The western flower thrips (Frankliniella occidentalis) is currently the most damaging thrips species in many greenhouse crops. The western flower thrips (Frankliniella occidentalis) can be found on a wide variety of plants, including many vegetable and ornamental crops in greenhouses, and on various weeds. It is an especially significant pest in cucumber, sweet pepper, eggplants, and many ornamental crops.
Life cycle and appearance of Western flower thrips
The western flower thrips (Frankliniella occidentalis) develops in six stages: egg, two larval instars, prepupa, pupa, and finally the adult insect. The eggs of the western flower thrips (Frankliniella occidentalis) are laid in leaves, flower petals and in the soft parts of stalks. They are inserted into the plant tissue with a saw-like ovipositor.
Larvae are nearly transparent white or yellowish to orange-yellow, with a large head and bright red eyes. Adult females are very variable in colour. They range from almost white through yellowish orange to almost black.
Western flower thrips (Frankliniella occidentalis) usually pupate in the ground, although pupae can also be found on leaves, in flowers or in other sheltered places. The prepupal and pupal instars can be recognized by their developing wing buds. Compared to the prepupa, the pupa has longer, more developed wing buds and longer antennae that are curved back over the head. The prepupal and pupal instars do not feed and only move if disturbed. In the adults both pairs of wings are fully developed.
Thrips cause damage to plants by piercing the cells of the surface tissues and sucking out their contents, causing the surrounding tissue to die. The resulting silver-grey patches on leaves and the black dots of their excreta indicate their presence in the crop. The vigour of the plant is reduced by loss of chlorophyll. When infestations become serious the leaves themselves can shrivel.
Western flower thrips (Frankliniella occidentalis) prefer to feed on developing plant tissues such as growing tips and flower buds. When these tissues develop further, the leaves and flowers can appear grossly deformed. Severely infested flower buds may not open at all. Fruits can also be damaged, even at low densities, giving rise to deformities such as the “pig-tail” fruit sometimes found in cucumber crops. In many ornamental crops, even very low numbers of thrips can cause damage by transmitting viruses, or by reducing aesthetic value by damaging flowers, e.g. in roses
The western flower thrips (Frankliniella occidentalis) is the most important vector for both tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV). Both viruses affect a wide range of plants, and often a single host plant may be infected by both viruses.