Biology and defensive secretion of myrmecophilous Thiasophila spp. (Coleoptera: Staphylinidae: Aleocharinae) associated with the Formica rufa species group

Various aspects of the biology of the myrmecophilous Thiasophila angulata and T. szujeckii (Staphylinidae; Aleocharinae), mainly associated with the Formica rufa species group, are studied. The composition of defensive gland secretions from adults of T. angulata has been analysed. The complete development (egg-L_1-3-pupa-adult form), including adult overwintering, of both species takes place solely in ant nests. Under laboratory conditions, this lasts for about 22 days in T. angulata, and the period elapsing between the old and new generations of insects is approximately two months. The mean fecundity of adults of this species (28 eggs) was determined, as well as the duration of its reproductive period (mean 28.5 days), and lifespan (mean 67 days). In natural conditions T. angulata, found within nests of Formica polyctena and F. rufa, produces three generations, and the sibling species T. szujeckii one generation per year. These two species differ in their phenologies and abundance dynamics of adults and larvae, which is linked to the size and temperature regime of the host nest. The results of this study uphold the recent separation of T. angulata and T. szujeckii based on morphological features of adults and selected molecular markers. Adults and larvae of T. angulata forage on both live and dead food items accumulated by the host, as well as on the host’s eggs and larvae. Both the beetle larvae and adults remain unmolested among the host workers. The adults use their defensive gland secretions, which contains substantial quantities of toxic quinones, when necessary. According to the current categories of myrmecophiles, T. angulata (and by analogy, T. szujeckii as well) should be classified as a species wholly integrated with the host.