4 Important Facts About Thrips

How To Identify Thrips In Greenhouses

The first time I saw thrips they were pointed out to me by my state agricultural inspector. He used a hand lens to show me thin, tiny, winged insects on the underside of flowering impatiens plants. He suggested bi-weekly scouting using blue or yellow sticky traps. The inspector would take a flowering plant and tap it over a sheet of plain white paper. Then they were easier to see. Thrips are a major greenhouse and grow room pest. They cause substantial economic damage as a vector of various plant viruses. Thrips are often overlooked because of their small size. They are about 1/20th inch long and pale orange to yellow colored. Adult thrips have two sets of fringed wings. Immature larvae lack wings. There are more than 7000 species of the insect order Thysanoptera. Many varieties do not feed on plants.

The Life Cycle of Thrips

The five-stage lifecycle of thrips can take up to 30 days to complete. However, it is quicker by up to 2 weeks when the temperature is higher. Adult females lay their eggs on or into the plant tissue. Most early growth in the two larval stages is on the underside of leaf surfaces. The 2 non-feeding stages are prepupae and pupae and usually happen in the soil or leaf litter but may also happen on buds and flowers. Upon reaching the adult stage they start feeding voraciously.

Thrips Damage

Western Flower Thrips (Frankliniella occidentalis) is the main species that cause damage to greenhouse crops. It is also the hardest to control. Damage is caused not only by feeding but also as a vector of Tomato Spotted Wilt Virus (TSWV) and Necrotic Spot Virus (NSV). Western Flower Thrips (WFT) and TSWV are found worldwide and cause major economic losses on ornamental and vegetable crops. Once a plant is infected with TSWV there is no cure. The symptoms of a TSWV infected plant are varied. Often leaves turn bronze and develop many small, dark spots. Leaves will have a wilted appearance. Plant growth is often stunted and leaves may drop prematurely.

Thrips Control

Thrips are a difficult pest to control. Mechanical control is a good place to start. Screening ventilation fans will help. A good scouting program is a must. Integrated Pest Management (IPM) using predatory insects such as green lacewings can help. Low-risk pesticides like neem oil and spinosad based insecticides applied with an Ultra Low Volume fogger (ULV) are very effective.