Ross Conrad spends 50 pages talking about the varroa mite, which he considers to be the current bane of the organic beekeeper.  Although I'm not interested in trying out his "soft chemical" controls (which are on a toxicity level similar to Bt), I'm intrigued by some of the other solutions he presents.  Conrad recommends using many or all of the options below in concert, and warns that ignoring mites will kill your hive within one to two years without some mite-reduction actions.

1. Breed for resistant bees.  Natural beekeepers seem to be unanimous in their admonition to stop buying out of town bees and to instead learn to breed bees that are well-suited to your local conditions.  Bees resistant to varroa mites may be more hygenic, brushing or biting mites off other bees' backs, and they may also be more prone to swarm.  Short of scientifically measuring these traits, if you reproduce the genetics of the hives that survive the winter in your apiary, you're automatically selecting for bees that will do better in your area.  (More on how to breed bees in a later post.)  Of course, this is a long term measure and won't help your bees survive this year.

2. Monitor for mites to know when to take drastic action.  Although Conrad mentions several mite-counting techniques, he takes a simpler approach and keeps his eye out for signs of high mite levels when he checks the hive.  Noticing mites on drone brood pulled apart during your hive check, or wandering around in the hive, is a sign that mite populations may be increasing and you need to keep an eye on the hive.  If you begin to see deformed wings on worker bees --- caused by a virus carried by varroa mites --- then mite levels are too high and you must take emergency measures.

3. Split off nucleus colonies.  The simple action of propagating your hive seems to put a damper on mite reproduction since splitting causes a pause in brood production within the hive.  Varroa mites reproduce by laying eggs on bee brood, so if the bees aren't producing brood, the mites can die out.

4. Use screened bottom boards.  By using a screened bottom board instead of a solid bottom board, when mites fall off a bee's back, they tend to fall through the holes onto the ground and die rather than jumping aboard the next bee who passes by.  Screened bottom boards reduce your mite levels by 10 to 20%, and Conrad notes that even in his northern location, leaving screened bottom boards open all winter doesn't cause increased winterkill.

5. Encourage mites to fall.  Various techniques can be used in conjunction with screened bottom boards to cause even more mite casualties by tricking mites into loosening their hold on a bee.  Plugging up all the holes in a hive and then filling the hive with the smoke of tobacco, black walnut, cedar, grapefruit leaves, or creosote bush for 30 to 60 seconds before airing the hive out causes major mite falls (although tobacco and creosote smoke may also harm the bees.)  Alternatively, you can sprinkle confectioner's sugar over your bees, which tempts the bees to groom mites off (but don't use confectioner's sugar during cold weather since it contains an inert ingredient that your bees will need to void from their systems.)  Both of these techniques should be used when no honey is present in the hive to prevent contamination, and most should be repeated two or three times over the course of a few weeks to catch mites on bees who were out foraging or were in capped brood cells during the first treatment.

6. Trap mites.  Since varroa mites like drone brood much better than worker brood, you can kill a lot of mites by putting a sheet of drone foundation in your hive, waiting for it to be drawn out and filled with capped brood, then freezing the frame for 26 to 30 hours to kill drones and mites.  You should repeat this technique throughout the year, moving the drone frame throughout the hive, but it does seem a little hard on all of those dead drones (who you need if you're going to breed your own new queens.)  Alternatively, Conrad builds mite traps that look like a deep frame, but with boards on each side covered in slits too small for a bee to fit through.  In the bottom of this little box, he puts a piece of sticky paper covered with methyl palmitate bait to attract and then catch the mites.  The sticky paper needs to be changed once in the middle of summer and the whole trap is removed in August.

7. Use heat to kill the mites.  A temperature of 116.6 degrees Fahrenheit will kill varroa mites, but not bees, so some beekeepers build special heating chambers into which they pour their bees once a year to delete the mites.  This sounds pretty tricky, but Conrad also mentions that painting your hive boxes a dark color might do the job for you --- at temperatures above 97, brood within the hive will die, but it might be worth it to let the hive get too hot a few times a year to keep mite levels manageable.

8. Use essential oils of thyme and mint.  A variety of chemical companies have started making "organic" mite controls out of thymol and L-menthol dissolved in a grease patty, but Conrad admits that these chemicals cause a temporary lull in egg-laying by the queen, which doesn't sound very healthy for the hive.  I wonder if you could plant a bed of thyme and mint around your hive and get mites to drop off workers as they pass over the anti-mite planting?

9. Make your foundation cells smaller.  I've discussed the benefits of foundationless frames previously.  Suffice it to say that if you get your bees to build cells a more natural size, mites don't fit in as well and mite populations plummet.

We're already using options 2 and 4 (and 7 accidentally when we had our hive meltdown last summer), and this year I plan to split our hives to start working on options 1 and 3.  I'm curious to see whether throwing a few black walnut leaves in the smoker when I check on the hive in the summer might act as a milder version of option 5, and I hope to remember to plant mint around the hives this year.  What organic techniques do you use to keep your hives' varroa mite levels within bounds?