Secondary Metabolites of Colocasia esculenta Extract as Green Insecticide Against the Cotton Leaf Worm, Spodoptera littoralis (Boisd.)
Egyptian Academic Journal of Biological Sciences F Toxicology & Pest Control
The journal of Toxicology and pest control is one of the series issued twice by the Egyptian Academic Journal of Biological Sciences, and is devoted to publication of original papers related to the interaction between insects and their environment. The goal of the journal is to advance the scientific understanding of mechanisms of toxicity. Emphasis will be placed on toxic effects observed at relevant exposures, which have direct impact on safety evaluation and risk assessment. The journal
... t. The journal therefore welcomes papers on biology ranging from molecular and cell biology, biochemistry and physiology to ecology and environment, also systematics, microbiology, toxicology, hydrobiology, radiobiology and biotechnology. www.eajbs.eg.net Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use. A petroleum ether extract of Colocasia esculenta leaves yielded two sterols which were identified as; β-sitosterol І, Stigmasterol ІІ, these secondary metabolites showed insecticidal, antifeeding and insect growth regulatory activities against the 4 th instar larvae of Spodoptera littoralis. So, the efficacy of this extract and two insect growth regulators belonging to different groups; methoxyfenozide (an ecdysone agonist) and lufenuron (chitin synthesis inhibitor) was assayed against the 4 th instar larvae of S. littoralis under laboratory conditions. C. esculenta extract, methoxyfenozide and lufenuron have sub-lethal concentrations LC 25 (17.8 gm/liter, 5.07 mg/liter and 0.80 mg/liter), respectively. It was observed that in case of both C. esculenta and methoxyfenozide treatments, the larvae undergo a precocious molting where promoted apolysis process but die due to failure in completing the molting process, at time shorter than the control ones. Ecdysis and sclerotization were incomplete and the pupa that emerged showed many deformities. The joint action of mixing C. esculenta extract at two concentrations (LC 10 and LC 25 ) with methoxyfenozide and lufenuron at two concentrations (LC 10 and LC 25 ) can be evaluated. All the mixtures of C. esculenta and methoxyfenozide have synergistic activity against treated larvae, while all the mixtures of C. esculenta and lufenuron have antagonistic activity. Biochemical characterization of enzyme activities related to molting process and cuticle synthesis showed that C. esculenta extract treatment caused significant disturbance in enzyme balances either decrease or increase comparing to control ones, the reason behind deformations and mortality may be as a result of change in chitinase, phenoloxidase and protease enzymes. These plant sterols І, ІІ may be considered to be efficient insect growth regulators, as well as having activity similar to phytosteroids, as was evidenced by their significant inhibition of molting processes.