Western flower thrips

Western flower thrips (Frankliniella occidentalis) is a remarkably polyphagous species with 244 plant species from 62 families being recorded as hosts. In the USA, the pest is found outdoors attacking the flowers of apricots, peaches and nectarines, plums, roses, carnations, sweet peas, Gladiolus, peas, tomatoes, Capsicum, Cucurbits and strawberries. Other hosts in the USA include: Beta, carrots, cotton, grapefruits, grapes, onions, Phaseolus, Purshia tridentata, safflower. In Europe it is generally found only on glasshouse crops on an ever-increasing range of host plants, but most commonly on chrysanthemums, Gerbera, roses and Saintpaulia.

Symptoms
The major symptoms of F. occidentalis infestation include a discoloration of the upper leaf surface, and indentation where damage occurs. The pattern of damage is coarser than damage by Thrips tabaci. Silvering, deformity, growth malfunction and brown bumps may also be present on the foliage of ornamental plants. 'Halo spotting', another symptom of thrips damage, consists of small dark scars surrounded by whitish tissue. On some host plants, e.g. Capsicum, oviposition causes a reaction of the surrounding plant tissue.

Thrips feeding causes discoloration and scarring of open blooms and petals. It also results in deformation of buds if the feeding occurs before they start opening. Thrips damage can be distinguished from spider-mite damage by the appearance of liquid faecal deposits which cause dark-green speckling, whereas spider mites produce black granules.

Eggs laid in petal tissue causes a 'pimpling' effect in flowers such as orchids.

Chemical
Chemical control is particularly difficult because of the secretive habit of the species and because of the appearance of resistance.

Non-chemical
Introduction of the pest into glasshouses in Europe has severely interfered with the routine practice of integrated pest control. Control treatments must be supplemented by hygiene measures within glasshouses. Biological agents such as Amblyseius barkeri and Neoseiulus cucumeris have also been used.