Impact of western flower thrips (Thysanoptera: Thripidae) on growth, photosynthesis and productivity of greenhouse sweet pepper

Low, medium and high densities of western flower thrips [Frankliniella occidentalis (Pergande)] were established in three greenhouses, in 1994 and 1995, to investigate the effects of thrips on growth, photosynthesis and productivity of greenhouse sweet pepper. Sweet pepper fruit was very susceptible to cosmetic injury which resulted in a reduction of the commercial grade of the fruit (quality). Damage by western flower thrips (WFT) on the fruit was direct and instant. Short periods of high thrips densities resulted in cosmetic damage to the fruit. The major period for fruit damage occurred in the 3rd to 5th weeks before harvest, when the fruit was growing rapidly. Approximately seven thrips per sticky trap per day from weeks #3 to #5 before fruit harvest will result in fruit being downgraded from commercial grade #1 to #2. Impact of WFT on plant growth, photosynthesis and marketable yield was indirect and cumulative. Leaf photosynthesis was reduced when plants were exposed to more than 1200 accumulated larval-days per plant and marketable yield was reduced when exposed to more than 1800 accumulated larval-days per plant. Plants recovered slowly from the thrips damage once yield loss had been detected. Therefore, thrips abundance should be maintained below 1200 larval-days per plant to prevent the negative impact of WFT on plant physiology and yield. The importance of these findings on pest management programs for WFT is discussed. (C) 1998 Elsevier Science B.V.