Effects Of Insecticidal Fraction F3-28 From Periploca Sepium On The Activities Of Digestive Enzymes In The Midgut Of Larvae Of Mythimna Separata Walker And Agrotis Ypsilon Rottemberg (Lepidoptera: Noctuidae)

Insecticidal fraction F3-28 was isolated from Periploca sepium Bunge by bioassay-guided fractionation.To study the mechanism of this fraction this study used the classical method, comparing the toxicity and the activities of the midgut digestive enzymes between Mythimna separata Walker and Agrotis ypsilon Rottemberg.The main results were as follows:1.The fraction F3-28 was not exhibite any insecticidal activity against fifth instar Agrotis ypsilon .The toxicity agaist fifth instar Mythimna separata was strong(LC50=0.5623mg/mL). After 4 hours the fifth instar Mythimna separata showed that the abdomen swoln and black.It could not move freely.The swell was severely as the time went by.It died at last.2.To determine the parametric for the activities of the digestive enzymes of the Mythimna separata Walker and Agrotis ypsilon Rottemberg,the study showed that the protease activity of Mythimna separata Walker was highest when the buffer was pH 11.0 0.1 mol/L Na2HPO4—NaOH, and the Agrotis ypsilon Rottemberg was pH 12.0 0.1 mol/L Na2HPO4—NaOH. The catalyze products of the protease had the highest absorption value when the wavelength was 419nm.The amylase activity of Mythimna separata Walker and Agrotis ypsilon Rottemberg were highest both when the buffer was pH 7.5 0.1 mol/L pHospHate buffer.The catalyze products of the amylase had the highest absorption value when the wavelength was 376 nm.3. the activities of protease, lipase and amylase of Agrotis ypsilon larvae were changed indistinctly.The results showed that the 5th instar larvae of Mythimna separata treated after 2, 4, 8, 10, 12, 24 and 48 h, compared with the larvae of control group, the activities of protease was 0.76, 2.53, 1.45, 1.88, 1.54, 1.46 and 1.70 times , respectively, and increase of the activity was not dependent on the concentration of F3-28.The activities of trysin-like was 1.60, 1.75, 1.60, 1.12, 1.39, 1.16 and 1.15 times(BAPNA as substrate)and 1.68, 1.95, 1.53, 1.26, 1.15, 1.13 and 1.14 times(TAME as substrate ), respectively, and the increase of the activity was dependent on the concentration of F3-28.The activities of chymotrypsin-like was 0.50, 1.66,,1.44, 1.18, 1.54, 1.08 and 1.03 times, respectively, and the increase of the activity was not dependent on the concentration of F3-28. The activities of amylase also was 1.60, 1.35, 1.27, 1.31, 1.23 and 1.20 times, respectively. But the lipase was changed inconspicuously. These results implied that the insecticidal mechanism of F3-28 might be related with the activation of the protease ,especially the activities of the trypsin-like in the midgut of the larvae.