I'm going to politely and respectfully dis-agree with a pesticide kill.
My opinion is two fold:
This hive, which you said was your strongest, issued a massive swarm (it's swarm season) that unfortunately, you missed, hence the capped queen-cells and no brood.
Second, these bees aren't very hygienic:They drop their dead right in front of the hive instead of carting them off.
I have a couple of these hives, every year. They make lots of honey so I let them be pigs lol. Other hives cart their dead away several yards so I don't see their cemetery.
I would like to know if I'm right or wrong so maybe send some corpses off to Beltsville, MD to find out?