Effects of cypermethrin and diazinon on the gut -amylase activity in the rice weevil, Sitophilus oryzae

Abstract

In the present study, effects of different concentrations of cypermethrin and diazinon were investigated on the -amylase activity of Sitophilus oryzae. A number of insect guts were dissected from the digestive system. They were rinsed in ice-cold phosphate buffer and after homogenization, were centrifuged (12000 rpm) at 4 °C for10 min. Supernatant was stored at -20 ºC for enzyme analyses. Fifty μl enzyme was mixed with 450 μl of each of chemical doses (0, 100, 500, 1000, 1500, 2000 and 2500 ppm ai) and kept for 30 min at room temperature before enzyme assay using -amylase kit and Autoanalyzer. Results showed that enzyme activity was significantly reduced after treatment with cypermethrin and diazinon. In general, enzyme activity reduction depended to the pesticide concentrations; however, this trend was sharper in diazinon treatment compared to that in cypermethrin treatment. At least 50% enzyme inhibitory was occurred in treatments compared to that in control. The maximum inhibitory was observed at 2000 and 2500 ppm doses in both insecticides without significant difference. Also, results showed that there was no significant difference between enzyme inhibitory activity of 100 and 500 ppm and 500 and 1000 ppm doses in cypermethrin treatment. Similarly, there was no significant difference between 500 and 1000 ppm doses in the diazinon treatment. In vitro toxicology and insecticide- enzyme interactions will create new opportunity for identification of potential insecticides effective on digestive processes of insect pests. Besides, insecticide-enzyme interaction studies will improve our knowledge about physiological systems.