Varying Levels of Cry1Ac in Transgenic Bacillus thuringiensis Berliner (Bt) Cotton Leaf Bioassays1

Research was conducted to determine levels of Cry1Ac in transgenic Bacillus thuringiensis Berliner (Bt) cotton leaves from four different commonly used bioassays. Significant differences in the amount of Cry1Ac were found among the different bioassay types. For bioassay arenas that prevented desiccation of leaf material, Cry1Ac levels remained stable for 10 d after tissue was excised from the plant. In other bioassay types, Cry1Ac levels increased in excised leaves over time because of desiccation that concentrated the transgenic protein. We conclude that careful descriptions of bioassay methodology are essential for laboratory studies documenting Cry1Ac levels and corresponding efficacy against lepidopteran pests.