## 4 Discussion  
This study is the first attempt to compare the effects of citric, formic, lactic, and tartaric acids on _V. destructor_ host attachment abilities. The mitoticide impact of formic and lactic acids was demonstrated in anterior field studies [15; 31; 44]; however, little is known about their effects on adherence abilities. We investigated mites' grip skills when their arolia were directly exposed to different organic acids. We chose concentrations of acids according to their common applications in the field. Indeed, formic acid is used in commercial products such as Varromed(r) at 5 mg/mL for trickling [32]. Colonies are treated in Switzerland with lactic acid at 150 mg/mL by spraying [31; 45]. In our conditions, twenty-four-hours post-treatment, we observed that citric, formic, lactic, and tartaric acids impaired the attachment abilities of mites. From a chemical perspective, we could suggest that the acidity of the tested molecules explained the results, regardless of the specific properties of each acid. However, in our preliminary experiment, we tested acetic acid (Figure A1), which did not significantly impact grip skill, preventing the idea that the acidity (pH) of the molecules was sufficient to disrupt attachment abilities in the conditions tested. In addition, it is known that citric, formic, lactic, and tartaric acids have different molar sizes; thus, the quantities of organic acids compared are very different from one another. Yet, even in molar concentration, the difference observed in the rate of fallen mites between acids was not adjusted. Several hypotheses arise from the fall of _Varro_ females after topical treatment of bees with acids. First, organic acids could interfere with the nervous system of mites and paralyse them, inducing the fall [46; 47]. Although it is unlikely for lactic acid, according to our previous findings [36] and the survival curve associated with it (Figure 4). Second, a toxic effect may lead to their fall [18]. It could be the case for tartaric acid, as it reduced _V. destructor_ lifespan; however, it seems not to be true for lactic or citric acid. Third, females' falls could be the result of an interaction between acids and the fluid under their arolia as well as a burn of their arolia, impairing their attachment abilities [36]. Many arachnids and insects leave a footprint under their arolia [48; 49; 50; 51]. Among them, the nature of the fluid may vary from proteins and polypeptides to polysaccharides or lipids. For ticks, the nature of the fluid seemed to be a biphasic oil-water emulsion with solid particles [24; 29; 52]. We do not know the nature of _V. destructor_ footprint fluid; however, we can hypothesise a similar nature to _Ixodides_ due to their close phylogeny [29]. It is therefore interesting to compare grip abilities between a hydrophilic substrate, here the wood, and  
Figure 6: Survival curves over 72 h for honeybees after organic acid treatment (drops on bees’ backs). a hydrophobic one, in our case the cuticle of the honeybee. We found out that for citric acid, mites fell significantly more from honeybees than from wood (when considering 580 mg/mL). On the other hand, tartaric acid at 150 and 600 mg/mL induced a significant fall in wood but not in honeybees. It is even more interesting when considering formic acid. This volatile acid is known for dysregulating cellular respiration in mites, leading to their death [53]. Here we described impaired grip skill on wood but not on honeybees, suggesting that adherence is not challenged in hive treatment. The physical and chemical properties of each acid are crucial when investigating their effects on mite attachment to a host. As a matter of fact, citric and lactic acids are known as biodemulsifiers [54; 55; 56], whereas tartaric acid is a well-known emulsifier [57; 58]. Accordingly, the nature of the fluid cannot be overlooked, as it may be destabilised through the interaction with acids, becoming slippery or sticky [59; 60].