(M5) CORN (FIELD): Zea mays L. 'Pioneer 31B13', 'Pioneer 3223' Southwestern corn borer (SWCB): Diatraea grandiosella (Dyar) Sugarcane borer (SCB): Diatraea saccharalis (F.) Corn earworm (CEW): Helicoverpa zea (Boddie) B. A. Castro, T. J. Riley, and B. R. Leonard LSU Agricultural Center Department of Entomology Baton Rouge, LA 70803-1710 Phone: (225) 388-1634 EVALUATION OF TRANSGENIC BT-CORN (MON810 EVENT) AGAINST NATIVE POPULATIONS OF SOUTHWESTERN CORN BORER, SUGARCANE BORER, AND CORN EARWORM, 1999. Two experiments were planted in a Gigger silt loam at the Macon Ridge location of the Northeast Research Station near Winnsboro, LA. Test 1 was provided with supplemental irrigation weekly as needed throughout the season. Test 2 was planted in a dryland area with no irrigation. Corn seed was planted on 7 May (Test 1) and on 10 May (Test 2) at a rate of 30,000 seeds/acre with a John Deere 7400 planter. Counter 20CR at 1.0 lb (AI)/acre was applied in-furrow at planting. Treatments (hybrids) were arranged in a RCB design with 5 replications in Test 1 or 4 replications in Test 2. Plots consisted of 8 rows (40-inch centers) x 45 ft. Corn stalk and ear shank tunneling caused by natural infestations of SWCB and SCB were recorded in the field on 8 Jul by estimating the number of injured plants in 20 ft of row per plot. CEW injury to ear kernels was evaluated in the laboratory on 13 Aug from hand-harvested ears in 10 ft of row per plot. Ear kernel injury was estimated by using the Widstrom method (1967, J. Econ. Entomol. 60(3): 791-794). Seed yields were obtained on 23 Aug by mechanically harvesting the 4 center rows in each plot and correcting to 15.5% moisture. Bt-corn hybrid Pioneer 31B13 significantly reduced stalk and shank tunneling compared to the non-Bt Pioneer 3223 hybrid. Significantly lower CEW ear injury was observed in Pioneer 31B13 compared to that in Pioneer 3223 in the irrigated test, but not in the non-irrigated test. Although yields were higher in Pioneer 31B13 plots compared to those in Pioneer 3223 in both tests, yield differences were significant only in the non-irrigated experiment.
