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ARS Home » Southeast Area » Stoneville, Mississippi » Southern Insect Management Research » Research » Publications at this Location » Publication #271166
Title: Susceptibility of field populations of sugarcane borer from non-Bt and Bt maize plants to five individual cry toxins

Author
item HUANG, FANGNENG - Louisiana State University
item GHIMIRE, MUKIT - Louisiana State University
item LEONARD, ROGERS - Louisiana State University
item Zhu, Yu Cheng
item HEAD, GRAHAM - Monsanto Corporation

Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2012
Publication Date: 5/7/2012
Citation: Huang, F., Ghimire, M.N., Leonard, R.B., Zhu, Y., Head, G.P. 2012. Susceptibility of field populations of sugarcane borer from non-Bt and Bt maize plants to five individual cry toxins. Insect Science. 19(5):570-578.

Interpretive Summary: Sugarcane borer is a major target pest of transgenic maize expressing Bt proteins in South America and the U.S. mid-south region. Resistance development in target pest populations is a major threat to the sustainable use of Bt crops. In our field trials in 2009, a significant number of live borers and plant injury of the sugarcane borer were observed in an experimental SmartStaxTM maize line. To determine if the field survival of sugarcane borer was due to resistance, comparative susceptibility of two field populations of sugarcane borer collected from non-Bt and Bt maize plants containing SmartStaxTM traits to five individual Cry proteins was evaluated by incorporating Bt toxins into a artificial diet. The five Bt toxins included two toxins (Cry1A.105 and Cry2Ab2) that were expressed in SmartStaxTM maize plants and three other common toxins (Cry1Aa, Cry1Ab, and Cry1Ac) that were not produced in SmartStaxTM. Larval mortality and growth inhibition on Bt diet were evaluated 7 days after release of neonates on the diet surface. The laboratory bioassays showed that LC50 values of Cry1A.105 and Cry2Ab2 for the population originated from Bt plants were 3.55- and 1.34-fold greater, respectively, than those of the population collected from non-Bt plants. In contrast, relative to the population from non-Bt plants, the LC50s of the population sampled from Bt plants were 3.85-, 2.5-, and 1.64-fold more sensitive to Cry1Aa, Cry1Ab, and Cry1Ac, respectively. However, the detected variations in Bt susceptibility between the two populations were well within the range of different field populations of the insect reported in previous studies for all of the five toxins examined. The results suggested that the observed field survival of sugarcane borer on Bt plants was unlikely due to resistance.

Technical Abstract: Sugarcane borer, Diatraea saccharalis (F.), is a major target pest of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the U.S. mid-south region. Resistance development in target pest populations is a major threat to the sustainable use of Bt crops. In our field trials in 2009, a significant number of live borers and plant injury of D. saccharalis were observed in an experimental SmartStaxTM maize line. To determine if the field survival of D. saccharalis was due to resistance, comparative susceptibility of two field populations of D. saccharalis collected from non-Bt and Bt maize plants containing SmartStaxTM traits to five individual Cry proteins was evaluated by incorporating Bt toxins into a meridic diet. The five Bt toxins included two toxins (Cry1A.105 and Cry2Ab2) that were expressed in SmartStaxTM maize plants and three other common toxins (Cry1Aa, Cry1Ab, and Cry1Ac) that were not produced in SmartStaxTM. Larval mortality and growth inhibition on Bt diet were evaluated 7 days after release of neonates on the diet surface. The laboratory bioassays showed that LC50 values of Cry1A.105 and Cry2Ab2 for the population originated from Bt plants were 3.55- and 1.34-fold greater, respectively, than those of the population collected from non-Bt plants. In contrast, relative to the population from non-Bt plants, the LC50s of the population sampled from Bt plants were 3.85-, 2.5-, and 1.64-fold more sensitive to Cry1Aa, Cry1Ab, and Cry1Ac, respectively. However, the detected variations in Bt susceptibility between the two populations were well within the range of different field populations of the insect reported in previous studies for all of the five toxins examined. The results suggested that the observed field survival of D. saccharalis on Bt plants was unlikely due to resistance.