What do we know?
Fungi, plants and animals are all descended from unicellular, flagellated, aquatic forms that became multicellular and radiated extensively when they colonized the land. The arthropod ancestors of insects colonized the land ca. 450 million years ago and the plants somewhat later ca. 425 million years ago. The common ancestor of fungi was probably parasitic in nature. After the divergence of the earliest branches, which are composed of insect and fungal endoparasites, the remaining fungi evolved filamentous growth, which aided the absorbance of nutrients through extracellular digestion and substrate attachment. Saprotrophic and mutualistic life styles evolved and allowed the ability to break down the chitin of the insect cuticle. Numerous transitions from pathogens to saprophytes have occurred, as well as the reverse, so that we today find insect pathogens among the earliest as well as the more recent fungal lineages. In some cases these parasite-host relationships are highly specific, but quite often one fungal species can infect a broad range of insect hosts.
CSE has long-standing expertise in the study of insect pathogenic fungi through the track record of the Eilenberg group, and cooperative projects in recent years have addressed some of the adaptations of generalist fungal pathogens such as Metarhizium in leaf-cutting ants and garden ants. Our current work on social insect diseases investigates how costly fungal infections are for colonies of ants and honey bees, and how colony-level genetic diversity and/or individual defences may limit the impact of fungal parasites. We focus on chalk brood (Ascosphaera) disease-pressure in honey bees, on Cordyceps infections in Camponotus and leaf-cutter ants and on Pandora infection of Formica ants. CSE research also tries to address general questions about infection characteristics across the major clades of insect pathogenic fungi and about the general ecological and evolutionary forces that determine the prevalence of sexual abd asexual stages.
What are the major trade trade-offs between individual and collective defence against social insect pathogenic fungi, and how do immune parameters affect social insect mating systems?
How variable are life-history traits of Cordyceps fungi, are host defences against behavioural manipulation by the parasite possible, and how do interactions with competitors and parasites affect Cordyceps life histories?
How variable are Ascospharea apis infection at local, regional and European scales, are castes of honey bees equally susceptible to chalk brood and is there genetic variation for chalk brood resistance in Danish honey bees?