Since 2006, honey bees have been repeatedly struck by a condition that destroys as many as 95 percent of the hives in a given area, and is thought to be killing over a third of the honey bees in the United States.
This can have devastating consequences, as about one third of all U.S. crops need these bees to thrive. The condition, called Colony Collapse Disorder (CCD), causes the bees to fly away from their homes and never return. It’s been an unsolved, devastating mystery for the bees and the many people who depend on the bees for their livelihood, but just last month an article published in the scientific journal PLoS ONE may reveal the culprits responsible: a microscopic fungus that somehow works with a virus.
The ancient honeybee: To understand how CCD affects not just honey consumption, but our civilization in its entirety, it’s important to appreciate the bee’s ancient roots. While the first, tiny plants appeared on land around 450 million years ago, flowering plants (angiosperms) didn’t evolve for another 320 million years. Early on, beetles were attracted by the nectar from these first flowers and helped pollinate the plants, inadvertently carrying some pollen from one flower to the next, rubbing some off on the stigma as they went. Flowering plant reproduction was greatly aided in this way.
Our protagonist, the humble bee, entered the scene around 100 million years ago. That’s about 30 million years after the first angiosperms. The first bee was tiny (about 3mm long) and thought to have evolved from a wasp. Like the beetles, the bee (Melittosphex burmensis) was attracted to sweet, colorful flowers. But it was more efficient, and soon became a vital part of the pollination process. M. burmensis is now extinct, but its descendents evolved together with flowering plants around the world, allowing them to become widespread and prolific. There are now over 250,000 species of flowering plants; over half need insects to reproduce, and over 20,000 species of bee play a central role.
People and the bees: People have collected wild honey and practiced beekeeping (apiculture) since as long as 20,000 years ago. Not only was honey eaten, but it was also used to treat burns and wounds (it has antibacterial properties), preserve food from spoilage, and create what is possibly the first alcoholic drink (about 6000 B.C.): mead. While this might seem like a long time ago, the particular bee species that people have utilized most, the European honey bee (Apis mellifera), is 60 million years old. Because these small, golden, furry bees form a compact hive, they’re relatively easy to transport into a field that needs to be pollinated.
In addition to being “travel size,” A. mellifera is also very industrious and well-organized; it’s certainly earned its keep. A single bee can pollinate thousands of flowers a day, amounting to five hundred million flowers annually for one hive. A bee makes more than 12 trips a day, normally flying about two miles from the hive, but will go as far as ten miles. And a returning forager bee communicates its entire trip, out and back, to other bees through their famous “waggle dance.”
The social structure of the bee hive is notoriously complex. In addition to the foraging worker bees, there are nurse bees, who groom and clean returning workers, guard bees, bees in charge of cleaning or building, and more. All the bees are female except the male drones, who die immediately after mating with the queen. The queen lays an amazing two thousand eggs a day. All of these roles are vital to keeping a healthy hive running.
These assiduous insects have become essential to our agricultural system, as approximately a third of all our crops (about 90 crops globally) need honey bees to thrive. This includes tomatoes, pumpkins, cranberries, blueberries, apples, peaches, and almonds. In California, the almond orchards, which brought in $1.5 billion in 2006 and account for 80 percent of the world’s almonds, need commercial pollinators the most. In 2000 in the U.S., the sale of crops pollinated by honey bees amounted to $15 billion. Some predict that without the honey bee not only would our crops fail, but whole ecosystems, and maybe civilization as we know it, would suffer significantly. The recent decline of the honey bee has consequently caused justifiable global concern.
Honey bee decline: Domesticated A. mellifera numbers in North America declined, from the 1940s to the 1980s, from about six to three million hives. This was thought to be due to beekeepers retiring, pesticides, normal bee diseases, and mites. However, it got much worse in 1987 when the Varroa destructor mite showed up. Not only does this mite latch onto the bee and suck out its circulatory system fluids, but through this process the mite also transmits a variety of viruses and other pathogens to the bee. These can cause paralysis, damaged appendages, and ultimately death. While beekeepers took extensive measures to reduce the infiltration of V. destructor into their hives, by 2006 only 2.4 million hives were alive in the U.S. Sadly, the worst was yet to come.
Colony Collapse Disorder (CCD): In November 2006, a Florida apiculturist discovered that, within a month, over 90 percent of his hives had emptied out. Although there’d be honey left in the hive, the bees would all be gone except for maybe a queen, a few immature workers, and some doomed larvae. It was the first reported case of CCD. Usually when a hive is infected, the bees die slowly, and corpses pile up on the ground outside of the hive entrance (often ejected by the nurse bees). But no dead bodies were found here (making autopsies impossible). The bees had vanished and the colony would surely collapse.
By January 2007, CCD was reported in 22 states, with some apiaries (bee yards) losing up to 95 percent of their hives. It was soon reported in several European countries as well, and has recurred every year since. By early 2008, it was in 36 U.S. states and killing over a third of the nation’s hives, including 20 percent of California’s domesticated honey bees. (Almond prices are almost certainly going to rise).
First likely suspects for CCD: Genetics studies have found that A. mellifera has a weaker immune system than some of its relatives. It’s thought that the honey bees might have traded a stronger immune system for their highly evolved social structure and the role of nurse bees in carefully screening each bee that enters the hive. Unfortunately, they can only check for so many things; the honey bee is very prone to microscopic pathogens. When researchers tried to find culprits responsible for causing CCD, the list of suspects was lengthy.
Several viruses were prime suspects. But while they were found in colonies with CCD, a single virus wasn’t found to be in all colonies with CCD. Some suspected viruses were even found in hives without CCD, and none were found that exactly matched the symptoms of CCD. Pesticides have also been highly suspect, but, again, their presence did not always correlate with CCD. The list went on and on.
Nosema ceranae was also a likely suspect. N. ceranae is a single-celled, parasitic fungus that can kill a hive in eight days. It’s native to the Eastern honey bee (Apis cerana), but at some point jumped to our protagonist, A. mellifera. It’s been found in its European cousin in samples from 1995. It can be transmitted by the V. destructor mite; the fungus invading the honey bee’s gut, reproducing there and destroying the epithelial cells that line the gut, weakening the bee by making it impossible to absorb food. The bee eventually starves to death. It’s easily spread to other bees within the hive.
In 2009, researchers in Spain reported that N. ceranae was correlated with CCD occurrences, as it was found in all hives with CCD; but U.S. researchers found the fungus in hives without CCD. As shown above, symptoms of N. ceranae infection also didn’t match the CCD symptoms reported, and the fungus has been around a lot longer than CCD. It remained unclear how, or if, N. ceranae was involved. Indeed, with so many pathogens suspect, yet none seemingly responsible for all the CCD cases, researchers came to suspect that multiple pathogens, or toxins, were causing CCD.
Recent breakthrough: Amid these mounting suspicions, a paper came out just last month in the scientific journal PLoS ONE pointing to dual efforts of a virus and Nosema ceranae in causing CCD. Researchers collaborated between several universities and with the U.S. Army to identify thousands of proteins present in normal and CCD-suffering hives (using a technique called mass spectrometry-based proteomics). They found that an invertebrate iridescent virus (IIV) (in the virus family Iridoviridae) was in hives with CCD, and that when combined with the fungus N. ceranae it was much more lethal to bees than when the bees were exposed to either one separately. The two culprits were not found together in healthy hives.
IIVs affect a variety of insects and can alter the infected insect’s growth, lifespan, reproductive ability, and other bodily functions. It can also be lethal. One strain of IIV is known to infect honey bees (IIV-24) and it can make them inactive, crawl unusually, and die. IIV-24 caused the death of nearly half of all honey bee hives in India annually during the 1970s. The researchers could not determine for certain the specific IIV strain in their samples.
How did CCD happen?: The authors of the recent breakthrough paper hypothesize that when the microscopic fungus N. ceranae weakens an infected bee’s gut lining, other pathogens, such as IIV, may then more easily infect the bee. But clearly there are still pieces to the puzzle that we haven’t placed, such as the timing of events that led up to this catastrophe first striking in late 2006. As mentioned above, the microscopic fungus N. ceranae was detected as early as 1995 in the U.S., and IIV wreaked havoc in India in the 1970s. It’s possible that either, or both, have been in the U.S. for decades. The mite Varroa destructor may transmit both these pathogens to honey bees, and it may be that it just took a while before enough mites were carrying this devastating combo.
Moving forward: During the CCD outbreaks, it’s been repeatedly reported that organic apiculturists have not been hit so hard, or at all, by CCD. One possible explanation for this is the use of such products as “Honey-B-Healthy,” which has been shown to somewhat protect honey bees against viruses and N. ceranae. Honey-B-Healthy is a mix of spearmint and lemongrass oils which the honey bees happily eat up and get all over their bodies. It’s not really a novel concoction, but definitely has some merit; lemongrass has been used for thousands of years in Africa by beekeepers. It’s thought that the oils strengthen the bees’ gut cells, which would protect against N. ceranae invasion. Because the entire bee becomes slippery with the oils, it may also be harder for pathogen-transmitting mites to grab on to them in the first place. But better defensive, and offensive, tactics need to be developed to save our vital honeybees.
For those of us who are not beekeepers and wish to help the honey bees, Michael Schacker, author of the book A Spring Without Bees recommends planting a bee garden to encourage wild honey bee populations. While apiculturists work hard to take care of their domestic honey bees, wild bees have been hit harder during these pathogen outbreaks. Visit Schacker’s blog “Plan Bee Central” for more information on how to plant a bee garden and take other actions to help our little, furry, pollinating friends.
For more on honey bees and their recent decline, see Michael Schacker’s book A Spring Without Bees, Rowan Jacobsen’s book Fruitless Fall, the recent PLoS ONE article “” Iridovirus and Microsporidian Linked to Honey Bee Colony Decline, Schacker’s blog “Plan Bee Central,” or Wikipedia’s articles “Colony Collapse Disorder” and “Honey Bee“.
Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at firstname.lastname@example.org.