Economic injury levels for western flower thrips (Thysanoptera : Thripidae) on greenhouse cucumber

Low, medium and high densities of western flower thrips, Frankliniella occi dentalis (Pergande), were established in three greenhouses at the Greenhous e and Processing Crops Research Centre, Ontario, Canada in 1996 and 1998 to develop economic injury levels for thrips on greenhouse cucumber. Thrips d ensities were monitored weekly using yellow sticky traps and newer counts. Fruit was harvested twice a week, graded for size, weighed, and rated for t hrips damage using three damage categories. Significant yield reduction was detected 4 wk after severe fruit damage was observed in the high and mediu m thrips density treatments in 1996 and 7 wk in 1998. Percentage of severe damaged fruit (P-F3) has significant linear relationships with the adult th rips density (x) that was sampled by sticky traps I wk before harvest (P-F3 = -0.2533 + 0.0528x) and that was sampled by newer counts 2 wk before harv est (P-F3 = - 0.2025 + 0.5490x). Based on the regression equations, economi c injury levels, expressed as adult thrips per sticky trap per day or adult thrips per newer, were calculated for various combinations of control cost s, yield potential and fruit prices. The economic injury levels for F. occi dentalis ranged from 20 to 50 adults per sticky trap per day or 3 to 7.5 pe r newer as determined under average greenhouse production conditions in Ont ario, Canada.