Hirsutella thompsonii, a fungal pathogen of mites. I. Biology of the fungus in vitro

Hirsutella thompsonii, a moniliaceous fungus pathogenic to mites, grew and sporulated on sterilised wheat bran. The effects of environmental factors were studied on the fungus grown on potato‐dextrose‐agar (PDA). The fungus was mesothermophilic. Growth, sporulation and conidial germination were best at 25^o‐30 ^oC. Conidia kept at 37 ^oC for 5 days on PDA died, but those held at 5 ^oC germinated upon a subsequent removal to 25 ^oC. Almost all conidial germ tubes survived an 8 h exposure to 3–5% r.h. and to 60% r.h., but subsequently the former grew poorly at 100% r.h. H. thompsonii sporulated equally well in continuous darkness or light, and produced typical chlorinous to light olive‐green mycelium and conidia under all conditions. A 2 h exposure of naked mycelium and conidia (which have melanised walls) to u.v. irradiation failed to kill the fungus.