Hi,

Sorry to hear about that experience with pests! 

I wonder if the green beetles you saw feeding on the tassel were adult corn rootworms. This article from Iowa State Extension has some nice close-up photographs to help you with identification.

While adult rootworms interfere with pollination, the larvae attack plant roots. That's good to know when you're looking at controls.

I would start with crop rotation. Corn rootworm larvae feed on the roots of grasses (corn is their preferred host) and cannot develop on the roots of broadleaf plants. So you could starve next year's larvae by planting tomatoes or peppers or squash where you planted corn previously. (This article is intended for large-scale corn growers, but it describes some of the limitations of using pesticides for corn rootworm.)

I hope that gives you something you can work with. Please write back if you have other questions.