They are 1 mm long, very slender insects with two pairs of transparent, sword-shaped wings with a fringe of bristles that rest alongside the body when not in use. They are yellow in colour with brown feeler tips. Typical characteristics are the type of bristles on the pronotum, the first abdominal segment, the wings and antenna with seven segments.
Thrips are good jumpers and can also fly when fleeing from predators. The use air currents to let themselves be carried over longer distances. Their tiny, flexible bodies enable them to get into all kinds of natural spaces in plants (calyx split, flowers etc.). Their mandibles consist of short stylets that are pushed out from their conical mouthpart and pierce the plant’s surface. This enables the thrips to feed on plant cells located at the surface, as well as pollen. They prefer younger tissue, most likely because it is softer and, thus, easier to pierce.
They suck out single cells of their host and, unlike aphids, do not produce honeydew, but only leave brown or green excretion droplets, which then dry. Females have an ovipositor on their abdomen, which is used to pierce the plant tissue and deposit eggs. The eggs are translucent and are almost invisible inside the plant tissue. Occasionally, the plant reacts by developing cork in the cells that have been pierced, which is easy to spot. Thrips larvae have a similar body shape to adults, but do not have wings and their antennae are coiled. They have two mobile larvae forms, one immobile pronymph stage and one pupal stage in the soil. Thrips palmi produces several generations per year.
Leaves that are affected develop silver-grey spots where air can get inside the sucked out cells. Sometimes cork develops where young plant parts have been sucked out or eggs have been deposited. Excretion droplets can be found around feeding spots. The damage shown in the images was caused by a different thrips species, but looks exactly the same.
The European Union is considered free from Thrips palmi. However, this quarantine pest has spread over parts of Asia and Central America.
Despite its name, Thrips palmi has nothing to with palm trees, but affects a variety of plants in the gourd family, nightshade family, Papilionaceae, orchids, sunflower family and others.
Thrips barely cause damage individually, however, mass infestation may cause problems – especially because this species has a tendency to develop pesticide resistance. There is concern that this pest could spread uncontrolledly in greenhouses if imported.
Thrips palmi could cause up to 90 % crop failure in vegetable cultures, both through sucking damage and also through the transfer of a number of dangerous tospoviruses.