THRIPS are straw-colored, elongated insects. Adults have narrow, fringed wings, and nymphs are wingless. They can move rapidly and prefer to shelter in crevices and folds in foliage and flowers. Thrips damage plants by feeding on leaf and flower tissue, leaving a silvery appearance. They also lay eggs in leaves and flower tissue and in young developing fruit (such as cucumbers). This damages leaves and flower petals and causes distortions in fruit and in the growing points. On tomatoes, thrips feeding causes “ghost rings” on the fruit. Western flower thrips can also transmit Tomato Spotted Wilt Virus, which is lethal to tomatoes and some ornamentals. Western flower thrips (Frankliniella occidentalis) is found in both vegetable and ornamental crops; onion thrips (Thrips tabaci) is usually a problem only in vegetable crops.
LIFE CYCLE: Both species of thrips have similar life cycles. The overall life cycle of Western flower thrips takes 21 days at 72°F (22°C). Females lay eggs in leaf tissue. Each female lays 6-10 eggs per day over her life span of 4-5 weeks. The eggs hatch in five days at 72°F (22°C). The nymphs feed on plant tissue for 8-10 days, then drop to the ground to complete development in protected sites on the floor. Thrips have an immobile stage, similar to a pupal stage (called a pseudo-pupa), which takes 7-10 days. When adults emerge they fly to upper parts of plants and begin laying eggs after a day or two.
CONTROL: Sound Horticulture offers several different options for biological control of thrips. You can use A. cucumeris (see Cucumeris) along with other thrips predators such as Orius insidiosis (see Orius) on flowering plants and Stratiolaelaps scimitus (formerly called Hypoaspis miles) to control thrips pupae in the growth media (see Stratiolaelaps). Read about the thrips predators listed below, and talk to Sound Horticulture about a thrips control strategy that works for you.