Crop Protection 27 (2008) 799–806 Geographical susceptibility of Louisiana and Texas populations of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) to Bacillus thuringiensis Cry1Ab protein Fangneng Huang a,Ã , Rogers Leonard b , Steven Moore c , Bisong Yue d , Roy Parker e , Thomas Reagan a , Michael Stout a , Don Cook f , Waseem Akbar a , Charles Chilcutt e , William White g , Donna Lee h , Stephen Biles i a Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA b Macon Ridge Research Station, Louisiana State University Agricultural Center, Winnsboro, LA 71295, USA c Dean Lee Research Station, Louisiana State University Agricultural Center, Alexandria, LA 71302, USA d College of Life Science, Sichuan University, Chengdu, China e Texas A&M University Agricultural Research & Extension Center, Corpus Christi, TX 78406, USA f Northeast Research Station, Louisiana State University Agricultural Center, St. Joseph, LA 71366, USA g USDA-ARS Houma, LA, USA h Louisiana State University Agricultural Center, East Carroll Parish Office, Lake Providence, LA 71254, USA i Texas Cooperative Extension, Texas A&M University, Port Lavaca, TX 77979, USA Received 10 August 2007; received in revised form 7 November 2007; accepted 8 November 2007 Abstract The susceptibilities of 18 field populations of the sugarcane borer, Diatraea saccharalis (F.), to two sources of Bacillus thuringiensis (Bt) Cry1Ab protein were determined using laboratory bioassays. Fifteen of the 18 field populations were collected from seven locations across Louisiana and the other three populations were sampled from the Gulf Coast area of Texas during 2004–2006. Neonates of D. saccharalis were exposed to a meridic diet treated with selected concentrations of Cry1Ab protein. Larval mortality was measured at 7 days after inoculation. Statistically significant differences in median lethal concentrations (LC 50 s) were detected among insect populations from different geographical locations, but the field populations remained as susceptible as a laboratory strain of D. saccharalis that had been maintained in the laboratory for 420 years without exposure to any chemical insecticides or Bt toxins. The LC 50 s of Cry1Ab protein, which was extracted from DKC69-70 Bt corn hybrid, ranged from 0.03 to 0.32 mg/g for the seven field populations collected during 2004. The LC 50 values based on bioassays with purified, trypsin-activated Cry1Ab protein from a recombinant Escherichia coli culture were 0.03–0.17 mg/g for the 11 field populations collected during 2005–2006. Small changes in Cry1Ab susceptibility were detected among crops, years of sampling, or locations. All field-collected insect populations, except one, exhibited lower LC 50 values than the laboratory strain. The results of this study suggest that field populations of D. saccharalis remain generally susceptible to the Cry1Ab protein after 8 years use of transgenic Bt corn in Louisiana and the Gulf Coast area of Texas. r 2007 Elsevier Ltd. All rights reserved. Keywords: Diatraea saccharalis; Cry1Ab; Bacillus thuringiensis; Susceptibility; Field corn 1. Introduction Evaluating the susceptibility of an insect pest species to insecticides across geographic areas is useful in assessing the potential risk of resistance development, understanding if variation in susceptibility among different populations is associated with the historical use of insecticides, and measuring the success of resistance management programs (United States Environmental Protection Agency, 2001). Significant variation in susceptibility to an insecticide among geographic populations of an insect species often ARTICLE IN PRESS www.elsevier.com/locate/cropro 0261-2194/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2007.11.007 Ã Corresponding author. Tel.: +1 225 5780111; fax: +1 225 5781643. E-mail address: fhuang@agcenter.lsu.edu (F. Huang).