Guide to Beekeeping: Varroa Rules

Varroa Rule Number 1: Learn about Varroa

It is well known that the Varroa mite, Varroa destructor, switched gears a few decades ago and moved from its primary host, Apis cerena, often called the Eastern Bee, native to southeastern Asia, to our managed European honey bee, Apis mellifera, which is in use in much of the rest of the world.

Apis cerena live in cavities like our bees, are a bit smaller and generally much more aggressive, and are more like their distant African cousins in that they produce lots and lots of bees that swarm and swarm and swarm rather than put that energy into honey production. Some selections have been made by beekeepers over the years, and there are lines of A. cerena now that are less aggressive, swarm less, and produce enough honey to make keeping them productive. For the most part, however, A. cerena are unmanageable, aggressive, and extremely competitive when forced to share an environment with A. mellifera.

A quick review of Varroa’s life cycle is instructive here. A pregnant female Varroa mite enters a honey bee colony on the back of a drifting bee, on a bee moved there by a beekeeper, or on frames shared between infested and uninfested colonies. This pregnant female searches for a larva that’s ready to spin its cocoon and have the cell capped by the nurse bees to protect it while it changes from larva to adult (honey bees have a typical complete metamorphosis cycle, much like a butterfly — egg, caterpillar/larva, cocoon, adult). The female mite heads to the bottom of the cell and hides beneath the larva buried in the larval food so it is not detected, and when the cell is capped it is inside the cell alone with the larva. She prefers drones over workers because drones take longer to evolve from larva to adult, and she can lay more eggs and produce more young while protected in the cell. But if there are no drone cells available, she takes a worker cell in a heartbeat. As soon as the cell is capped, she moves up from below, attaches herself, begins feeding on the larva for a protein meal, lays a male egg, continues feeding, lays another egg, then another if time allows. During this very short time, the male matures and mates with his sisters. When the larva leaves the cell, with it leave the original female and one or more pregnant females, ready to continue the process.

The initial host/parasite relationship that developed over eons has struck a balance between A. cerena and Varroa: Simply, the parasite agreed not to completely kill an A. cerena colony by infesting only drone brood, and the A. cerena agreed to let the mites kill some of the drones and limited just how many it could infest by limiting the number of drones it would produce. And since swarming is a big part of the A. cerena cycle, the Varroa never had a good opportunity to build up to large numbers in an individual colony before — poof! — everybody was gone, and it’s time to start all over again. Because of these two behaviors, that agreement still works.

Now, enter well-intentioned people from parts of the world where A. cerena doesn’t exist. They bring bees that don’t swarm nearly as much, are far less aggressive, make much more honey, and are bigger and take longer to develop — A. mellifera.

As soon as A. mellifera was introduced to A. cerena regions, Varroa saw an evolutionary advantage to feeding on this new host. And they did so with devastating results. Because of the longer development time, and the fact that A. mellifera didn’t limit the number of drones it produced, the pregnant female mite had opportunity and time to lay more eggs before the adult bees emerged from the cell and mite reproduction increased significantly in an A. mellifera colony. Moreover, because A. mellifera didn’t swarm nearly as often, the mites had more time to build up huge populations, thus constantly damaging both larval and adult bees — and now both drones and, here’s the kicker, workers — and after shorter and shorter times the colony would abscond or collapse.

It didn’t take long for Varroa to gain a foothold in every A. mellifera colony brought to the original area in Indonesia, and once established on A. mellifera, and with no negative reports from its association with A. cerena, infected A. mellifera bees were moved all over the world with Varroa mites in tow. Now the only place these mites are not found is Australia.

Now, add the final blow — viruses. Part of the A. cerena/Varroa agreement must have contained something about not transmitting viruses, or the viruses weren’t destructive, or A. cerena has an immune system able to cope with them since that doesn’t seem to be an issue with these two. But with A. mellifera,Varroa infestations, that is, the direct damage done to the adult or larval bee in and of itself compromise the immune system of the bee, so our bees have one strike against them from the start.

When a mite feeds on a honey bee infected with one or more viruses, those viruses are transmitted first to the mite, and from the mite to the next bee it feeds upon. And it gets worse: That infected bee can pass along those viruses to juvenile bees when feeding, to the queen when cleaning or feeding, from queens to eggs, from workers to drones, and from worker to worker.

But several other things are going on at the same time. The primary infective virus — deformed wing virus — continues to mutate, becoming more, or sometimes less, virulent. At the same time, note that beekeeping doesn’t represent the feral population at all. Great groups of colonies are closely confined to beeyards, as opposed to being far apart and mostly isolated. This artificial situation lends itself to multiple simultaneous infestations when an infested colony absconds or crashes.

When first introduced, mites always won and A. mellifera colonies always died. Then, chemicals came into play that would kill mites and not bees (killing a bug on a bug), but even though the chemicals didn’t kill bees, they weren’t kind to them either, and the beeswax these chemicals came in contact with simply soaked up this poison, and still, often the mites would win. But after almost 100 years of trying to work it out, some A. mellifera colonies began to handle the problem.

Evolution and compromise are both slow in the insect world. But experience does pay, and those longest exposed, A. mellifera bees from eastern Russia, gained an upper hand and began to show resistance to Varroa mites, and the two, as with Varroa and A. cereana, began to be able to live together.

But there’s another scenario that seems to be working that’s letting bees and mites coexist. It takes the route of the African bees that seem to have few problems with these mites. Their plan of attack isn’t extreme hygienic behavior or excessive grooming, even aggressive grooming. Rather, their method relies on keeping colonies small so there isn’t ever a lot of brood, frequent swarming so there are breaks in the brood cycle several times a season, and, like most feral bees, isolation from many, or even any, nearby colonies.

This approach works with the mite cycle and the honey bee cycle, but the downside is very little honey, or honey bee production. Both negatives in the beekeeping business.

This is where we are today with Varroa. Some A. mellifera bees have some resistance, tolerance, or avoidance. Most don’t, and there are very, very few major government- or university-organized programs designed to breed resistance into the population. Progress has been, and is being, made by smaller regional groups that are spread out and who select for resistance and tolerance plus the other positive factors needed to raise bees — productivity and gentleness. These, unfortunately, have little funding, too few members, and lack of solid organizational direction to be nationally effective. But they are making progress, and if this is the route you chose, seek them out and favor those queens.

This, then, is Varroa. Know it well, fear it, and strive to control it. And there are ways to do this without chemicals.

Varroa Rule Number 2: The Best Way to Control Varroa is the Worst Way to Make Honey

The more brood there is in a colony, the more opportunity there is for Varroa to reproduce and build. And, since a pregnant mite can produce about 2.5 Varroa mites in drone cells and about 1.2 mites in worker cells — that’s more mites than bees — lots of brood means lots and lots of mites. Just after the honey bee population in the hive reaches its profitable peak population — relative to a summer honey flow — and slowly begins to decline, the Varroa population reaches its peak exactly at the time that drone populations begin to decline. There’s a time when an untreated susceptible colony has the most mites, and both worker and drone brood is declining. So what’s left for the next generation of Varroa mites? With even less drone brood, worker brood comes in as first choice. The scenario here is pretty clear: Varroa outnumber workers, the Varroa/virus complex escalates, and soon most bees in a hive have been infected with a virus — often several. This reduces life spans and keeps nurse bees from being fully able to care for the young, foragers from being able to compete at 100 percent, and the remaining drones from being competitive in mating. The colony is in trouble and, in all likelihood, collapses because younger and younger bees become foragers to feed the steady supply of brood, but the foragers are already sick, die young, or fly away and don’t return. This is the classic, predictable, unavoidable conclusion to an untreated colony, or a colony with little or no tolerance or resistance to these mites.

But while it is desirable, even envious, to have bees that handle mite populations, no matter how they do it, many don’t, and the mite population builds to unmanageable levels and beekeeper input is required to reduce that population. Here’s where the real world of mite control and honey production come head to head. To avoid mite populations building, you stop them before they start, or you interfere with the buildup after it gets going.

A strong overwintered colony with few mites (you are checking mite populations, right?) is your best bet because it has the fewest bees and lowest amount of brood. If the colony is strong, a split and a treatment (see the next section) then will knock the population right down to almost zero. Leave the splits queenless (or confine the queen from the original and don’t introduce, or release, a queen into the split) for a brood cycle (three weeks), and all that remains are exposed mites with no place to go. Monitoring will support this, but even a moderate population of bees can remove many — sometimes all — of these unprotected mites. After the broodless period, the queens are released and the colony can expand. But the colony has missed a three-week growth spurt — three weeks without any new bees introduced right at the time the colony needs new bees the most. That’s bad for honey production. But, you do have healthy bees and they don’t have mites.

Another technique is to introduce treatments very early in the season. Placing drone comb traps and using soft chemicals will reduce mite populations enough for the colony to build, but even a severely reduced mite population will also continue to build. Monitoring the mites then becomes more important. If levels reach a detrimental point, which will be on the upside of the colony’s growth curve, a late spring or early summer split will help. Of course, this will provide a setback, again, for your honey production. But each split now has half the mites the parent colony did, and requeening, or at least stopping brood production for a cycle, will dramatically reduce mites while the colony makes some honey.

Treating each right now adds another layer of protection, certainly. A soft treatment with honey supers on will stop many of any remaining mites, and no brood slows those remaining even more. Requeen after a brood cycle, replace honey supers, if removed, and your colony is ready for a fall flow and a healthy winter. This technique is effective if your area has a slow period after the early spring flows and before the heavier summer bloom begins — sometimes called a summer dearth or a June gap. It’s a window of opportunity for the colony’s cycle to be intentionally interrupted but reduce the honey crop the least. It is also labor and time intensive.

Varroa Rule Number 3: Use IPM Treatments for First, Soft Next, and Hard Never

Realistically, beekeepers with many colonies seldom have the time or help to carefully monitor individual colonies and manage each independently. There’d be just too much record keeping. On a commercial scale, a beeyard is a manageable unit. Some percentage of colonies from each location are tested, and the whole yard is treated for the level of infestation detected. This means each yard, whether ten colonies, fifty, or more, is treated the same. The next yard may not be treated at all. The next treated twice. It all depends on the results of the test. So test.

Testing is important. Treatments are expensive, and avoiding a treatment is the first, best choice. Time of year is also important, and if there’s a honey flow on, many treatments are not allowed or the honey has to be pulled so a treatment can be applied.

From an IPM perspective, isolation, full sun, drone trapping, eliminating any nutritional stress, making sure you have strong colonies with healthy and productive queens, and above all else, staying as far away from commercial agriculture as possible is as important as eliminating other pests and diseases and are all the best choices. Second choice, then, are the few chemical treatments that can be used with honey supers on. Next are the organic acid treatments because they leave no residue in the wax and are mostly easy on the bees. That’s the thing to consider about the organic acids, however. Applied at the wrong time, or the wrong way, they can and will harm brood, bees, and queens, and under some circumstances, beekeepers. These acid vapors are very effective and safe when used correctly. But know that the essential oil compounds leave residues and, though not as toxic as the harder chemicals, they do not go away. The harder chemicals leave toxic residues, and those are to be avoided.

Buy this book from our store:The Backyard Beekeeper

More from The Backyard Beekeeper:
• Guide to Beekeeping: Bees’ Rules
• Guide to Beekeeping: Queen’s Rules
• Guide to Beekeeping: Beekeeper Rules
• Guide to Beekeeping: Beekeeping Rules

Excerpted from The Backyard Beekeeper by Kim Flottum. Used with permission from Quarry Press, © 2018.