Contribution towards the study of the specificity of Laboulbeniales (fungi, ascomycetes), with particular reference to the transmission, habitat preference and host-range of Laboulbenia slackensis

The contribution tests the hypothesis of the host-physiology regulated specificity of Laboulbeniales. Field data and gradient analysis are used to determine whether host and parasite habitat preferences are different. The impact of habitat factors on parasite prevalence, growth and development suggest an impact of environmental factors on specificity. Experiments were carried out with Laboulbenia slackensis (Ascomycetes, Laboulbeniales), an ectoparasitic univorous fungus of Pogonus chalceus (Coleoptera, Carabidae). Relative growth of Laboulbenia slackensis populations was significantly affected by environmental conditions, i.e., the soil composition, temperature, salinity, under which the typical host was reared. Transmission of the fungus was fully analysed and its impact on specificity and specialization discussed. Optimal conditions for the development of the fungus were determined and corresponded with the optimal habitat selected by the typical host, i.e., pure saltmarsh clay. Artificial infections with L. slackensis showed that the fungus was potentially plurivorous on Carabidae and that its specificity did not fully account on the host physiology or integumental characteristics. L. slackensis and other congeneric representatives were successfully transferred to a large number of atypical carabid host species. Successful establishment of L. slackensis on an atypical host significantly depended on environmental conditions, i.e., the soil composition, under which the atypical host was reared. The host was essential, but not alone sufficient, for the establishment of the fungus. It was postulated that the specificity of L. slackensis, observed in nature, depended both on its host specificity and its environmental preferences. A new hypothesis for host specificity of Laboulbeniales is formulated and suggestions for further research are given. A fully illustrated Flora of the Laboulbeniales of Belgium is given as well as keys, descriptions and critical comments.