Fig. 1.
.—(A) Result of a freeze-killed brood (FKB) assay for two colonies showing (left panel) low uncapping and removal rates after 24 h and (right panel) high uncapping and removal after 24 h. The FKB assay is performed by freezing a section of capped honey bee brood (see left image) with liquid nitrogen. Once thawed, the frozen section is placed back inside the colony. After 24 h the section is removed once more and the number of uncapped and removed cells is counted. Hygienic behavior is scored as the percentage of cells uncapped and/or removed divided by the number initially frozen. (B) Hygienic response of independently selected populations and a baseline population after three generations of selection (baseline population was not artificially selected). Black points and whiskers represent mean and Standard Error for each sampled population while individual points represent individual colony measurements. Baseline population expressed hygiene significantly less than the two selected populations (68%; ANOVA; F2,38 = 25.8; P < 0.000001; Tukey HSD P < 0.00001, ***for selected vs. baseline; Tukey HSD selected vs. selected = 0.29. n.s.).