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

Plant essential oils (EOs) were tested against 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 toward tested EOs. Our results showed LC50 values, the range of toxicity was in the decreasing order of 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.