**3. Results**

#### *3.1. Longevity of Bees*

About 90% of caged bees in each treatment group survived the first 15 days (Figure 1). After day 30, less than 30% of bees were left alive in the five treatment groups, which included the Apifonda control. The steepest declines in bee survival occurred between days 15–30 post-treatment (Figure 1). Treatment differences were detected among the five treatment groups (Figure 1; F = 2.968; df = 4; *p* = 0.028). The longevity of the bees receiving the highest HMF concentration (1500 mg HMF/kg) was reduced when compared with other HMF treatment groups and untreated control bees (Figure 2).

**Figure 1.** Survival rates of caged bees (expressed in %) are shown in 5 day intervals for each treatment group and the untreated control group (Apifonda). Bars indicate ± SD.

**Figure 2.** The relative number of live caged bees on the 15th, 20th, 25th, and 30th day of the experiment. The figure shows dates with the highest differences of survived bees between treatment groups. Asterisks indicate statistically significant differences between treatment groups. The Tukey test shows a difference at *p* < 0.05 (\*) and at *p* < 0.01 (\*\*).

#### *3.2. Nosema Ceranae Spores*

After newly emerged bees were fed on 100 mg/kg HMF for 10 days, *Nosema* was detected in dead bees at an average density of 2.6 × 10<sup>6</sup> spores/bee. From day 11 until the end of the experiment, spores were present in variable numbers in each of the treatment groups. The highest number of spores (6.6 × 106) was observed between days 26 and 30 in untreated control bees (Figure 3). From day 21 until the end of experiment, the highest number of spores per individual bee (5.76 × 106) was noted in the group receiving 100 mg/kg of HMF in Apifonda candy. There were no statistically significant differences between the groups in the interval between day 10 and day 20 (F = 0.642; df = 4; *p* = 0.634). From day 21 until the end of the experiment, there was a statistically significant difference between treatment groups. A high density of *Nosema* spores (3.55 × 106) was detected in the younges<sup>t</sup> bees (10–15 days) exposed to 1500 mg/kg of HMF in Apifonda, and a lower *N. ceranae* spore density was found in bees that died later in the course of the experiment.

**Figure 3.** The number of *Nosema ceranae* spores counted in dissected bees. The average values are expressed in millions of spores per worker bee. HMF quantity is expressed as mg/kg of HMF in Apifonda candy. The control group received only Apifonda candy. Asterisks indicate a statistically significant difference of *N. ceranae* spore counts inside a treatment group on different sampling dates. The Tukey test shows a difference at *p* < 0.05 (\*) and at *p* < 0.01 (\*\*).Note that *N. ceranae* spores were not detected in bees from treatment groups 3 and 4 at the first sampling date. Across all treatment group, 350 bees were examined.
