Larval survival and plant injury of Cry1Ab-susceptible, -resistant, and -heterozygous genotypes of the sugarcane borer on transgenic corn containing single or pyramided Bt genes

To delay resistance development, a gene-pyramiding strategy has been employed to develop transgenic plants that express multiple Bt toxins which target a same group of insect pests. The first two commercialized pyramided Bt corn technologies in the U.S. for managing lepidopteran pests are Genuity VT Triple Pro and SmartStax. Both were first commercially planted during the 2010 crop season. In this study, larval survival and plant injury of Cry1Ab-susceptible, -resistant, and –heterozygous genotypes of the sugarcane borer, Diatraea saccharalis (F.), on five commercial corn hybrids were evaluated in the greenhouse. These corn hybrids included two non-Bt corn and three Bt corn representing three transgenic technologies, YieldGard, Genuity VT Triple Pro and SmartStax. Larval survival and stalk tunneling were recorded after 21 days of infestation with 10-20 neonates on each potted plant. After 21 days, 43-57% of larvae survived on non-Bt corn plants. Larval survivorship on YieldGard was 4.7% for Cry1Ab-SS, 29.4% for Cry1Ab-RS, and 36.6% for Cry1Ab-RR. Both pyramided Bt corn hybrids were very effective against sugarcane borer regardless of the insect genotypes. The 21-day survivorship on the two pyramided Bt corn hybrids was <2% for Cry1Ab-SS and Cry1Ab-RS, and <5% for Cry1Ab-RR. Larvae of Cry1Ab-RS and -RR caused significant tunneling inside the plant stalks of non-Bt and Cry1Ab corn plants, while they just produced little injury on the two pyramided Bt corn. The results showed that the pyramided Bt corn can overcome the Cry1Ab resistance and thus should offer a means for Bt resistance management in sugarcane borer.