BEHAVIORAL AND PHYSIOLOGICAL-RESPONSES OF GRASS GRUB LARVAE (COSTELYTRA-ZEALANDICA) FEEDING ON PROTEASE INHIBITORS

Growth of first instar Costelytra zealandica larvae was significantly reduced after 6 weeks when reared on an artificial diet containing 0.3 and 1% soybean trypsin inhibitor (SBTI), 0.1% and 0.3% potato inhibitor II, and 0.3% potato protease inhibitor I and cowpea trypsin inhibitor. Limabean trypsin inhibitor at 1% significantly stimulated growth compared with that on diet with corresponding levels of added casein. A direct relationship between increased free-trypsin activity and decreased larval growth was observed. Sequential measurement of enzyme activity in third instar larvae feeding on SBTI was compared with that of larvae feeding on casein. The increase in enzyme activity was observed after 14 days in larvae feeding on SBTI. Larvae preferred to feed on SBTI-free diet when given a choice between diet containing this inhibitor at 0.3% and added casein at 0.3%.