Efficiency of emergency conservation methods: a case study of the alcon blue butterfly (Phengaris alcon) and its specific parasitoid

Abstract

A complicated life history and specific habitat requirements make the Alcon blue butterfly Phengaris alcon a very sensitive species to land-use change. Eggs are oviposited on some Gentiana and Gentianella plants, in whose flowerheads larvae initially feed, after which they continue their development as social parasites in the nests of specific Myrmica ants, once they have been adopted by workers. One of the main threats to their existence is mowing at a time when most individuals are still on gentians. In our research, we tested an emergency conservation method on a site of the butterfly subjected to this kind of pressure in the Białowieża Forest (NE Poland). Previous studies showed that the focal population (dependent on Gentiana pneumonanthe and Myrmica scabrinodis) was characterized by an extremely high density of adults as well as of Ichneumon eumerus, i.e. the rare and specific parasitoid of P. alcon. In mid-August 2020 we performed an unplanned experiment to save caterpillars present in freshly cut plants. We selected about 1800 shoots bearing the eggs or egg shells of the butterfly. Seven hundred and fifty preadoption larvae were transported to the site and placed close to the nests of host ants located in patches without G. pneumonanthe. In the following season we observed that the P. alcon infestation rate of experimental colonies was similar to a control patch, and proportions of parasited pupae did not differ, either.Implications for conservation. Our experiment proved that such actions can be highly effective as emergency conservation methods, and possibly also in (re)introductions of P. alcon.