DAMAGE THRESHOLD FOR THRIPS TABACI (THYSANOPTERA, THRIPIDAE) IN MONOCROPPED AND INTERCROPPED LEEK

Based on field data collected during three consecutive years, in exper iments with leek and leek intercropped with subterranean clover (Trifo lium subterraneum), the relationship between larval populations of Thr ips tabaci on leeks, the level of injury and the market quality of the product were described. This resulted in a way to monitor both thrips populations and market quality during the growing season by the feedi ng symptoms and in damage thresholds in monocropped and intercropped l eeks. It was found that a given number of thrips larvae per plant caus ed less injury on intercropped leek plants than on monocropped leeks. This proved to have consequences for the damage thresholds in both gro wing systems. The total effect of intercropping in leeks is based on t hrips population suppression and a reduced development of feeding symp toms.