There are 7,400 species of thrips in the world and quite a few are serious pests of plants. Some of the more commonly known thrips are Greenhouse thrip (Heliothrips haemorrhoidalis_), Western Flower Thrips (Frankliniella occidentalis_) and Plague thrips (Thrips imaginis). Thrips are 0.5mm – 15 mm long and range in colour from white to yellow to black. Thrips generally have wings that are fringed but this can only be seen with magnification. Thrips attack the flowers, fruit and foliage of a variety of plants. Roses, fruit trees, azaleas, gladioli and a variety of vegetables such as tomatoes, onions and beans all suffer from thrip attacks. Thrips lay eggs inside plant tissue and the pupae feed on plant juices. Thrips also lay eggs in unopened buds making it difficult to control the insect. Thrips also spread plant viruses; for example tomato thrips and western flower thrips spread the tomato spotted wilt virus.
Thrips scrape the surface of the leaves and petals, and suck the sap, leaving a white mottled appearance on leaves. Other symptoms are browning on petals and fruit, and flower drop. If left unchecked the leaves, new shoots and flowers will become deformed and stunted. Wilting and browning can also occur.