The effect of woodlots, natural areas and agricultural land in the landscape on a generalist herbivore insect species in cropland was investigated. The abundance of onion thrips (Thrips tabaci) was compared in leek (Allium porrum) fields in 43 agricultural landscape plots of different sizes in The Netherlands. The total area of woodlots, other natural and agricultural areas within a radius of 1000 and 5000 m around each field was measured using a geographic information system (GIS) framework, LGN3plus. Numbers of onion thrips were significantly lower in leek fields in agricultural landscapes with a larger total area of woodlots. The results suggest that woodlots decrease density of onion thrips and their symptoms in leek fields. Possible mechanisms are discussed.