This is my first year with a top bar hive....even with the first few weeks here in Michigan with a terribly cool spring the bees were quit busy building the hive. I fed them all they needed for 6 weeks. It's now mid July, summer is here and the bees are all visible through my inspection window. I noticed they seem to be moving very slowly, not active as in the first few weeks. They have only built 8 bars of combs......anybody have any advise?