Honey bees, Apis mellifera , have a diverse community of pathogens. Previous research has mostly focused on bacterial brood diseases of high virulence, but milder diseases caused by fungal pathogens have recently attracted more attention. This interest has been triggered by partial evidence that co-infection with multiple pathogens has the potential to accelerate honey bee mortality. In the present study we tested whether co-infection with closely related fungal brood-pathogen species that are either specialists or non-specialist results in higher host mortality than infections with a single specialist. We used a specially designed laboratory assay to expose honey bee larvae to controlled infections with spores of three Ascosphaera species: A. apis , the specialist pathogen that causes chalkbrood disease in honey bees, A. proliperda , a specialist pathogen that causes chalkbrood disease in solitary bees, and A. atra , a saprophytic fungus growing typically on pollen brood-provision masses of solitary bees. Results We show for the first time that single infection with a pollen fungus A. atra may induce some mortality and that co-infection with A. atra and A. apis resulted in higher mortality of honey bees compared to single infections with A. apis . However, similar single and mixed infections with A. proliperda did not increase brood mortality. Conclusion Our results show that co-infection with a closely related fungal species can either increase or have no effect on host mortality, depending on the identity of the second species. Together with other studies suggesting that multiple interacting pathogens may be contributing to worldwide honey bee health declines, our results highlight the importance of studying effects of multiple infections, even when all interacting species are not known to be specialist pathogens.
Vojvodicet al.Frontiers in Zoology2012,9:5 http://www.frontiersinzoology.com/content/9/1/5
R E S E A R C HOpen Access Virulence of mixed fungal infections in honey bee brood 1,2* 31 1 Svjetlana Vojvodic, Jacobus J Boomsma , Jørgen Eilenbergand Annette B Jensen
Abstract Introduction:Honey bees,Apis mellifera, have a diverse community of pathogens. Previous research has mostly focused on bacterial brood diseases of high virulence, but milder diseases caused by fungal pathogens have recently attracted more attention. This interest has been triggered by partial evidence that coinfection with multiple pathogens has the potential to accelerate honey bee mortality. In the present study we tested whether coinfection with closely related fungal broodpathogen species that are either specialists or nonspecialist results in higher host mortality than infections with a single specialist. We used a specially designed laboratory assay to expose honey bee larvae to controlled infections with spores of threeAscosphaeraspecies:A. apis, the specialist pathogen that causes chalkbrood disease in honey bees,A. proliperda, a specialist pathogen that causes chalkbrood disease in solitary bees, andA. atra, a saprophytic fungus growing typically on pollen broodprovision masses of solitary bees. Results:We show for the first time that single infection with a pollen fungusA. atramay induce some mortality and that coinfection withA. atraandA. apisresulted in higher mortality of honey bees compared to single infections withA. apis. However, similar single and mixed infections withA. proliperdadid not increase brood mortality. Conclusion:Our results show that coinfection with a closely related fungal species can either increase or have no effect on host mortality, depending on the identity of the second species. Together with other studies suggesting that multiple interacting pathogens may be contributing to worldwide honey bee health declines, our results highlight the importance of studying effects of multiple infections, even when all interacting species are not known to be specialist pathogens. Keywords:Apis mellifera,Ascosphaera, Competition, Mixed infections, Virulence
Introduction Variation in virulence (i.e. diseaseinduced host mortal ity) among pathogens is shaped by evolutionary pressure emanating from the combined life histories of pathogens and hosts [1]. However, virulence is difficult to predict when interactions are not restricted to a single host and pathogen, but involve multiple infections [2,3]. Conflict between coinfecting strains can lead to different within host dynamics, with consequences for virulence, trans mission and host resistance [4,5]. Examples illustrating aspects of this interactioncomplexity areDaphia magna
* Correspondence: vojvodic.sv@gmail.com 1 Center for Social Evolution, Department of Agriculture and Ecology Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK 1871 Frederiksberg C, Denmark Full list of author information is available at the end of the article
infections with bacteriaPasteuria ramosaand micro sporidiumOctosporea bayeri[6], helminths occupying mammalian guts [7],Plasmodium chabaudiclones infecting mice [8], andMetarhizium anisopliaevar.ani sopliaeandAspergillus flavusfungi infecting leafcutting ants [9]. Increased virulence of mixed infections can be due to increased pathogen densities [1012] or to the host immune system being less efficient in clearing up multiple infections e.g. [13]. However, in some cases, the virulence of a mixed infection merely reflects the virulence of the most virulent strain/species e.g. [5,14,15]. The outcome of parasite interactions can also result in underexploitation of the host and a reduction in virulence, possibly as a result of cooperation between parasites when benefits are shared [16,17].