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Nosema bombi is a microsporidian, a small, unicellular parasite recently reclassified as a fungus that mainly affects bumble bees. The parasite infects numerous Bombus spp. at variable rates, and has been found to have a range of deleterious effects on its hosts.[1]

Nosema bombi
Scientific classification
N. bombi
Binomial name
Nosema bombi
Fantham & Porter, 1914


Life cycle stagesEdit

Nosema bombi, like other microsporidians, has two major life cycle stages, a spore stage and a vegetative stage. In most cases, the spore is ingested by the host, infecting host cells in the gut lumen and the Malpighian tubules.[1] During reproduction and proliferation the parasite spreads within the host. Fresh spores are then released into the environment via feces or a decaying host.


The parasite is believed to rely mainly on horizontal transmission between colonies via infected workers contaminating shared food sources such as pollen or nectar, but there is some evidence that it may also be transmitted vertically.[2] Males may transmit the infection to new queens during mating. N. bombi infection prevalence has been reported to vary widely over time. For example, Manlik et al. (2017) reported that N. bombi infection prevalence in buff-tailed bumble bees (Bombus terrestris) fluctuated between 2% (2010) and 81% (2003) in Neunforn, Switzerland.[3]

Effects on hostEdit

Studies have found conflicting results as to the effects of N. bombi on bumble bee health.[4] Some field studies have found little to no negative effects on colony size or success, while others have found that infected queens produce smaller colony sizes and reduced sexual offspring.[5] Under laboratory conditions, the fungus has been found to affect the survival and efficiency of adult individuals as well as the sperm counts of male offspring.


Of the estimated 250–300 bumble bee species in the world, several are now being commercially mass-reared and distributed for crop pollination. When screened, many of these commercially reared bumblebees have been found to contain pollinator parasites.[6] There is some concern that higher infection rates among commercial colonies may lead to N. bombi spillover into wild bumble bee populations.[7]


  1. ^ a b Oliver Otti & Paul Schmid-Hempel (2007). "Nosema bombi: a pollinator parasite with detrimental fitness effects" (PDF). Journal of Invertebrate Pathology. 96 (2): 118–124. doi:10.1016/j.jip.2007.03.016.
  2. ^ Samina T. Rutrecht & Mark J. F. Brown (2008). "Within colony dynamics of Nosema bombi infections: disease establishment, epidemiology and potential vertical transmission". Apidologie. 39 (5): 504–514. doi:10.1051/apido:2008031.
  3. ^ Oliver Manlik; Regula Schmid-Hempel & Paul Schmid-Hempel (2017). "Parasite infection of specific host genotypes relates to changes in prevalence in two natural populations of bumblebees". Infection, Genetics and Evolution. 56: 125–132. doi:10.1016/j.meegid.2017.11.019.
  4. ^ B. Imhoof & P. Schmid-Hempel (2006). "Colony success of the bumble bee, Bombus terrestris, in relation to infections by two protozoan parasites, Crithidia bombi and Nosema bombi" (PDF). Insectes Sociaux. 46 (3): 233–238. doi:10.1007/s000400050139.
  5. ^ Oliver Otti & Paul Schmid-Hempel (2008). "A field experiment on the effect of Nosema bombi in colonies of the bumblebee Bombus terrestris" (PDF). Ecological Entomology. 33 (5): 577–582. doi:10.1111/j.1365-2311.2008.00998.x.
  6. ^ Graystock P, Yates K, Evison SEF, Darvill B, Goulson D, Hughes WOH. The Trojan hives: pollinator pathogens, imported and distributed in bumblebee colonies. Journal of Applied Ecology, 50(5): 1207-1215
  7. ^ Sheila R. Colla; Michael C. Otterstatter; Robert J. Gegear; James D. Thomson (2006). "Plight of the bumble bee: pathogen spillover from commercial to wild populations" (PDF). Biological Conservation. 129 (4): 461–467. doi:10.1016/j.biocon.2005.11.013.