This past fall I closely monitored a number of colonies in separate yards to measure the efficacy of OAV as a late summer treatment for me here. An unexpected observation was the large and quick spike in mite counts in a few colonies. I know that this has been observed and discussed here often. This is my speculation and only that as I don't have hard data.

Sudden mite immigration was isolated to only a few specific colonies. Without digging up the exact records, my memory is counts going from the 1-2% range to 5 and as high as 15% in a 10 day period, all while OAV applications were being applied at 5 day intervals. I speculate that the main cause of immigration is from robbing and not drift.

Drift I believe would be more uniform in its distribution. Aside from the normal drone and confused forager drift we always see I don't think a collapsing colony would pick a particular colony to drift to in a yard of a couple dozen. The colonies that experienced the spike were not collapsing so it was not drifters taking advantage of easy access. When I have observed robbing in my own yards it is the small mating nucs and weak colonies that are the victims and I have tried to fallow the robbers home to see who was the culprit. In mating yard situations I have even tried to remove  the robbing colony to no avail. I believe that once robbing gets going the news travels and a lot of colonies get involved. That would lead to a spike in all the robbers if the robbed colony had a high mite load which thankfully is not the case in my yards. 

A strong colony in a yard that finds a weak or collapsing colony within its foraging area but not in its own yard would have more exclusive access and thus get the lion's share of the mites from that colony as it robbed it out. I have heard others say that a portion of the bees from a colony being robbed will travel home with the robbers as well. The yard that had the colony with the highest spike was closest to the village of Dayton and my guess is that they found a weak managed colony to rob. In my other out yards there are no managed colonies within range but as I have used these locations for years I suspect that some of my own escaped swarms are in the trees and collapsing in the fall. 

Needless to say that late summer robbing (and that is when I experience it most) makes fall mite management much more complicated. All the more support for an early winter non-brood treatment or an extended treatment during that period that will catch the immigrants. Randy's towels would fill the bill nicely or dread to say a 56 day Apvar. We have a foot of snow and been below freezing for over a month so it looks like this might be the second year in a row that I have missed the narrow window of broodlessnses and acceptable temps for an OA treatment.

Scratching my head, and wishing all a Happy New Year.

Paul Hosticka 
Dayton WA

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