The European corn borer actually is a misnamed insect. At least two-thirds of the "worm" stage of its life is spent feeding on the surface of leaves and leaf sheaths. Only during the latter part of its life does it tunnel into the stalk and become a borer.
Cox, H. C.; Lovely, W. G.; and Brindley, T. A.
"DDT Granules - A New Way to Kill Corn Borers,"
Iowa Farm Science: Vol. 10
, Article 6.
Available at: https://lib.dr.iastate.edu/farmscience/vol10/iss9/6