The unprecedented disappearance of honeybees has been big news for the last six years. Since bees are crucial pollinators for agriculture, their unexpected absence, now known as colony collapse disorder, is felt everywhere, from apple orchards to buckwheat farms.
As scientists and beekeepers work to find the cause of colony collapse, they have uncovered natural mechanisms bees already have in place to protect themselves from harm.
Though colony collapse disorder is not yet understood, most scientists now agree that it is the confluence of many factors and does not have one cause, as was originally thought. Early theories focused on single actors like mites or viruses, but as researchers studied the affects of pesticides and other pathogens, they began to see a bigger picture of environmental stress coming from a number of sources.
“The thing to understand about honeybees is that they’re an organism not native to North America, introduced for agriculture,” Irene L.G. Newton, an assistant professor of biology at Indiana University, said. “They are managed and artificially inseminated. The number of drones used for that insemination is [probably] unknown to you. There have been concerns about the genetic diversity of stocks and within the colonies.”
Since it was first identified in 2006, colony collapse has been documented in North America, Western Europe and even Taiwan. In all of these regions, honeybees are manipulated to pollinate specific crops at particular times. Subce honeybees are nonnative in many of the countries where they are used, their populations are managed entirely by humans (excluding small feral offshoots).
Beekeepers, known as apiarists, have incredible influence over national bee populations. Apiarists buy inseminated queens, set up hives and take measures to protect the health of their bees, including treating them with antibiotics. However, these preventative steps can have unintended consequences.
In trying to explain colony collapse disorder, scientists have come across a number of mechanisms that bees naturally use to defend against immune threats. One recent study conducted at Wellesley College Massachusetts looked at bacteria found in the digestive systems of bees, and found that bee colonies with high overall genetic diversity had more types of bacteria in their systems than less genetically diverse bees. In turn, the bees with more types of bacteria in their guts and hives were more resistant to pathogens overall.
The study pointed out that if genetic diversity ultimately plays a role in population health, then beekeepers need more information about how their queens are being fertilized so they can make informed choices about where they source their queens. Since queens can be fertilized by more than one male bee, or drone, at a time, apiarists can have diverse populations if their queen is fertilized by a diverse group.
“If you are a regular honeybee keeper, from a hobbyist all the way up to a honey bee farmer, it’s very hard for you to assess the diversity of your colonies,” Newton, one of the study authors, said.
In order to assess the impact of genetic and bacterial diversity, the researchers used queens that had either been fertilized with the semen of 15 drones or only one drone to produce diverse or uniform colonies.
After two months the specially prepared queens repopulated the colonies and the researchers began sampling the bacteria in bee digestive tracts. They also looked at the bacterial makeup in a bee food source called bee bread, which bees “bake” by packing pollen into honey combs with special bodily secretions.
By genetically sequencing the bacteria they found, the researchers were able to get a specific picture of which bacteria were present and how many types of bacteria there were.
“Diversity is generally more stable,” Newton said. “You have a more stable network of community interactions. When you have a less diverse community that’s when you have specific failure points. Our assertion is that if you have healthy bees they won’t succumb to disease in the first place.”
The idea that genetic diversity can impact the presence of good bacteria in a colony is starting to gain traction in the field. “This is really an interesting study. No one has really looked at this aspect,” Susan Cobey, a bee breeder and geneticist at University of California, Davis and Washington State University, said.
“You have a very small cottage industry that produces queens so they have narrowed the gene pool…It just seems like everything points to how important genetic diversity is within the bee population, within the colony.”
The idea that bees naturally provide themselves with pathogen protection likewise emerged in another recent study about honeybees’ ability to defend against parasites. The study examined the plant resins that honeybees use to line their hives in the wild, known as propolis.
Instead of using the wax they naturally produce, which has similar structural and water repellent properties, bees exert energy to collect and distribute resins, forming them into what is known as a propolis envelope. The researchers hypothesized that the choice of resin over wax must be advantageous in some way to merit the additional effort needed to collect it.
To test this, they painted the inside walls of 12 colonies with resin, while leaving 11 colonies resin-free as a control. Next they introduced parasites and monitored the colonies for larva, infant bees, that were infected or dead.
The researchers found that whether the colonies had been treated with resin or not, the bees still hunted for resin at an increased rate in the presence of fungal infection. While 1 percent of bees might normally dedicate their foraging to resin, up to 10 percent were hunting for resin when the colony was facing the fungal threat.
“Regardless of whether they were enriched or not, they collected more resin,” Mike Simone Finstrom, a postdoctoral associate at North Carolina State University and lead author on the study, said.
In addition to the increased collection, the colonies that had been treated with resin had lower instances of larval infection and seemed to experience less overall challenge as a result of the fungus.
These two factors combined led researchers to conclude that not only does resin have antimicrobial properties, but that bees are also aware of this and know how to “self-medicate” in response to a parasitic threat.
“There’s all this sort of negative information out there about colony collapse disorder, but this really highlights the fact that bees are really complex and have really complex defenses against all kinds of things…we just need to promote that a little bit more,” Finstrom said.
The connection between resin and reduced fungal load is still only a correlation, but it holds promise as an instructive example of protective bee behaviors. “Propolis does quiet the immune system and it seems that the pathogen loads are less. And they use it extensively in other countries for human medical use,” Cobey said.
“The black honey bee was introduced here, but pretty much went out of popularity because of its huge propolis production. It was messy, but if you look at that close social network of a honey bee colony they must have some mechanisms to control diseases.”
Though researchers still do not agree about the cause or causes of colony collapse disorder, they do increasingly acknowledge the myriad sources of concern. “Colony collapse is really complicated. There’s no real consensus about what the true cause is,” Finstrom said.
“I think the only thing that’s agreed upon is it’s multiple interacting factors. It’s not necessarily the same interacting factors in each case, and because it’s so complex I think again that’s where we can focus on helping the bees get healthy using their own behaviors.”
