Agricultural land management modify environments in such a way that ecosystem functions are impaired. The establishment of exotic plants, favoured by agricultural land management, may alter the foraging behaviour of native floral visitors and consequently the pollination service they provide. To determine whether agricultural land management affects the pollination service provided by floral visitors for the most abundant plant species in a Pampean grassland ecosystem, we compared the pollination service of native and exotic entomophilous plants in landscape fragments with or without current agricultural usage. Both the quantity [number of conspecific pollen grains deposited on stigmas] and quality [proportion of heterospecific pollen grains deposited on stigmas] of the pollination service was estimated for three to nine entomophilous plants in each landscape fragment. Agricultural land management reduced the quality of the pollination service due to an increase in the deposition of heterospecific pollen on stigmas.