Studying feral honey bees is giving us a window into how they are able to persist in such a challenging world
Domesticated animals often do fine if they are turned loose into the wild to fend for themselves — sometimes more than fine. Feral cats, for example, have been so successful at hunting and reproducing that they are listed as one of the most harmful invasive species globally. Feral horses, hogs, goats, and dogs, among others, also have sustained populations independent of human care, and in some cases they act as pathogen reservoirs, spreading disease to closely related wild animals. Even domestic honey bees have feral counterparts, if you know where to look.
Dr. Margarita López-Uribe, an assistant professor in entomology at Pennsylvania State University, began studying feral honey bee colonies in North Carolina. There, she found that feral and managed bees had different levels of immune gene expression despite having similar levels of pathogens.1 “That study sparked an interest in understanding how it is that feral colonies can survive the winters without beekeeping management,” she says.
Unlike most domestic animals, honey bees are plagued by diseases and parasites for which there is often no cure, only management, owing to their social existence and high pathogen transmissibility. As beekeepers, we are ethically and economically obligated to keep our colonies as healthy as we can through management, but this reduction of selective pressure — which is necessary for the evolution of natural mechanisms of disease control — coupled with the difficulties of selective breeding, means that domestic colonies are unlikely to ever become the self-sufficient survivors we would all love them to be.
Feral colonies, however, experience the full force of parasite, pathogen, and nutritional pressure, and studying them can show us what the bees are really made of. While it is immoral to withhold treatments and willfully keep animals, even insects, suffering with disease, feral honey bees escaped this animal ethics dilemma when they escaped the beekeeper’s apiary. “We know that most managed colonies that don’t receive treatments for varroa die within the first year,” López-Uribe says. And yet, “wild” colonies can still persist. “How are feral bees doing it?”
López-Uribe and Chauncy Hinshaw, a doctoral student in the Department of Plant Pathology and Environmental Microbiology, recently published work with their colleagues at Penn State showing that feral honey bees had higher loads of deformed wing virus (DWV) and elicited a stronger innate immune response compared to their domestic counterparts.2 In this study, the researchers defined a “feral” colony to be an established swarm that already survived one or more winters without intervention prior to the study.
Because the feral colonies were located in inaccessible cavities, it was not possible to measure features like mite levels, brood area, or honey stores. But Hinshaw, López-Uribe, and Katy Evans (another researcher involved in the work) could net foragers entering and exiting the hive to measure their pathogen loads and immune gene expression, then compare these metrics to those from nearby managed colonies, which forage in similar landscapes and experience a similar climate. The researchers collected foragers in the spring and fall across two years, while also recording which colonies lived and died.
Of the three pathogens that they measured — DWV, black queen cell virus, and Nosema ceranae — only DWV differed between managed and feral bees. Since varroa is its primary vector and feral colonies are not receiving varroa treatments, the researchers inferred that these colonies probably also had high mite loads. And yet, these bees were still able to survive.
The feral colonies appear to be tolerating the virus (and likely also the mites), rather than resisting it. In immunological terms, tolerance refers to the ability to withstand high pathogen loads without incurring substantial damage to host health. Resistance, however, is actually limiting the pathogen’s ability to reproduce. For example, a varroa-tolerant colony could have high varroa loads, but not appear to be hindered and may never develop parasitic mite syndrome. A varroa-resistant colony, rather, would express behaviors like grooming or varroa-sensitive hygiene to damage or remove the mites, thus limiting the mite burden altogether.
Since the feral colonies had comparatively high DWV loads but, for the most part, still survived, they were exhibiting tolerance. The high levels of immune genes recorded by the researchers show that the bees were also actively fighting the infection to some degree, but such immune activation also comes with a cost.
Resources invested in a sustained immune response are resources not available to be used for other things, like producing and secreting brood jellies, wax, or pheromones. Think of how tired you feel if you catch the influenza virus, rhinovirus, or the dreaded coronavirus.
“We have data that suggest that actually, the upregulation of these immune genes may be an indicator of stress in the individuals,” López-Uribe says. “Other studies have also demonstrated that the high levels of immune gene expression may impact the “biological age” of the bees. So, there are certainly trade-offs for bees if they exhibit high levels of immune gene expression, which likely impact the energetic budget of the bees.”
Since only non-invasive data could be collected on the feral colonies, we don’t know exactly how those costs manifested here. It is entirely possible, perhaps likely, that the feral colonies were not as productive, in terms of honey yields or population growth, as the managed colonies. Yet, surprisingly, the feral and managed colonies still had comparable odds of surviving the winter. In the first year of the study, feral and managed colonies had the same survival rate at 63%. In the second year, feral colonies had slightly higher survival rates, at 47% compared to 38%.
This might be because although managed colonies have a helping hand, in terms of fighting disease and parasites, they are also part of somebody’s business — the aim of which is, obviously, to make money. To achieve that, it’s tempting, for example, to take honey and feed back just enough sugar to get away with, or make as many splits as you reasonably can. But management for profitability could be taking an additional toll.
While it’s not clear exactly what was done to or how much profit was made from the managed colonies in this study, the similar ….