Beekeeping.... it's a learning experience.

A few weeks ago I went out to the hive to find a pile of dead bees in front of the hive. I suddenly felt so sad and sick to my stomach. I quickly opened up the hive to find that EVERY last drop of honey that was there had vanished and there were barely any bees there approximately 500-1,000.... when our hive had consisted of about 5,000+. There were dead bees in the comb and the bees that were there were dragging out dead bees as fast as they could, they had piled up on the porch of the hive. We are not 100% sure what happened but we suspect a pesticide. We had added a super a few months prior because our first super was full of honey. They had not worked the comb in the top super and there were no bees there so we removed it. I began feeding the bees a mixture of sugar water & honey. We are now attempting to merge a super from one of my father in laws hives to our hive. We have placed a piece of newspaper between the two and the plan is that they will slowly chew through to each other, slowly getting acquainted. The hive that we are merging has about 3,000 bees in it and is FULL of honey. I am hoping they accept each other & this gets them through the winter.