My new cherry tree NW of Baltimore didn't seem to have many bugs
fertilizing it. Just 4 when I looked, two honey bees and two other
things about half as big and all black.

Is this because of the deaths of so many honey bees?

What were these other things?

I'm not sure they were even big enough to do the accidental fertilizing
that honey bees do.

Do you think this will cause a shortage of fruit on the tree? It had
loads of flowers,

If there isn't much fruit, how do I fertilize the flowers myself next
year? A brush? A toothbrush?