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 (R) VT Triple Pro (TM), and Genuity (R) SmartStax (TM). 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 (R) Corn Borer, Genuity (R) VT Triple Pro (TM), and Genuity (R) SmartStax (TM). YieldGard (R) Corn Borer corn contains a single Bt protein (Cry1Ab), while Genuity (R) VT Triple Pro (TM) and SmartStax (TM) 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 (R) 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 Cry1Ab-RS, 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 (R) 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 (R) VT Triple Pro (TM) or SmartStax (TM) traits should offer a means for Cry1Ab resistance management in D. saccharalis. (C) 2012 Elsevier Ltd. All rights reserved.