Economic Injury Levels for Western Flower Thrips (Thysanoptera: Thripidae) on Greenhouse Sweet Pepper

Low, medium and high densities of western flower thrips, Frenkliniella occidenialis (Pergande), were established in 3 greenhouses at the Greenhouse and Processing Crops Research Centre, Ontario, Canada, in 1994 and 1995 to develop economic injury levels for thrips on greenhouse sweet pepper. Pest densities were monitored weekly using yellow sticky traps. Fruit was harvested weekly, graded for size, weighed, and rated for thrips damage using 3 damage categories. Fruit damage was significantly related to thrips density. Economic injury levels ranged from 10 to 26 adult thrips per sticky trap per day, depending on the seasonal stage of sweet pepper production and market prices. These levels can be used as a guideline to assist growers in improving the timing of insecticide applications and for determining the upper thrips densities for effective biological control.