The more the better: Fatty acids are predictive markers of honey bee, Apis mellifera, worker longevity

Fatty acids (FA), stemming from nutrition, form triglycerides that are key components for insect energy reserves. In managed Apis mellifera colonies, supplementary feeding is common practice, yet micronutrients and microbiota (i.e. B-vitamins and probiotics) are often neglected. Given that B-vitamins are obligate cofactors for FA metabolism, and probiotics likely play key roles as well (i.e. Lactobacillus spp. synthesize B-vitamins), understanding how they contribute to FA acquisition remains unknown. Indeed, FAs are established predictors to A. mellifera longevity, and as such, are a logical point of interest in long-lived “winter” bees, where A. mellifera colony losses typically occur. Here, in a hoarding cage trial, freshly emerged adult winter workers were exposed to antibiotics (ABX) to decouple innate benefits associated to native gut microbiota, or left unexposed to ABX (N=72 cages, N=2088 experimental workers). Subsequently, all workers were fed different diets containing either probiotics, B-vitamins, with replicate treatments given ad libitum access to pollen (mimicking real-hive scenarios) or left blank (control). At the end of the trial, a subsample (n=356) had their total FA contents analyzed using Gas Chromatography coupled to Flame Ionization Detector (GC-FID). Irrespective of dietary treatment, every worker contained all 11 identified FAs, aligning our results with a priori evidence and highlighting their underlying key roles for bee physiology and health. We show for the first time that B-vitamins alone did not improve the overall abundance of individual FAs (g), yet significant differences were associated with presence/absence of bacteria and/or access to pollen, reconfirming likely ties of microbiota aiding in nutrient breakdown of complex polysaccharides found in pollen. Finally, of clear importance, there was a positive significant correlation between total lipid content and worker longevity (+2.4 median day lifespan increase / mg of FA), thereby confirming the relevance of FAs for honey bee worker longevity.

Methods
The data here were collected at the Institue of Bee Health (Bern, Switzerland), in autumn 2019. Subesequent Fatty Acid (FA) analysis took place at the University of Fribourg (Fribourg, Switzerland). The data has been processed (i.e. analyzed) with the open-source software R, and the script and the corresponding data are available here for download. Please refer to the publication (materials and methods) for in-depth details about data collection, FA extraction, and data analysis.