Overproduction of digestive enzymes compensates for inhibitory effects of protease and alpha-amylase inhibitors fed to three species of leafrollers (Lepidoptera : Tortricidae)

The larvae of 3 leafroller species-Epiphyas postvittana (Walker), Planotort rix octo (Dugdale), and Ctenopseustis obliquana (Walker)-were chronically f ed 6 digestive enzyme inhibitors in artificial diets over a 2-wk period, an d their growth rate and digestive enzyme activities were measured. The inhi bitors were fed singly and in selected combinations. Three protease inhibit ors were extracted from potatoes (proteinase inhibitors1. and 2-POT1 and 2- and carboxypeptidase inhibitor-CPI) and the 4th was bovine pancreatic tryps in inhibitor (BPTI). The 2 alpha-amylase inhibitors were extracted from whe at, the dimer and tetramer. POT1 and BPTI alone significantly reduced the g rowth rate of E. postvittana and P. octo. Most combinations of inhibitors d id not reduce growth rate further than the single most effective constituen t. However, ingestion of any of the inhibitors affected digestive enzyme ac tivity. alpha-Amylase inhibitors increased lu-amylase activity (up to 10-fo ld). BPTI, either singly or in combination, reduced measurable trypsin acti vity (10-fold) and raised chymotrypsin activity (up to 8-fold) in all speci es. In larvae chronically fed POT1 or BPTI, in vitro tests showed that the sensitivity of caseinase and chymotrypsin to protease inhibitors was unchan ged. However, a very small amount of insensitive trypsin was produced. Beca use larval growth rate was so rarely significantly affected when inhibitors were added to the diet, whereas major enzyme activities were significantly altered, the question of compensation of one digestive enzyme for another is discussed.