Many European and North American countries have reported losses in honey bee populations over recent years. Although multiple factors appear to be involved in this decline, the influence of pathogens may be particularly important. 

In the present study, we analyzed the presence of the major honey bee pathogens and neonicotinoid insecticides in ten professional apiaries (five affected by high honey bee colony mortality and five asymptomatic apiaries). 

Our results confirm that Nosema ceranae and trypanosomatids are very prevalent in the apiaries affected by depopulation and high colony loss. By contrast, and while they have been demonstrated to be highly toxic to bees, neonicotinoid insecticides do not seem to play an important role in colony mortality in these apiaries. 

The main conclusions of our study are that: (1) pathogens are highly prevalent in depopulated symptomatic colonies; (2) all the pathogens detected can potentially produce a substantial reduction in host fitness and such effects are probably exacerbated when more than one pathogen coincides; and finally, (3) although neonicotinoids are very toxic to bees, they do not seem to play an important role in the symptoms of the colonies analyzed. 

These results are in agreement with earlier data and they confirm the need to control parasites (such as N. ceranae) in order to ensure the health of bee colonies and to prevent their collapse. 

Passive laboratory surveillance in Spain: pathogens as risk factors for honey bee colony collapse
Cepero, A; Martin-Hernandez, R; Bartolome, C; Gomez-Moracho, T; Barrios,
L; Bernal, J; Martin, MT; Meana, A; Higes, M
JOURNAL OF APICULTURAL RESEARCH, 54 (5):525-531

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