It is one of the some 8,000,000 beetles that inhabit the earth. What, other than resting on the plant, is it doing? Is it eating a plant? Is it eating other insects?

Well it's not a Japanese beetle so that's only 7,999,999 to go. :-)

It's just hanging out and buzzing around slowly. It was fighting/mating with a 2nd one yesterday.

It's not a beetle, but a moth. It's the dreaded Squash Vine Borer (called SVB as a shortcut).

Here is a link that might be useful: {{gwi:45184}}