Inheritance of Resistance to the Cry1Ab Bacillus thuringiensis Toxin in Ostrinia nubilalis (Lepidoptera: Crambidae)

Authors

Analiza P. Alves, University of Nebraska-LincolnFollow
Terrence A. Spencer, University of Nebraska-LincolnFollow
B.E. Tabashnik, University of Nebraska-Lincoln
Blair Siegfried, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

April 2006

Comments

Published in J. Econ. Entomol. 99(2): 494Ð501 (2006). Copyright 2006 Entomological Society of America. Used by permission.

Abstract

Laboratory selection with Cry1Ab, the predominant Bacillus thuringiensis (Bt) toxin in transgenic corn, Zea mays L., produced >1000-fold resistance in two laboratory strains of European corn borer, Ostrinia nubilalis (Hubner). We tested the offspring of various crosses to determine the mode of inheritance of resistance to Cry1Ab. Patterns of inheritance of resistance were similar in the two resistant strains. The progeny of reciprocal F₁ crosses (resistant male x susceptible female and vice versa) responded alike in bioassays, indicating autosomal inheritance. The median lethal concentrations (LC₅₀ values) of F₁ were intermediate between the resistant and susceptible parents, indicating approximately additive inheritance. However, the dominance of resistance increased as the concentration of Cry1Ab decreased. Analysis of progeny from backcrosses (F₁ x susceptible strain) suggests that resistance was controlled by more than one locus. In particular, the fit of observed to expected mortality improved as the number of putative loci increased from 1 to 10. The polygenic nature of resistance in these two laboratory strains suggests that major genes for resistance to Cry1Ab were not common in the founding populations of O. nubilalis. A low initial frequency of major genes for Cry1Ab resistance might be an important factor in delaying evolution of resistance to Bt corn in this pest.