RESUMEN
Colony collapse disorder (CCD) has affected bees worldwide in recent decades, with southwestern Spain being no exception. This disorder is one of the main causes of Apis mellifera mortality and is believed to be caused by environmental, social and sanitary conditions. Dietary supplementation can help to improve some parameters of the general status and sanitary condition of bees, such as infestation by certain recurrent pathogens, including Varroa destructor and Nosema ceranae, by enhancing immune and social response. Thus, the aim of this study was to test a liquid hydrolysed protein supplement on the health and general status of the hive in several apiaries with access to the same natural food and under similar climatic conditions. We selected two groups of ten hives (supplemented by either placebo or protein) from five apiaries where the number of adult bees, amount of brood (open and operculated), honey and pollen reserves, infestation by V. destructor, N. ceranae, deformed wing virus (DWV) and chronic bee paralysis virus (CBPV) were measured. Additionally, we assess the expression of four immune system-related genes and a gene encoding vitellogenin. At the end of this work, treated hives showed a significant increase in open brood and a decrease in V. destructor infestation. Also, these hives showed a significant decrease in the mortality rate after the cold season. Therefore, supplementation with this product improved the health of the hive and could be a promising tool against bee colony loss.