and protease enzymes activities. Photoperiod and sampling interaction
also was revealed for these traits (Table 1). Maximum activity of α-
amylase and lipase was observed in 24:0 (LD) photoperiod regime
and was significantly higher than those under other photoperiod regimes,
whereas protease showed the highest activity during 0:24 (LD)
regimes (Fig. 1).
Changes in digestive α-amylase activity of cotton bollworm during
day and night in four photoperiod regimes are shown in Fig. 2. In all
four photoperiod regimes, a circadian variation was observed in α-
amylase activity. The highest and lowest enzyme activities were recorded
at 12:00 h of the continuous light photoperiod and 9:00 h of the 16:8
(LD) photoperiods, respectively. In the insect groups kept under continuous
light and continuous dark photoperiods, α-amylase activity
changed in a bimodal manner with two peaks at 12:00 and 3:00 h and
more activity at 12:00 h. Whereas, there was only one peak during
light and dark period exposures of 16:8 (LD) (at 24:00 h) and 12:12
(at 15:00 h) regimes.