In the wetland form the eggs are mostly laid on Gentiana asclepiadea (e.g. northern foreland of the Alps) and Gentiana pneumonanthe. The eggs are deposited on both flower buds and leaves. The young caterpillars live in the ovary and from autumn in ant nests (Myrmica ruginodis, M. scabrinodis).
The young larva of the dry habitat form mostly feeds in the ovaries of Gentiana cruciata. Later the caterpillars live usually in the nests of the ant Myrmica schencki.
Rarely also other gentians are used for oviposition (e.g. Gentianella germanica), provided they are in a suitable stage.
Maculinea alcon mainly inhabits fens with gentian occurrence. The dry habitat form occurs in juniper grasslands, pastures and other dry grassland formations usually on limestone.
Maculinea alcon flies from late June to early August in a single generation in most high density. So I know it from a last site near Memmingen (Germany) in a small fen rest with less than 100 plants of Gentiana asclepiadea where several dozen butterflies can be found (yet!).
Endangerment: strongly endangered
Maculinea alcon is heavily endangered through the destruction of unprofitable wetlands and dry grasslands by fertilization, grazing cattle, too early mowing (habitats should be mowed not until early October!), drainage, afforestation, succession and general eutrophication.
The former species complex rebeli/alcon is according to recent research considered as belonging to one species Maculinea alcon. Obviously the taxon rebeli does not refer to the former populations thought belonging there (e.g. Swabian Alb, SW-Alps), but to a special form occurring in the eastern Alps in higher altitudes without Gentiana cruciata (see species portrait Maculinea rebeli).
Maculinea alcon ist distributed from Northern Spain across central and Eastern Europe to Central Asia. To the southeast it extends to Northern Greece (e.g. Mount Phalakro). But there further research is needed (compare Maculinea rebeli).