Antoł, W. | Search bioRxiv

bioRxiv2025

Do shifts in honeybee crop microbiota enable ethanol accumulation? A comparative analysis of caged and foraging bees

Honeybees encounter low environmental doses of ethanol, primarily through fermenting nectar, which can have both beneficial and detrimental effects on their functioning. Yet, ethanol traces can also be detected in the crop of caged bees with no access to environmental food sources. This raises the possibility that endogenous ethanol accumulation could occur under restricted conditions, with microbial contributions as a potential mechanism. The crop microbiota, although less diverse than that in other gut segments, plays important roles in food fermentation and pathogen defense. We hypothesized that captivity-induced shifts in crop microbiota may facilitate fermentation, resulting in measurable ethanol. To test this, we compared the crop contents of naturally foraging hive bees and caged bees reared without access to the natural environment. Ethanol levels were low in both groups and did not differ significantly, but non-zero measurements were more frequently observed in caged bees. Microbial community structure differed strongly in - and {beta}-diversity. Caged bees showed reduced abundance of nectar-associated genera (e.g., Apilactobacillus) and an increase in genera that include known ethanol-producing strains, such as Gilliamella and Bifidobacterium. While we did not directly assess metabolic activity, our results suggest that captivity alters microbial communities in ways that may influence ethanol levels. This raises broader questions about how microbe-host interactions modulate host phenotypes under different environmental conditions.

ecology↗

bioRxiv2025

Honeybees show an increased preference for dietary alcohol when parasitized

Parasitic infections often alter host behavior, including foraging and the consumption of bioactive substances. In honeybees (Apis mellifera), infection with the common gut parasite Nosema ceranae causes metabolic disruption and increased mortality. Ethanol is a naturally occurring bioactive compound found in nectar, and honeybees exhibit high tolerance and resilience to chronic exposure. However, whether bees actively use ethanol during infection remains unclear. Here, we investigated whether N. ceranae-infected honeybees alter their ethanol consumption. In a feeding experiment, infected and uninfected bees were given a choice between plain sucrose solution and ethanol-spiked food (0.5% or 1% ethanol). We measured food consumption, survival, and spore load. Although overall food intake did not differ between groups, infected bees consumed a significantly higher proportion of ethanol-spiked food. Survival analysis showed that a diet containing 1% ethanol caused higher mortality than a diet containing 0.5% ethanol; however, among bees on a 1% ethanol diet, this negative effect was less pronounced in infected individuals than in controls. Spore load did not differ between treatments. These results suggest that N. ceranae infection induces a shift in feeding behavior towards increased ethanol intake, which may benefit infected bees by reducing mortality. This may reflect a self-medication response, although alternative explanations - such as parasite-induced manipulation or ethanol-induced changes in host physiology and immunity - remain possible. Further research into ethanols effects on Nosema spores is needed. Nonetheless, our findings provide insights into honeybee interactions with bioactive compounds and suggest that ethanol may be a behaviorally relevant dietary substance.

pathology↗