I have 5 hives, and have kept bees for over 6 years. I'm also a woodworker. Last year, I built an observation hive, with 6 frames. It was in our bedroom, so I could pretty much watch it every day. By March of this year, the hive had dwindled to a queen and about 10 adult bees. There were no larva. I've read about it working both ways, where there is plenty of larva, and no adults, but here's my personal theory:
Several pesticides have been developed that cause the males to be sterile. Possibly the female as well? She mates with multiple males, so the male sterility should be sporadic. What if the queen ends up laying sterilized eggs due to her sterility? Now, the queen I had was laying very well up through the winter, then stopped. You would expect the queen to be replaced if she wasn't laying - but I believe that's the case only when her scent diminishes. The other bees don't supercedure her during the winter when she's not supposed to be laying, because it is pherome based, not quantity based.
What if there were an insecticide that cause the queen to either be unable to lay, or lay stillborn eggs. Her scents would remain the same, but the other workers wouldn't kill her or raise another queen because her scent was still strong. That scenario would work perfectly for my hive. She was still plenty strong enough to fly above the hive when I opened it up. Plenty of capped honey as well.
What if in a higher order insect like the bee, she only suffered this for a short time, then started laying again? Depending on the timing, the hive would die out, or show a queen and a couple bees sitting on a large store of larva. Since during the winter, the bees start at the bottom and work out, they will start with the spring stores - those of wild blossoms, and then get into the ones collected later in the summer - possibly pesticide laden. Based on that timing, she may get her laying back due to clean spring stores after dwindling due to eating summer nectar with a pesticide. Then she would lay a lot of eggs and larva, but there would be no adults to take care of them.
One last suggestion is that it is not a pesticide, but an abundance of a plant. Soybeans produce naturally occurring phyto-estrogens. Wild sweet potatos also have estrogen affecting chemicals. I don't know enough about the biology of an insect to react to certain biological hormones, but considering that it seems the commercial growers were the ones more affected, it would be interesting to look at that possible connection as well.