Nosema spp.
These microsporidians parasitise invertebrates. Most nosema infect insects and the best-known parasitize bees. These get infected by ingesting spores of the fungus. Multiplication in the epithelial cells leads to the lysis of the infected cells and the release of new spores within 10 days. Transmission of nosema between individuals is facilitated by prophylaxis in eusocial bees. Nosema can prevent colonies to thrive in the spring, following overwintering, and are thus considered as a pest by beekeepers..JPG)
Nosemosis has become an emerging disease in the last decades and is now listed by the World Organization for Animal Health (Office International des Epizooties - OIE) because of its role in the worldwide decline of bees. A growing number of studies thus reveal the influence of pesticides in nosema outbreaks. For instance, Pettis et al. (2013) investigated the interaction between pesticide exposure and the susceptibility of the honeybee Apis millifera to the gut pathogen Nosema ceranae. The results indicate that bees exposed to pesticides were more likely to become infected. Interestingly, fungicides had the strongest effect on bee's susceptibility to infection, confirming the high resistance of nosema spores to extreme environments. Moreover, the researchers found that in many samples, bees carried a significant proportion of pollens from weeds rather than from cultivated crops in the sampled areas. It is thus likely that the exposure of foraging bees to pesticides is currently underestimated.
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