Honeybee intestines retain low yeast titers, but no bacterial mutualists, at emergence

Honeybee symbionts, predominantly bacteria, play important roles in honeybee health, nutrition, and pathogen protection, thereby supporting colony health. On the other hand, fungi are often considered indicators of poor bee health, and honeybee microbiome studies generally exclude fungi and yeasts. We hypothesized that yeasts may be an important aspect of early honeybee biology, and if yeasts provide a mutual benefit to their hosts, then honeybees could provide a refuge during metamorphosis to ensure the presence of yeasts at emergence. We surveyed for yeast and fungi during pupal development and metamorphosis in worker bees using fungal‐specific quantitative polymerase chain reaction (qPCR), next‐generation sequencing, and standard microbiological culturing. On the basis of yeast presence in three distinct apiaries and multiple developmental stages, we conclude that yeasts can survive through metamorphosis and in naïve worker bees, albeit at relatively low levels. In comparison, known bacterial mutualists, like Gilliamella and Snodgrassella, were generally not found in pre‐eclosed adult bees. Whether yeasts are actively retained as an important part of the bee microbiota or are passively propagating in the colony remains unknown. Our demonstration of the constancy of yeasts throughout development provides a framework to further understand the honeybee microbiota. Take Away The honeybee intestine possesses a characteristic bacterial microbiota that is obtained from nestmates after emerging from the comb's cell. It is generally assumed that upon eclosion, the bee's intestine effectively lacks a bacterial community. We investigated the presence of yeast throughout honeybee development, focusing on emerging worker bees. We found that, in contrast to bacteria and other microbes, the honeybee gut can possess a diverse set of yeasts at emergence, albeit at low density. We discuss possible active or passive roles played by these yeast species as worker bees commence in‐hive nurse duties.