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Effects from Microsporidia infections in Bombus spp

The impact of Nosema bombi on colony founding and transmission was studied by inducing N. bombi infection via administration of N. bombi spores from Bombus terrestris adults to individual worker and queen larvae in open cells of B. terrestris colonies. Administration of 312 500 spores to queen larvae resulted in 35 infected queens out of 113 queens (31%). There was no effect from treatments on mating success and hibernation mortality. The founding rate of new colonies after hibernation of the control queens was 33% whereas the success of ÒNosemaÓ queens was 4% (2 of 48 queens). It is concluded that N. bombi infection has a negative impact on colony founding. It should be noted that several queens where the parasite could not be detected in the intestines, had parasite DNA in ther ovaries using molecular detection techniques developed in the project. This suggests transovarial parasite transmission, although this transmission route remains to be verified.

Using laboratory infection experiments the pathology and fitness effects from this parasite was studied. If infection occurs at an early stage of colony development, virtually all individuals are infected and spores are found in different tissues. Although the classical fitness parameters were not influenced by the treatment, the functional fitness of males and young queens was reduced to zero from the infection. Further, the survival of workers from infected colonies and infected males is highly reduced. With such severe effects, Nosema bombi even seems to decrease its opportunities for transmission to the next host generation. The results demonstrate the negative impact from infection and suggest that the parasite need to infect colonies and/or queens that will go into hibernation late in the season. Otherwise the negative impact from infection will impair parasite transfer to the following season.

The results will be published in scientific media and have been presented at scientific conferences. The results are also communicated to the bumble bee breeding industry through the project End User meeting and, the Technical Report from the End User meeting and the project website.

The results produced are important for understanding the host-parasite adaption. Such knowledge that can be used to develop sound control strategies for the breeding industry.

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