If you're out checking your corn, you're going to find a few bugs. There may be a plant cut here and there. Perhaps another plant here or there that looks like the leaves were chewed on. Or maybe one or two are wilted. Insects are out there, and there will be some activity. What matters is if you see one or tow over a wide area, or several. Once you see several plants damaged within an area, entomologists recommend doing actual scouting and insect counts so you can determine if a treatment would be warranted. When entomologists make up what they call threshold treatment tables, they try to balance the potential yield damage the insect could cause against the cost of the chemical and application to control the insect.
If you dig in the soil, you're going to find white grubs. They'll have brown heads but white bodies. Some will geed on roots. Again, it's not usually a pest that causes tremendous concern, but it can take out a few plants. And under very unusual conditions, like a cool, wet stretch, it can take out enough plants to cause damage.
Wireworm is another pest in this category. Easily visible, about an inch long, copper colored and thin as a wire, hence their name, they are famous for tunneling through the heart of seedlings when corn is about 4 to 6 inches tall and before soil temperatures grow very warm. Once temperatures get warm in the soil, they migrate deeper, seeking cooler temperatures, and no longer bother corn. However, bad infestations have been known to wipe out several acres of corn. Usually they occur in patches, and are worse where lots of organic matter have been applied to the soil.
Two problems make wireworm a tough enemy if they happen to strike one of your fields, First, there is no rescue treatment. If damage is severe enough, you can plant over and hope soils are warm enough hey wont return that season. Second, their lifecycle extends up to 7 years, Once in a field, you can expect them to return in that same part of the field again. Fortunately, once you know what they are there and have identified them correctly, you can use seed treatments and insecticides the next time you plant corn there to prevent major problems.