Sleeping Beauties: Horizontal Transmission via Resting Spores of Species in the Entomophthoromycotina

Abstract

Many of the almost 300 species of arthropod-pathogenic fungi in the Entomophthoromycotina (Zoopagomycota) are known for being quite host-specific and are able to cause epizootics. Most species produce two main types of spores, conidia and resting spores. Here, we present a review of the epizootiology of species of Entomophthoromycotina, focusing on their resting spores, and how this stage leads to horizontal transmission and persistence. Cadavers in which resting spores are produced can often be found in different locations than cadavers of the same host producing conidia. Resting spores generally are dormant directly after production and require specific conditions for germination. Fungal reproduction resulting from infections initiated by Entomophaga maimaiga resting spores can differ from reproduction resulting from conidial infections, although we do not know how commonly this occurs. Reservoirs of resting spores can germinate for variable lengths of time, including up to several months, providing primary infections to initiate secondary cycling based on conidial infections, and not all resting spores germinate every year. Molecular methods have been developed to improve environmental quantification of resting spores, which can exist at high titers after epizootics. Ecological studies of biological communities have demonstrated that this source of these spores providing primary inoculum in the environment can decrease not only because of germination, but also because of the activity of mycopathogens.

The Study of the Germination Dynamics of Plasmopara viticola Oospores Highlights the Presence of Phenotypic Synchrony With the Host

“…The different post-maturation length of MT and MTc oospores and the decrease of T 50 in MT samples at the start of grapevine growing season indicated the presence of synchrony of the pathogen with the host in field. A relationship between phenology of parasites and animal hosts has been previously observed in cases where there is a preferential parasitism of a particular host development stage ( Dick, 1992 ; Hajek et al, 2018 ) and was confirmed also in the case of plant hosts. In the oak-powdery mildew pathosystem ( Desprez-Loustau et al, 2010 ), both sporulation by the pathogen and the host susceptible stage were delayed with increasing altitude of the sites, and in the blueberry– Monilinia vaccinii-corymbosi pathosystem, germination of the overwintering structures synchronized with bud break of the host ( Lehman and Oudemans, 2000 ).…”

Long noncoding RNAs are potentially involved in the degeneration of virulence in an aphid-obligate pathogen, Conidiobolus obscurus (Entomophthoromycotina)

“…After exhausting the host nutritious materials, the fungi can kill the hosts and sporulate to start new infection cycle. They ultimately cause epizootics and collapse the host populations in the natural environment [ 13 , 14 ]. Researchers have manufactured several mycelium-based formulations, such as mycelial mats, millet granules, and alginate pellets, to apply entomophthoralean fungi for field pest control but have encountered an issue of unstable performance in control efficiency [ 15–17 ].…”

Mechanisms Underlying the Transmission of Insect Pathogens

“…The other strategy, being a “creeper”, means that this phenotype will produce less conidia, but more mycelia, allowing hyphae to grow through the soil and increase the chance of encountering a host. The soil as a reservoir for the prolonged survival of resting spores of insect pathogenic fungi from the order Entomophthorales and the horizontal transmission of these fungi is the topic of the article by Hajek et al [4]. In order to infect, these resting spores must produce an infective conidium.…”