Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2013
Publication Date: March 25, 2013
Citation: Showler, A., Abrigo, V., Cook, S.C. 2013. Transgenic Bt corn varietal resistance against the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Cramibidae) and implications to sugarcane. Crop Protection. 48:57-62. Interpretive Summary: Strong host plant resistance against the Mexican rice borer, a pest of corn, rice, sorghum, and sugarcane, has not been developed. Field and laboratory tests were conducted to assess resistance in two transgenic Bt varieties of corn, Pioneer 31G71 and Golden Acres 28V81. We found that Pioneer 31G71 became infested, but that the number of adults emerging from the stalks was greatly reduced when compared against non-Bt varieties used as controls. Golden Acres 28V81, although used for oviposition, offered almost complete resistance against stalk boring. Pheromone trapping at the edges of Bt variety cornfields showed that adult populations were lower than at the edges of non-Bt corn fields. This study suggests that Bt genes might result in similarly strong resistance when inserted in other vulnerable crops, such as sugarcane.
Technical Abstract: 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 approximately 70%, indicating its possible use as a trap crop. Rearing larvae on 5, 50, 500, and 5,000 micrograms 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.