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Distribution and frequency of Microsporidia in Bombus spp. in Europe

Bumble bees collected from 7 European countries across 2003, 2004 and 2005 were examined for the incidence of the microsporidium Nosema bombi. In 5358 mostly visually examined bumble bees, we detected an average infection rate of 9 % across years and countries. Of the 30 European bumble bee species examined, N. bombi was detected in 16 of them, for which 9 species represent new records. The incidence of infection varied both spatially (country to country) and temporally (2003 versus 2004 and 2005).

Of the two most commonly collected taxa, Bombus pascuorum (N = 1566) and Bombus terrestris/lucorum (N = 1842), the infection rate differed significantly between host species (18.2% of B. terrestris/lucorum individuals infected, 3.4% of B. pascuorum individuals).

Bombus pascuorum showed no differences in the rate of infection among castes and sexes (worker, queen, male) or across years. In contrast, B. terrestris/lucorum showed a clear, significantly higher incidence of infection in males compared to workers or queens. The incidence of microsporidia was much higher in the latter half of the bumble bee flight season (July to September), with 10.6 % prevalence across species, years and countries, than in the early part (end of March to June), with a prevalence of 2.9 % of individuals infected. The same annual trend was seen for each of the castes and sexes.

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Swedish Univ. Agric. Sci
Box 7044
750 07 Uppsala
Sweden
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