Assessing the quality of different ant species as partners of a myrmecophilous butterfly

We assessed the quality of different ant species as partners of the faculta tively myrmecophilous lycaenid butterfly Glaucopsyche lygdamus. We compared disappearance and parasitism rates of G. lygdamus larvae in the field, and development of non-feeding pre-pupae in the laboratory, when individuals w ere untended or tended by one of four ant species. Formica podzolica was th e only ant species to provide a clear benefit to G. lygdamus, in the form o f reduced larval parasitism relative to untended larvae. F. 'neogagates' (F . neogagates + F. lasioides) and Tapinoma sessile were essentially neutral partners, providing no significant cost or benefit for any of the parameter s measured. Relative to untended individuals, association with F. obscuripe s significantly increased larval disappearance and significantly decreased pupal mass. Thus, F. obscuripes may act as a parasite of the general associ ation between G. lygdamus and ants under certain conditions. Ant species al so differed in their persistence as tenders of G. lygdamus larvae once an i nteraction was established. Over the lifetime of a larva, F. podzolica and F. obscuripes usually remained as the attendant ant species on plants over consecutive census dates, while F. 'neogagates' and T. sessile were frequen tly replaced, most commonly by F. obscuripes. It remains to be determined i f disappearance and developmental outcomes reported here reflect true fitne ss costs (i.e. reduced survivorship and lower reproductive success) for G. lygdamus. The potential and limitations for specialization in association b etween G. lygdamus and high quality ant partners are discussed.