They usually spray Cypermethrin or Fipronil because it’s cheapest. – http://store.doyourownpestcontrol.com/pest-control-products/generic-insecticides
Bees are interestingly resilient because their lifecycle is so short (only the queen lasts up to 7 years – which is why people like eating/consuming/rubbing royal jelly on themselves hoping to live longer – but it’s a integral genetic modifying hormone in the food that does that). Most bees last 3 to 5 weeks, so what is being observed is when a productive hive is sprayed in the daytime, 80% of the colony is usually out foraging. They return and smell the poison and try to figure out what is killing their sisters (the males are only useful once in their lifetimes and that’s to pollenate/impregnate another queen, once. Then they die.)
What happens next depends on the numbers. They will not usually attempt to reoccupy a sprayed nest, but they tend to gather nearby, similar to what happens during normal swarming (when a hive gets too crowded and they generate one more queen and the old one takes 1/2 the colony with her to make a new hive). But in the case there is no queen (because she’s been killed by the insecticide), the existing workers will still swarm, and relocate and attempt to re-raise a new queen within that 5 week timespan. If there were one or two drones left in the mix, they can impregnate a worker (who normally could only lay infertile eggs) and begin rearing a new queen (by feeding royal jelly and propolis to the larvae).
Otherwise, that particular colony just gradually dies off because the workers need sufficient numbers to maintain sufficient heat inside a new hive to raise the larvae. (workers can gather food, produce drones/males and build wax, but they can’t lay eggs as fast as a queen to regenerate an entire colony).
What you could do, if you happen to have a suitable backyard available, or another tree, is to make up a bee box home and place it up where it would be out of the direct path of anyone nearby (we even use cardboard boxes with a small 1-inch hole punched in it when we just want to relocate a colony). Then you try to get a few slabs of the old comb from the old colony from the inside where it was least likely to have been sprayed and take half and just lay it in the box, and the other half and kind of rub the honey and wax around the inside of the box. (This procedure is based upon there being an absence of bees around, of course. If the bees are still active and you do not have prior experience handling bees, I would always recommend you let trained people handle this part – they can help you learn how to do it properly, if you wish to learn about bee management.)
The smell attracts the remaining foragers and they will usually try to rebuild the colony inside the box. (which is how we end up adopting new feral colonies, if it’s not swarming season.) We can use the same technique to “capture” a wild swarm (they dont’ sting when they’re swarming because there’s no new home to protect yet). By basically taking an empty frame box and making it smell good to them and placing (or dumping) the swarm directly into the box with frames for them to build comb upon.
Without the frames, they will just attach their comb to the top of the box and build a naturally-shaped hive. You can also contact http://honeylove.org/ – which is our new parent organization throughout Southern California. Go Bees!