ARE INSECTS RESISTANT TO PLANT PROTEINASE-INHIBITORS

Six species of Lepidoptera were evaluated for their susceptibility to serine proteinase inhibitors from cabbage, Trypsin and chymotrypsin ac tivity from larval Pieris rapae and Pieris napi were not significantly inhibited (0-18%), in vitro, by cabbage proteinase inhibitors, while the serine proteinase activity in the midguts of larval Plutella xylos tella was moderately inhibited (40-50%), and Trichoplusia ni, Lymantri a dispar, and Helicoverpa tea were substantially inhibited (55-85%) by cabbage proteinase inhibitors, These results suggest that the growth and development of the latter three species should be reduced followin g ingestion of these inhibitors. However, chronic ingestion of cabbage proteinase inhibitors only reduced the growth and development of T. n i. This lack of biological activity of the proteinase inhibitors again st the other two species was explained by a shift in the relative prop ortion of digestive enzymes in response to ingestion of proteinase inh ibitors. Following ingestion of cabbage proteinase inhibitors, the pre dominant trypsin-like enzyme(s) in the midgut of larval L. dispar and H. tea were resistant to inhibition by cabbage trypsin inhibitors (13- 18% inhibited), while the trypsin(s) in T. ni was moderately susceptib le (37% inhibited). These results were confirmed for H. tea and T. ni feeding on proteinase inhibitors in tomato foliage, This is the first demonstration of adaptation to proteinase inhibitors, and has importan t implications for gene regulation and physiological plasticity.