Summary: Eugenol is a chemical constituent of Clove and Cinnamon Bark essential oils; thymol is a chemical constituent of Thyme and Oregano essential oils. Together or separately, these chemicals have been shown to have a positive effect on bee health.
The chemical activity of essential oil constituents is diverse. Sometimes these constituents act as single chemicals to influence other molecules or to bring about a reaction. Other times, constituents can work with each other and increase one another’s potency. When constituents work together in this way, they are acting synergistically. Two such essential oil constituents, which may act singly or synergistically, are eugenol and thymol.
Eugenol is a primary chemical constituent in Clove and Cinnamon Bark essential oils. As the name may suggest, thymol is a main constituent in Thyme essential oil and is present in Oregano oil. Extensive published research outlines the activities of eugenol and thymol, both separately and synergistically, in insects. These activities are varied, but are often beneficial. As research suggests, eugenol and thymol can have significant and practical effects for one at-risk group of insects: bees.
Thymol and Honeybees
It is widely acknowledged that bees are increasingly threatened insects, with colonies collapsing and populations declining at an unprecedented rate. A prevalent concern among beekeepers is the Varroa mite, which is a tiny external parasite of honeybees. When the Varroa mite attaches to a honeybee, it weakens its host by sucking fat bodies and transmitting diseases. This mite is thought to have the most significant adverse effect on honeybee health.
A 1999 review compiled the varroacidal effects of more than 150 essential oils and essential oil constituents.1 Of all the essential oil components, thymol not only exhibited the highest and most consistent varroacidal activity, but was also well tolerated by the honeybees. In addition, a 2017 study found that a continuous release of vaporized oregano oil into honeybee hives helped manage the mite infection rate, with relatively low toxicity to the bees.2
Synergy of Thymol and Eugenol for Bumblebees
Eugenol or its derivative, methyl eugenol, is found in over 450 species from 80 different plant families. Eugenol’s presence in plants of the Lamiaceae family is extensively documented. Many eugenol-containing members of Lamiaceae also contain thymol, such as oregano, thyme, and marjoram. A 2017 study found that eugenol and thymol could work synergistically to stunt the growth of a certain bumblebee gut parasite in vitro.3 This is an incredible find, since bumblebees (and therefore their gut parasites) are frequently exposed to eugenol and thymol simultaneously while foraging.
Eugenol and Orchid Bees
Eugenol is also one of many compounds that are attractive to males of certain species of South American orchid bees. These bees are thought to collect eugenol in order to synthesize pheromones, which are chemicals used to trigger a social response in other members of the same species. Because of these bees’ penchant for eugenol, it is frequently used to bait and attract them for scientific study.
Eugenol and thymol are remarkably useful compounds for bees. Plenty of research supports the agricultural use of these compounds, singly or synergistically, to promote a healthy bee population. As additional research emerges, we may continue to see eugenol and thymol prove their value in a variety of biological applications.