Diversity and abundance of entomopathogenic fungi at ant colonies.

The purpose of this study was to identify whether entomopathogenic fungi in the genera Metarhizium and Beauveria were found at ant nests. These fungi have been used in studies of ant social immunity, however experimental conditions used may not normally be representative of that found within ant colonies. The presence of insect pathogenic fungi including Metarhizium and Beauveria was assessed in soils at 22 ant nests in Ontario, Canada. Soil samples were plated onto selective agar, fungi were isolated and DNA extracted and the fungi identified by amplifying the internal transcribed spacer region (ITS) and comparing sequences to those found in GenBank. We found that Metarhizium species were found in soils in and around most ant nests. Concentrations of Metarhizium in the soil were not influenced by the presence of ant nests suggesting co-existence rather than avoidance or seeking behaviour. Thus, Metarhizium appears to be a good pathogen to study ant-fungal interactions. Beauveria on the other hand, was not found in any of the samples indicating a decreased likelihood that ants encounter this pathogen. Other fungi found at relatively high concentrations at ant nests include Pochonia and Purpureocillium species, both recognized as nematode pathogens.

Localization of the insect pathogenic fungal plant symbionts Metarhizium robertsii and Metarhizium brunneum in bean and corn roots.

Metarhizium is an insect pathogenic fungus and a plant root symbiont. Here the root association patterns (rhizoplane or endophytic colonization) were analyzed in common beans (Phaseolus vulgaris) and sweet corn (Zea mays) using M. robertsii and M. brunneum under various vermiculite treatments (control, with sucrose, with an insect) at two time points of plant growth (10 and 20 days). We observed that M. brunneum and M. robertsii preferentially endophytically colonized the hypocotyl, however, greater rhizoplane colonization was observed at the regions proximal to the hypocotyl in both plants. Vermiculite amended with an infected insect resulted in greater endophytic and rhizoplane colonization at 20 days compared to 10 days, for both plants as well as for both Metarhizium species. Regardless of the vermiculite treatment, corn was preferentially colonized compared to bean. Sucrose amendment in the vermiculite and infected insect amended vermiculite only showed differences in rhizoplane colonization. The greatest root association occurred with M. brunneum with an infected insect and that in corn after 20 days.

"Sleepers" and "Creepers": A Theoretical Study of Colony Polymorphisms in the Fungus Metarhizium Related to Insect Pathogenicity and Plant Rhizosphere Colonization.

Different strains of Metarhizium exhibit a range of polymorphisms in colony phenotypes. These phenotypes range from highly conidiating colonies to colonies that produce relatively more mycelia and few conidia. These different phenotypes are exhibited in infected insects in the soil. In this paper, we provide a theoretical consideration of colony polymorphisms and suggest that these phenotypes represent a range of strategies in the soil that Metarhizium exhibits. We call these different strategies "sleepers" and "creepers". The "sleeper" phenotype produces relatively greater amounts of conidia. We use the term "sleeper" to identify this phenotype since this strategy is to remain in the soil as conidia in a relatively metabolically inactive state until a host insect or plant encounter these conidia. The "creeper" phenotype is predominantly a mycelial phenotype. In this strategy, hyphae move through the soil until a host insect or plant is encountered. We theoretically model the costs and benefits of these phenotypic polymorphisms and suggest how evolution could possibly select for these different strategies.