One non bt-corn hybrid (Pioneer 3489),two bt-corn hybrids with the Yieldguard event (Pioneer 34RO7 and Novartis NX6236),or one bt-corn hybrid with the Knockout event (Novartis N64-Z4)were seeded in duplicate 2.9-ha fields.On September 4,50 plants were collected from each field and examined for corn borers.