Location: Corn Insects and Crop Genetics Research
Title: Evaluation of tolerance to Bacillus thuringiensis toxins among western bean cutworm (Lepidoptera; Noctuidae) Authors
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 25, 2013
Publication Date: December 9, 2013
Citation: Dyer, J.M., Sappington, T.W., Coates, B.S. 2013. Evaluation of tolerance to Bacillus thuringiensis toxins among western bean cutworm (Lepidoptera; Noctuidae). Journal of Economic Entomology. 106(6):2467-2472. Interpretive Summary: The Western bean cutworm (WBC) has been an emerging pest in the corn belt of the United States since movement out of its native range of western Nebraska starting in the late 1990s. WBC can cause severe damage to corn ears and kernels of conventional as well as transgenic corn that express Bacillus thuringiensis (Bt) toxins Cry1Ab and Cry1F. Conducting field trials has been difficult due to inconsistent natural infestations, and the study of Bt toxin resistance levels have not been feasible because no methods were available to propagate WBC in the laboratory. Protocols were developed to maintain a colony of WBC in the laboratory, and this colony was used to determine the level of larval resistance to Bt toxins. These procedures and findings are important for the understanding of WBC survival on transgenic corn, and offer a gateway for ARS, university and private sector scientists to evaluate methods for the control of WBC in field corn, sweet corn and dryland beans.
Technical Abstract: The Western bean cutworm (WBC), Striacosta albicosta, is a destructive insect pest of dry beans within its native range of western Nebraska and eastern Colorado. However, starting in the early 1990s, a range expansion of S. albicosta has resulted in damage to corn crops through the Midwest and more recently in 2010 into western Pennsylvania and southern Ontario. Larval feeding damage to corn is generally observed on ears and kernels, which is not completely controlled by commercial transgenic hybrids that express Bacillus thuringiensis (Bt) Cry1Ab and Cry1F toxins. Inadequate protocols for rearing S. albicosta have hindered controlled efficacy experimentation in the laboratory and field. We report an S. albicosta laboratory colony which has been maintained for eight continuous generations on meridic diet, and mated and propagated in the laboratory. These rearing procedures were adapted for Bt toxin diet-overlay assays, where 14 day exposure of neonates to Bt toxin showed that WBC are insensitive to Cry1Ab concentrations = 10,000 ng cm-2. In contrast, exposures of neonates showed reduced developmental rates at = 125 ng Cry1F toxin cm-2, which resulted in effective concentration estimates of (EC50 = 1,187.5 ng cm-2; EC95 = 10,000.5 ng cm-2). The research reported herein describes a laboratory rearing method for WBC. The ability to mass produce this insect will enhance fundamental research of this pest, including an evaluation of tactics to control feeding damage in corn.