Each time I think I’ve written my very last post on varroa, something else comes up. This time, it was a question about how to treat for mites now that we know mites eat fat bodies instead of hemolymph.
Based on what I’ve read, I would say that if you are following current best practices for controlling varroa, you shouldn’t have to make any changes in your mite management protocol. Current practices were developed based on what works best, regardless of what the mite was eating. Someday that may change, especially if someone develops a different way to treat based on the new information. But for now, it doesn’t change much in the field.
The mites are the same old mites—only our understanding of them has changed. However, the new information does help to explain many of the things we see in a colony overrun by mites, and it helps explain why things go downhill in a such a hurry.
Dr. Samuel Ramsey discovered that mites do not eat hemolymph alone. Instead, they seek out fat bodies which are found in the honey bee abdomen. Because fat bodies are essentially bathed in hemolymph, it is easy to see why earlier researchers missed the connection.
Ramsey also learned that varroa mites found riding around on adults—especially those on the ventral side of the abdomen—are actually biting into the bee and eating. Like diners riding the dinner train, these mites are feasting while they get ferried about the hive. Not good news.
Up until this discovery, the theory was that the mites were parasitic on the developing pupa, entering the cell just before capping and then feeding beneath the capped cell. We also believed that after the bee emerged, mites had a phoretic stage, and it was these phoretic mites that we occasionally saw in the hive or riding a bee.
But phoresy is a situation in which an organism is riding on a host but not acting as a parasite. This new information shows us that the mites are not phoretic when they are riding around on adults, but rather they are parasitic in that stage as well. Basically, we now know the mites are feeding throughout their lives: under the cell cap they feed on pupae and loose in the hive they feed on adults.
Treating for mites
For a number of years, the standard advice has been to treat your colony for mites before the winter bees develop. For most of North America, this means treating in August such that the treatments are completed by the end of the month.
The winter bees, which emerge beginning in September or October, are the long-lived bees that tend the colony until spring. In healthy bees, the fat bodies act as protein reserves that allow spring brood to be raised even in the absence of sufficient pollen. If these bees are not healthy and strong they won’t last until spring, or they won’t have enough protein reserves to feed the young.
To keep the winter bees healthy and prevent infection by virus, the colony must be virtually free of varroa as it goes into fall. If treatment is delayed until after the winter bees are born, the treatment will do little good. A treatment in November, for example, will kill the mites but it won’t help the bees that are already infected with virus. Often, a colony treated late will collapse as quickly as one not treated at all.
Before Ramsey’s findings, we believed the winter bees were weakened primarily by infection from virus. This is probably still true, but now we know that honey bee fat reserves are also compromised by the mites, a situation that shortens their lives or makes them incapable of feeding brood even when they are virus free.
Monitor before you treat
As for a treatment schedule in North America, August is still the most important time to go after the mites. Depending on your local situation, you may need to treat more frequently, but the late summer treatment is the most critical, especially in terms of timing.
In any case, monitoring for mites is vital. You shouldn’t treat if you don’t need to, and monitoring mites with an alcohol wash (preferred) or sugar roll will give you the information you need. After treatment, you should count again to assure yourself that the treatment worked. If you are a treatment-free beekeeper and find a collapsing colony, consider destroying the colony before it delivers its mite load to your other colonies, neighboring colonies, or feral stock.
Honey Bee Suite