Yeah, those are aphids. They suck the juices of the plant, and so can cause the leaves to be a bit curled and damaged. However, they're really not mobile; you can clean them off with a strong jet of water. Just hose them onto the ground, they won't find their way back. However, you'll have to do this every day for a while, as eggs left behind will hatch, and they reproduce quickly.

If you leave them, their predators will eventually show up and start munching on them, but may not kill them all.

They're a nuisance, and kinda gross, but really not worthy of the big guns (in my opinion) unless things get really out of hand, and you notice decreased vigor.

Hope that helps!

Lara

Yeah, Lara's right.
Just wash 'em off, or even brush 'em off, or squish 'em, if it gives you satisfaction.

Compared to the Japanese Beetle invasion you described, aphids are pretty small beans.

Jeri

And then feed your birds all winter and into the spring so they stay around and eat the aphids in the spring.

They are not worth insecticide. Squish or spray with the hose until the lady beetles show up to polish them off. Once there are a few lady beetle larvae the aphids vanish within 24 hours.

I just have a spray bottle with dish soap and water that I spray only on the plants affected.
I don't have Japanese Beetles or thrips, but consider the aphids a minor annoyance.