That's the result of a corn worm of some type, in late corn esp they'll drill down into the swirl chewing in secret, their poop rises to the surface as the leafs grow up and out from the swirl center. They will damage the tassel if it gets that far along. Your favorite pesticide spot applied down the swirl or a good eye with a pair of tweezers should take care of it.

My first guess would be Ostrinia nubilalis European corn borer, https://extension.entm.purdue.edu/fieldcropsipm/insects/euro-cornborer.php Under some conditions Helicoverpa zea Common earworm will do similar damage but to a lesser extent and with little visible sawdust. https://www.sare.org/Learning-Center/Fact-Sheets/Organic-Insect-Management-in-Sweet-Corn/Text-Version/Corn-Earworm