none Two aphidiid parasitoids: Aphidius matricariae Hal. and Lysiphlebus cardui (Marsh.) are recorded for the first time in Poland. L. cardui seems to be one of the numerous parasitoid species of Aphis fabae cirsiiacanthoidis Scop. associated with Piladelphus coronarius L. Both parasitoid species L. cardui and A. matricariae seem to play the non-important role in the natural control of the abundance of the Aphis fabae fabae Scop. in the beet agroecosystem. The competition between L. cardui and L. fabarum (Marsh.) on the black bean aphid (Aphis fabae complex) on the different host plants has been described. The specificity of above mentioned parasitoids to the A. fabae complex has been discussed. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Competition; Land and freshwater zones; Palaearctic region; Europe Aphidius matricariae; Lysiphlebus cardui (Braconidae ); Hemipteran hosts; Aphis fabae complex; Parasite prevalence & host specificity; Host specificity; Prevalence; Aphis fabae complex (Hemiptera); Poland; Bydgoszcz; Prevalence & host specificity in hemipteran hosts Lysiphlebus fabarum (Braconidae); Hemipteran hosts; Aphis fabae complex; Parasite prevalence & host specificity; Host specificity; Prevalence; Aphis fabae complex (Hemiptera); Interspecific competition; Lysiphlebus cardui; Poland Aphis fabae complex (Aphidoidea); Hymenopteran parasites; Aphidius matricariae & Lysiphlebus; Parasite prevalence & host specificity; Host specificity; Prevalence; Aphidius & Lysiphlebus (Hymenoptera) parasites; Poland; Bydgoszcz; Hymenopteran parasitoids, prevalence & host specificity