I do not like to use chemicals in my garden.
I'm too the typical person who dislikes the use of chemicals, if I have to grow my plants to eat by myself (and mine is a self-production) I don't want to eat the chemicals I can find without problems in all the food I buy...
I noticed today that something is munching on the leaves!
Anyways, talking about something important I want to say that at the beginning I had an idea of what were these bugs, and then, thanks to Almost Eden I realized I was right: you are talking about stink bugs.
I don't have a precise advice for you, I don't know whether you only keep in your garden corn or, like me, you have a lot of different crops, but if the place in which you hold corn is little, you can also use gloves in order to take them with your hands and kill them. You can throw them on the ground and kill the bugs. I know it sounds strange but my grandparents have always been doing it without problems even though I have never done something of this kind...