Freiland~kologische Untersuchungen an der Gastameise Formicoxenus nitidulus (Nylander, 1846) unter besonderer Berücksichtigung der Nesttemperatur (Hymenoptera: Formicidae)

Ölzant, S.

Abstract: Ecological field investigations of the guest ant Formicoxenus nitidulus (Nylander, 1846), with emphasis on nest temperature (Hymenoptera: Formicidae). - Formicoxenus nitidulus lives as a xenobiont with the mound-building wood ants Formica polyctena, F. rufa, F. pratensis, F. truncorum, F. lugubris, F. paralugubris, F. aquilonia and F. exsecta. Their distribution ranges from Norway to Greece and from the Scottish Hebrides to Eastern Sibiria. It has been hypothesised that F. nitidulus selects wood ant mounds with higher and more balanced nesttemperatures. However, F. nitidulus does not take advantage of all potential host-nests. This leads to the question which criteria must be fulfilled in order to make the survival of F. nitidulus possible. Moreover, it has been stated that the presence of F. nitidulus indicates a good physical condition of its host population and can therefore be used as an indicator of good health of an wood ant population. The results presented in this study support this hypothesis to a large extend. It could be shown that F. nitidulus prefers larger and more evenly built host nests. Additionally, these nests show a higher mean temperature throughout each month than those which are not inhabited by F. nitidulus. In contrast, the results did not confirm that Formica-nests without F. nitidulus are in a bad physical condition. However, if an inhabited Formica nest is abandoned by the F. nitidulus colony, then it can be assumed that either changing environmental conditions or a weakened host population are responsible for a deterioration inside the nest. The exodus of the guest ant could therefore be a first indication for the beginning of a deterioration of the host ant's living condition. This study also shows that nest temperatures alone are not responsible for the absence of F. nitidulus. Also nest material of Formica-nests has been found to be crucial. All nests without a F. nitidulus colony, were composed of significantly coarser nest material. It is concluded that in addition to nest temperature, the material from which nests are constructed is a significant factor for the occurence of F. nitidulus in a host nest.

Myrmecologische Nachrichten 4: 1-10; printable