I suspect insects of some sort destroyed...

Well, you’ll have to wait until your lawn is full again next season. Then, if the grass is looking wilted or in need of water, the answer may be a root-feeding insect. You can then look for the insects by peeling back some of the sod. If you see brown patches, something is probably feeding on the grass blades. Look for these insects hiding in the thatch or natural debris on your lawn. Or examine the blades themselves; a close examination might reveal the bugs. Control depends on what you find, but maintaining a generally healthy lawn with appropriate moisture, mowing, and soil is the best pest control method.