Acaricidal Activities against Varroa destructor and Chemical Composition of Korean Propolis Essential Oils

Varroa destructor is an ectoparasitic mite and one of the major contributors of honey bee population decline over the world. Propolis is a resinous gum material collected by bees from surrounding plants used for sealing and protecting hives, and was reported to have acaricidal effects on Varroa mites. In this study, we compared the chemical composition of propolis essential oils (PEOs) from three sites, Andong, Gongju field and mountain, and tested their acaricidal effects against Varroa mites in the laboratory. Propolis volatiles of Korean origin were composed predominantly of sesquiterpenes, aromatic compounds, and fatty acids. The major constituents in Andong PEO were the sesquiterpenes, β-eudesmol (31.97%) and γ-eudesmol (9.55%), and benzoic acid (10.21%). Gongju field PEO had the aromatic principal constituents bis(2-ethylhexyl) phthalate (14.73%). On the other hand, the predominant compounds in Gongju mountain PEO were 2-methylbenzyl cyanide(17.93%) and 2-propen-1-one, 1-(2,6-dihydroxy-4-methoxyphenyl)-3-phenyl-, (E)-(17.15%). Our GC-MS analysis showed variation in chemical composition at different sites, which might be due to differences in vegetation. Gongju mountain PEO exhibited the strongest activity against V. destructor (LD₅₀ = 294.86 µg/mL) among the evaluated propolis essential oils. However, the acaricidal activities of Gongju mountain was lower than that of the positive control, tau-fluvalinate (LD50 =142.85 µg/mL). Further studies on propolis samples collected from different sites may reveal more potent acaricidal PEOs, potentially contributing to the development of safer environmental controls for mites.