A few weeks ago I bought a couple of aquarium thermometers. On the 9th December I put the sensor of one of them in a hive close to home, thrusting it an inch or so down between the top bars of the brood box where the cluster seemed densest. The temperature display is on a small screen which I tucked away in a mini-nuc box on top of the hive to protect it from the weather.
I checked the temperature at 5pm on a cold, almost freezing, evening and it was 79.7 degrees Fahrenheit so there was probably some brood below. That suggested that I shouldn’t apply oxalic then as many of the mites would be protected within cells.
After a cold spell, the temperature reduced and was down to 56.7 on the 20th December in the morning but later in the day was up to the 70s again suggesting that, although there may have been a brief break, they were brood rearing again and it was therefore time to apply oxalic. I have a screen and tray under another hive nearby and it was averaging a drop of 2 mites a day.
I made up some oxalic solution using the recipe on Dave Cushman’s website: 1 part by weight of oxalic acid crystals; 10 parts by weight of water and 10 parts by weight of sugar, making 420 grammes in total.
Since then I have been gradually doing a round of my scattered hives, dosing them with about 5cc per seam. The weather has been warmer than ideal so the bees weren’t clustered and I had to guess how many seams to inject. I got a couple of stings from one of the hives, my first for months, but there was no reaction. I always try to get a sting or two during the winter to keep my immunity up.
I checked the tray of the nearby hive on the 23rd December just before applying the oxalic and there had been no mites since I last looked 2 days earlier. Yesterday, Christmas Eve, roughly 24 hours after the application, there were 9 mites. Today there were 46! I swept them into my handkerchief to bring home and examine under a microscope.
I still have a few hives to treat so I must get on with it as soon as this wet and windy weather permits.