ADAPTATION OF SPODOPTERA-EXIGUA LARVAE TO PLANT PROTEINASE-INHIBITORSBY INDUCTION OF GUT PROTEINASE ACTIVITY INSENSITIVE TO INHIBITION

Tobacco plants were transformed with a cDNA clone of chymotrypsin/tryp sin-specific potato proteinase inhibitor II (PI2) under the control of a constitutive promoter. Although considerable levels of transgene ex pression could be demonstrated, the growth of Spodoptera exigua larvae fed with detached leaves of PI2-expressing plants was not affected. A nalysis of the composition of tryptic gut activity demonstrated that o nly 18% of the proteinase activity of insects reared on these transgen ic plants was sensitive to inhibition by PI2, whereas 78% was sensitiv e in insects reared on control plants. Larvae had compensated for this loss of tryptic activity by a 2.5-fold induction of new activity that was insensitive to inhibition by PI2. PI2-insensitive proteolytic act ivity was also induced in response to endogenous proteinase inhibitors of tobacco; therefore, induction of such proteinase activity may repr esent the mechanism by which insects that feed on plants overcome plan t proteinase inhibitor defense.