Tilia americana is known as a source of large quantities of high-quality honey.
Honey bees are not badly affected by the tree, but their behavior is difficult
during a basswood honey flow -- the tree makes nectar for only a few hours a
day, and for the remainder of the day, the bees tend to be unpleasant to work
with. But I've never heard that it was due to any sort of toxicity; rather,
honey bees always become testy when a source of nectar suddenly dries up. In
any case, the colonies remain healthy.