The investigations conducted in 1994 and 1996 concerned aphids infesting fields and neighbouring semi-natural habitats – midfield thickets with trees and the vegetation growing on the ditch margins. Aphids were caught into Moericke traps placed at the plant level. The material collected was studied to determine aphid number, dominance of individual species, similarity of dominance structure of aphid communities (Renkonen Index) and diversity of aphid communities (Shannon-Weaver Index). Aphids were collected in the field and in the natural habitats neighbouring the field. In both years black bean aphid (Aphis fabae Scop.) was either the dominant or sub-dominant species in every habitat studied. A relative species diversity of aphids occurring in semi-natural habitats was significantly highe rthan that in the adjacent field. The results of these investigations indicate that the crop affects aphid fauna flying onto neighbouring midfield thickets.