ADAPTATION OF HELICOVERPA-ARMIGERA (LEPIDOPTERA, NOCTUIDAE) TO A PROTEINASE-INHIBITOR EXPRESSED IN TRANSGENIC TOBACCO

A giant tare proteinase inhibitor (GTPI) cDNA was expressed in transge nic tobacco using three different gene constructs. The highest express ion level obtained was ca. 0.3% of total soluble protein when the cDNA was driven by the Ambidopsis rbcS ats1 promoter. Repeated feeding tri als 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 o n GTPI-expressing tobacco or GTPI-containing diet were examined to mon itor the spectrum of digestive proteinases in the midgut. Total protei nase activity was reduced by 13%, but GTPI-insensitive proteinase acti vity was increased by up to 17%. Trypsin was inhibited by 58%, but chy motrypsin and elastase were increased by 26% and 16% respectively. The se results point to an adaptive mechanism in this insect that elevates the levels of other classes of proteinases to compensate for the tryp sin activity inhibited by dietary proteinase inhibitors.