Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/8/2008
Publication Date: 1/1/2009
Citation: Wu, X., Leonard, R.B., Zhu, Y., Abel, C.A., Head, G.P., Huang, F. 2009. Susceptibility of Cry1Ab-resistant and -susceptible Sugarcane Borer (Lepidoptera: crambidae) to Four Bacillus thuringiensis Toxins. Journal of Invertebrate Pathology. 100:29-34. Interpretive Summary: In recent years, the sugarcane borer has expanded its geographic range and has become a dominant corn borer species across the mid-southern region, especially in Louisiana and Texas. In Louisiana, field corn was seriously damaged by late-season populations of the sugarcane borer. Yield losses to non-Bt corn from this stalk boring pest exceeded 30 percent in recent years. During 2004-2007, a major Cry1Ab resistance allele was documented in three populations of the sugarcane borer collected from northeast and central Louisiana. These Bt-resistant insects can complete larval development on commercial Cry1Ab corn hybrids (YieldGard) and showed a significant level of resistance (> 100-fold) to a Cry1Ab toxin. The resistance allele detected in the sugarcane borer represents the first major resistance allele to the proteins found in commercial Bt corn for any corn stalk borer species. Information on cross-resistance of insect pests to insecticides is essential in understanding resistance mechanisms and development of management strategies. The objective of this study is to determine the susceptibility of the Cry1Ab-resistant sugarcane borer to four Bt Cry proteins, including the proteins that are present in MON 89034: Cry1Aa, Cry1Ac, Cry1A.105, and Cry2Ab2. Results generated from this study provide valuable information about the ability of MON 89034 hybrids to control corn borer populations in the mid-southern region of the United States and in development of future Bt resistance management strategies for the sugarcane borer.
Technical Abstract: Sugarcane borer, Diatraea saccharalis (F.), is a primary corn stalk borer pest targeted by transgenic corn expressing Bacillus thuringiensis (Bt) proteins in many areas of the mid-southern region of the United States. Recently, genes encoding for Cry1A.105 and Cry2Ab2 Bt proteins were transferred into corn plants (event MON 89034) for controlling lepidopteran pests. This new generation of Bt corn with stacked-genes of Cry1A.105 and Cry2Ab2 will become commercially available in 2009. Susceptibility of Cry1Ab-susceptible and -resistant strains of D. saccharalis were evaluated on four selected Bt proteins including Cry1Aa, Cry1Ac, Cry1A.105, and Cry2Ab2. The Cry1Ab-resistant strain is capable of completing its larval development on commercial Cry1Ab-expressing corn plants. Neonates of D. saccharalis were assayed on a meridic diet containing one of the four Cry proteins. Larval mortality, body weight, and number of surviving larvae that did not gain significant weight (< 0.1 mg per larva) were recorded after 7 days. Cry1Aa was the most toxic protein against both insect strains, followed in decreasing potency by Cry1A.105, Cry1Ac, and Cry2Ab2. Using practical mortality (larvae either died or no significant weight gain after 7 days), the median lethal concentration (LC50) of the Cry1Ab-resistant strain was estimated to be >80- , 45-, 4.1-, and 0.5-fold greater than that of the susceptible strain to Cry1Aa, Cry1Ac, Cry1A.105 and Cry2Ab2 proteins, respectively.