High Sensitivity of Tropilaelaps mercedesae to Lithium Chloride: A Novel Acaricidal Candidate for Honey Bee Health

The rapid global expansion of Tropilaelaps mercedesae necessitates urgent alternatives to conventional acaricides due to emerging resistance. Hypothesizing that the lithium-sensitivity observed in other Mesostigmata species extends to this mite, we evaluated the toxicity of lithium chloride (LiCl) as a novel control candidate through ex situ dose-response bioassays and an in situ pilot field trial. Ex situ contact bioassays quantified the dose-response relationship, revealing a 12-hour LC50 of 45.9 mM. These results indicate that T. mercedesae is intrinsically more than 3.5-fold more sensitive to LiCl than the widespread Varroa destructor , ex situ . Subsequently, field efficacy was evaluated in a pilot trickling trial on infested A. m. ligustica colonies. Repeated administration of 500 mM lithiated sugar syrup induced characteristic tremors and a sharp increase in mite fall, confirming that the acaricidal effect manifests in situ even in the presence of brood. Our findings demonstrate that lithium is a highly effective, naturally occurring candidate for Tropilaelaps management. The observed high sensitivity and distinct intoxication symptoms warrant larger-scale trials to refine application protocols and evaluate in situ efficacy and long-term colony safety for sustainable apiculture.