Rapid gastrointestinal passage may protect Bombus terrestris from becoming a true host for Nosema ceranae

• Published in: Applied and environmental microbiology Vol. 86; no. 12
• Main Authors: Gisder, Sebastian, Horchler, Lennart, Pieper, Franziska, Schüler, Vivian, Šima, Peter, Genersch, Elke
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 02.06.2020
• Subjects: Apis mellifera; Bees; Bioassays; Biodiversity; Bombus; Bombus terrestris; Bumblebees; Deoxyribonucleic acid; DNA; Ecosystem services; Fluorescence; Fluorescence in situ hybridization; Food security; Histology; Human security; Infections; Infectivity; Invertebrate Microbiology; Microscopic analysis; Nosema ceranae; Parasites; Pathogenesis; Pollination; Spores; Virulence; Wildlife conservation
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.00629-20

Pollination provided by managed honey bees as well as by all the wild bee species is a crucial ecosystem service contributing to the conservation of biodiversity and human food security. Therefore, it is not only the health status of honey bees, but also the health status of wild bees that concerns us all. In this context, recent field studies suggesting inter-species transmission of the microsporidian parasite from honey bees ( ) to bumblebees ( ssp.) were alarming. Based on these studies, was considered an emerging infectious agent of bumblebees, the impact of which on its new host was still elusive. In order to investigate infectivity, virulence, and pathogenesis of infections in bumblebees, we performed controlled laboratory exposure bioassays with by orally inoculating the bees with infectious spores. We comprehensively analyzed the infection status of the bees via microscopic analysis of squash preparations, PCR-based detection of DNA, histology of Giemsa-stained tissue sections, and species-specific fluorescence -hybridization. We did not find any evidence for a true infection of bumblebees by Through a series of experiments we ruled out that spore infectivity, spore dosage, incubation time, or age and source of the bumblebees caused these negative results. Instead our results clearly demonstrate that in our experiments no infection and production of new spores took place in bumblebees after they ingested spores. Thus, our results question the classification of as emerging infectious agent for bumblebees. Emerging infectious diseases (EID) pose a major health threat to both humans and animals. EID are for instance those that have spread into hitherto naïve populations. Recently, the honey bee-specific microsporidium has been detected by molecular methods in field samples of bumblebees. This detection of DNA in bumblebees led to the assumption that infections are an EID of bumblebees and resulted in speculations on the role of this pathogen in driving bumblebee declines. In order to answer the question whether is an emerging infectious agent for bumblebees, we experimentally analyzed host susceptibility and pathogen reproduction in this new host-pathogen interaction. Surprisingly, we did not find any evidence for a true infection of by questioning the classification of infections as EID of bumblebees and demonstrating that detection of microsporidian DNA does not equal detection of microsporidian infection.