Efficacy of three insect growth regulators on growht and development of the Egyptian cotton leafworm Spodoptera littoralis, Boisd.
2011
Badawy, M.E. | Rabea, E.I. | Nasr, H.M.
The direct and latent effects of the three commercial insect growth regulators lufenuron, methoxyfenozide and teftubenzuron on the 2nd and 4th instar larvae of susceptible strain of cotton leafworm Spodoplera littoralis were studied. The insecticides proved to be high toxic to the test insect larvae and they showed adverse effects on pupae, and emergence d adults. The larvae suffered from more mortality when they were fed for a longer period on the diet that treated with concentrations of 1 and 2.5 mg (a.i)/Kg diet. The significant high mortality percentages were observed at all tested concentrations with teflubenzuron followed by lufenuron and then methoxyfenozide and the result clearly showed that the 2nd instar larvae were more sensitive to the compounds tested, compared to those of the 4th instar. Larval weight gain was considerably decreased as concentration increased and the reduction in weigh was highly effective in case of teflubenzuron followed by lufenuron and then methoxyfenozide. The affected larvae ceased feeding within 48h and most *eths occurred during moulting to the next instar. Some larvae failed to pupae successively. The insecticides varied in kit influences on chitinase and PPO activity, and these enzymes could have relation with their toxicity against S. littoralis larvae. The susceptibility of the fourth larval-stage S. littoralis to these insecticides evidenced a similar pattern however; the activity was lower than that obtained with the second larval-stage. So, when these insecticides should be used for S littoralis larvae control, dosage and timing of application should be carefully considered.
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