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Considering they have only stubby little legs—and no wings, fins, or driver’s licenses—varroa mites have no trouble getting around. Varroa mites have many routes of transmission. In fact, they have an entire public transport system built and maintained by the very host they parasitize. Seems unfair, doesn’t it?
While many routes of transmission from colony to colony have been documented, some are more important than others. Here’s a list of common ways mites get around, and there could be others.
1. Mites on flowers
Of all the possible methods of mite transmission, this one seems the least likely. Mites are attracted to the pheromones of bees, so it seems far-fetched that a mite would jump off a bee onto a flower and wait for another bee to arrive.
However, if a varroa-laden bee lands on a flower and begins to groom, it is possible that she will dislodge a mite. If so, that mite has no choice but to wait for another honey bee to come along and give her a lift. Surely this happens from time to time, but it’s probably not a major means of transmission.
2. Beekeeper assistance
Beekeepers can easily move mites between colonies when they exchange frames of bees or brood between hives or when they make splits. If they have outyards and move their bees between yards, the spread of mites can be faster.
3. Drifting worker bees
Not all honey bees make it back to their own colony. It is well known that if you have a row of hives, the hives on the ends will slowly gain population while the ones in the middle lose it. These bees are the drifters.
If these lost bees are carrying pollen, nectar, or other needed stores, they are usually welcomed into the new colony. The unseen gift, though, could be phoretic mites tucked between the bee’s segments which are happy to jump off and make themselves at home.
4. Wandering drones
Unlike foragers, drones are not too particular about where they spend the night. Drones are very likely to stop in at any old colony and the foragers usually let them in. Wandering drones are often considered to be a major mode of varroa mite transmission.
5. Swarming bees
If a colony has mites, so will the swarm that comes from it. It only takes one mite to begin a new infestation.
6. Absconding bees
Bees don’t always abscond in massive groups like a swarm but may leave a hive in onesies and twosies. This can happen when:
- a colony is collapsing from disease or parasitism
- when the bees are starving
- when a colony remains queenless for a long period
- when a colony is decimated by bears or other predators
- after a fire or flood
- whenever the bees’ home is destroyed or becomes uninhabitable
The bees fly off and some may be lucky enough to find another colony to join, carrying with them their trove of mites and/or other diseases.
7. Robbing bees
Whenever a bee colony becomes weak it is a potential target. Bees from healthy robust hives are often eager to empty out the pantry of a weaker hive and ferry the treasure back home, a form of kleptoparasitism that is greater in some races of honey bees than others.
Oftentimes the weak hive is riddled with varroa mites, and it may even be collapsing for that reason. The robbing bees end up with more than they bargained for, taking home both honey and a blood-thirsty population of varroa mites. Aha! What do they say about greed?
Varroa mite transmission is a never-ending problem
The take-home message is that your colony can pick up an infestation of varroa at nearly any time of the year. The best practice is to monitor your hives regularly to see if you have a problem, and then decide on a course of action if you do.
Honey Bee Suite