This is an all too common mentality. People (especially new beekeepers), will: inspect their hive, look at the bees, not see mites, and conclude they must not have mites. This is a huge mistake in logic.For example, in a fully crowded hive of 50,000 bees how hard is it to find the queen? It’s the biggest one of the bunch! Should be easy right? We all know this is not the case. You have to dig for her, and have a very keen set of eyes to spot the queen.
The threshold for mites is 7% infestation of phoretic varroa mites (mites that are hatched and riding on bees). This translates to 3500 mites in a colony of 50,000 (you are already screwed at this point). Of these 50,000 many of those mites are on foragers which are typically out of the hive during a daylight inspection. This does not even include the exponential amount of mites living in the brood cells reproducing (which is arguably the more important number). What if you have a 1% infestation rate in late spring? It is very unlikely you will spot 1 mite per 100 bees, but that is enough to be well over the amount of mites the bees can handle come fall if left unchecked!
A key point to remember is that the relative infestation (percent, or mites per 100 bees) is more important than total mite population—a large colony can handle more mites than a small one. At much above a 2% infestation in spring, honey production drops off severely. At much above 5% in fall, colony winter survival suffers (although the fall “economic injury threshold” numbers by various authors range from 1% to 11%) (Currie & Gatien 2006). We will return to percent infestation, and economic injury levels in my next article.
Unchecked, varroa can really multiply! A 12-fold increase is typical in a short season consisting of 128 days of brood rearing (Martin 1998). However, its population can increase 100- to 300-fold if brood rearing is continuous! (Martin and Kemp 1997).
For more on Varroa Population Dynamics: http://scientificbeekeeping.com/ipm-3-strategy-understanding-varroa-population-dynamics/
If, a queen is so damn hard to find, how could you possibly expect to find a tiny bug living on a tiny bee?
The general rule of thumb, is if you see a mite on a bee chances are you are already infested. This is why it is so important to check sticky boards, do sugar or ether rolls. Even that isn’t really effective because it doesn’t measure mites in the reproductive cycle (in the cells). You can try uncapping drone comb to get an idea about mites; or, worker cells in the fall after drone rearing has ceased.
The only reliable visual cue is examining bees for DWV (deformed wing virus), but by then your hive is already in the midst of collapse.
Hypothetically, if that hive makes it through the winter that does not make them “survivor” bees. It simply means come spring when brood rearing starts up again those bees are going to get more mites, much faster than a “clean” colony. This is why many beekeepers treat in the spring and in the fall, these are the most pivotal times for curbing mite reproduction. Let us examine some common ways to deal with mites:
Mel Disselkoen developed an idea known as the MDA Splitter Method: http://www.mdasplitter.com
This method relies on the timely method of splitting (typically the summer solstice), to create a brood less period while the bees create a new queen. This creates a 28 day (give or take) period (dependent on mating), where the mites cannot reproduce. It does not eliminate the mites but simply reduces them to a level that is under the mite threshold. By staying under this threshold, the bees can “handle” the mites going into winter. This is a more natural approach, but is dependent on a few factors. It is extremely dependent on timing. The idea is to interrupt the varroa mites reproductive cycle (x1.8/ 13 days) so that when the varroa mites are in danger of crossing the threshold they are “knocked down”. They typically cross that threshold when the queen slows down her laying in preparation for fall, while the mite keeps breeding. When the new queen begins laying all those mites with no brood to lay in rush for the first few cells of brood to reproduce and essentially suffocate themselves.
I like this concept for two reasons: It’s a natural Integrated Pest Management technique; as well as creates your surplus of overwintered nucleus colonies. It is win/win, but I would be skeptical about putting all my eggs in that basket. If you wish to remain treatment free, not a bad idea.
What if you combined that method with an Oxalic Acid treatment? Oxalic acid will kill 95% of the mites in a brood less colony. It is still an organically accepted method. You would go into winter with almost no mites.
Sugar Dusting? Some have luck with it. It certainly works in theory. Some people don’t have luck with it. What does it does? Well the hard numbers say it will knock down 1/6th of your phoretic mite population (the ones on the bees). This means that about 16.7 percent of the mites won’t have a chance to reproduce (in theory). The amount you sugar dust them, the more effective the results. Done weekly mites can be kept at a sustainable level. Scientifically speaking, its efficacy is contested. It will knock mites off but is it reliable enough to be your only “treatment method”?
Drone Comb? Its works, but does it work for you? Mites are naturally attracted to drone comb and prefer to reproduce in it. The idea is place drone comb in the hive, the queen lays in it, the mites go into the drone cells, and the cell is capped. The beekeeper then removes the drone comb exactly four weeks later and kills the cells (heating, freezing, uncapping, etc) and kills the mites while still in a reproductive state. Some studies show through the course of a season this can reduce mite populations by 25%. How could this possibly be a bad idea? Well that is dependent on the type of beekeeper you are. If you forget to remove the drone comb, you will actually be increasing your mite load. So this method demands timely vigilance akin to queen breeding. Are you going to want to lift all those boxes of honey off later in the season to remove those combs? It is a great deal of fucking weight! Are you breeding queens, or making splits? You might want those drones for your queens to mate with!
For more info on drone trapping/sugar dusting check: http://scientificbeekeeping.com/fighting-varroa-biotechnical-tactics-ii/
What about screened bottom boards? Don’t the mites fall through the screen and reduce their population? Think again, despite being a hopeful effort many scientific studies concluded that it does nothing for mite population. Most of the mites that fall through the screen are old, sick, or injured –they were going to die anyway. It is still marketed as reducing varroa population, and I suppose you still trust that shady used cars salesman, right? It is however a way to get an idea about your mite population. By an idea I mean after a treatment (we already discovered natural drop off isn’t that reliable), using powdered sugar, acids, miticides, etc.
Ether/Alcohol/Sugar rolls are a slightly more reliable method of getting a number of phoretic mite counts. If in 100 bees, you find six mites you are under the threshold right at six percent right? Wrong. Once again, if you have 6 percent phoretic mite infestation that means there are 1.8 times that in the brood cells. In 1-15 days you’ll be at 6.8 percent phoretic mites. In 15 days you will be well over that 7 percent threshold. The cycle continues.
Let’s say you can’t see any mites so you don’t bother doing anything about them. We can assume you probably have mites, we all have them, don’t be ashamed it is just part of beekeeping nowadays. But you chose to be ignorant, not treat, or do anything about them. What are some likely outcomes?
You notice one hive is weak in the fall (could be varroa), so you combine it with another hive to bump it up for winter –What you just did was introduce a shitload of mites into a brood rich colony essentially sacrificing two hives instead of one.
You don’t notice that hive is weak in the fall –that hive gets robbed out and the phoretic mites jump onto the robbing bees and infest those colonies. That hive probably dies, and the mite population grows in the hives doing the robbing. Or you inspect it, see its weak, and combine it with the first possible solution.
That hive dies overwinter –This is actually the second best outcome, as it does not spread it.
That hive makes it over the winter –This hive begins brood rearing in the spring and will reach their mite threshold very quickly, as well as being succumbed to many varroa related illnesses.
You do treat –The hive will not die from varroa, or varroa related illnesses (could still starve, or fail to overwinter). However the remaining mites that live are the ones that are resistant to that treatment, and will be the ones breeding in the spring. Over time that treatment might not be as effective. This has been demonstrated with the plethora of different mite applications on the market, the mites will build a resistance to it.
As a result, we can conclude with this: Just because you can’t see mites does not mean you do not have them; If you do see mites you are probably close to your threshold limit; there are many methods of trying to stay under this threshold limit; the math is confusing; and we are damned if we do, and we are damned if we don’t.