18.104.22.168. Course of infection in individual bees
The course of infection is checked in individual bees or in a group of tested bees. The time lap between spore counts has been highly variable between different authors and the goal of the experiment (Alaux et al., 2010a; Alaux et al., 2010b; Czekonska, 2007; Forsgren and Fries, 2010; Malone and Stefanovic, 1999; Paxton et al. 2007). Generally speaking, a greater sample size and increased frequency of sampling will allow for more confidence in the data. Since individual feeding of honey bees is time consuming, the interval between sampling and the number of bees investigated must, nevertheless, be limited. Because N. apis spores are not produced from new infections until at least 3 days post infection (Fries, 1988 ; Fries et al., 1996 ; Forsgren and Fries, 2010), with the first spores of N. ceranae produced slightly later (Forsgren and Fries, 2010), sampling should be initiated no earlier than 4 days post infection. With a 2 day time interval between sampling, a relatively detailed data set on spore development can be accomplished. Because of variations in spore development between different bees, the sample size should never be below 3-4 bees per cage and treatment, and for statistical reasons, the more bees used, the better (see the statistics section in the BEEBOOK paper on miscellaneous methods (Human et al., 2013)).