Contrary to popular hearsay, freezing will kill all life stages of both the greater wax moth (Galleria mellonella) and the lesser wax moth (Achroia grisella).
To kill the moths, you must monitor both time and temperature. For example, the Mid-Altantic Apiculture Research and Extension Consortium (MAAREC) publishes the following guidelines to kill both species of wax moth:
20 degrees F for 4.5 hours or
5 degrees F for 2 hours.
Similarly, the Department of Primary Industries in Victoria, Australia advises
-6.7 degrees C for 4.5 hours or
-12.2 degrees C [10 degrees F] for 3 hours or
-15 degrees C for 2 hours
These numbers convert exactly. Nevertheless, beekeepers come up with all kinds of wild stories about freezing them for weeks on end, only to have the caterpillars start crawling around when the frames thaw. Don’t believe it.
Here are some points to consider if you freeze your frames for wax moth control:
- Check your freezer temperature with a reliable thermometer—don’t depend on the dial.
- Measure times from the point when the frames, combs, wax, or super reaches the desired temperature. Don’t start timing from the moment you put them in the freezer.
- Remember: if you return thawed frames to a super that was not frozen, re-infection can occur immediately.
- The same is true if you return frames to an area that contains adult wax moths, such as a storage building or honey house.
- If you wrap frames tightly in plastic wrap before freezing—and leave them wrapped afterwards—you can protect them from re-infestation. Wrapping also keeps condensation from forming on the combs and frames while they return to ambient temperature.
Freezing times don’t have to be exact as long as you meet the minimums. For example, my freezer is 9 degrees F. I just wrap my frames in plastic and freeze overnight . . . or over 30 nights. There’s no need to create an ordeal.
One reason the myth persists is that some beekeepers have reported that wax moths survived the winter in their hives in spite of the fact it was less than 20 degrees for weeks on end. This is most likely true because it is not 20 degrees inside a healthy beehive. The cluster keeps the wax moths warm and cozy all winter long. But as long as the colony remains healthy and strong, it will destroy most of the moths as it expands in spring.
So just remember, wax moths are not an inexorable pest destined to take over the world—they are both predictable and manageable. When the day comes that they can drop me in the freezer, then I’ll start to worry.