Bees live alongside a huge variety of microbes, and these vary from harmless commensal relationships to disease-causing pathogenic relationships. The influence of these microbial associations on the health of bees is important to understand because of the essential ecological role bees provide as pollinators.
The nesting and foraging habitats of bees predispose them to pervasive exposure to microbes, predominately fungi. Fungi produce spores as their transmission stage, and they are often very long-lived and adept at attaching to the external surfaces of the body of bees. They are spread around pollinator populations, often via flowers, which represent a shared food resource for multiple species of bee, or via shared nest sites or nest re-use. The characteristics of fungal transmission (spore longevity and external attachment to bees’ bodies) contribute to the pervasive nature of these microbes.
Despite their pervasive nature, bee-associated fungi are an understudied group.
Our review summarises our current knowledge of aspects of the biology and ecology of bee-associated fungi. We describe the biology of both different types of bee-associated fungi, and the bees that those fungi are associated with. Two key findings from our review stand out. Firstly, there is a huge disparity in the amount of research carried out on fungi that are associated with managed compared to wild bees. This disparity has left gaps in our understanding of the epidemiology of potentially dangerous pathogenic fungi, and their true risk to bee health, therefore, remains unknown. Secondly, co-infection by multiple strains and species of fungi, as well as other microbial groups (such as bacteria and viruses) can have a synergistic effect on the virulence of pathogenic fungi and can induce pathogenesis by fungi that would otherwise live a commensal relationship with the bee.
We propose that the historical research focus on commercially important (managed) species such as the honey bee, should shift to include wild and solitary species. Not only because they tend to be less resilient to environmental stressors, but because their importance (often specialized role) as pollinators of both crops and wildflowers is increasingly evident. As solitary bees are relied on more for commercial pollination, denser aggregations will lead to higher prevalence of fungal diseases. Pollinators are also regularly moved trans-continentally to meet global pollination needs, leading to transport of their associated fungi. This exacerbates the problem of higher virulence because of co-infection.
A two-fold problem therefore exists – lack of knowledge combined with increased exposure. A greater understanding of the biology and prevalence of fungal parasites across the spectrum of bees, social and solitary, native and exotic, is of paramount importance in mitigating the impact of fungal diseases in bees.
These findings are described in the article entitled, The biology and prevalence of fungal diseases in managed and wild bees, recently published in the journal Current Opinion in Insect Science. This work was conducted by Sophie EF Evison from the University of Sheffield and Annette B. Jensen from the University of Copenhagen.