Circadian oscillation in lipase activity during all four photoperiod regimes
was almost similar to that of α-amylase. Like α-amylase, the
highest and lowest lipase activities of cotton bollworm digestive system
were observed at 12:00 h in continuous light photoperiod and 9:00 h of
the 16:8 (LD) photoperiods, respectively (Fig. 3). The highest circadian
variation in both lipase and α-amylase activities was detected under
continuous light condition. The lipase activity was decreased and
reached in its lowest level when the insects were exposed to 12:12
(LD) photoperiod regime.
Although the trend of circadian oscillation in protease activity was
similar in some extent to those of α-amylase and lipase activity, there
was major difference, in contrast to two other digestive enzyme
systems, the highest total protease activity and the most significant circadian
variation was recorded during continuous dark photoperiod regime
(Fig. 4). Like lipase activity, the lowest circadian variation in the
protease activity was also observed under 12:12 (LD) photoperiod regime.
The peak times of the midgut digestive enzymes of cotton bollworm
were summarized in Table 2