Thrips

Thrips are minute slender bodied insects belonging to the order Thysanoptera. In our area, they are relatively small (a few millimeters), while there are some in the tropics that reach a half inch long. They have unusual wings which are basically stalks with bristles coming off them. The mouthparts are also unusual. They are arranged in a cone which protrudes downward from the ventral side of the head. There are two stylets and a single mandible which rasps or pierces plant tissues. As cells are ruptured, the liquid is “slurped” up by the insect.

Development is transitional between incomplete metamorphosis and complete metamorphosis. The last larval instar (stage) is quiescent and nonfeeding. After this stage, the thrips become an adult. Some actually form cocoons, just prior to this stage, in the soil. There are several generations per year.

Damage to plants usually appears as a silvery mottling or blotching. On monocots (i.e. gladiolas) the damage appears to be more of a streaking. On some plants, damage may appear like that of spider mites. While thought of as plant pests, there are some species that are predacious. Interestingly enough, some will bite people. Some major pest species in our are include: western flower thrips, gladiolus thrips, and onion thrips.

Controlling thrips can be somewhat difficult, particularly when they get into blossoms. Management of thrips and other insects can be found in the Pacific Northwest Control Handbook, a book which is revised annually and can be found in any WSU County Extension office.