Deformed Wing Virus Case Study: A Cautionary Tale

Spotting deformed wings in a hive is one of the saddest and more worrisome things that can happen during a routine inspection. Spotting lots of them in one hive is downright scary. This is a story of some beekeeping detective work around an unusual case of DWV in a hive that I found this spring.

The Background

We marked this particular hive as one to watch right away this spring. First, it was small and not growing so we gave it some more time. Then we noticed too much drone brood so we marked it for queen replacement. Finally, I went in to replace the queen and discovered that there was no worker population left; the majority of the bees were drones and an alarming number (20%ish) of the drones had deformed wings. In total, there were only two frames of bees in the box.

Things to Know About DWV

There are a few important things to know about deformed wing virus:

1. It is a virus so there is no medical treatment for it. A strong, healthy hive can fend it off just like we can fend off a mild cold or flu virus.

2. It is vectored by varroa. This means that when a mite feeds on an infected bee, the virus can replicate in the mite so that the next bee the mite feeds on gets a stronger "dose" of the virus. This increases the speed of spread and the severity of the infections.

3. It can be asymptomatic. By the time you see deformed wings, the viral load is already quite high. It can spread to queens and from queens to brood.

What Did I Do?

Immediately I shut down the hive. I closed the front entrance as well as the top entrance so that no bees could leave the hive and potentially find their way into nearby hives. The next day, I came back to do a varroa mite test (since this disease is often associated with high mite loads).

Since I had determined that this hive was a write-off, I shook ALL of the bees off the frames into a nuc box and took two full-cup samples for alcohol washes. There were ZERO mites.

(For the record, I would have been shocked to find mites. We treated aggressively through the winter and the hives had active mite treatments on them at the time).

So Why DVW with no Mites?

This is where the detective work comes in.

The cause of this odd case of DVW goes all the way back to last spring. Coming out of winter, we did all of our spring mite tests and found zero mites. So we didn't treat. Unfortunately, by the time our bees came back from the out-yards in late August, our mite numbers were astronomical.

Of course, we quickly treated at that time with Formic Pro, which is a hard-hitting varroa treatment that quickly brought our numbers back down.

But the damage was already done. Just because the mites go away, doesn't mean the virus goes away.

So these bees were sick going into winter, the time of year when they are most susceptible (just like us!). The queen was likely sick as well, passing the virus on to her offspring. And so they were sick coming out of winter. The mites were long gone, but the virus was still very much there.

The Moral of the Story

Although it might sound like I am cautioning you to treat for mites even when you don't see mites in a test, that is not my intention. I don't want to promote prophylactic treatment. What I do want to promote is a deep understanding of the dynamics of varroa populations in your hive. This is where I will point you to my tutorial on Randy Oliver's varroa calculator.

I don't think that I should have treated last spring when I didn't find mites in a test. But I definitely shouldn't have waited until late August. I think the model would show that a mid-summer treatment (maybe Formic Pro with the honey supers on) might have prevented this.

The true moral of this tale is to stay ahead of the mite curve. Let go of traditional time-of-year based treatment schedules. Keep testing and treat as soon as you need to.

Looking for more?

Looking for more beekeeping education? You can find my virtual, on-demand course Intermediate Beekeeping for Year 2 and Beyond at https://courses.rushingriverapiaries.com/courses/intermediate-beekeeping

Or if you'd prefer a more tailored experience, you can join my mentorship group at https://www.patreon.com/thehivementorship