Taxonomy of the Acarine Parasite Hirsutella Thompsonii

SUMMARY

Cultural features and morphology of 11 isolates of the hyphomycete Hirsutella thompsonii, an important pathogen of various eriophyoid mites, are described and illustrated. Three morphologically distinct groups of H. thompsonii were distinguished and accordingly three varieties are proposed: H. thompsonii var. thompsonii, var. vinacea and var. synnematosa. The variety vinacea is characterized by vinaceous colonies and a different host, Acalitus vaccinii. The strains accommodated in the var. synnematosa were isolated from Eriophyes spp. and related genera. In fresh culture they produce cream-colored cylindrical synnemata, bearing two kinds of phialides: (1) single phialides with solitary conidia and (2) densely crowded phialides with catenulate conidia. In all three varieties two different conidiogenous structures are formed: (1) solitary often proliferating phialides producing one or more globose, verrucose conidia and (2) polyblastic conidiogenous cells with smooth-walled, subglobose to ellipsoidal conidia. Although H. thompsonii differs in some morphological characters from other species in the genus, its maintenance in Hirsutella is proposed.