A Unique Population in a Unique Area: The Alcon Blue Butterfly and Its Specific Parasitoid in the Białowieża Forest

摘要

Caterpillars of the Alcon blue butterfly Phengaris alcon feed initially inside flowerheads of Gentiana plants but complete their development as ‘cuckoos’ in nests of Myrmica ants being fed by workers. Social parasitism protects larvae from most natural enemies and only specialized ichneumon wasps are able to infiltrate host colonies and parasitize them. Across its range P. alcon forms different ecotypes adapted to specific ants and plants. Complicated ecological requirements make the butterfly a very local and threatened species and sensitive to environmental changes. We investigated an isolated and previously unknown population in the high nature value area, i.e., the Białowieża Forest (NE Poland). Using the marking technique we estimated the seasonal number of adults at 1460 individuals and the density (850/ha) showed to be the highest among all hygrophilous populations studied so far. Premature P. alcon were found exclusively in nests of M. scabrinodis and from as many as 75.5% pupae Ichneumon cf. eumerus wasps were reared. The exceptional abundance of both P. alcon and its parasitoid (its population could be estimated at about 4500 adults) can be explained by a high density of nests host ants in vicinity of host plants. This unique system deserves special conservation care.