Storage of stock suspension

It should be emphasised that for infection experiments, newly made up spore suspensions should be used, prepared the same day or the day before the experiment and kept in the refrigerator. For N. apis, storage of spores for later preparations of new suspensions can be made by freezing adult infected bees or already prepared spore suspensions. For N. ceranae the situation is drastically different since the spores rapidly loose viability if frozen (Fenoy et al., 2009; Fries, 2010). A protocol needs to be developed whereby infective spores of N. ceranae can be reliably stored over longer periods without serious loss of viability.