We did not think that we had a mite problem this year. We have been checking drone brood for mites as we worked our hives this summer and saw very few mites compared with other years. We had run a few tests with a drop board under a hive and seen two or three mites after a 24 to 48 hour time period. Other beekeepers in the Seattle have been reporting light mite loads. We did not think we had a problem.
We ran a test. First, we put drop boards in 7 of the 8 hives that we keep at the Urban Horticulture Center. The mite counts after 48 hours were under 10 except for one hive that had a count of 55 mites. 3 hives received Hopguard and 3 got Mite Away Quick Strips and one got nothing. The first product is derived from Hops and the second is a slow release pad treated with formic acid. Neither product is considered a pesticide and both are approved for use while the honey supers are on the hive (our honey collection is done for the year).
The difference in results was dramatic. In the hives treated with Hopguard, there was a subsequent mite drop of from 10 to 15 mites in 24 hours after treatment. In the hives with the formic acid treatment, the mite drop was in the hundreds for all three hives. The six treated hives are in a row and the treatments were alternated. The hives treated with Mite Away Quick Strips were not as active as the other hives so we want to keep the experiment going past the 7 day treatment period to see how the bees fare. The weather during the application period was overcast or rainy with a daytime high in the low to mid 60’s.