Hygienic Bees

varroa on bee
A varroa mite sucking on a bee. If left untreated and if the hive cannot control the infestation, the hive will collapse. Survivor bees are better at dealing with varroa.

If you are a new beekeeper or looking into becoming one, you’ve probably already heard about Colony Collapse Disorder (CCD). When a seemingly thriving hive collapses suddenly, it is said to have suffered from CCD. However, there is no clear cut symptom or disease that can be identified as the culprit of CCD, but there is a very clear front runner. The front runner would be the Varroa Destructor, or Varroa mite. The varroa mite’s natural host has been the Asian honey bee (apis cerana) and it has just recently (circa 1980’s) evolved to parasitize the European honey bee (apis melifera). The European honey bee and beekeepers were completely caught off guard by the varroa mite and it’s the reason why there are so many resources being spent to study the mite and develop methods to control it.

There is tons of information online about the varroa mite, so I won’t explain its biology in great detail. Think of the varroa mite as a bee tick. The varroa mite will enter the hive, latch on bees to suck their blood, and parasitize the brood. After the mite has fed itself and its new babies on the bee brood (in pupa stage), the new mites will emerge with the new (weakened) bee and begin the cycle all over again. Using this reproductive method, the varroa mite can reproduce much faster than the bees, which leads to massive infestations within the colony. But wait that’s not all, the varroa mite is also a vector of bee diseases such as deformed wing virus. Deformed wing virus is easy to spot as the new bees suffering from this have deformed shriveled wings.

Apistan is a widely used chemical treatment against varroa

So what are the solutions being developed to control the mites? The first and most effective is the chemical approach. There are a few very efficient synthetic miticides that are currently being used worldwide to control the mite. If you’ve read our section on “our philosophy” you know that we are not fans of the chemical approach as the chemicals undoubtedly end up on our honey. So let’s concentrate on the “natural” or biological approaches.

The first natural approach that I’d like to cover is the “natural” or “small” cell approach. The idea behind this approach is that we need to get back to a more natural brood comb cell size (4.6mm – 4.9mm) and away from using “standard” wax foundation that has a cell size of 5.4mm. The idea is that bigger bees take longer to develop and therefore give more time for the varroa mother to lay more eggs. So by cutting down the amount of time that it takes a worker bee to develop also cuts down the amount of viable varroa mites produced in that brood cycle.

Cell size 4.8mm
We measured brood comb from a feral beehive that we captured. On average, the cells were 4.8mm in diameter. We have seen cells as small as 4.5mm.

I know that there are a lot of proponents of the small cell approach and I think that it has some merit. The issue with most beekeepers is that this solution is not very practical, mostly because it requires going “foundationless” which means allowing the bees to make the cells whatever size they want to make them and not using a sheet of wax foundation with predetermined cell sizes (most commonly 5.4mm). Recently, there have been a few manufacturers that started producing “small cell” foundation at 4.9mm, even so, for reasons I will not discuss here, this is still a more cumbersome approach, especially for the novice beekeeper. There is also very little scientific evidence that this approach actually works. We have experimented with small cell and still have hives with small cell foundation but we typically see little difference in survival rate compared to hives on “regular” foundation. To us, this is an indication that genetics is more important that cell size when it comes to controlling varroa infestations. Having said that, we have measured quite a bit of brood comb from feral beehives and can attest to the fact that the “natural” sized cells that they are building is between 4.5mm-5.0mm.

The second natural approach is breeding bees that can cope with high varroa infestation levels (and the diseases they carry) or bees that can limit or interrupt the varroa breeding cycle. So far, much effort has been put into breeding “hygienic” bees that can detect varroa mites in capped brood cells and remove the bee pupa before the varroa mite can reproduce. This seems to be a very promising trait and it is one that feral bees are already using to survive. We have seen varying levels of this hygienic behavior in our own bees. Most hives that have this hygienic behavior seem to control varroa and it doesn’t appear to bother them too much.

cells chewed open
It is not natural for bees to uncap brood once it has been sealed.  However, hygienic bees can detect varroa and uncap and remove the pupa. 90% of the time, if you pull out an uncapped pupa, you will find varroa.

We have also witnessed beehives that survive severe varroa infestations by doing a few interesting things. First, the queen will stop laying eggs. This means that there will be no new brood and if there is no new brood, there is no host for the varroa mite to reproduce. Secondly, the bees will begin to sacrifice the pupa that they determine have been infested by varroa. This is very interesting behavior because the last thing the bees want to do is sacrifice the pupa that they have spent so many resources to rear. Not only do they waste resources, but they also lose their next generation workforce. In a way, the hive enters a controlled “self-destruction” mode where they have to harm themselves in order to harm the varroa mite. Lastly, the beehive will rapidly collapse in population, probably because of the die off old bees that aren’t being replaced by new bees. After a few weeks of this self-destruction mode, the varroa mite is flushed out (mostly) and most beehives seem to bounce back.

The white/gray flakes on this bottom board are dried up varroa infested pupae that the bees have removed from their cells. This hive suffered a severe varroa infestation, but managed to recover.

This behavior typically happens in the fall when varroa infestations are at their worst. It really helps if there is some forage available for the bees to produce at least one cycle of new brood to enter winter with a fresh batch of young bees. Luckily for us, we do not have harsh winters in California and the bees usually have some forage available even in late fall.

It really seems like hygienic bees have the best shot at beating back the varroa problem. For this reason, many research institutions and breeding programs are focusing on breeding this trait into their bee stocks. Here at Estrada Farms we don’t have the resources to monitor infestation levels in beehives year round or to instrumentally inseminate virgin queens to precisely control genetics (yet). We simply rely on the tried and true principle of survival of the fittest. This approach has been working well for us, to the point that we largely stopped taking calls to collect swarms or remove bee hives for a few years due to not having room for them; however, we recently secured another bee yard and will resume collecting survivor bees. We have seen it time and again that these feral survivor bees have a few tricks up their sleeve to control varroa mites, including being hygienic.

If you are looking into buying a beehive, ask the beekeeper how they control the varroa mite. If the answer is through chemical treatments, I would not buy from them. There are plenty of beekeepers that are now raising hygienic bees (to some extent) and we need to support those that are moving in the right direction. If we do this, the varroa mite and its problems will soon be a thing of the past.

If you have any questions about our bees, feel free to contact us.

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