I have problems with fourlined plant bugs every year on Russian sage, catmint and other minty plants especially, so I'm assuming that's the critter we're talking about (technically not a beetle but a "true bug" so feeds differently, beetles chew while bugs pierce the plant with a beak and suck up the juices). No problem finding one in the garden for a photo op but only adults around at this stage, is this the pest in question?:
I either ignore the damage (there's only one generation a year), hand squish them if there aren't too many on a plant, or use insecticidal soap or Trounce (insecticidal soap plus pyrethrins). These sprays have to contact the bugs so best to apply when it won't dry quickly, like early in the morning. That has two other pluses, one is that the bugs tend to be more sluggish in the cool of the morning so not as evasive, and secondly the bees don't get up very early. And as Elaine mentioned, if you start treatment before the flowers are open that also helps avoid harming the bees.
