Baseline susceptibility and resistance allele frequency in Ostrinia furnacalis related to Cry1 toxins in the Huanghuaihai summer corn region of China.

BACKGROUND Ostrinia furnacalis (Guenee) is one of the most destructive pests of corn and is a major target of transgenic corn expressing Bt (Bacillus thuringiensis) toxins in the Huanghuaihai summer corn region of China. Prior to the widespread commercialization of transgenic Bt corn, it is necessary to estimate baseline susceptibility to Bt toxins and Bt toxin resistance allele frequencies in O. furnacalis. RESULTS The median lethal concentrations (LC50 s) of the Bt toxins Cry1Ab, Cry1Ac and Cry1F for 15 different populations ranged from 0.887 to 1.617 ng/cm2 , 1.251-2.594 ng/cm2 and 4.146-6.465 ng/cm2 , respectively. The LC99 s of 93, 45, and 197 ng/cm2 for Cry1Ab, Cry1Ac and Cry1F, respectively, killed more than 99% of individuals of 8 O. furnacalis populations collected in 2017 and were identified as diagnostic concentrations for monitoring susceptibility in O. furnacalis populations in this region. Using the F2 screening method with these diagnostic concentrations, the resistance allele frequencies related to Cry1Ab, Cry1Ac and Cry1F were found to be 0.002 (0.000283-0.006484), 0.001 (0.000030-0.004295) and 0.001 (0.000030-0.004295) in 2018, respectively. CONCLUSION Fifteen populations of O. furnacalis collected in the Huanghuaihai summer corn region of China were all susceptible to Cry1Ab, Cry1Ac and Cry1F toxins and the susceptibility had no significant variation among these O. furnacalis populations. The estimated resistance allele frequency to Cry1Ab, Cry1Ac and Cry1F was rare in this region. This provided essential knowledge for making decision of commercialization of Bt maize and for monitoring resistance development and evaluating resistance management strategies in the future in the Huanghuaihai summer corn region of China. This article is protected by copyright. All rights reserved.