Heritability and stability of resistance to Bacillus thuringiensis in Ostrinia nubilalis (Lepidoptera: Pyralidae)

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Abstract
Realized heritability, h2, of resistance in European corn borer, Ostrinia nubilalis (Hübner), to Bacillus thuringiensisBerliner ssp. kurstaki endotoxins was examined in five resistant laboratory colonies. These colonies were reared on a meridic diet that incorporated a commercial formulation of B. thuringiensis, Dipel ES. Resistance in these colonies reached 42–67× by the seventh to twentieth selected generations and then plateaued. The realized heritability of resistance averaged 0.17–0.31 over all selected generations for the five colonies. In the three Iowa colonies, the highest realized heritability, 0.18–0.33, occurred during the second period of selection (seventh to thirteenth selected generations). In the two Kansas colonies, the highest realized heritability, 0.36 and 0.46, occurred during the first period of selection (first to sixth selected generations). In the absence of selection pressure, resistance in the southwest Kansas colony decreased from 62× to 42× after two generations, and remained at about that level for the next five generations.