Hive humidity affects mite reproduction
Don’t you love it when someone validates your opinions? Especially someone who knows something? Here’s what happened. Last week I wrote a post called Mitekeeping for everyone, in which I say that the most important thing a beekeeper can learn is the Varroa mite life cycle and how it relates to the honey bee life cycle.
Then, the very next day, I discovered an article in the new Bee Culture (October 2012, Volume 140, Issue 10, p. 22) called “Varroa Mite Reproductive Biology.” In it, Michigan State University bee researcher Zachary Huang writes, “The Varroa mite is currently the most severe pest of managed honey bees worldwide. Understanding the Varroa mite’s reproductive biology will therefore allow us to better manage this important pest.” Exactly right.
In the article Zachary explains many of the factors that affect mite reproduction and life cycle, including the brood caste, the age of the host larvae, details of the phoretic stage, the host species (Apis mellifera vs A. cerana), cell size, etc. But the thing that most caught my attention was a short paragraph on hive humidity.
According to the article, mite reproduction drops significantly when the relative humidity is high. In one study (Kraus and Velthuis, 1997) at 59-68% relative humidity, 53% of mites produced offspring, whereas at 79-85% relative humidity only 2% of the mites produced offspring. Zachary goes on to explain that, he too, has had experience with this phenomenon in his lab.
Right away I contacted Zachary to ask him if anything is known about how this works and whether it is wise for beekeepers to continue lowering hive humidity in the winter. I was really worried about this because hive moisture is my favorite “bad guy.”
He responded that 1) nothing is known about how high humidity affects Varroa reproduction and 2) it is still good to control hive humidity in winter for other reasons. And since there isn’t much brood being raised at that time, the effect on mite reproduction is probably minimal.
Okay, I can relax for the moment. But seriously, read the article. It is filled with tidbits that will improve your Varroa mite i.q. It certainly improved mine.