WESTERN FLOWER THRIPS (THYSANOPTERA, THRIPIDAE) IN GREENHOUSES - POPULATION-DYNAMICS, DISTRIBUTION ON PLANTS, AND ASSOCIATIONS WITH PREDATORS

Studies were conducted in commercial greenhouses to examine seasonal population dynamics of western flower thrips, Frankliniella occidentalis (Pergande) on two crops: bell peppers, Capsicum annuum (L.) and long English cucumbers, Cucumis sativus (L.). Yellow sticky traps were used to monitor density and sex ratio of the dispersing adult population. Leaf and flower samples were taken to determine the spatial distribution of adults and larvae, and to investigate the relationship between trap catch and density of F. occidentalis on the plants. Trap catch peaked at different times during the growing season in each greenhouse. As trap catch increased, numbers of F. occidentalis adults and immatures on flowers and leaves also increased. On both crops, the majority (84-95%) of adults in flowers were females. Greater than 85% of larvae were found on leaves. Adult male F. occidentalis were rarely found on plants, even when traps were catching high numbers. Female F. occidentalis were always found in flowers before they were found on leaves and were found on sticky traps only when the thrips population started to increase. Used together, sticky traps and flower monitoring allow quick detection of potential "hot spots" of thrips activity. Control measures can be applied immediately on a local rather than grand scale. Introductions of the predatory mite Amblyseius cucumeris (Oudemans) did not control the thrips population in most of the greenhouses monitored. However, the minute pirate bug, Orius tristicolor (White), shows promise for future use as an effective biological control agent in commercial vegetable greenhouses.