Honeybees, the most-loved insect, and a vital part of the pollination system that ensures we have fruit, nuts, and veggies in the stores to buy and eat, have a nemesis. In recent years you’ve likely seen concerns over Colony Collapse Disorder (also known as CCD) but what you probably haven’t heard about are the Destructors. A tiny mite, named Varroa destructor, that is. It may sound like a supervillain, but… ok, yes, it’s a supervillain. I mean, what else do you call a parasite that hitches a ride, weakens the worker bees, and finally kills the hive’s babies before they can grow up? Fortunately, modern science has given us tools to combat the supervillains, er, mites. We’ve come a long way since Gregor Mendel’s pottering with pea plants and the later work of Punnet and his squares. Which is a good thing, since bee reproduction is complicated, so heredity and deciding which bees fight off the mites best would be difficult without some help.
That help comes in the form of the honeybee genome sequence, but first, let’s talk about why the mites are an issue, and what some bees do to control their damage. Varroa mites are an external parasite on honeybees, sucking their blood (Nalen, 2010). On adult bees this is bad enough, weakening them, but on the brood (developing larva in wax cells) it is devastating, maiming or killing the larvae before they can develop into adults. As a result, Varroa earns the dubious title of the world’s most devastating pest of honeybees. Beekeepers have been fighting them off with pesticides and careful management of hives, but believe that Varroa have killed off almost all the wild hives in the Northern Hemisphere, where weakened hives cannot withstand the additional stress of winter on top of mite damage. However, even as this massive die-off was happening, beekeepers also noted that some wild hives, and some domestic, were better able to withstand the ravages of the tiny bee vampire, the mite (J Carter Loftus and Michael L Smith, 2016).
In this paper, Genome-Wide Association Study of a Varroa-Specific Defense Behavior in Honeybees (Apis mellifera), authors Andreas Spotter, Pooja Gupta, Manfred Mayer, Norbert Reinsch, and Kaspar Bienefeld ask whether it is possible for honeybees to be genetically selected for good housekeeping. The bee hives who survive detect mite damage to brood very early, and then break open the cell, removing the infected brood to discard. Can that be selected for, and would it help beehives survive the mites with less intervention needed from beekeepers? This would be a great savings in economic investment, time, and a possible resurgence of wild hives. The medications that are used to treat bees are already failing due to growing mite resistance, and concern about possible contamination of honey harvested from treated hives. If the workers who display hygienic behavior – the good housekeepers – could be studied for their genes, and then that study narrowed down to the specific genes that drive the behavior, perhaps a new strain of bees could be developed (Andreas Spotter, 2016).
It was a daunting task. Anyone who has ever seen a beehive in action knows that bees don’t sit still for long. In order to observe the workers and decide who was a good housekeeper, the researchers had to tag and observe 22,000 bees. Later, they narrowed those down to a mere 122 that showed the traits they wanted to study genomically. In the process, they determined that bees who detected the infected brood had heighted olfactory sensitivity – the bloodhounds of the bee world, as it were – which helped them find the sick baby bees. This was, they decided, a very useful trait not only for hives afflicted by Varroa, but two of the other villains in the bee’s world, American Foulbrood and chalkbrood. Even more than the damage cause by Varroa, those two are stinky, enough so that even nose-blind (relatively) humans can detect them in a hive who is infected. The authors modestly state “our study makes a significant contribution,” and they are quite right, breeding a better bee that can detect the pathogens in their hive is very important to the long-term survival of honeybees (Andreas Spotter, 2016).
Finding specific genes associated with behavior is not an easy process, and it is not always precise. In this case, the honeybee genome is not yet fully mapped out, so more studies will be needed to pinpoint the genes related to Varroa resistance. However, the research outlined in this paper was able to identify and confirm suspected genes as being related to traits that are desirable in bees that can smell out problems, deal with them, and more, can remember it for later (Andreas Spotter, 2016).
Honeybees are not the only pollinators. There are many other insects, birds, and even mammals who pass along a plant’s genetic cells in exchange for a sweet treat of nectar. But humans and honeybees are very closely tied together in a millennia-old association involving honey, better gardens (morphed later into big agriculture) and hive protection from large predators. Economically, bees are big business these days. So a study that can lead to a better bee, resistant to that supervillain the Destructor, is a valuable tool which can be used to build a solution to combat not only the mite, but the bacterial, viral, and fungal diseases that ride along with it (Nalen, 2010).
Future research, along with a full genome map of the honeybee, will hopefully lead to the genetic engineering of a bee that can keep a clean house, detecting dying brood early enough to prevent the spread of the mite and other diseases. Further studies to pinpoint genes that are responsible, and then breeding bees with these genes inserted or highly-expressed (which means that they will make more of the desired genes) would be interesting to see what happens. In this study, they just looked at the genes. Later, having bees that could demonstrate what those genes could do… look out, Destructor! The super-bees are coming.
References
Andreas Spotter, P. G. (2016). Genome-Wide Association Study of a Varroa-Specific Defense Behavior in Honeybees (Apis Mellifera). Journal of Heredity, 1-8.
J Carter Loftus and Michael L Smith, a. T. (2016). How Honey Bee Colonies Survive in the Wild: Testing the Importance of Small Nests and Frequent Swarming. PLOS One.
Nalen, J. D. (2010, June). Featured Creatures. Retrieved from Entomology and Nematology: http://entnemdept.ufl.edu/creatures/misc/bees/varroa_mite.htm
Why I chose this topic:
I chose to look for articles relating to honeybees, as my father is a beekeeper and I have spent extensive time working on his hives and planning with him for them. Treating bees is a tedious chore that must be precisely planned for the harvest of honey, and still doesn’t always allow the hive to survive a winter, which is not only expensive, but for keepers like my father who get attached to their ‘girls,’ quite sad. I am looking forward to seeing where this genetic information takes breeding programs in the future.