Go out at night and look on the undersides of the leaves with a flashlight, Bill. I had this happening to one of my brug plants inside our pool cage and it was a small, bright green caterpillar. Couldn't see them in the daylight, but at night they showed up pretty well.
I just picked them off by hand for a few nights and solved the problem, but if it is widespread, you could try spraying them with Bt. It's available as a concentrate at any nursery or big box store, and is a naturally occurring bacterium that just affects caterpillars that chew the sprayed leaves. Safe for edibles.
If you don't see caterpillars, it could be Sri Lanka weevils, but they chew more on the edges of leaves. They are nearly 1/4in. and white so easy to spot at night, but in the daytime, they hide on the undersides of the leaves too - avoiding being eaten by birds, I think. They really do need to be picked off by hand, or shaken off the plants and collected for extermination. No chemical solution seems to work on them, at least as far as I've heard.
