A large arrow scratched in the dirt signals the entry point Carson Dugger uses to find the rootworm traps he’s been monitoring this summer in a corn field near Grinnell. After fighting through seemingly endless endrows, Dugger marches quickly to examine the first of four traps in the field.

“The males emerge first. Now we’re seeing more females as well as males,” Dugger says as he counts the rootworm beetles on the square yellow sticky trap. In addition to counting numbers, he looks to see if female beetles are loaded with eggs.

“If she has already laid her eggs, you’re going to have a problem next year,” says Dugger, who is entering his senior year as an agronomy major at Iowa ...