It's basically pyrethrum. It kills the larvae and young pretty well, but it's not as effective on adults.

Aside from hand-picking it's one of the more effective organics for stink/squash bugs when properly applied, though.

Johnny's says it's their preferred poison for squash bugs -- but just remember not to spray when bees or other beneficials are active, since it's broad spectrum and doesn't differentiate between good and unwanted bugs.