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).
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:
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!
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.
