Circadian variation in midgut digestive enzyme activity in cotton bollworm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Abstract

In this study, total protease, α-amylase and lipase activity of cotton bollworm were studied under four different photoperiod regimes. Insects were reared from first larval stages on artificial diet under controlled conditions (26±2°C temperature, 60±5 % RH) in incubators under four photoperiod regimes, including light (24: 0), dark (0: 24), 12:12h (L:D) and 16:8h (L:D). Sixth larval stage was used for enzyme assays and after dissection, alimentary canal of larva was separated from body and transferred to 1.5ml micro tubes containing 1ml cold glycine–NaOH, pH10 buffer. Contents of tubes were homogenized and centrifuged, and the supernatants were used as enzyme source. Sampling was carried out for 24h at 3h intervals. The enzyme activity (α-amylase and lipase) was measured using diagnostic kit and azocaseinolytic assay carried out for total protease assays. Results indicated that photoperiod regimes changed enzyme activity profile, and digestive enzyme activity was significantly changed during the diel period. Alpha-amylase activity increased from 9:00h to 15:00h in all the studied photoperiods. Alpha-amylase and lipase activity in light photoperiod was more than the dark one, but total protease activity increased in dark photoperiod especially from 12:00 to 18:00h, compared with the other photoperiods. A slight increase in digestive enzyme activity was observed at 3:00h in light and dark photoperiods.