Host ant use by Phengaris (= Maculinea) alcon (Lepidoptera, Lycaenidae) in Poland

Phengaris alcon is a socially parasitic butterfly which is endangered or vulnerable in many European countries. Host-ant specificity of the butterfly was studied at nine sites throughout Poland. Except for one locality, we found P. alcon full-grown larvae and pupae exclusively in M. scabrinodis nests, which confirms that the presence of this ant species is vital for all populations to thrive. Therefore we can exclude with high probability the existence of geographical variation of the specificity of butterfly-ant interactions observed in Western Europe. The infestation rate was 32% and the mean number of P. alcon prematures was 3.4. On the site in the Polesie region we found 53 larvae in one colony, but in all other cases we observed up to 10 individuals. M. vandeli, which is known as an alternative host for the ‘scabrinodis’ race of P. alcon, was observed only in the Swietokrzyskie region and it was parasitised with a similar rate to the primary host. M. scabrinodis was also the most common ant on the site almost everywhere. Only in the Biebrza National Park was the habitat of the butterfly dominated by M. gallienii. The very rarely observed event of a nest infested simultaneously by P. alcon and P. teleius was recorded in the Upper Silesia. Our findings are important for the practical conservation of P. alcon in Poland, especially as we noted the deterioration of habitats of the butterfly on a local scale.