Sublethal Effects of Some Essential Oils on the Developmental and Reproduction of the Spodoptera Littoralis (Boisduval)

The cotton leafworm spodoptera littoralis (boisd.); is one of the most destructive pests. it can infest more than 120 economically important crops all year round and causing a great loss. the management of s. littoralis has been typically carried out by chemical pesticides, however, there has been an increasing interest in natural products, particularly those of plant origin, to control this pest. plant essential oils (eos) were tested for s. littoralis larvae. responses varied according to eos species and all eos were proved to be toxic to the larvae. however, the highest mortality was observed in the oils of orange, sesamum, and camphor. the slope values indicated that the insect population was relatively heterogeneous in their susceptibility to tested eos. our results showed lc50 value, the range of toxicity was in the decreasing order for orange˃ sesamum˃ camphor˃ pepper˃ pumpkin against both s. littoralis 2nd and 4th instars. the influence of lc25 values of biological parameters manifested in decreased the adult emergence and prolongation of the larval and pupal period. the percentage of larvae that survived and succeeded to pupate decreased the result of treatment by lc25 values. longevity, fecundity, fertility, and natality were monitored in the surviving adults. the most significant effect of eos was determined with respect to natality. compared to the control, all the tested eos caused a significant reduction in natality. while 1210.2 viable larvae were obtained in the control, the number of viable larvae obtained from those treated was lower, ranging from 35.8 % (for orange oil) up to 81.9 % (for pumpkin oil). based on the presented results, eos, orange, sesamum, and camphor. generally, sublethal effects of eos exhibit significant effects on the population dynamics of s. littolaris where, reduction of adult natality by more than 75 % in this pest.