Updated 12/07/2020
No, not hypothermia, no need to freeze any bees. Hyperthermia is the opposite of hypo, and is heating varroa mites to a level that is lethal to the mite but not the honey bee (Apis Mellifera & Apis Cerana).
First, The Mite
As beekeepers, Varroa Destructor is enemy #1 and without treatment is almost guaranteed to result in the colonies death within 2 years if unchecked, assuming you are not a treatment free beekeeper with VSH bees. There is evidence out there that indicates treatment of colonies for varroa, may in fact be handicapping the bees. But if you do not plan to go treatment free with an aggressive gene selecting process and just decide to not treat bees, you will end up with most likely dead out hives. This article is geared for those that treat their bees, and I am not going to get into the merits of treating vs not treating in this article.
It is believed that the mite originated in Asia and has since spread through out the world, leaving only a few Hawaiian islands and Australia free of the mite. The mite feeds off of the fat of the bee and the colonies pupae, which is crucial for many bodily functions such as hormone and energy regulation, immunity, and pesticide detoxification, the bee is left in a severely weakened state. The mite is also a vector for at least five debilitating bee viruses, including RNA viruses such as the deformed wing virus. This weakening, also makes bees far more sensitive to poor habitat and pesticides. This is why CCD is a result of many factors but at the keystone of issues is the varroa mite.
Varroa Treatment with Hyperthermia
Hyperthermia is well documented in scientific papers as an effective tool in killing varroa mites on bees as well as within the brood cells [1] [2]. The key is that the honey bee has a higher temperature threshold than the mite does and when exposed to specific temperatures over specific time frames, the mature mite as well as the mites in the pupae cells are destroyed leaving the mature bee completely unharmed.
The temperature that affects the varroa mite was discovered during the ’70s and Kommissar in 1985 that provided definitively that bees and Varroa mites have a different tolerance to heat. Essentially the mite eventually dies from the development of heat shock proteins within their body while the bee doesn't.
Through testing and scientific experiments[1] , a temperature of 42ºC (107.6ºF) for 2 hours has an efficacy of 100% on immature varroa and 20% on mature varroa within 48 hours. Good but not good enough.
In those same studies a temperature of 42ºC for 3 hours produces 100% results on adult and immature mites within 48 hours. But is dangerously close to the temperature that bee brood also start to die, which is at 43ºC (109.4ºF)
When a colony is treated at 41ºC (105.1ºF) for 3 hours the bee brood still sees a 100% mite mortality of the immature mites and around 40% of adult varroa is dead after 48 hours. These are good results and most importantly at a level that has no affect on drone fertility[1][3].
Side Effects
If the hyperthermia is done properly, it is very affective against the varroa destructor and done in a way that uses zero chemicals. There is a side effect to some of the bees, that results in their sucrose responsiveness. This ultimately is the bees ability to determine better nectar sources from others, which means that the bees responsible for accepting nectar in the hive to transport to honey stores has a more difficult time determining which foraging bee is more successful in finder sucrose rich nectar.
This is however counter balanced, as the same study that shows that the hyperthermia significantly increases the bees life span, therefore the bees ability to gather more nectar compensates for the potential lower sucrose nectar foraging.
Pros vs. Cons
There is no doubt hyperthermia works at killing the varroa mites, and when done properly has little to no impactful side effects. If you are to compare the side effects of chemical treatments, which I will cover in another post, and that have significant side effects and also needs to be performed with precision as not to kill your bees. It becomes obvious that hyperthermia, when done properly is a great way to control mite infestation and potentially increase your profit margins. "No chemical" honey sells for much more than ones that do use chemical treatment. Look at Manuka and Hawaiian honey as an example for a specialty honey selling for far more than $3/ lb.
Now I know I am writing this on a website that sells a product that uses hyperthermia (or will) and I can assure you in no way does that sway my opinion and research (take that as you will). I personally have never used a chemical on my hives, and if you do thats OK as long as it is done properly and is effective. But I also started researching other methods which has brought me to what could be a better way, as it is effective, less chemicals is better(my opinion), and it can yield a healthier honey product for the people that consume it. So take some time, read the sited papers if you wish and consider hyperthermia for your colonies.
[1] 02 March 2020 https://link.springer.com/article/10.1007/s13592-020-00743-8
[2] 07 November 2019 https://www.deepdyve.com/lp/springer-journals/hyperthermia-treatment-can-kill-immature-and-adult-varroa-destructor-LR0DsUgQL0