EFFECTS OF PROTEASE INHIBITOR CONCENTRATION AND COMBINATIONS ON THE SURVIVAL, GROWTH AND GUT ENZYME-ACTIVITIES OF THE BLACK FIELD CRICKET, TELEOGRYLLUS-COMMODUS

Growth and survival responses were determined for the black field cricket Teleogryllus commodus fed 6 different protease inhibitors (SBTI, WGI-1, POT-1, POT-2, BPTI and CpTI), either singly or in combination, at a range of concentrations in diets containing 3 different levels of casein. Several inhibitors caused high levels of mortality at concentrations as low as 0.1% (w/v) on diets with low or moderate casein. In all cases the efficacy of the protease inhibitors in reducing cricket growth was strongly influenced by the level of dietary casein as well as by the concentration of the inhibitor. POT-2 and SBTI were particularly effective. Two-way combinations of protease inhibitors caused significant mortality and reduced growth as effectively as the best single inhibitors at all dietary casein levels. A synergistic effect was obtained from the combination of POT-1 (binds strongly to SAAPLpNA hydrolysing enzyme) and WGI-1 (binds strongly to trypsin). A time-series study using POT-2 showed that this inhibitor caused continual suppression in the activity of the digestive endopeptidases trypsin and SAAPLpNA hydrolysing enzyme, but no reduction in the activity of the exopeptidase leucine aminopeptidase. Increased levels of enzyme inhibition at the higher POT-2 concentration were directly reflected in the feeding trials where greater growth suppression was also observed.