Thrips

Orius + Amblyseius swirskii systems.

Thrips damage flowers and foliage. Swirskii + Orius provide season-long suppression...

About Thrips

Thrips are small, fast-moving pests that feed by rasping and sucking plant tissue. In UK horticulture the main species of concern are the western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci). These pests cause silvery scarring, distorted growth and can transmit plant viruses such as TSV and INSV, making early detection and biological control essential.

Symptoms of Thrips Damage

• Silvery scarring on leaves, flowers or fruits
• Small black faecal spots (“tar spots”)
• Distorted growth and flecking on young tissue
• Flower deformation and poor fruit set
• Presence of tiny, slender insects when tapping foliage

Why Biological Control Works

Thrips have vulnerable larval stages that spend time on the plant surface or drop to the compost, making them ideal targets for predators and soil-dwelling beneficials. Two of the most effective agents are Orius laevigatus, a robust predatory bug that feeds on all thrips stages including adults, and Amblyseius swirskii or Amblyseius cucumeris, which target first-instar larvae.

Common UK Thrips Species

• Frankliniella occidentalis — Western flower thrips (WFT)
• Thrips tabaci — Onion thrips
• Chaetanaphothrips signipennis — Banana thrips (occasionally encountered)

IPM Recommendations

• Introduce Amblyseius predators early, before thrips adults establish
• Use Orius for control of adults and to clean up flower hotspots
• Place blue sticky traps to monitor incoming thrips pressure
• Improve hygiene and remove old flowers where larvae hide
• Mist lightly or raise humidity to disrupt thrips development
• Maintain a preventative population of predators through the whole season

Preventative vs Curative Strategy

Preventative: Slow-release sachets of Amblyseius cucumeris or Amblyseius swirskii should be placed early in the crop, especially in propagation and young plants.

Curative: When adult thrips are abundant or when flower damage is visible, introduce Orius laevigatus for fast knockdown. Orius is particularly valuable in summer crops where thrips pressure spikes.

Environmental Notes

• Amblyseius cucumeris performs well in cooler UK conditions
• Amblyseius swirskii excels in warm summer crops and heated glass
• Orius requires higher light levels to thrive—early introductions help
• Low humidity and high temperatures accelerate thrips reproduction