Hi Ted.  This is a rather shocking number.  I think one of the major differences between Apivar and other treatments is that Apivar is slow acting – it may be effective, but it’s slow acting.  That’s one reason they recommend leaving Apivar strips in the hive for at least 6 weeks.

I had a similar situation last summer before I took off to Europe.  Since I wouldn’t be around for 4 weeks, I used Apivar because other treatments require shorter periodic intervention.   So, for my hives, I started at about a 2% level before treatment but when I got back, they averaged about 6% (17 mites per 300).  Highest was 20.  Treatment had been going for about 4 1/2 to 5 weeks.

What I did was enlist the nuclear option:   I did oxalic vapor treatments every 5 days for 4 weeks.  Harsh, I know.  I thought this might negatively impact my queens, but all 8 survived and the colonies looked strong going into winter. ( I did have one winter loss, but that’s because the cluster was too small, I believe).

If I were in your shoes, I hit the problematic colony with at least one treatment of oxalic (maybe more) or Formic-Pro to knock the population down.  Maybe the Apivar is working, but it’s working slowly.  I think it’s best to get the population knocked down soon and not wait for Apivar.  But I’d consider continuing Apivar after the population looked in check (but I have not researched this aspect).

This is probably what I’d do.