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

<p>Fatty acids (FA), stemming from nutrition, form triglycerides that are key components for insect energy reserves. In managed <em>Apis mellifera</em> 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. <em>Lactobacillus</em> spp. synthesize B-vitamins), understanding how they contribute to FA acquisition remains unknown. Indeed, FAs are established predictors to <em>A. mellifera</em> longevity, and as such, are a logical point of interest in long-lived "winter" bees, where <em>A. mellifera</em> 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 <em>ad libitum</em> 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 <u>G</u>as <u>C</u>hromatography coupled to <u>F</u>lame <u>I</u>onization <u>D</u>etector (GC-FID). Irrespective of dietary treatment, every worker contained all 11 identified FAs, aligning our results with <em>a priori</em> 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.</p>