In dryland cereals in NE Spain, the harvester ant, Messor barbarus L., is responsible for a high percentage of seed removal. A direct density dependent response of seed predators to seed patches may help regulate weed populations. In this study, we investigated if seed removal rate by harvester ants is influenced by weed seed density. For this reason, 60 circular areas of 1 m 2 were created inside four 50*50 m blocks after cereal harvest Lolium multiflorum L. seeds were applied at 1000, 2000, 5000, 10000 or 20000 seeds/m 2, in ten randomly selected areas each; the remaining 10 were used to test the methodology used to retrieve the seeds. After 24h, the remaining seeds were collected using vacuum cleaners or a D-vac and seed removal rates were estimated. In three of the four blocks, seed removal was extremely high (99-100%), and the response was therefore density independent Here, nests densities ranged from 468 to 900 nests/ha. In the fourth block seed removal was 91%, and here nest density was lower (284 nests/ha).
