Isolation is ideal, and mostly impractical any more. But for some it has worked for years. No new bees in the neighborhood can make it work…but there’s more tools to use when Varroa does, finally, show up…and we all know it will.
So…the second best tool? You know the answer – keeping bees that deal with Varroa, and don’t die from Varroa. And there are a whole bunch of ways this works. Combined, they bring together an Integrated Pest Management program, which includes, as already mentioned avoidance, but also resistance, removal, cleanliness, and other techniques that involve more behavior or physical action than genetics, but genetics count just as much. But let’s explore some of the physical activities that bees, and beekeepers can do that help bees cope with a resident mite population.
There’s the obvious…removal.
Hygienic behavior is often cited as a tool that honey bees use to rid their nest of unwanted…stuff. A clean bottom board is one sign, but breeders have moved the bar so much higher in recent years that this really bears investigating.
The basics are that a patrolling house bee senses…smell, feel, sound – it’s not clear but most likely smell…and detects a larva that has been infected with…Varroa, with AFB, even EFB or Chalkbrood or sacbrood, or is infected with, or has died for some reason. Even chilled brood may fall here.
Removing dead brood isn’t all that new, and if you’ve ever had chilled brood you know the score. But it’s when a pupa dies beneath a cell cap, is detected and then removed…that’s something. Better, when a papa isn’t even dead but is simply infested with a Varroa mother, and maybe a few of her offspring, and is detected…that’s even better.
Some bees exhibit hygienic behavior in the extreme. Maybe too extreme. They will uncap a cell, investigate the contents, and, if infested remove, and if not, reseal the cap. That’s a bit much, but it is hard on Varroa populations, but it’s also a bit hard on bee populations. Too much of a good thing…and you can end up with fewer bees. This behavior, labeled Varroa Sensitive Hygiene, is a valuable genetic tool to use in your queen breeding systems. You want some of this…you want Varroa removed, with extreme prejudice if you catch my drift.
I’m a bit leery of extreme hygienic behavior in a hive, but when only a small proportion of the bees have it then it tends toward being less destructive overall. It’s a tradeoff I suppose…too much of a good thing can be dangerous, but not enough can also be dangerous. The balance is hard to find.
Overall, it’s this hygienic behavior that rids the hive of many of the mites. For some bees it is exhibited in grooming behavior, cleaning exposed mites off other bees and dropping them between frames, or better, biting them enough to do damage to a leg. Bees’ mandibles aren’t designed to be a defensive tool, but in the process of pulling the mite off another bee occasionally the mite is damaged. If you happen to look close and see a mite with a dent in its shell like the photo, you can bet it met a painful end because of a biting mite.
There are bees being selected that actually go after legs…some call them ankle biters…and sever a section or two off a leg. Once a mite’s integument is compromised it shortly dies of dehydration as they don’t ‘heal’ once wounded, and quickly die. Researchers at Purdue are selecting for this trait and have improved the percentage of mites killed this way significantly. Let’s hope it gets even better.