Effect of Indoxacarb on some biological and biochemical aspects of Spodoptera littoralis (Boisd.) larvae

The efficacy of Avaunt (Indoxacarb 15% EC) on newly ecdysed 2nd and 4th instar Spodoptera littoralis (Boisd.) larvae was evaluated. Results of the conducted bioassay showed that 2nd instars were more susceptible than the 4th instars as the LC50 and LC90 values were 0.63 and 3.1 ppm for 2nd instar larvae and 2.0 and 18.75 ppm for 4th instar larvae, respectively. The total development period of the subsequent larval instars following the treatment of 2nd or 4th instars by their respective LC50 Indoxacarb was significantly extended by 2.8 and 3 days, respectively. Furthermore, percentage pupation and adult emergence were significantly less than their equivalent control. The biochemical study carried out on 2nd and 4th instar larvae, 24 h following their feeding on castor oil bean leaves treated by their determined LC50 of Indoxacarb, showed that the treatment of 2nd instar larvae caused a 32.6% and 82.7% decrease in the content of carbohydrates and lipids in larvae than their value in the control. These two respectively mentioned components were also reduced in treated 4th instar larvae by 56.4% and 76.5% than their control. Although, total protein was slightly increased by 8.7% in 2nd instars following treatment, it was found to decrease by 24.9% in treated 4th instar than that in untreated insects. The disturbance in the carbohydrate level was expressed by impairment in the activity of carbohydrate enzymes in treated 2nd and 4th instar larvae. In both treated instar larvae there was a significant increase in the enzyme activity of alpha and beta esterase as well as in glutathione S-transferase. Meanwhile, a significant decrease in the enzyme activities of both acetyl choline esterase and acid phosphatase was recorded in treated larvae.