The initially phytophagous caterpillars of Maculinea alcon and M. rebeli complete their development in Myrmica ant colonies as social parasites. Recent genetic studies show no differences at the species level among various populations of each butterfly taxa. Usually M. alcon and M. rebeli are identified by habitat and larval food plants (Gentianaceae) and host ant specificity is also considered to be an important feature. However most of the ecological characteristics overlap at least in some parts of their distributions. The developmental and survival characteristics of caterpillars reared by different Myrmica species were compared in laboratory experiments and in the field. Morphologically indistinguishable M. alcon and M. rebeli, which originated from Polish populations, are very similar in terms of host specificity i.e. larvae survived both with M. scabrinodis and M. sabuleti. However they showed different growth characteristics. The earlier flight period of M. rebeli, which is synchronized with the phenology of Gentiana cruciata, resulted from the quick growth of caterpillars in Myrmica nests in the pre-winter phase, when they gained about half of their final body biomass. After the end of winter they recommenced growth almost immediately. M. alcon larvae entered diapause shortly after adoption by ants and began to increase in weight significantly just one month after the onset of spring, which synchronized their development with that of their larval food plant, G. pneumonanthe. Therefore neither population group is transferable between habitats and should still be regarded, at least, as distinct conservational units.
Host-ant specificity of Maculinea alcon, an endangered obligatory myrmecophilous lycaenid butterfly, was studied at two sites in southern Poland (Świętokrzyskie Mts near Kielce). M. alcon larvae and pupae were found in nests of both Myrmica vandeli and M. scabrinodis, which is the typical host in Poland and Southern Europe. To our knowledge this is the first record of M. vandeli as a host of M. alcon. Our results show that M. scabrinodis and M. vandeli are about equally suitable as hosts. We hypothesize that both host ant species are closely related and have similar chemical profiles, and that the M. alcon "scabrinodis-vandeli" populations we studied belong to the M. alcon "scabrinodis" race. More than half of the M. alcon pupae, both from M. vandeli and M. scabrinodis nests, were parasitized by a single wasp species of the genus Ichneumon, which also suggests that the cuticular chemistry of the two ant species is similar.