Checked one of my hives today- this has been my best-producing, most-active hive. There was a large pile of dead bees in front of the entrance: probably 100 or more. We had also noticed some dead bees about 10ft away from the hive last week, but werent sure where they had come from.
When I opened it, it is obvious there are fewer bees and some newly hatched brood seem to have died as they exited from their cells. There were also a lot of dead bees on the inner cover.
There looks to be some evidence of robbing (capped honey cells that are torn up) but this was an extremely strong, vigourous hive, so I don't think all the dead bees are from fighting robbers. Maybe after the die-off they were robbed.
My working hypothesis is that the foragers got into some pesticide, but the dead newly hatched brood worries me.
I've not had anything similar happen in the last 3 years. All my other hive are fine. Any thoughts?