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In a nutshell:
Found mainly on the lower parts of plants; major pest of peppers and many ornamentals; plant cell feeders—causes silvery patches on leaves and fruit; live exclusively on leaves; often present on weeds.
What are Impatiens thrips?
The impatiens thrips (Echinothrips americanus) is native to eastern North America and is becoming a big problem in greenhouse cultivation. Unlike many other thrips, this species completes its entire life cycle on the plant leaves. Infestations usually begin on a few plants and then spread. In greenhouses, the first thrips appear near entrances, along walkways or in warm places near walls. An infestation of impatiens thrips begins low on the plant, and the adults don’t fly well. As a result, they don’t often get caught on sticky traps, so finding them requires careful inspection. Infestations usually aren’t noticed until they're serious.
What kinds of plants do they attack?
Impatiens thrips attack a wide variety of plants, but they’re a major pest of peppers and many ornamental plants—roses, gerbera and potted plants in particular.
What do they look like?
This species of thrips is relatively large, with adult females measuring about 1.6 mm long and males about 1.3 mm. Both males and females are dark brown to black with orange between their body segments. They have dark wings that are white at the base. Their distinct colouration makes it impossible to confuse this species with other pest thrips.
The female deposits her eggs into the leaf tissue. The eggs are kidney shaped and white or yellow in colour.
Larvae begin to feed immediately after hatching and are a translucent white or yellow colour, as are the pre-pupal and pupal stages. Pupation also occurs on the leaf and pupae are immobile and only move if disturbed.
How do I know if my plants are under attack?
Adults and larvae feed by piercing the leaf cells and sucking out their contents. This damage leads to silvery patches on the surface of the leaf.
Serious infestations can cause leaves to shrivel completely and fall off and cause fruit to develop silver patches as well. In peppers, the older growth at the bottom of the plant becomes discoloured.
Adult thrips prefer to feed along the veins on the underside of leaves, but they can also be found on the upper surface. They stay close along the veins and don’t move much, unless disturbed. Large populations will spread over the entire leaf.