Toxicity of essential oil compounds against diamondback moth,Plutella xylostella,and their impact on detoxification enzyme activities

Essential oils are by-products of plant metabolism that are now known to interfere with basic metabolic, physiological and behavioral functions of insects, thereby having promise for use as pest control agents. Accordingly, four essential oil compounds, thymol, 1,8-cineole, linalool and pulegone, were evaluated against the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Yponomeutidae), to determine their acute toxicity. Thymol and 1,8-cineole were highly toxic to third instars with a LD₅₀ of 0.22 and 0.41 μg/larva, respectively. Linalool and pulegone were moderately active against this insect species, exhibiting <45 % mortality in up to 15 μg/larva. However, in biorational mixtures pulegone was synergistic to both thymol and 1,8-cineole where the increase in activity was almost twofold. Thymol and 1,8-cineole, though active individually against P. xylostella larvae, were antagonistic as biorational mixtures. Linalool was antagonistic in all combinations. In various assays with detoxification enzymes in treated conditions, there was a significant increase in enzyme levels both in vivo and in vitro. Thymol and 1,8-cineole were the active toxicants against P. xylostella, with significant potential to control this pest as biorational mixtures in a synergistic combination with pulegone. Induction in enzyme levels by these compounds suggests possibilities of resistance, which at present remains a speculation, but cannot be summarily ignored because the induction of enzymes due to involvement of detoxification enzymes in the metabolism of a broad range of xenobiotics and secondary metabolites in plants is well known.     

Antifeedant activity of Jatropha gossypifolia and Melia azedarach senescent leaf extracts on Spodoptera frugiperda (Lepidoptera: Noctuidae) and their potential use as synergists

BACKGROUND: To reduce rates of synthetic insecticide applications, natural product alternatives and synergists are needed. A study has been made of the toxicity of ethanolic senescent leaf extracts (SLEs) of Jatropha gossypifolia and Melia azedarach on larvae of the noctuid pest Spodoptera frugiperda. Their effects as syngergists and inhibitors of several enzyme activities are also reported. RESULTS: When added to the diet, M. azedarach SLE showed lower toxicity than J. gossypifolia SLE. However, after 2 weeks on the diet, the M. azedarach SLE proved to be lethal to 100% of the larval population. Artificial diets with both SLEs have an antifeedant effect on armyworm larvae. Acute toxicity after topical application in a dipping assay was relatively low for both J. gossypifolia and M. azedarach SLEs (LC₅₀ of 2.6 and 1.4 g L^?1, respectively, after 24 h). However, mixtures of the SLEs of M. azedarach and J. gossypifolia had a strong synergistic effect with cypermethrin. Synergism was higher with the J. gossypifolia SLE, perhaps because it contains several natural products with a methylenedioxyphenyl moiety. Both extracts inhibited P450, general esterase and acetylcholinesterase activities in vitro and in vivo. CONCLUSION: Both J. gossypifolia and M. azedarach SLEs are antifeedants to armyworm larvae when present in the food, and also have a synergistic effect with cypermethrin in topical assays. Although the synergistic effect is less than with piperonyl butoxide, both SLEs have some inhibitor activity against detoxification enzymes and acetylcholinesterase. Thus J. gossypifolia and M. azedarach SLEs may be considered as ecofriendly approaches for the control of S. frugiperda in order to reduce cypermethrin usage. Copyright © 2012 Society of Chemical Industry     

The insecticidal potential of Piper ribesioides (Piperales: Piperaceae) extracts and isolated allelochemicals and their impact on the detoxification enzymes of Spodoptera exigua (Lepidoptera: Noctuidae)

Phytoparasitica - The dried twigs of Piper ribesioides were used to prepare various extracts in different solvents. Each extract was evaluated for their toxicity against 2nd instar larvae of...