Evaluation of Bacillus thuringiensis transgenic field corn for management of Louisiana corn pests

Efficacy of Bt corn hybrids expressing an insecticidal delta-endotoxin through different transformation events was evaluated in Louisiana. Efficacy levels were determined for southwestern corn borer (SWCB), Diatraea grandiosella Dyar; sugarcane borer (SCB), Diatraea saccharalis (F.); corn earworm (CEW), Helicoverpa zea (Boddie); and fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). Insect (neonates and third instars) susceptibility was evaluated on Bt and non-Bt corn plants (V6 and R1 stages) in field plots and plant tissue in laboratory studies. Bt corn hybrids with MON810 and CBH351 transformation events sustained significantly (P < 0.05) less injury caused by SWCB, SCB, and FAW during infestations at midwhorl stage. SWCB, SCB, and CEW infestations during silking stage were significantly reduced in Bt hybrids with the MON810 event. However, CEW infestations at silking stage were not significantly (P > 0.05) reduced in the Bt hybrid with the CBH351 event compared to respective non-Bt equivalent hybrid. Performance of BT11 and 176 events against CEW infestations at silking stage was not consistent under observed field conditions. SWCB and SCB were highly susceptible to the MON810 event in leaf tissue experiments. However, consistency in performance of the MON810 event against SWCB and SCB varied among Bt hybrids containing that event. SCB expressed less susceptibility to leaf tissue containing the CBH351 event than to leaf tissue with the MON810 event. Plant resistance to SWCB and SCB attack increased as plants matured, independent of the presence of a Bt construct. Higher CEW survival was observed on Bt silks than on Bt leaves regardless of Bt event. Economic returns above technology fee were consistently observed in central and most areas of northeast Louisiana. Economic returns in northwest Louisiana were highly dependent on corn market prices. Under growing conditions and investment levels observed, soybeans and in some cases grain sorghum production might offer higher economic benefits compared to Bt corn production for late-crop planting in some areas of Louisiana.