Laboulbeniales on beetles: host utilization patterns and species richness of the parasites
Fungi of the order Laboulbeniales are obligate ectoparasites that are easy to detect on the integument of their arthropod hosts. This apparency, and other characteristics that suit them for the role of ‘model’ group in the exploration of parasite biodiversity patterns, are discussed. Salient features of the general biology of these organisms are summarized and past patterns of species description reviewed. In recent years, much as in the fungi as a whole, roughly equal proportions of new species have been described from tropical and temperate regions. Comparison of the known Laboulbeniales mycobiotas of Europe, Asia and ‘tropical Asia’ reveals that most of the more significant parasite genera are more or less equally well represented in each region. Patterns of host utilization are also largely similar, with more than 50% of host species recorded from each region belonging to the two beetle families Carabidae and Staphylinidae. However, there are indications that parasite species that are not confined to a single host species have significantly broader geographical ranges than any of their hosts. The pattern of host utilization in the relatively fully-inventoried assemblage of beetles of a tropical forest in North Sulawesi is described, in terms of the taxonomic group membership, habitat affiliation and feeding biology of recorded hosts. On the basis of the Sulawesi dataset and other available data on host exploitation patterns at various spatial scales, we suggest that between 2 and 5%, i.e. between ca 40000 and ca 100000 of an estimated 2 million extant beetle species, are hosts of one or more species of Laboulbeniales. Known and predicted levels of host specificity imply that a global figure for Laboulbeniales species exploiting Coleoptera is likely to be between 10000 and 50000 species. A smaller number of Laboulbeniales species, probably no more than half the number associated with beetles, are to be found on other arthropod hosts. Ways in which these estimates might be refined are discussed.