Urban beekeeping in New Mexico's largest city.
I have one hive and tested it using the alcohol wash method on 7-25-20 (3 mites/271 sample size) and again 8-16-20 (2 mites/357 sample size). I did not treat the hive after either sample. I inspected the bottom board for mites on 8-30-20 and didn't find any. Does it make sense that the mite count would decrease between the 2 test dates?
First off, thanks for being a responsible beekeeper and testing for mites. It does make sense that you sometimes see different mite counts between the two dates. There can be a number of reason for the difference. That is why it is important to test often. Testing often can allow one to see trends. There is also something called sampling error. When you think about testing for mites, we need to account for all of the many variables involved in sampling. Our responsibility is to identify best practices for testing (sampling) and use the same steps each time we test. Some experts recommend testing from a brood frame, some recommend sampling from an outer non-brood frame closest to the brood frames. The point is to pick a method and then stick to it for all samples. This helps standardize the sampling method. We see in the media election polls. Similar polls come up with different results. That is all part of statistics which is what we are doing when ever we sample for mites. We take a small sample (300 bees) and then try to estimate the mite population in the hive (universe) based on that sample. The Honey Bee Health Coalition states that: "Sampling several times throughout the year helps reduce sampling error and increase confidence in sampling results. Frequent sampling can detect mite increases at critical times of the season." Keep testing, follow best practices, realize there are many variables involved that can potentially explain different counts.