Selection for resistance to Bacillus thuringiensis Cry2Aa in Ostrinia nubilalis (Lepidoptera: Crambidae)

Zea mays is one of the main crops cultivated in the world and has been modified genetically to express toxins from Bacillus thuringiensis for control of certain pests.  Ostrinia nubilalis (Hubner), the European corn borer, is a destructive pest of corn and is a major pest that is targeted transgenic Bt corn. Cry2 Bt toxins are currently deployed in pyramided Bt corn in combination with other Bt toxins, but resistance to this toxin has not yet been identified.  A laboratory colony derived from field-collected insects was reared in the laboratory for 14 generations with continuous exposure to Cry2Aa to select for resistance. After selection, resistance was evaluated using diet bioassays to determine the level of the resistance based on the mortality and growth inhibition rates.  In addition, susceptible and resistance strains were exposed to Cry 1F, Cry 1Aa, Cry 1Ab, and Cry 1Ba to determine cross resistance among different Bt toxins, and  reciprocal crosses were used to estimate the inheritance of resistance.  Results of these tests indicate that a moderate level of resistance (25-fold) to Cry2Aa was achieved, although cross resistance to other Bt toxins was not observed or was very minimal.  The resistance was incompletely dominant and there appeared to some differences in response of reciprocal crosses suggesting a possible resistance partially sex-linked.