Abstract
the susceptibility of the 4th instar larvae of the Egyptian cotton leafworm, Spodoptera littoralis (Boisd.) to the chitin synthesis inhibitors, nomolt was evaluated in the laboratory for 10 generations. The fourth instar larvae were treated with various concentrations of nomolt insecticide for 48 hrs in each generation until F10 and LC50s were calculated after 7 days post-treatment in each generation. The obtained results showed that the resistance ratios of the selected generations were increased to 1.2709, 1.2894, 2.3034 and 3.0117 folds, the F3, F6, F8 and F10 generations, respectively. Based on the biological aspect, larval durations were increased significantly in the selected generations compared to the control. Furthermore, the percentage of pupation was reduced in all the treated generations, which being 56.7, 55.0, 43.85, 27.35, 24.66 and 33.56% the adult emergence was significantly affected as it was 82.09, 70.33, 37.71, 55.06, 41.18 and 43.65% in treated F0, F1, F3, F6, F8 and F10 of the selected generations, respectively. The activities of the measured enzymes at 6 days after treatment of the fourth instar larvae showed up and down pattern through the selected ten generations. The activity of α and β esterases as well as protease enzymes was back to normal activity as that of control in the tenth generation meanwhile chitinase enzyme activity remained significantly higher than that of the control.
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