In summer 1989 investigations were made, concerning flower-visiting beneficial insects on different flowering plants situated in a wheat field. During the investigations it became evident, that Centaurea cyanus shows a wide spectrum of visiting beneficial insects, attracted by extrafloral nectaries. Whereas most syrphids were found on the flowers of Centaurea cyanus, another group of visitors consisting of Formicidae, Chrysopidae, Coccinellidae, Vespidae and Ichneumonidae were observed on the extrafloral nectaries. A refractometric analysis of the sugar solution in extrafloral nectaries of Centaurea cyanus showed a concentration of 71% to 76%. Centaurea cyanus proved to be an important food source for many beneficial insects. Especially the extrafloral nectaries attract groups of insects, normally not observed on visiting flowering plants. Therefore the occurrence of Centaurea cyanus offers good possibilities to stabilize population density of beneficial insects in agricultural ecosystems.