Time-of-day specific changes in pesticide detoxification ability ofSpodoptera litura(Lepidoptera: Noctuidae)

Circadian clocks govern daily physiological and molecular rhythms, and putative rhythms in the expression of metabolizing xenobiotics have been described in insects. Such rhythms could have important consequences for outcomes of chemical exposures at different times of the day. The proportion of photophase (light) and scotophase (dark) also influence the enzyme activities. Several studies have been done on the mechanism of insecticide resistance in Spodoptera litura exposed to chemical insecticides. This study is aimed at understanding the circadian variations of cypermethrin detoxification mechanisms in S. litura. The toxicity of insecticide, cypermethrin exposed to three different photoperiods in 3rd instar larvae of S. litura has been investigated. Detoxification enzyme profiles of α- and β-esterases, glutathione S-transferase (GST), and cytochrome P450 (Cyt P450) were assessed. The results showed that larvae were more tolerant to cypermethrin treated larvae at 8 h L: 16 h D photoperiod as compared with two other photoperiods tested. We observed significant increases in α- and β-esterases and cyt P450 activities in 4 and 8 h at different photoperiods. GST activity was significantly changed at different photoperiods at different timings. Activities of specific detoxification enzymes fluctuated during the time, and for specific insecticides, the concentration resulting in 50% mortality varied significantly during the different photoperiods. The time of the day when chemical exposure is imposed should be an important consideration in the experimental design, and use of pesticides.