2.2.5. Viability control of Nosema spores

The viability of spores to be tested is rarely checked, although it is a crucial point to ensure the reliability and reproducibility of the results. In particular regarding N. ceranae, it can be considered as a key point because of the high sensibility to cold temperatures of N. ceranae, spores (Forsgren and Fries, 2010). N. apis spores also loose infectivity after freezing, but in a matter of years (Bailey, 1972) rather than a week as shown for N. ceranae (Fries, 2010). Spore viability can be tested using three methods: colouration and infectivity tests (in vivo and in vitro). The advantage of colouration is that suspensions can be checked before use, in vivo tests are useful for confirmation of spore viability used for infection experiments.