarely justifies spraying, and that row covers are the most effective way to keep thrips-borne viruses off young plants.
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
UC IPM Pest Notes: Thrips, UC ANR Pub. 7429 (Bethke, Dreistadt & Varela; updated 05/2014)
UC IPM Floriculture & Nurseries Guidelines, Pub. 3392: Thrips (updated 01/2022)
UC IPM, Relative Toxicities of Pesticides Used in Floriculture to Natural Enemies (updated 01/2022)
UF/IFAS EDIS ENY-883: Western Flower Thrips (Cluever, Smith, Funderburk & Frantz, 2015)
McDonald, Bale & Walters 1998, Eur. J. Entomol. 95: 301–306 (development and temperature)
RHS Advice: Thrips; Indoor plants: sap feeders (accessed Sept 2026)
Koppert: Thripex, Swirski-Mite, Thripor-L and Entomite-M product pages (accessed Sept 2026)
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.