Antiparasitic effects of three floral volatiles on trypanosomatid infection in honey bees

Authors: PALMER-YOUNG, EVAN - Non ARS Employee; MARKOWITZ, LINDSEY - University Of Maryland; Grubbs, Kyle; ZHANG, YI - Guangdong Academy; Corona, Miguel; SCHWARZ, RYAN - Fort Lewis College; Chen, Yanping - Judy; Evans, Jay

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2022
Publication Date: 9/26/2022
Citation: Palmer-Young, E., Markowitz, L.M., Grubbs, K.F., Zhang, Y., Corona, M.V., Schwarz, R., Chen, Y., Evans, J.D. 2022. Antiparasitic effects of three floral volatiles on trypanosomatid infection in honey bees. Journal of Invertebrate Pathology. 194:107830. https://doi.org/10.1016/j.jip.2022.107830.
DOI: https://doi.org/10.1016/j.jip.2022.107830

Interpretive Summary: Honey bee parasites are costly to beekeepers and agriculture by increasing management and replacement costs and limiting the impacts of honey bees on pollination and honey production. This study examined an important gut parasite of honey bees and several plant compounds that are found in nectar, with the goal of identifying natural inhibitors of bee disease. One compound, cinnamaldehyde, significantly reduced parasite levels while not have a negative impact on bee survivorship. This study presents an ecological approach for understanding bee disease resistance in the field and the possible benefits of nectar and pollen compounds on honey bee health.

Technical Abstract: Trypanosomatid gut parasites are common in pollinators and costly for social bees. The recently described honey bee trypanosomatid Lotmaria passim is widespread, abundant, and correlated with colony losses in some studies. The potential for amelioration of infection by antimicrobial plant compounds has been thoroughly studied for closely related trypanosomatids of humans and is an area of active research in bumble bees, but remains relatively unexplored in honey bees. We recently identified several floral volatiles that inhibited growth of L. passim in vitro. Here, we tested the dose-dependent effects of four such compounds on infection, mortality, and food consumption in parasite-inoculated honey bees. We found that diets containing the monoterpenoid carvacrol and the phenylpropanoids cinnamaldehyde and eugenol at >10-fold the inhibitory concentrations for cell cultures reduced infection, with parasite numbers decreased by >90% for carvacrol and cinnamaldehyde and >99% for eugenol; effects of the carvacrol isomer thymol were non-significant. However, both carvacrol and eugenol also reduced bee survival, whereas parasite inoculation did not, indicating costs of phytochemical exposure that could exceed those of infection itself. To our knowledge, this is the first controlled screening of phytochemicals for effects on honey bee trypanosomatid infection, identifying potential treatments for managed bees afflicted with a newly characterized, cosmopolitan intestinal parasite.