COLORADO POTATO BEETLES (LEPTINOTARSA-DECEMLINEATA) ADAPT TO PROTEINASE-INHIBITORS INDUCED IN POTATO LEAVES BY METHYL JASMONATE

Potato plants were treated with gaseous methyl jasmonate (MJ) to obtai n leaves with high induced levels of cysteine and aspartic proteinase inhibitors. Induced papain inhibitor activity was estimated at 4% of t otal protein, Other conditions produced leaves with low and moderate l evels of this inhibitor. Development of Colorado potato beetle larvae was similar when they were reared on leaves containing low, moderate a nd high levels of papain inhibitor, Nevertheless, general proteinase a ctivity was significantly reduced (42%) in insects reared on the high inhibitor diet, while proteinase activity that was insensitive to indu ced inhibitors in juice from MJ-treated leaves had increased two-fold. Activities towards the specific cysteine proteinase substrate p-Glu-P he-Leu-pNA were the same in guts from insects reared on the three leaf types, However, juice from MJ-treated leaves inhibited as much as 67% of this activity in guts of insects reared on the low inhibitor diet compared to only 27% of the activity in gut extracts from insects rear ed on MJ-treated leaves, indicating a 2.5-fold induction of cysteine p roteinase activity insensitive to potato proteinase inhibitors. None o f the activities towards another specific cysteine proteinase substrat e L-Arg-pNA were sensitive to inhibitors from MJ-treated leaves, but g uts of insects fed these leaves had a 3.5-fold induction of this prote inase activity compared to those reared on plants containing low papai n inhibitor levels. These data suggest that Colorado potato beetle lar vae compensated for inhibited gut proteolytic activity during chronic intake of papain inhibitors by synthesizing insensitive proteinase(s).