Some species of thrips can cause a mottling on foliage and flowers of a wide range of garden and glasshouse plants.

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Western flower thrips (Frankliniella occidentalis) on Primula obconica

Quick facts

Scientific name: Insect order Thysanoptera
Plants affected: A wide range of plants can be affected
Main symptom: Mottled foliage and flowers
Most active: April-September

What are thrips?

Thrips (also known as thunder flies) are an order of insects, the Thysanoptera.  Around 150 species are found in Britain. Whilst many feed by sucking sap from leaves and flowers many do not cause noticeable damage to host plants.  A few species can however cause mottling to some garden plants.

Thrips vary in colour but otherwise show little obvious diversity in their appearance. The adult insects are narrow bodied and up to 2mm in length. They have two pairs of strap-like wings, which are fringed with hairs, and these are folded back over the dorsal surface of the thrips when it is at rest. The immature (nymph) stages are wingless, generally creamy yellow and paler than the yellowish-brown or blackish-brown adults. There are several species of thrips that can cause damage in glasshouses and gardens.

Thrips can be hard to detect, shaking foliage over a white sheet of paper or similar can reveal the thrips which can then be examined, ideally with a magnifying lens.


Leaves fed upon by thrips often become dull green and later develop a silvery-white discolouration on the upper surface. The discoloured areas are usually marked by many tiny black excrement spots.

When thrips feed on developing tissues at the shoot tip or in flower buds they are can cause distorted growth. Flower petals are marked by a white flecking where the pigments have been lost and heavy feeding damage may prevent flower buds from opening.

Some thrips, such as onion thrips and western flower thrips, can transmit plant viruses.

The problem

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