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

Abstract

Caterpillars of the Alcon blue butterfly Phengaris alcon are initially endophytic and feed inside the flowerheads of Gentiana plants, but complete their development as social parasites in the nests of Myrmica ants, where they are fed by workers. Its specific and complicated ecological requirements make P. alcon a very local, threatened species, sensitive to environmental changes. We investigated an isolated and previously unknown population in an area of high nature value—the Białowieża Forest (NE Poland). Using the mark–release–recapture method we estimated the seasonal number of adults at 1460 individuals, and their density (850/ha) was the highest among all populations using G. pneumonanthe studied so far. The site is also unique due to the presence of the specific parasitoid Ichneumon cf. eumerus, and parasitoids are considered the ultimate indicators of the biodiversity of Phengaris systems. Since 75.5% of P. alcon pupae were infested we could estimate the seasonal population of adult wasps at about 4500 individuals. The high abundance of both P. alcon and its parasitoid may be explained by favorable habitat characteristics, i.e., the strong presence of host plants and the high density of nests of Myrmica scabrinodis, which is the only local host ant of the butterfly.

Spatial and Temporal Patterns of Genetic Diversity and Structure in Danish Populations of the Alcon Blue Butterfly Phengaris alcon (Denis & Schiffermüller)

“…Comparing our data with that from Belgium and the Netherlands [43] shows that Danish populations have about the same effective number of alleles as Belgian and Dutch populations, but the heterozygosity of Danish populations is lower than of Dutch populations (Figure S3). Although comparing genetic diversity between studies using different genetic markers is problematic [74,75], this fits in with other population genetic studies on P. alcon across Europe, where populations more central in the distribution range have higher genetic diversity and more peripheral and isolated populations have lower diversity [31,34,44,76]. This pattern is common for many butterfly species [77], including others in the family Lycaenidae [78,79], although it is not so clear in some other Phengaris species, such as P. arion and P. teleius, where effective population sizes in each generation are smaller [49,76,80,81].…”

“…Low genetic diversity and small effective population sizes seem to be common in P. alcon in Denmark [40][41][42] and elsewhere in Europe [29,43], but see [44] for a very different situation in eastern Poland. At the same time, the small populations are often poorly connected, leading to strong genetic differentiation between them.…”