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 appare ncy, and other characteristics that suit them for the role of 'model' group in the exploration of parasite biodiversity patterns, are discus sed. Salient features of the general biology of these organisms are su mmarized and past patterns of species description reviewed. In recent years, much as in the fungi as a whole, roughly equal proportions of n ew species have been described from tropical and temperate regions. Co mparison of the known Laboulbeniales mycobiotas of Europe, Asia and 't ropical Asia' reveals that most of the more significant parasite gener a are more or less equally well represented in each region. Patterns o f host utilization are also largely similar, with more than 50 % of ho st species recorded from each region belonging to the two beetle famil ies Carabidae and Staphylinidae. However, there are indications that p arasite species that are not confined to a single host species have si gnificantly broader geographical ranges than any of their hosts. The p attern of host utilization in the relatively fully-inventoried assembl age of beetles of a tropical forest in North Sulawesi is described, in terms of the taxonomic group membership, habitat affiliation and feed ing biology of recorded hosts. On the basis of the Sulawesi dataset an d other available data on host exploitation patterns at various spatia l scales, we suggest that between 2 and 5 %, i.e. between ca 40 000 an d ca 100 000 of an estimated 2 million extant beetle species, are host s of one or more species of Laboulbeniales. Known and predicted levels of host specificity imply that a global figure for Laboulbeniales spe cies exploiting Coleoptera is likely to be between 10 000 and 50 000 s pecies. A smaller number of Laboulbeniales species, probably no more t han half the number associated with beetles, are to be found on other arthropod hosts. Ways in which these estimates might be refined are di scussed.