title: Resistance to Bt maize in Mythimna unipuncta (Lepidoptera: Noctuidae) is mediated by alteration in Cry1Ab protein activation.
abstract: Bt maize cultivars based on the event MON810 (expressing Cry1Ab) have shown high efficacy for controlling corn borers. However, their efficiency for controlling some secondary lepidopteran pests such as Mythimna unipuncta has been questioned, raising concerns about potential outbreaks and its economic consequences. We have selected a resistant strain (MR) of M. unipuncta, which is capable of completing its life cycle on Bt maize and displays a similar performance when feeding on both Bt and non-Bt maize. The proteolytic activation of the protoxin and the binding of active toxin to brush border membrane vesicles were investigated in the resistant and a control strain. A reduction in the activity of proteolytic enzymes, which correlates with impaired capacity of midgut extracts to activate the Cry1Ab protoxin has been observed in the resistant strain. Moreover, resistance in larvae of the MR strain was reverted when treated with Cry1Ab toxin activated with midgut juice from the control strain. All these data indicate that resistance in the MR strain is mediated by alteration of toxin activation rather than to an increase in the proteolytic degradation of the protein. By contrast, binding assays performed with biotin labelled Cry1Ab suggest that binding to midgut receptors does not play a major role in the resistance to Bt maize. Our results emphasize the risk of development of resistance in field populations of M. unipuncta and the need to consider this secondary pest in ongoing resistance management programs to avoid the likely negative agronomic and environmental consequences.
authors.affiliation: Department of Environmental Biology, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
authors.forename: Joel
authors.initials: J
authors.lastname: González-Cabrera
authors.forename: Matías
authors.initials: M
authors.lastname: García
authors.forename: Pedro
authors.initials: P
authors.lastname: Hernández-Crespo
authors.forename: Gema P
authors.initials: GP
authors.lastname: Farinós
authors.forename: Félix
authors.initials: F
authors.lastname: Ortego
authors.forename: Pedro
authors.initials: P
authors.lastname: Castañera
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000378:metabolism*; D004731:Endotoxins; D006460:Hemolysin Proteins; D007305:Insecticide Resistance; D007306:Insecticides; D008871:Microvilli / Q000378:metabolism; D009036:Moths / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D018675:Toxicity Tests; D003313:Zea mays
chemical_list: D000083722:Bacillus thuringiensis Toxins; C029103:Bacillus thuringiensis protoxin; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D011498:Protein Precursors; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: Bacillus thuringiensis; Binding assays; Bioassays; Cry proteins; Proteases; Resistance; Resistance management; Toxicity