By: Helen Beilinson
The Araña Caves in Valencia, Spain are famous for the rock art left by prehistoric people. Aside from more traditional images featuring human figures hunting with bows and knives, there is a portrait of a human gathering honey from a beehive high in a tree, surrounded by a swarm of honeybees. Estimated at 8,000 years old, it is the oldest known depiction of humans consuming honey. Millennia later, we are still eating honey, although our methods for obtaining honey have gotten much simpler and safer. However, the last three decades have been harsh for the apiculture (beekeeping) industry, with our honey supplies diminishing frightfully rapidly. The problem lies in honeybee populations being threatened, but fortunately, research aimed at understanding why honeybee death is at such a high point and how it can be stopped.
Honey is a sweet, thick liquid food made by various species of bees foraging nectar from various species of flowers. Distinct kinds of honey, differing in taste, viscosity, and other properties, arise from varying combinations of bee species feasting on different flowers. After collecting nectar from flowers, honeybees convert it to honey by regurgitating the nectar and allowing the liquid within it to evaporate, while it is stored in wax honeycombs that the bees build within their beehives. Although it is incredibly sweet and delicious for humans and many other animals, its acidity, lack of water (thanks to the evaporation process by which it is made), and low presence of hydrogen peroxide, mean that most microorganisms cannot live in honey. In fact, when burial chambers of Egyptian royals were discovered, the pots of honey they had buried with them (to ensure a sweet transition into the afterlife) were entirely unspoiled, and just as delicious, after thousands of years.
Aside from being a delectable addition to tea, Greek yogurt, and Nutella sandwiches, honey has medicinal applications, thanks again to its biochemical properties. In 220 BCE during the Qin dynasty, a Chinese medicine book was published praising the ability of honey to cure indigestion. Folk healers in Mali use it topically to treat measles, and my dad used to put honey in my nose when I was a kid because according to Russian folk medicine, if you let honey flow through your nose to your mouth, you can get rid of a stuffy nose. I cannot speak to honey’s curative abilities in indigestion and against measles, but I can say that for at least a day after honey being put in my nose, I didn’t need to blow my nose even once.
Since the 1980’s, the honeybee population has been drastically declining, nearly halving in those years. Not only does this pose a threat to the apiculture industry, it also means that any foods pollinated by bees are also facing the prospect of being threatened. According to the United States Department of Agriculture, one in three foods directly or indirectly benefit from honey bee pollination. The loss of honeybees has been linked to various causes, particularly to infection. Bees have very strong and interesting immune systems, but bee populations are often being infected with many new emerging pathogens that lead them to die more quickly. Additionally, Colony Collapse Disorder (CCD) has also been connected to the loss of honeybees. This is a mysterious phenomenon in which worker bees, who physically collect pollen and nectar and make honey, leave their hives and queen bees behind. In essence, this renders the hive nonfunctional. It is not known what exactly causes CCD, but many believe that when worker bees get infected, they will leave their hives to die independently, preventing the risk of getting their queen bee sick.
One of the biggest threats to the beekeeping community is the parasitic mite, Varroa destructor. This mite reproduces in honeybee colonies, sucking the circulating fluids of adult bees for food. If the mite is infected with a microorganism and this microorganism is present in the saliva, this microorganism can spread to the honeybee. Recently, a group of scientists published their discovery of the mechanism by which a virus takes advantage of this means of transmission.
Deformed wing virus (DMV) causes wing and abdominal deformities, as well as affects the cognitive functions, in its bee hosts. Infected bees not only have a drastically reduced lifespan, they are thrown out of their hives in an attempt to prevent the spread of the disease to other individuals. Because of this innate mechanism bees have to eliminate sick bees from their hives, DMV is not an exceptionally good virus at spreading. In fact, only about one in ten colonies are affected by DMV, and those colonies infected tend to eliminate the virus quite readily. Unfortunately, DMV not only can replicate within honeybees, but it can also quite readily expand in the mite, V. destructor. The mite acts as a species in which the viral population can be concentrated and also makes viral spread much faster and more efficient. When mites are also infected with DMV, frequency of the virus in colonies increases from 10 to 100 percent. This relationship is arguably the single greatest inducer of CCD. Although the relationship between DMV and mites was previously known, the details of how these two species work together to aid each other’s replication were not well understood.
It was known that DMV suppresses the immune system of honeybees. To gain an understanding of how the virus affects the bees, the authors of the aforementioned study assessed how the bee larvae respond to different levels of virus infection, without the presence of the dust mite. They found that with increasing levels of virus, the larvae had lower melanization and encapsulation indexes. Melanization is the process by which melanin, the dark pigment in skin, is concentrated, and encapsulation is the process by which the larvae can uptake things, like pathogens to neutralize, from their environment. These processes are linked in that when foreign objects occur in the larva, they are encapsulated and these capsules are subsequently deposited with melanin (melanization) and other toxic molecules to mark them for elimination. The genes responsible for these processes are genes involved in the immune responses of these honeybees, controlled by a factor called NF-κB.
The authors found that in honeybees with more virus particles, there was a greater effect on the expression of their immune genes: the more infected the bees are, the less NF-κB they express. Less NF-κB means less immune genes being expressed, leading to decreased immune responses, such as melanization and encapsulation. The authors observed that these responses are also increasingly dampened with more viral particles.
From the observation that the dampening of the immune response was proportional to virus presence, the authors hypothesized that mites would replicate better on honeybees with more virus and would replicate worse on honeybees with less virus. To test this, the scientists infected the larva first with DMV. After some stages of development, they placed only one mite on each bee. After the honeybees were able to grow independently, they assessed how many mites were on each bee. The proportion of mites on an individual bee correlated with the amount of virus in each bee, such that if a honeybee had lots of virus, the honeybee was covered in tons of mites. Any lucky honeybee to have only a few viruses or none at all had practically no mites living on it.
The close relationship between the Varroa mite and DMV has been a major cause of CCD in honeybees around the world. Many current treatments and prevention techniques against this disease have been targeted at eliminating the mite from bee colonies. However, this study has shown that by reducing the viral load in a bee population, it could directly reduce the mite burden, as well. Studying the basic biology of this complex relationship has shown that the current methods of treating honeybees may not be the best way to tackle the problem, highlighting the importance of basic science. Without the virus suppressing the immune system of the bees, the mites are not as able to feed on their honeybee hosts. Not only will targeting DMV help the honeybees combat the dust mites, but it will also maintain the strength of their immune systems to fight off any other pathogens that enter their colonies and keep honey a staple in many dishes around the world.