The efficacy of transgenic corn hybrids expressing an insecticidal Bacillus thuringiensis (Bt) δ-endotoxin from different transformation events was evaluated in field corn, Zea mays L., against the southwestern corn borer, Diatraea grandiosella Dyar, and sugarcane borer, Diatraea saccharalis (F.). Susceptibilities of neonates and third instars were determined on Bt and non-Bt corn plants (V6 and R1 stages) in field plots and corn leaf tissue feeding exposure in laboratory bioassays. Bt corn hybrids associated with MON810 and CBH351 transformation events sustained significantly less injury by southwestern corn borer and sugarcane borer during mid-whorl stage infestations compared with their respective non-Bt hybrid equivalents. Southwestern corn borer and sugarcane borer feeding injury to ear leaf-sheath and husk tissues during the silking stage of corn was significantly reduced in MON810 and CBH351 Bt corn compared with their respective non-Bt hybrids. However, resistance levels to feeding injury in Bt hybrids associated with the MON810 event were significantly higher than that in the hybrid associated with the CBH351 event. Southwestern corn borer and sugarcane borer caused more feeding injury to husk tissue than to ear leaf-sheath tissue in both Bt and non-Bt hybrids infested during the silking stage. Laboratory performance of the MON810 event against southwestern corn borer and sugarcane borer varied among hybrids associated with the same event. Third instars of southwestern corn borer were highly susceptible to MON810 Bt corn hybrids in leaf tissue experiments. However, sugarcane borer larvae were susceptible to the MON810 event only in one of the Bt hybrids evaluated. Sugarcane borer mortality was significantly lower after 96 h of feeding exposure on CBH351 Bt corn leaf tissue than on MON810 Bt corn leaf tissue. Plant resistance to southwestern corn borer and sugarcane borer increased as plants matured, independent of the presence of a Bt construct. These results are essential to estimate the importance of Bt transgenic corn in areas of southern United States and other areas where mixed populations of southwestern corn borer and sugarcane borer are predominant and cause severe damage to corn production.
RESUMEN La eficacia de híbridos de maíz transgénico que expresan δ-endotoxinas de Bacillus thuringiensis (Bt) a través de diferentes eventos de transformación fue evaluada en maíz duro (Zea mays L.) contra el barrenador del maíz del suroeste, Diatraea grandiosella Dyar, y el barrenador de la caña de azúcar, Diatraea saccharalis (F.). Se determinaron las susceptibilidades de larvas neonatales y de tercer instar en plantas de maíz Bt y maíz no-Bt convencional (en las etapas de desarrollo V6 y R1) tanto en lotes de campo como en bio-ensayos de laboratorio a través del consumo de tejido de hojas frescas. Los híbridos de maíz Bt asociados con los eventos de transformación MON810 y CBH351 recibieron significativamente menos daño por el barrenador del maíz del suroeste y el barrenador de la caña de azúcar durante infestaciones en la etapa de cogollo comparado con el daño observado en sus respectivos híbridos no-Bt convencionales. El daño causado por el barrenador del maíz del suroeste y el barrenador de la caña de azúcar a la vaina de la hoja de la mazorca y tusas se redujeron significativamente con los eventos MON810 y CBH351 comparados con el daño observado en sus respectivos híbridos no-Bt convencionales durante infestaciones en la etapa reproductiva del maíz. Sin embargo, el nivel de resistencia al consumo de tejido por barrenadores que se observó en el evento MON810 fue significativamente mayor que el observado con el evento CBH351. El barrenador del maíz del suroeste y el barrenador de la caña de azúcar consumieron mas tejido de la tusa que de la vaina de la hoja de la mazorca tanto en híbridos Bt como en híbridos n
