Bees and Poplars, Poison Ivy, and Propolis

I need some feedback from Mid-Atlantic bee experts (or specifically you folks in the Eastern Panhandle or Western Maryland).

Yesterday I recorded bees returning loaded with a very orange pollen.  My friend thought it was from poplars.  Tulip trees (Liriodendron tulipifera) are sometimes called Tulip poplar or yellow poplar by older foresters and the lumber industry, and I knew of only younger Tulip trees nearby.  Cottonwoods (Populus deltoides) are in the same genus as aspens, the true poplars in the Salicaceae family.  We have a giant cottonwood down by the river and of course, they produce seeds like no other tree, but their pollination should have been complete many weeks earlier (March or April).  You'll hear us confuse this in the video.   Now that I've done some reading, I'm guessing he was talking about tulip trees, not cottonwoods.

But the next day I was building a new horse trail / walking trail and heard a lot of buzzing.  When I went exploring I found honeybees pollinating the Poison Ivy (Toxicodendron radicans and formerly Rhus toxicodendron and Rhus radicans).  I haven't finished researching this, but I've learned some believe that the raw honey helps build a resistance to the allergic reaction from exposures to the plant oil.  Interestingly, I've also read that many people are allergic to the Cashew tree (Anacardium occidentale), in the same Anacardiaceae family as poison ivy, and that makes them more expensive to harvest.

So after further exploration, I now think the orange material these bees were transporting is propolis from the cottonwoods.  According to the well-researched Wikipedia article, propolis is believed to reinforce the structural stability of the hive, reduce vibration, make the hive more defensible by sealing alternate entrances, prevent diseases and parasites from entering the hive, inhibit bacterial growth, and prevent putrefaction within the hive.  And while bees usually carry waste out of and away from the hive, they sometimes seal larger invaders in propolis, essentially mummifying it and making it odorless and harmless.