Damage threshold for Thrips tabaci (Thysanoptera: Thripidae) in monocropped and intercropped leek

Based on field data collected during three consecutive years, in experiments with leek and leek intercropped with subterranean clover (Trifolium subterraneum), the relationship between larval populations of Thrips 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 feeding symptoms and in damage thresholds in monocropped and intercropped leeks. It was found that a given number of thrips larvae per plant caused less injury on intercropped leek plants than on monocropped leeks. This proved to have consequences for the damage thresholds in both growing systems. The total effect of intercropping in leeks is based on thrips population suppression and a reduced development of feeding symptoms.