Quantification of viral loads in honey bee colonies managed with different beekeeping practices

Among the pathogens of the honey bee, viruses are receiving increasing attention. Indeed, immunosuppressing agents, such as agrochemical pollution, the reduction of pollen variety, and the parasitic mite Varroa destructor, which also plays a role in virus transmission, may turn latent viral infections into overt ones. In the frameshift of the Interreg-Alcotra project "Innov'api", we are comparing the efficacy of two control strategies against V. destructor: the conventional treatment with a synthetic acaricide (Apivar©) and a newly introduced practice based on brood removal in combination with oxalic acid applications. With this aim, we are monitoring several colonies from selected apiaries where both methods are used, in Piemonte (Italy), Occitanie and Provence-Alpes-Côte d'Azur (France) regions. Besides the plurality of environmental and climatic conditions, this survey embraces different management practices, such as stationary and migratory beekeeping. Multiple parameters are evaluated both in the production season (summer) and in the pre- and post-wintering periods over three years. Adult and brood population, honey production and mite population are estimated in the field. Frozen samples of adult bees are brought to the laboratory to quantify viral loads (DWV, ABPV complex, CBPV, BQCV, SBV) by Real-time qPCR. On the same samples, the gene expression of three markers of the physiological status of the colonies (vitellogenin, insulin-receptor 1, adipokinetic hormone receptor) is assessed. We show here the preliminary results of this study, with a special focus on the seasonal variations of the viral loads in the monitored honey bee colonies.