Researchers working out of UC Davis’ Harry Laidlaw Honey Bee Research Facility have published a new paper demonstrating that honey bee workers that specialize in an important disease-related task are likely to also specialize in another disease-related task. The researchers suggest this kind of association among tasks may be an understudied component of how honey bee colonies fundamentally operate and how they defend themselves against disease.
Honey bee colonies consist of upwards of 80,000 individuals all working towards a common goal of colony survival. Like a highly sophisticated factory, honey bees divide up labor and utilize assembly lines and specialized workers to be as efficient as possible. One task that honey bees perform is hygienic behavior—in which a worker bee detects that a capped pupa (a developing young bee) is infected with a pathogen, uncaps the cell of the infected pupa, and drags it out of the colony before it gets other bees sick.
Hygienic behavior is an effective colony defense against many diseases and has been studied consistently for quite some time now. Much is known about the behavior and the bees that perform it, but most research has focused only on hygienic workers performing hygienic behavior. In other words, little work has focused on what else hygienic workers do besides hygienic behavior. In this particular study, the authors were interested in testing whether hygienic bees also had a propensity to groom other workers, take out dead bodies from the hive (known as undertaking), or apply antimicrobial tree resin to the nest (known as propolis or cement work) since these behaviors also contribute to colony disease defense.
In this study, the authors used glass-walled observation hives that allow for bees to be monitored while working in the colony.
The researchers started the experiment by introducing a frame of frozen killed pupae to the focal observation hive, which is a standard way of triggering workers to perform hygienic behavior.
They then marked bees performing hygienic behavior with paint through mesh fabric so they could be individually identified. Marked workers were then followed for three days to observe how many additional times they performed hygienic behavior as well as what other tasks they performed.
The authors found that workers that performed hygienic behavior once are more likely to also remove dead adults from the bottom of the hive when compared to workers that don’t perform hygienic behavior at all. This bias for removing dead adults was especially pronounced in workers that performed hygienic behavior repeatedly. What this means is that workers that specialize in hygienic behavior (perform the task repeatedly) are much more likely than other workers to also specialize in undertaking. These results strongly suggest a link between two key behaviors that help keep the colony healthy.
Much like hygienic behavior, undertaking is a task that has been well-studied. Although these two tasks seem rather similar, this study is the first to provide evidence that they are performed, at least in part, by the same set of workers. The authors suggest that these two tasks are performed by an overlapping set of bees because: 1) this subset of workers are the most sensitive to death and disease cues, whether they come from dead pupae or dead adults and 2) because limiting the number of workers handling dead and diseased bees is probably beneficial for limiting disease transmission within the hive. Hence, the association between these tasks may be important both for the factory-like efficiency of the colony but also separately beneficial for its role in limiting the spread of diseases in the hive.
For more information:
*Perez AA, & *Johnson BR (2019) Task repertoires of hygienic workers reveal a link between specialized necrophoric behaviors in honey bees. Behavioral Ecology and Sociobiology, 73(9), 123.
** Link to the paper: https://link.springer.com/article/10.1007/s00265-019-2731-7
*Denotes UC Davis ABGG-affiliated authors
All photos and videos taken by Adrian Perez unless otherwise specified