3.3.3. Stressors' Impact

In order to determine which stressors affected the most honey bees, Sankey diagrams were generated for each stressor (Figure 5). All the most studied stressors (parasitic and infectious agents, insecticides, chemical veterinary treatments and beekeeping practices other than chemical veterinary treatments) affected the majority of the parameters studied at all scales. There was an exception for veterinary treatments and insecticides, for which about 50% of the parameters studied at the colony level were not impacted. GMOs, although little studied, did not generally have much effect. In particular, results showed no effect on bee mortality and few impacts were observed at the colony or individual level. However, the studied GMOs were mainly bt maize, and as bees are not sensitive to the *bacillus thuringiensis* toxins [34], it is consistent that these GMOs were not demonstrated to have an impact. On the other hand, all the articles dealing with the impact of climate or habitat fragmentation (Figure 5) showed effects, particularly at the colony level. Since the number of publications was very low, the actual effects on bee health should be confirmed by other studies. Exposure to metals appeared to have a significant molecular impact on bees, but very few studies were conducted and none studied colony endpoints. It would therefore be interesting to fill this gap and to relate the molecular effects to the possible effects on the colony.

**Figure 5.** Examples of Sankey diagrams obtained for the stressors "insecticides" and "habitat". The flux represents the number of parameters studied at each biological scale (on the left of the diagram) which have been impacted or not (on the right).
