DOI: 10.36347/sajb.2021.v09i02.004

Pages: 36-57

Egyptian cotton leafworm, Spodoptera littoralis, is one of the key pests that cause great damage to cotton plant as well as other field and vegetable crops. Plant products, as a promising alternative to the synthetic insecticides, have now been established worldwide. In this work we studied for the first time the insecticidal activity of the sesquiterpene compound, nerolidol, and its effect on growth, development and metamorphosis of S. littoralis. The newly moulted larvae of 5th (penultimate) or 6th (last) instar larvae were fed on castor bean leaves previously treated with seven concentrations of Nerolidol (400, 200, 100, 50, 25, 12.5 & 6.25 ppm) for 24 hr. The most important results could be summarized as follows. Nerolidol exhibited various degrees of insecticidal activity against larvae, pupae and adults, regardless the instar under treatment. Nerolidol was found more toxic after treatment of last instar larvae (LC50=42.24 ppm) than after treatment of penultimate instar larvae (LC50=50.01 ppm). A remarkable reduction of larval weight gain was recorded, in a dose-dependent course. Similarly, the larval growth was drastically suppressed. The larval and pupal durations were significantly prolonged. Some percentages of the treated 5th instar larvae failed to completely moult into the 6th instar, only at the higher three concentrations. Also, some larvae developed into larval-pupal intermediates. Nerolidol exerted a strong inhibitory action on the pupation rate in a dose-dependent course while the adult emergence was partially blocked, only at the higher concentrations. Nerolidol failed to exert anti-morphogenic action on S. littoralis after treatment of 5th instar larvae, but treatment of 6th instar larvae only with the higher two concentrations resulted in an impaired morphogenesis of some pupae.