In the previous lesson we looked at the life of the Varroa mite and how their behaviors and reproductive patterns have the potential to decimate a honey bee colony.
Now we look at what can be done to combat the significant danger presented by Varroa.
Thankfully, it is not all down to us as beekeepers. Bees already exhibit some remarkable behaviors themselves, specifically focused on reducing the threat from Varroa. There is ongoing research into this and leveraging these behaviors represents one of the more promising avenues to reducing the negative impact of Varroa mites.
Varroa Sensitivity Hygiene
Given the apparent chaos within a hive at first glance, there is a remarkable degree of collaboration and very intentional behaviors by its bees.
Take the remarkable behaviors associated with Varroa Sensitivity Hygiene (VSH). This is a trait among certain lines of bees to detect the presence of Varroa mites under capped cells and to clear them out! This is such a well-established idea that scientists and beekeepers casually refer to such bees as “VSH bees”. You can purchase a VSH queen, for example.
It is not known how VSH bees detect the mites under the cap, but smell is the most likely explanation. When a cleaning VSH worker determines that a cell is infected with Varroa mites, she will create a tiny hole in the capping. Then “remover bees” will follow up by enlarging the hole and either eat the pupa or remove it.
For reasons that are not yet fully understood, the remover bees have preferences as to which pupae they remove. Pupae go through eight stages, from pre-pupae as stage 1 through to stage 8. Remover bees will remove pupae that are in stages 2- 4 when they have less pigmentation.
Another mystery is that remover bees clean up pupae from worker bee cells more readily than drone cells. Again, the reasons for this are unclear.
Regardless of how VSH bees detect and respond to Varroa, it is a remarkable trait. Here is an incredible video of VSH bees exhibiting this trait, with a mite coming out of the cell as the workers complete their work.
The Role of Science
Of course, VSH is an attractive trait in bees from the perspective of beekeepers, whether commercial or hobbyists. The question is how beekeepers can obtain bees with VSH traits?
The answer came from the USDA Honey Breeding, Genetics and Physiology Lab, in Baton Rouge. The bright minds there selectively bred a line of bees with VSH tendencies. In fact, the results were even more beneficial, beyond “merely” an ability to fight Varroa. The grooming characteristics of VSH bees also mean they are less vulnerable to American Foulbrood, Chalkbrood, Wax Moth and Small Hive Beetle.
So the benefits of VSH are very clear, and by raising selectively for VSH and using VSH queens, we can provide a central figure that will benefit the colony as a whole. Use of a VSH queen in a colony results in a marked increase in resistance to Varroa, even when the rest of the bees are not VSH bees.
Bring a bee up to have good hygiene and all sorts of good things happen!
The Role of the Beekeeper
Recognizing the Risk
Bees help the fight against Varroa.
So does science.
What about beekeepers? Well, the story there isn’t quite so positive.
It is widely accepted that Varroa represents one of the greatest challenges to honey bees. Their track record of causing widespread losses is beyond debate. Yet, a study by the Bee Informed Partnership found that most hobbyists do nothing to specifically control Varroa. Those who take this simplistic stance experience greater losses.
So what exactly can an informed and motivated beekeeper do to help?
Step 1 is awareness. As we have stated, there are mites in every hive, some passive and harmless and others a potential death threat to the colony. The detection of Varroa, in itself, is not a serious cause for alarm, given the potential for the bees to take care of the issue themselves. What is more important is the extent of the Varroa population in your hive. At some point the number of Varroa exceeds the ability of the bees to combat the threat and at that stage the colony is in big trouble.
There are a number of ways to assess the number of mites. One involves dead bees and other involves bees coated in sugar!
In both cases, you need a sample of bees. You will collect around 300 or so bees, which equates to about 1/2 cup. This can be done by scraping the side of a jar down across a frame, causing bees to fall in. Do this a few times and you will soon have your 300 bees, so just put the cap on.
Now you have to decide whether you would like to use the dead bee option or the surviving bees option. Though a debate rages as to whether this should be a concern when conducting tests, you can probably guess which one we prefer.
Open the cover on the jar slightly and spray in automotive starter fuel (ether). You just killed the bees in the jar, but at least they can now help you determine the mite count. The ether roll may also be used if you are researching with bees that have already died.
Start rolling the jar around and continue for about 5 minutes. The bees will regurgitate honey from their honey stomachs and the mites – also dead by now – will stick to the glass in this honey. That gives you the opportunity to count them easily. See below for how to interpret that number.
If you wish to keep your bees alive the sugar roll test is an alternative.
Get hold of a canning jar with a two-part cap and replace the inner cap with some mesh wire. Pour in 1/2 cup of powdered sugar and roll the bees – active, confused but still living bees – in that sugar. The plan here is that the sugar particles cause the mites to lose their grip on their host bees.
Then rapidly shake the jar upside down, such that the sugar AND the mites come out onto a light-colored sheet. The mites will be visible against that background.
The ether and sugar roll methods are illustrated in this excellent video.
Assessing the Count
Both methods produce a count of mites. Bearing in mind that you have around 300 bees, you can calculate the percentage of mites to bees. Less than five percent (about 15) is considered acceptable and anything above this may justify treatment.
As to assessing the overall number of mites, use the percentage to estimate the number of bees in your hive, but keep in mind that your sample only represents about 20% of the mites – you captured them from mites that were on host bees, rather than uncapped cells.
A variety of Varroa Testing Kits are available from the PerfectBee Store.
Screened Bottom Boards
Another common way to obtain an estimate of the mites in your beehive is by using a screened bottom board, rather than a solid board.
Mated female mites sometimes come out of the cell, waiting for a passing bee. A certain percentage will fall through the hive to the screened bottom board.
The screened bottom board has a meshed screen allowing the mites to fall through, but not bees. Under the mesh is a sticky board, which will collect all sorts of material over time, including fallen mites.
It is a testament to the long history of beekeeping, the attention to detail and a burning desire to identify and resolve problems, that scientists have determined acceptable “per day” counts of fallen mites! In any one day, knowing the size of the colony, the time of year and the number of mites that have fallen over a day, you can determine whether you have a Varroa problem!
Sounding like the proverbial broken record, let us state again that prevention is better than cure. So what steps can a beekeeper take to avoid an outbreak of Varroa? Here are the basic principles.
Race of Bees
Some races are more resistant than others. Russians, for example, are relatively resistant to Varroa.
As we have seen, VSH bees are tremendously useful, so consider purchasing at least a VSH queen. But a full compliment of VSH bees is even better.
This is a fascinating approach, leveraging the fact that Varroa prefer drone cells. Foundation with larger cells called drone foundation is placed in the hive. This essentially acts as a “bait” for mites. Assuming the queen has ready access to the drone foundation, she will lay drone (unfertilized) eggs.
After the cells are capped, remove and place in your freezer for a couple of days. This will kill the mites and the drone brood. The next morning uncap the drone brood and replace the frames back in the hive. Workers will clean up, removing the dead drone and the mites too.
Soon enough, the cells will be used again for drone brood. Then just repeat this process.
If your efforts – and your bees efforts – to contain Varroa have failed, then you have a serious issue. Treating for Varroa is not easy, though there are a number of options. Full coverage of these many options is beyond the scope of this individual lesson. But here is an overview of the options available to you.
“Hard chemicals” are one choice, but obviously have the potential to damage your bees, not just the mites. Another challenge is that many of these treatments must be applied when there are no honey boxes installed, so as to not taint honey that might be ingested by humans.
“Soft chemicals” exist in nature and, in some cases, are quite common in honey. Their use places less stress on your bees. Options here include formic acid, oxalic acid and lactic acid. Some essentials oils are often used too. ApiLife VAR is a commercial product made with thymol and essential oils.