Honeybees need both nectar and pollen, the latter to feed to developing bees in their larval stage. From what i understand, bees will collect pollen from several plants that do not also produce nectar -- flowers producing wind-born pollen, like corn and oak.
There are different 'chestnuts,' but whether the flowers produce nectar or not, maybe bees seen on the flowers are simply collecting pollen. If you see pollen on the bees' hind legs in their pollen 'baskets,' then that tells you they're collecting pollen. When they forage, apparently they stick to either pollen or nectar, and the pollen each bee gathers will be from only one species, although when they unload and head back out they may begin to fixate on a different species.
The Mass/Rhode Island chapter of the Am. Chestnut Foundation are meeting on Zoom this Sunday, 12/6/2020, and there's a discussion of bees and chestnuts. I'm curious...
