Abstract
As in many other locations in the world, honeybee colony losses and disorders have increased in Belgium. Some of the symptoms observed rest unspecific and their causes remain unknown. The present study aims to determine the role of both pesticide exposure and virus load on the appraisal of unexplained honeybee colony disorders in field conditions. From July 2011 to May 2012, 330 colonies were monitored. Honeybees, wax, beebread and honey samples were collected. Morbidity and mortality information provided by beekeepers, colony clinical visits and availability of analytical matrix were used to form 2 groups: healthy colonies and colonies with disorders (n = 29, n = 25, respectively). Disorders included: (1) dead colonies or colonies in which part of the colony appeared dead, or had disappeared; (2) weak colonies; (3) queen loss; (4) problems linked to brood and not related to any known disease. Five common viruses and 99 pesticides (41 fungicides, 39 insecticides and synergist, 14 herbicides, 5 acaricides and metabolites) were quantified in the samples.The main symptoms observed in the group with disorders are linked to brood and queens. The viruses most frequently found are Black Queen Cell Virus, Sac Brood Virus, Deformed Wing Virus. No significant difference in virus load was observed between the two groups. Three acaricides, 5 insecticides and 13 fungicides were detected in the analysed samples. A significant correlation was found between the presence of fungicide residues and honeybee colony disorders. A significant positive link could also be established between the observation of disorder and the abundance of crop surface around the beehive. According to our results, the role of fungicides as a potential stressor for honeybee colonies should be further studied, either by their direct and/or indirect impacts on bees and bee colonies.
Highlights
The evolution of pollinator populations has been the subject of an increasing number of studies, most of them showing worrying negative trends [1,2,3,4]
There was no significant difference in viral content between the group with disorders or the healthy one, and independently of the visit for any of the three most abundant viruses (2-way ANOVA tested by permutations, Deformed Wings Virus (DWV): p = 0.731, Black Queen Cell Virus (BQCV): p = 0.373, Sac Brood Virus (SBV): p = 0.54)
We observed a decrease of virus content from summer to fall 2011, independently of the group, for BQCV (p,0.001) and SBV (p,0.001) but not for DWV (p = 0.271)
Summary
The evolution of pollinator populations has been the subject of an increasing number of studies, most of them showing worrying negative trends [1,2,3,4]. Bees contribute to ecosystem services and their decline threatens pollination of both wild and cultured plants, endangering biodiversity, food and fibre production [9,10]. This decline may have an impact on the production of other goods with pharmacological uses (e.g. honey, propolis) [11,12], and scientific and technological inspiration (e.g. development of visual guided flight robotics) [13]. Other studies describe similar mortality trends [8,19,20] as well as unspecific symptoms: increased colony mortality and/or weakening [21,22,23], queen failure [21,23,24,25] or honey yield reduction [21]
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