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

Abstract

Three species within the Entomophthora muscae (Cohn) Fresenius complex (Entomophthora schizophorae Keller & Wilding, E. muscae s.str., and E. muscae "group B") were investigated for resting spore formation in vivo in the house fly (Musca domestica L.). Resting spores of E. muscae group B were experimentally induced from August to the beginning of February, while no resting spores were ever observed in E. schizophorae infected M. domestica or in flies infected by E. muscae s.str. originating from M. domestica. When newly dead fly cadavers containing E. muscae group B resting spores were kept moist, cystidia emerged from the abdomen; this is the first report of cystidia in the genus Entomophthora. Resting spore production was significantly affected by both temperature and E. muscae group B strain. More infected flies formed resting spores when kept 1 week at 10°C compared with constant exposure at 22°C, but the tendency of the different E. muscae group 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°C with a 16 h light : 8 h dark photoperiod within 1 week, but no germ conidia were observed.

The genus Entomophthora: bringing the insect destroyers into the twenty-first century

“…In temperate regions where the host insect disappears during the winter season, resting spores are considered to be the overwintering stage of the fungus. That resting spores are seasonally or ecologically driven is also supported by resting spores never having been observed in E. muscae isolates from house flies caught in artificially-heated cowstables in Denmark (Thomsen et al 2001 ). Although fly populations oscillate inside farm buildings, a few house flies are always present so it is thought that E. muscae can slowly spread via conidia from host-to-host during winter.…”

“…fly hosts that overwinter in clusters in heated attics (Eilenberg et al 2013 ). In contrast, E. muscae isolated from cabbage flies ( Delia radicum ) in Denmark are more prone to form resting spores (Thomsen and Eilenberg 2000 ; Thomsen et al 2001 ). Resting spores have also been observed in vitro (Eilenberg et al 1990 ), but exact clues to what triggers their formation is not clear.…”

“…Since many fungi in the genus Entomophthora have multinucleate cells throughout their life-cycle, including the protoplast stage, hyphal bodies, mycelium, conidia and resting spores, it further complicates unambiguous observations of nuclei fusion and resulting reduction in number of nuclei. Fusion of two nuclei has been observed in Conidiobolus thromboides ( McCabe et al 1984 ) , whereas 3–6 nuclei were observed in E. muscae resting spores from in vitro cultures (Thomsen et al 2001 ). Although not strictly binucleate, this shows a reduction in the number of nuclei in resting spores potentially indicating nuclear fusion.…”

Resting spore formation of aphid‐pathogenic fungus Pandora nouryi depends on the concentration of infective inoculum

“…In previous studies, possible effects of environmental factors on the resting spore formation of fungal pathogens were often concerned but photoperiod and relative humidity were rarely found to be influential. Factors recognized to affect resting spore formation in vivo vary with host-pathogen interactions, including fungal isolates and temperature for Z. radicans on aphids (Glare et al, 1989), host age for Entomophaga maimaga on gypsy moth (Hajek and Shimazu, 1996), and temperature and host origin of isolates for Entomophthora muscae on house fly (Thomsen et al, 2001). For P. nouryi, more isolates with different host and geographic origins are needed in the future studies to demonstrate what biotic or abiotic factors may affect its resting spore formation.…”

A Third Way for Entomophthoralean Fungi to Survive the Winter: Slow Disease Transmission between Individuals of the Hibernating Host

“…Another member of the E. muscae complex, Entomophthora schizophorae, is peculiar in that resting spores produced in vivo are not known [ 2 , 8 , 13 ] despite that the fungus infects dipterans living indoors (e.g., it infects M. domestica [ 14 , 15 ] and outdoors in temperate conditions [ 2 , 16 ]. For example, in a two-year study of this fungus in carrot flies, Chamaepsila rosae , [ 16 ] a high prevalence of E. schizophorae was documented but solely in the conidial stage.…”