Researchers have reported differential and conflicting responses of com (Zea mays L.) to insecticides. Our research was conducted to determine if tillage and corn genotypes cause the variation in response. Two experiments were conducted. In one 3-yr study no-tillage (NT) and conventional tillage (CT) were main plots and four insecticide treatments were split plots (2.2 kg a.i. Carbofuran ha-I (CF 2.2), 1.1 kg a.i. Carbofuran ha- 1 (CF l. I), 2.2 kg a.i. Terbufos ha-1 (TF 2.2), and a untreated control (C). In the other study six hybrids were main plots with the same insecticides as split plots. Grain yield was measured at harvest. Treatments with CF 2.2 gave higher grain yield in NT, but TF 2.2 gave equal grain response in CT. When "Asgrow RX777" (developed using TF) was treated with TF 2.2, it averaged 32 q ha-I more grain than the C. Also, "Dekalb XL71" (developed using CF) yield 28 q ha-1 more grain with CF 2.2 than with the C. These results suggested that a hybrid will respond better to the insecticide used during its breeding development.