If you have Bt corn, you likely didn't see much corn borer damage, unless you saw some shothole feeding early in the season on refuge plants. People who grew non-GMO corn in Indiana may have noticed more corn borer damage than normal.
The damage could show up in smaller ears on infested plants. One farmer found it showed up as dropped ears. He was ready to blame it on the hybrid until he shut the combine off, walked standing corn and found that there was evidence of corn borer feeding in most places where he found an ear on the ground.
Sometimes the evidence was feces left behind in the ear shank area where the ear had ben. He found one ear with a perfect hole in the end that had been attached to the stalk, round and just the right size for a corn borer larva to burrow through the shank. Once weakened, some of these shanks can no longer hold up the weight of the ear so they let go, allowing the ear to drop.
He also found a larva itself in a stalk once he split it open. These are either the second or third generation corn borers for the season, since the pest has multiple life cycles. Two cycles per year is most common.
Hybrids can drop ears without corn borer present, experts say. Some hybrids are more prone to doing so than others. That became evident in 2012. It was also evident last year that almost any hybrids can drop a few ears if there is enough stress. It's a function of the connection from the ear to the plant growing weak during stress and not being able to hold onto the ear. If you find dropped ears, do some investigation to determine if the hybrid just let go, or if there was some intervention by corn borer or another insect that set the ear up to fall.