Transgenic Bt corn resistance against Mexican rice borer, Eoreuma loftini, and implications to sugarcane

The Mexican rice borer, Eoreuma loftini (Dyar) attacks crops including corn, Zea mays L., rice, Oryza sativa L., sorghum, Sorghum bicolor (L.) Moench, and sugarcane, Saccharum spp., but strongly resistant varieties of any kind, native or otherwise, have not been identified.  A field plot corn variety test using two transgenic Bt varieties, Pioneer 31G71, expressing the Cry1F insecticidal protein, and Golden Acres 28V81, expressing the Cry1A.105, Cry2Ab2, and Cry3Bb1 insecticidal proteins, and two non-Bt controls, Dekalb DKC 69-72 and BH Genetics 9050, all four commonly grown in the Lower Rio Grande Valley of Texas, showed that, although oviposition preference was not affected, 28V81 resisted larval stalk boring to the extent that Mexican rice borer injury was almost nonexistent.  Pioneer 31G71 was infested nearly as much as the controls, but larval development to adulthood was reduced by »70%.  Rearing larvae on 5, 50, 500, and 5,000 μg of corn leaf tissue per ml of artificial diet showed that, while the three lowest concentrations did not affect larval growth and development, the high concentration of 28V81 reduced survivorship to the pupal stage, decreased weight of 4-wk-old larvae, and prolonged development to pupation.  Lower numbers of pheromone trap-captured adults at the edges of commercial Bt and non-Bt corn fields showed that populations were lower at the Bt cornfields, suggesting a lesser rate of adult production.  Because corn is a preferred host plant over sugarcane, sorghum, and rice, use of resistant transgenic Bt corn varieties will likely protect the crop from the substantial injury that can be caused by the pest.  This study also suggests that Bt genes might result in similarly strong resistance when inserted in other vulnerable crops such as sugarcane.