*3.1. Survival Tests*

Survival results of the test using organic acids, detailed in Figure 3.1A, showed a clear toxic effect of p-coumaric acid [pCA], abscisic acid [ABA] and the highest concentration of acetic acid [AA\_H] compared with control treatment (*p* < 0.001). On the other hand, acetic acid [AA\_L] at the lowest concentration (four times lower than [AA\_H]) kept the survival response at the same level of the control treatment [CTR] and fumagillin [DCH]. The administration of *S. cerevisiae* live cells caused a progressive toxic effect to *N. ceranae* infected bees, reaching less than 50% of live bees at day 9 post-infection (Figure 3.1B). When bacteriocins were administered, a toxic effect was only detected for the highest dose of nisin [NIS\_H]. The remaining treatments did not show significant changes in honey bees' survival. Toxicity curves shown in (Figure 3.1C), related to wine-derived products, demonstrated no toxicity of wine vinegar [WV] with control treatment and fumagillin [DCH]. On the contrary, sulphites caused significant toxicity in bees (*p* < 0.001). The two plant extracts assayed [OPT and PP] caused a toxicity level higher than CTR and DCH, as detailed in (Figure 3.1D).

**Figure 1.** Survival of honey bees. (**A**) Survival curves for treatments in the test on "organic acids"; (**B**) Survival curves for treatments in the "test on microbial origin compounds"; (**C**) Survival curves for treatments in the test on "wine derivatives"; (**D**) Survival curves for treatments in the "plant extracts"; Asterisk (\*) indicate significant differences with control treatment (Kaplan–Meier survival analysis, log-rank test; Statistical details for each test: 1A (*p* < 0.001, 52.256, df = 5); 1B (*p* < 0.001, 25.167, df = 7); 1C (*p* < 0.001, 176.870, df = 3) and 1D (*p* < 0.001, 51.352, df = 3). [AA\_L] Acetic Acid

lower concentration; Acetic Acid higher concentration [AA\_H]; *p*-Coumaric Acid [pCA]; Abscisic Acid [ABA] ; *Saccharomyces* sp. [SC]; a mixture of gramicidin A, B, C, and D [GRA]; Nisin higher concentration [NisA\_H]; Nisin lower concentration [NisA\_L]; Fumagillin [DCH]; infected control without treatments[CTR]. [\*] *p* < 0.001).

#### *3.2. N. ceranae Quantification*

In collected honey bees, natural infection of *N. ceranae* was predominantly absent, indeed the highest detection did not exceed 2.0 Log NcU.
