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

Transgenic corn (Zea mays L.) products expressing multiple Bt proteins targeting a same group of insect pests have become commercially available in the U.S. The first commercialized pyramided Bt corn technologies for managing lepidopteran pests include Genuity® VT Triple ProTM and Genuity® SmartStaxTM. In this study, larval survival and plant injury of Cry1Ab-susceptible (Cry1Ab-SS), -resistant (Cry1Ab-RR), and -heterozygous (Cry1Ab-RS) genotypes of the sugarcane borer, Diatraea saccharalis F., on five commercial corn hybrids were evaluated in a leaf tissue bioassay and two greenhouse trials during 2010–2011. The five hybrids included two non-Bt corn and three Bt corn hybrids representing three transgenic technologies: YieldGard® Corn Borer, Genuity® VT Triple ProTM, and Genuity® SmartStaxTM. YieldGard® Corn Borer corn contains a single Bt protein (Cry1Ab), while Genuity® VT Triple ProTM and SmartStaxTM contain two and three pyramided Cry genes targeting above-ground lepidopteran pests, respectively. An average of 75.5% of larvae survived after 6 d on non-Bt corn leaf tissue. The 6-d survivorship on Cry1Ab corn leaf tissue was 3% for Cry1Ab-SS, 19% for Cry1Ab-RS, and 35% for Cry1Ab-RR larvae, while none of the three insect genotypes survived for 6-d on the leaf tissue of the two pyramided Bt corn hybrids. After 21 d on whole plants in the greenhouse, 42.6–62.5% of larvae survived on non-Bt corn plants. Larval survivorship rates on YieldGard® Corn Borer plants after 21 d in the greenhouse were 4.7–5.6% for Cry1Ab-SS, 29.4–32.5 % for Cry1Ab-RS, and 36.6–45.6% for Cry1Ab-RR. Both pyramided Bt corn hybrids were very effective against D. saccharalis regardless of the insect genotype with 21-d survivorship of <2% for Cry1Ab-SS and Cry1AbRS, and <5% for Cry1Ab-RR. Cry1Ab-RS and -RR caused significant entry/exit holes and tunneling inside the plant stalks of non-Bt and YieldGard® corn plants, while they caused little injury on the two pyramided Bt corn hybrids. The data generated from both the leaf tissue and whole plant tests showed that the Cry1Ab-resistant D. saccharalis was susceptible to the pyramided Bt corn hybrids. The results suggest that the pyramided Bt corn containing Genuity® VT Triple ProTM or SmartStaxTM traits should offer a means for Cry1Ab resistance management in D. saccharalis.