The conservation on the abundance and diversity of insect pollinators is a decisive action to avoid the negative impact that the lack of these insects can produce on agriculture, on food production and security, and on environmental sustainability. More than one third of the world's agricultural production depends on Apis mellifera pollination. During the last years there is an alarming increase in the collapse of honey bee colonies where bee pathogens like Varroa destructor mites, the microsporidia Nosema ssp. and viruses participate actively. Colony decline might compromise not only food security but also present and future income to the growers. The aim of this project is to determine the phenology and interaction of the microsporidia Nosema ceranae and viruses including acute bee paralysis virus (ABPV), Israeli acute paralysis virus (IAPV), Black queen cell virus (BQCV) Chronic bee paralysis virus (CBPV) and Deformed wing virus (DWV), in four Mediterranean countries: Spain, France, Portugal and Israel. The possible synergisms between N. ceranae and viruses will be also accomplished. These objectives will be developed in the basis of our working hypotheses: - Since Nosema weakens the bee immune system and damages the midgut of the bee it is conceivable that a more virulent strain of virus (including recombinant strains) could emerge from the interaction. - Understanding the phenology of N. ceranae infections and proper management and treatment could ameliorate/ avoid the synergism between Nosema and viruses diminishing the probability of appearance of more pathogenic virus strains improving colony health and survival. To achieve our goals we will first study the prevalence and phenology of N. ceranae in each participating country and we will monitor for the presence of the above mentioned viruses. Then we will investigate the relationship between outbreak of viruses and N. ceranae infections (in colonies treated for Varroa). If we discover positive correlations between a specific-virus outbreak and nosemosis we will identify the virus strain involved in it and compare it with strains of the same virus present at low or asymptomatic levels in the colonies. The possibility to compare among territories with or without V. destructor (vector of viruses) and / or without N. ceranae (if possible) will provide us a broader knowledge on interactions between pathogens. Finally we will examine the impact of treatments against Nosema and pollen supply on the outcome of the virus infections. We are certain that the findings of this project, which involves an active and unique cooperation among partners representing Mediterranean countries covering a wide array of environmental and beekeeping management conditions, will contribute to ameliorate the damage caused by the expansion of N. ceranae through a rational implementation of existing treatments to avoid emergence of synergistic pathogens that accelerate colony collapse compromising food security.