Formation and germination of resting spores from different strains from the Entomophthora muscae complex produced in Musca domestica

Three species within the Entomophthora muscae (Cohn) Fresenius complex (Ent omophthora schizophorae Keller & Wilding, E. muscae s.str., and E. muscae " group B") were investigated for resting spore formation in vivo in the hous e fly (Musca domestica L.). Resting spores of E. muscae group B were experi mentally induced from August to the beginning of February, while no resting spores were ever observed in E. schizophorae infected M. domestica or in f lies infected by E. muscae s.str. originating from M. domestica. When newly dead fly cadavers containing E. muscae group B resting spores were kept mo ist, cystidia emerged from the abdomen; this is the first report of cystidi a in the genus Entomophthora. Resting spore production was significantly af fected by both temperature and E. muscae group B strain. More infected flie s formed resting spores when kept 1 week at 10 degreesC compared with const ant exposure at 22 degreesC, but the tendency of the different E. muscae gr oup B strains to form resting spores persisted with shifting temperatures. After 4 months of incubation under natural winter conditions in Denmark, E. muscae group B resting spores germinated on water agar at 20 degreesC with a 16 h light : 8 h dark photoperiod within 1 week, but no germ conidia wer e observed.