Impatiens thrips (Echinothrips americanus) is an increasing problem in greenhouse cultivation, having spread to many countries within the last 30 years. The thrips have mostly been able to spread as a consequence of the trade in foliage plants.
Impatiens thrips (Echinothrips americanus) has a wide range of hosts. In addition to many ornamental plants it also attacks sweet pepper, cucumber and eggplants. It lives exclusively on the leaves and is often present on weeds in greenhouses.
Life cycle and appearance of Impatiens thrips
Impatiens thrips (Echinothrips americanus) develops in six stages: egg, two larval instars, prepupa, pupa, and finally the adult insect.
Impatiens thrips (Echinothrips americanus) completes its entire development from egg to adult on the plant, specifically on the leaves. Eggs are deposited in the leaf tissue, while subsequent stages are found on the upper- and undersides of the leaf. Pupation occurs on the leaf rather than on the ground. The prepupae and pupae remain immobile on the leaf tissue. Adults are found on both upper- and undersides of the leaves.
This species of thrips is relatively large. Both males and females are dark brown to black in colour with orange pigmentation between the segments, and the dark wings are white at the base. This colouration distinguishes the species from most other thrips species commonly found in greenhouses.
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.
Echinothrips americanus is often found low in the crop. In sweet pepper the damage can be seen as discolouration of older leaves at the bottom of the plant.