*2.2. Hypopharyngeal Gland Protein Content*

The hypopharyngeal gland protein contents of control bees treated with propolis extract (CO-50P) and not treated with 50% propolis extract (CO-0P) were significantly higher than the infected bees (*χ*<sup>2</sup> = 31.75, df = 3, *p* < 0.0001, Figure 3), they were 1470.0 ± 65.06 μg/bee and 1326.23 ± 103.4 μg/bee, respectively. The *N. ceranae*infected bees treated with propolis extract (NO-50P) had significantly higher protein levels, 963.0 ± 52.77 μg/bee, in comparison to the infected bees not treated with propolis extract (NO-0P), which had 486.0 ± 32.5 <sup>μ</sup>g/bee of protein, respectively (*χ*<sup>2</sup> = 31.75, df = 1, *p* = 0.0002). The similar trend was found in both groups of bees treated with 0.5COS (*χ*<sup>2</sup> = 31.39, df= 3, *p* < 0.0001, Figure 4). The highest protein content was found in the control bees treated with COS (CO-0.5COS) (1500.0 ± 76.01 μg/bee), and it was not significantly different from that of control bees not treated with COS (CO-0COS) (*χ*<sup>2</sup> = 31.39, df= 1, *p* = 0.5657). However, infected bees treated with 0.5 ppm COS had significantly increased protein content of the hypopharyngeal glands (1006.0 ± 44.4 μg/bee), in comparison with *N. ceranae*-infected bees that were not treated with COS (486.0 ± 32.5 μg/bee).

**Figure 3.** A box plot showing the median levels of hypopharyngeal gland protein contents across the treatments from the propolis extract experiment: control bees (CO-0P) (grey), control bees treated with propolis extract (CO-50P) (green), *N. ceranae*-infected bees not treated with propolis (NO-0P) (red) and infected bees treated with 50% propolis extract (NO-50P) (light green). The hypopharyngeal gland protein content was measured 14 days p.i. The boxes indicate the interquartile range, while the vertical bars indicate the range of the data. The different letters above each box plot represent significant differences (Kruskal–Wallis test: *χ*2= 31.75, df = 3, *p* < 0.0001).

**Figure 4.** A box plot showing the median hypopharyngeal gland protein content levels from the COS experiment. The following treatments are shown with each box plot: control bees not treated with COS (CO-0COS) (grey), control bees treated with 0.5 ppm COS (CO-0.5COS) (purple), *N. ceranae*infected bees not treated with COS (NO-0COS) (red) and infected bees treated with 0.5 ppm of COS (NO-0.5COS) (light blue). The hypopharyngeal gland was measured on day 14 p.i. The boxes represent interquartile ranges, while the vertical bars indicate the range of the data. The different letters above the box plots represent significant differences (Kruskal–Wallis test: *χ2*= 31.39, df = 3, *p* < 0.0001).
