none During 1997-1999, occurrence of hymenopteran parasitoids of cereal aphids was observed in different localities in Slovakia. Altogether, seven species of aphid parasitoids were recorded. The total numbers of particular species over the last three years were as follows: Aphidius uzbekistanicus (160 individuals - 42.4%), Aphidius ervi (83 individuals - 22.0%), Aphidius rhopalosiphi (66 individuals - 17.5%), Ephedrus plagiator (40 individuals - 10.6%), Praon volucre (26 individuals - 6.9%), P. gallicum (1 individual - 0.3%), and Aphidius picipes (1 individual - 0.2%). The abundance of the parasitoids in each year was: 185 individuals (49.1%) in 1999, 122 individuals (32.4%) in 1998, and 70 individuals (18.6%) in 1997. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Palaearctic region; Eurasia; Europe Aphidiidae; Braconidae; Hemipteran hosts; Aphidoidea; Prevalence; Slovakia; Prevalence in hemipteran hosts, winter wheat crops Aphidoidea; Hymenopteran parasites; Aphidiidae & Braconidae; Prevalence; Slovakia; Hymenopteran parasite prevalence, winter wheat crops