4.1.2. Analysis of generated data

In order to evaluate compiled experimental data, two different analyses to measure virulence can be performed. The first virulence indicator is the lethal concentration (LC) value (Thomas and Elkinton, 2004), which indicates the spore concentration at which 50 % (LC50) or 100 % (LC100) of the individuals are killed. To calculate this measure, the proportion of dead larvae from the number of exposed larvae is plotted against spore concentration. From such graphs, one can to estimate the spore concentration needed to kill a given proportion of the exposed population. These graphs also allow to deduce - for a certain analysed strain - the approximate spore concentration present when a specific percentage of the exposed population is dead.

Another measure of virulence is the lethal time (LT) (Thomas and Elkinton, 2004) which is the time it takes the pathogen to kill 50 % (LT50) or 100 % (LT100) of the infected animals. In order to obtain this measure, the time course of infection must be determined. Cumulative mortality per day is calculated as percentage of all individuals which died from P. larvae infection during the course of the experiment (total number of P. larvae-killed animals until the end of the experiment). Average values are calculated every day from at least three independent replicates, and plotted against every time point (day post-infection).