By now everyone knows that the honey bees are very difficult to keep alive. You’ve heard about Colony Collapse Disorder and bees dying in record numbers. What I bet most of you DIDN’T know is exactly why bees are dying.
People and Bees Don’t Mix
It’s true. Humans have been a thorn in Mother Nature’s side ever since we expanded out of Africa and started walking upright. For honey bees, there are many hardships that we put them through.
- migratory beekeeping
- spreads pests and diseases from across the country
- pesticides
- as well as fungicides, herbicides, and every other deadly chemical cocktail we spray everywhere
- habitat loss
- loss of quality AND amount of floral sources
- loss of large trees to call home
- bad beekeepers
- yes, they exist!
- global climate change
- no, it’s NOT a conspiracy
- invasive species of parasites and pathogens
I could definitely give my opinion on each of these points but today I am going to focus on the last one.
Invasive Species
World wide trade has it’s good points and it’s not-so-good points. We now have the ability to travel and transport goods from one side of the globe to the other in a matter of days. But that convenience comes at a cost. One of those costs is the spread of a foreign species to an area that has no competitors or predators to speak of. Infamous examples would be the Kudzu vine in the south, rabbits in Australia, and various species of Carp in American lakes and rivers. What you don’t often hear about, however, is the unintended introduction of pathogens and parasites from other countries.
Origin Story
The Varroa mite is a parasitic arachnid not unlike a tick. It was first discovered as early as 1904 in Asia on the Asian honey bee (Apis cerana). The mite and the honey bee in that region have co-evolved over time so that neither species is seriously affected by the other. During the 1940’s, the varroa mite was transported to Africa, Europe, and finally North America via beekeepers who brought their hives into these regions. Once the beekeepers went back to their original countries, the varroa mites were now on a new host, the European honey bee (Apis mellifera) which we know simply as “honey bees”.  It was discovered in the United States in the mid-80’s.
Having a pesky hitchhiker coming on board a ship or a plane is one of the consequences of global agriculture which we still experience to this day. Unlike the Asian honey bee, European honey bees had no evolutionary history in which to deal with this parasitic newcomer. Unfortunately for the honey bee, the Varroa mite became a far worse problem than anyone could have foreseen.
One Nasty Bug
The Varroa mite loves to grab onto a bee and hitch a ride into the hive. The mite then finds where larva are getting ready to be capped with beeswax. The mite sneaks into the cell and hides underneath of the larva. When the bees cap the cell with beeswax, the fertile mite lays an egg. This first egg produces a male mite. The “mother” mite then lays eggs which become female mites every 30 hours until the bee emerges from the cell. These daughters then mate with their brother and exit the cell with the bee. These impregnated females then hitch rides to another cell to start the cycle all over again.
It’s the Little Things
What advantages did the Asian honey bee have that the European honey bee did not? Why has the varroa mite been able to overrun bee hives so effectively? Let’s explore that a little bit more.
- Asian honey bees have several characteristics that make living with Varroa much more tolerable. Asian bees will swarm and abscond (abandon their home) much more readily than the European honey bee. This causes what we refer to as a “brood break”. Meaning, the bee’s reproductive cycle is suspended which, in turn, disrupts the mite’s reproductive cycle. This slows down and restricts how quickly the varroa’s numbers increase within the colony.
- Asian honey bees have a shorter development time from egg to adult. The Asian honey bee is a full-fledged adult in only 19 days while the European honey bee takes 21 days to mature. That gives the Varroa mite two full days to pop out an additional offspring. That one extra mated female mite per bee larva exponentially increases the mite population to very high levels. The mite population can double every 3-4 weeks between spring and fall.
- Asian honey bees display a very high level of grooming. They are constantly grooming each other and will shake or vibrate to let another bee know that they need groomed. This helps to dislodge mites from the bees and interrupt their hitchhiking ride.
- Varroa mites feed almost exclusively on Asian honey bee drone (the male) larva. In the honey bee world, the drone’s only purpose is to mate with the queen. When Varroa met the European honey bee, they were able to feed on the worker larva as well as the drone. Therefore, every function in the hive, from pollen collecting to nursing young bees, is weakened because of this parasite. Also, more prey for the Varroa means more food and, therefore, quicker population buildup.
Oh! My Liver!
It was previously believed that the Varroa mites fed on the hemolymph, or blood, of the honey bees. Recent research from Samuel Ramsey, however, has shown that the mites are actually feeding on the fat bodies of the bee. These fat bodies, containing vitellogenin, act as an organ that not only provides storage for extra food reserves, but they also produce royal jelly and provide hormone functions. Such functions include:
- regulating foraging behavior
- act as antioxidants and help extend the life of the bee
- regulate the insect’s growth
- aids in immune system function
- helps the bees to live longer and survive the winter months
So, as you can see, a honey bee that has had their fat bodies eaten by a parasite is a honey bee that is going to have some serious health problems.
The Bug Has Bugs of Its Own!
As if feeding on the fat bodies of the honey bee weren’t bad enough, the Varroa mite vectors as many as 20 different viruses to the bee when feeding. The most damaging is Deformed Wing Virus, also called DWV. In the photo below, you can see that the bee’s wings are shriveled and almost nonexistent. A bee that can’t fly is … well …. not going to live for long. It certainly cannot help the colony collect water, pollen, or nectar. It cannot even help defend the hive. Other members of the colony will most likely kick the diseased bee out of the hive. This virus has developed into even more dangerous (virulent) strains thanks to the Varroa mite’s ability to hitch a ride to another hive.
When a virus becomes too lethal and kills its host before it can spread, then that lethal strain of the virus dies with its host. However, when the virulent DWV kills a colony of honey bees, other bees from nearby hives come into the dead/dying hive to collect any leftover honey that is in the now undefended colony. The Varroa mites that are carrying the virulent strains of DWV then hitch a ride on to these “robber” bees and go on to infect the next colony. This usually occurs in the Fall when the mite’s population (and virus load) are at their highest. A hive will die, the mites will hitchhike to another hive, and then that new colony will most likely not make it through the winter with all of the extra mites it picked up.
How to Kill a Little Bug on a Big Bug
So here we have a tiny bug that lives on a small bug. This is what makes it is so difficult to control the Varroa Destructor mite. How do we kill it without harming the honey bee? Better yet, how do we kill the mite without contaminating the hive, and the honey that we eat, with whatever chemical we use to kill the mites? Unfortunately, we do not have a perfect solution yet. Because of the increased virulence of DWV, if you do not control a mite’s numbers then the colony will die. If a hive is left untreated, it runs a much higher risk of collapsing and dying than a treated hive. Integrated Pest Management (IPM) techniques help to reduce the mite’s numbers but require a lot of work on the beekeeper’s part. Thankfully, some organic acids are available to use inside of a hive. The vapors from these acids are able to kill a large amount of mites while minimizing any damage done to the rest of the colony. They also do not contaminate the honey or beeswax inside of the hive.
A little Hope on the Horizon
Thanks to the work of people such as Randy Oliver (http://scientificbeekeeping.com) and Samuel Ramsey, there has been a lot of great research conducted on Varroa mites and how to combat them. If you’d like to help contribute to a worthwhile honey bee research project, please click here.
Also, there have been a multitude of breeding programs to try and breed a honey bee more tolerant to Varroa mites. You can use these new Queens and breeding techniques in your own apiary to continue the breeding process. In this way, you can develop a strain of bee that can survive a little better on its own.
You can use some very simple IPM techniques to help disrupt the mites’ breeding cycle. The most effective, in my opinion and observation, are drone brood trapping and creating a brood break by splitting your colonies.
Honey bees and the pollination they provide are a very important part of our ecosystem and to our country’s agricultural system. We need to breed a more resistant honey bee that can survive the Varroa mite infestation. Until then, beekeepers will have to continue to scrap and fight with this scourge of the honey bee.
Please leave your thought or questions in the section below.
Bee safe.
