To the multiple factors that have already been identified, potential synergies between these factors must be added. This is a little studied phenomenon until now. Most scientific studies on bees and their abnormally high death rate have focused on the analysis of factors isolated from each other. However, it is possible that the factors interact.

Synergy refers to the phenomenon by which multiple factors acting together produce an effect that is more than the sum of the effects expected from each of them taken individually.

For example, a mixture of pesticides can have much more powerful effects than effects of these products considered individually. The Belgian study conducted by the University of Liège- Gembloux under the COLOSS Network (Prevention of honey bee COlony LOSSes, a research network bringing together researchers, veterinarians and beekeepers from 60 countries) highlighted the presence of 18 pesticides in hives in the form of traces.

Contaminants and diseases can also act in concert, producing additive (effects undergo simple addition) or potentiator (the effect of two factors combined is greater than the sum of effects of each factor taken separately) effects. A study by INRA on the combination of imidacloprid with the Nosema fungus, which this lab has studied in detail, belongs to this latter scenario .

Multiplicity of factors and research

In recent years, faced with multiplicity of factors of decline and lack of data on their individual and/or cumulative role, various research programmes have been launched. ALARM (Assessing, LARge scale environmental Risks for biodiversity with tested Methods), an ambitious European programme conducted from 2004 to late 2008 in partnership with 52 research organisations, aimed at scientifically assessing the risks to terrestrial and aquatic biodiversity and the potential consequences of its decline in Europe. This programme was structured around four axes related to climate change, chemicals, invasive species and pollinators.

This programme was continued for pollinators by the STEP (Status and Trends of European Pollinators) programme. Launched by the European Commission in May 2012, this project has several objectives including the preparation of a red list of the main groups of European pollinators (especially bees) and assessment of the relative importance of potential factors in the decline of these pollinators: climate change, loss and fragmentation of habitat, agrochemicals, pathogens, invasive alien species, light pollution and their interactions. STEP shall also measure the ecological and economic impact of this decline and degradation of the pollination services and floral resources.