Adaptation of Helicoverpa armigera (Lepidoptera: Noctuidae) to a proteinase inhibitor expressed in transgenic tobacco

A giant tare proteinase inhibitor (GTPI) cDNA was expressed in transgenic tobacco using three different gene constructs. The highest expression level obtained was ca. 0.3% of total soluble protein when the cDNA was driven by the Ambidopsis rbcS ats1 promoter. Repeated feeding trials with Helicoverpa armigera larvae fed on clonally derived T-0 and T-1 plants expressing GTPI demonstrated that, relative to those fed on control plants, some growth inhibition (22-40%) occurs, but there was no increase in larval mortality. Proteinase activities of larvae fed on GTPI-expressing tobacco or GTPI-containing diet were examined to monitor the spectrum of digestive proteinases in the midgut. Total proteinase activity was reduced by 13%, but GTPI-insensitive proteinase activity was increased by up to 17%. Trypsin was inhibited by 58%, but chymotrypsin and elastase were increased by 26% and 16% respectively. These results point to an adaptive mechanism in this insect that elevates the levels of other classes of proteinases to compensate for the trypsin activity inhibited by dietary proteinase inhibitors.