Abstract
BackgroundNosema ceranae infection not only damages honey bee (Apis melifera) intestines, but we believe it may also affect intestinal yeast development and its seasonal pattern. In order to check our hypothesis, infection intensity versus intestinal yeast colony forming units (CFU) both in field and cage experiments were studied.Methods/FindingsField tests were carried out from March to October in 2014 and 2015. N. ceranae infection intensity decreased more than 100 times from 7.6 x 108 in March to 5.8 x 106 in October 2014. A similar tendency was observed in 2015. Therefore, in the European eastern limit of its range, N. ceranae infection intensity showed seasonality (spring peak and subsequent decline in the summer and fall), however, with an additional mid-summer peak that had not been recorded in other studies. Due to seasonal changes in the N. ceranae infection intensity observed in honey bee colonies, we recommend performing studies on new therapeutics during two consecutive years, including colony overwintering. A natural decrease in N. ceranae spore numbers observed from March to October might be misinterpreted as an effect of Nosema spp. treatment with new compounds. A similar seasonal pattern was observed for intestinal yeast population size in field experiments. Furthermore, cage experiments confirmed the size of intestinal yeast population to increase markedly together with the increase in the N. ceranae infection intensity. Yeast CFUs amounted to respectively 2,025 (CV = 13.04) and 11,150 (CV = 14.06) in uninfected and N. ceranae-infected workers at the end of cage experiments. Therefore, honey bee infection with N. ceranae supported additional opportunistic yeast infections, which may have resulted in faster colony depopulations.
Highlights
A significant decrease in the number and biodiversity of pollinators has been observed over the last 50 years
Weakened honey bees are more attacked by many diseases, inter alia those caused by fungi such as Nosema apis and Nosema ceranae belonging to the Microsporidia phylum, Balbiani 1882 [3]
The analysis revealed that N. ceranae is a sister species to N. bombi, whereas the weight of evidence is consistent that N. apis is a basal member of the Nosema clade [4, 5]
Summary
A significant decrease in the number and biodiversity of pollinators has been observed over the last 50 years. A wide spread of N. ceranae is responsible for numerous honey bee infections in Europe [13, 14] and is believed to be displacing N. apis all over the world [5, 15, 16, 17, 18] We hypothesized that such an invasion by a new pathogen developing in apian intestines [19] may affect development of other intestinal microbiota. There is a need for field research into the impact of N. ceranae on N. apis and honey bees as well as honey bee intestinal yeast populations Is it significant for the protection of honey bees, and for broadening the knowledge concerning inter-pathogen relations occurring during new pathogen invasions. In order to check our hypothesis, infection intensity versus intestinal yeast colony forming units (CFU) both in field and cage experiments were studied.
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