The latent effects of three plant oils; namely thyme , bitter and neem on certain biological and biochemical parameters of the 6 th instar larvae of Spodoptera littoralis treated as 2 nd and 4 th instars with the LC 50 values of these oils. The results showed that the 2 nd instars were more susceptible to all the tested oils than the 4 th instar larvae. All treatments recorded significantly difference in all durations for both 2 nd and 4 th instars. Also, highly significant prolongation in pupal duration and the most prolonged oil was occurred by thyme on the 2 nd instars, while bitter was more effective on the 4 th instar larvae. Longevity of both sexes was reduced specially for male moths. No significant reduction was noticed on female longevity as a result of pretreated 2 nd but significant reduction was recorded for pretreated 4 th instars especially with thyme. Highly significant reduction in pupal weight produced from the treated 2 nd and 4 th larval instars with the three products. All oils caused deformations with various degrees for larvae, pupae and adults resulted from the treated 2 nd and 4 th instar larvae. The highest deformations exist in larval-pupa intermediate by thyme as pretreated 2 nd and 4 th of the larval instars. Bitter gave the highest pupal deformation as the pretreated 4 th instars followed by neem for the 2 nd and 4 th instars. Generally, all oils exhibited higher effect on the males. Total malformation during all generation recorded its maximum value with neem treatment as 2 nd instars then thyme was the most effective in both 4 th and 2 nd of the larval instars followed by bitter. Highly significant stimulation in chitinase and α-& β-esterases activity was recorded with all treatments and the most effective one caused by thyme followed by bitter. Highly significant inhibition in protease activity and acetylcholine esterase (AChE) was attained by (bitter & thyme) and (neem & thyme) oils, respectively. While high significant stimulation was recorded in protease and non significant stimulation of AChE was noticed by neem and bitter, respectively.

Seven chemical insecticides were tested for their ovicidal activity against Spodoptera littoralis eggs, using two methods, namely dipping of tafla leaves containing 0-1 day old eggs and o-day old eggs were deposited on insecticide residues on tafla leaves. Rynaxypyr was the most promising. It was taken as the standard insecticide and given an arbitrary index value of 100 units, when 0-1 day old eggs were treated directly by dipping in insecticide solution. As for the indirect ovicidal activity, emamectin benzoate came first and was given arbitrary index value of 100 units. On the other hand spinetoram, in comparison showed the least indirect ovicidal effect. Regarding the inhibitory action, it was obvious that rynaxypyr and indoxacarb exhibited high inhibitory activity (100%) in suppressing the number of deposited eggs when moths were subjected to 100 ppm and it was followed closely by pyridalyl, emamectin benzoate and spinetoram being 97.8, 97.0 and 95.3%, respectively. However, all insecticides showed variable degrees of inhibition at the least concentration tested (0.1 ppm), except spinosad and spinetoram having no inhibition activity for deposited eggs.

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