Multi-stress approach for the assessment of decline causes for honeybee

Honeybee decline is a problem of high concern since a complex pathology (Colony Collapse Disorder) brought to worldwide events of colony losses. Many adversities may be responsible of this decline: recrudescence of old and new pathologies, contamination from pesticides and emerging contaminants (e.g. nanoparticles) and environmental stresses. Stress factors may interact among them with additive or synergic effects and, currently, a multi-stress condition is accepted as the most probable decline cause for honeybees. Experimental hives were placed in two experimental sites in Northern Italy: an exposure site ES and a control site CS (14 km far from ES, agricultural field and significant human settlements). ES is located inside an experimental farm where a high-voltage electric line is present together with a complex and controlled pesticide application schedule for orchards. In the ES, two experimental area were set up (one just below the electric line, with the combined presence of electromagnetic fields and sublethal pesticide exposure SPE, and one exposed only to SPE). Honeybees were sampled from April to October 2017 weekly for health status (mites, virus, bacteria spores and fungi), and population parameters (queen and brood status and food stokes, together with daily mortality), and monthly for biomarker analyses (acetylcholinesterase, catalase, glutathione S-transferase and alkaline phosphatase activity, amount of reactive oxygen species, lipid peroxidation, and DNA fragmentation). Preliminary analysis revealed that population parameters and biomarkers were both affected by stresses. Effects on biomarkers were registered in relation to pesticide applications. Multi-stress position showed the most severe effects, leading to colonies death. Colony losses were related to the development of different pathologies. Reduced immunity defences and social disorders by frequent queen replacement seem to be the main effects related to the multi-stress condition.