Effects of ingested essential oils and propolis extracts on honey bee (Hymenoptera: Apidae) health and gut microbiota

Authors: EWERT, ALLYSON - Louisiana State University; Simone-Finstrom, Michael; Read, Quentin; HUSSENEDER, HUSSENED - Louisiana State University; Ricigliano, Vincent

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2023
Publication Date: 12/6/2023
Citation: Ewert, A.M., Simone-Finstrom, M., Read, Q.D., Husseneder, H., Ricigliano, V.A. 2023. Effects of ingested essential oils and propolis extracts on honey bee (Hymenoptera: Apidae) health and gut microbiota. Journal of Insect Science. 23/6. https://doi.org/10.1093/jisesa/iead087.
DOI: https://doi.org/10.1093/jisesa/iead087

Interpretive Summary: Honey bee hives require frequent human inputs to maintain colony health and productivity. Beekeepers use variety of natural treatments to control disease and reduce the use of synthetic chemicals. However, despite their popularity in beekeeping, there is limited information regarding the impact of ingested natural products on bee health. Here, we tested the effects of different essential oils and propolis extracts on honey bee lifespan, nutrient assimilation, xenobiotic detoxification, and gut microbiota abundance. We found that lemongrass oil, spearmint oil, and propolis extracts lengthened worker lifespan, while thyme oil shortened lifespans. None of the treatments affected nutrient assimilation as measured by head and thorax weight, but all resulted in lower expression of detoxification-related CYP genes. The core gut microbiota generally demonstrated resilience to the introduction of natural products to the diet, with no significant shifts observed in the abundances of the eight bacteria targeted. Our results suggest that in addition to propolis’s structural role in the hive and its positive effects through volatile exposure, it may also exert health-modulating effects when ingested. Thyme oil, a commonly used treatment, was toxic at field-realistic dosages and should be reconsidered as a feed additive. We conclude that propolis extracts, lemongrass oil, and spearmint oil are relatively safe for bee consumption, with apparent health-promoting effects.

Technical Abstract: Managed honey bee (Hymenoptera: Apidae: Apis mellifera Linnaeus) hives require frequent human inputs to maintain colony health and productivity. A variety of plant natural products (PNPs) are delivered via feed to control disease and reduce the use of synthetic chemical treatments. However, despite their popularity in beekeeping, there is limited information regarding the impact of ingested PNPs on individual bee health. Here, we tested the effects of different essential oils and propolis extracts on honey bee lifespan, nutrient assimilation, xenobiotic detoxification, and gut microbiota abundance. We found that lemongrass oil, spearmint oil, and propolis extracts lengthened worker lifespan, while thyme oil shortened lifespans. None of the PNPs affected nutrient assimilation as measured by head and thorax weight, but all resulted in lower expression of detoxification-related CYP genes. The core gut microbiota generally demonstrated resilience to the introduction of PNPs to the bees’ diets, with no significant shifts observed in the abundances of the eight bacteria targeted. Our results suggest that in addition to propolis’s structural role in the hive and its positive effects through volatile exposure, it may also exert health-modulating effects when ingested. Thyme oil, a commonly used treatment, was toxic at field-realistic dosages and should be reconsidered as a feed additive. We conclude that propolis extracts, lemongrass oil, and spearmint oil are relatively safe for bee consumption, with apparent health-promoting effects.