Statistical analysis
Hygienic behaviour was quantified as the percentage of
cells with capped brood that had been cleaned out (cell
uncapped and dead brood removed) after 48 h. We also
recorded the developmental stage of the four types of
untreated brood (eggs, young larvae, old larvae and
capped cells), which were analysed as separate variables.
Using R 3.0.0 (R Development Core Team, 2013),
we used Spearman correlation coefficient to test the
relationship between the median values of hygienic
behaviour and the removal of untreated brood at various
stages. Subsequently, we performed a power analysis
(Champely, 2012) using a power factor of 0.88 to
correct for the lower efficacy of Spearman compared
with Pearson correlation (Siegel & Castellan, 1988