Abstract: Three special substrates were used in enzyme activity analysis to evaluate the effects of pH on the digestive protease activity in the midgut of locust Catantops pinguis (Stål). The results showed that the pH value in the midgut of locust had no difference between the sexes, which was 6.92±0.043 in male and 7.03±0.054 in female. Three serine digestive proteases in midgut were identified by three special substrates. The optimal pH of the active alkaline trypsin-like enzyme (BAPNA as the substrate) was 8.5 in the female and 10.5 in the male; the optimal pH of weak alkaline trypsin-like enzyme (TAME as the substrate) was 9.0 in the female and 9.5 in the male; the optimal pH of chymotrypsin-like enzyme (BTEE as the substrate) was 8.5 in the female and 8.0 in the male. The statistical results showed that pH affected the serine protease activity obviously (P<0.01), and the activity of the same protease in the female was remarkably different from that in the male (P<0.01), meaning the activity of trypsin-like enzyme in the female was higher than that in the male at the optimal pH, while the activity of chymotrypsin-like enzyme in the male was higher than that in the female at the optimal pH. In the range of pH in midgut, the female has a higher digestive protease activity than the male, suggesting that the female has a stronger capacity to deal with the food intake to get more nutrients for reproduction (forming eggs). The digestive proteases remain active over a wide pH range, which may give this locust an adaptive advantage of feeding on a wide range of plants in the field.

Key words: Catantops pinguis, midgut, protease, activity, pH