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The discovery of eco-friendly plant-based insecticides is currently booming in research with an attempt to replace synthetic chemical insecticides causing tremendous adverse effects. The present work studied the insecticidal potential of ginger, an important medicinal plant. Four crude extracts from Zingiber officinale rhizomes were evaluated for their contact toxicity against second instars of Spodoptera litura, Spodoptera exigua and Spodoptera frugiperda using the topical application. The hexane extract exhibited the strongest toxicity to S. exigua with the LD50 of 9.92 and 8.40 µg/larva at 24 and 48 h posttreatment, respectively, followed by S. frugiperda. Comparative toxicity of the most abundant secondary metabolites from the hexane extract, gingerols and shogaols, against both insects concluded that 8-shogaol (5) was identified as the most active compound against S. frugiperda with the LD50 of 7.68 and 3.96 µg/larva at 24 and 48 h posttreatment, respectively. [ABSTRACT FROM AUTHOR]

Plants produce arrays of secondary metabolites that act synergistically to deter and/or intoxicate herbivores. In this study, we evaluated the toxicity of piperine and β-asarone, individually and in binary mixtures, to examine their synergistic effects against larvae of two generalist herbivores, Spodoptera litura and Mythimna separata. Acute toxicity of piperine after topical application was lower than that of β-asarone for second instar larvae of both S. litura and M. separata (LD50 53.65 and 7.52 µg/larva, respectively, after 24 h). However, all mixtures produced synergistic, antifeedant effects. Mixtures of either 56.65 or 7.52 µg/larva of piperine + 18 µg/larva of β-asarone were highly synergistic in term of their acute toxicity (synergistic factor 11 and 44 for S. litura and M. separata, respectively). The more concentrated mixture also had the strongest antifeedant effects when presented on artificial diet to both species, S. litura and M. separata (56.64% and 62.30% at 24 h, respectively). Our results suggest that the combination of piperine and β-asarone is a greater deterrent than either pure compound alone. Use of this mixture may provide better crop protection rather than that offered by single compounds for controlling lepidopteran pests. [ABSTRACT FROM AUTHOR]

Botanical insecticides as a means of controlling insects present an alternative approach that is safer than the use of synthetic insecticides. The present study identified the insecticidal activity of extracts of the rhizomes of Alpinia galanga (L.) Willd. and seven isolated phenylpropanoids against the second instar of Spodoptera litura Fab. by topical application. The ethyl acetate extract had the highest toxicity on this insect with LD50 values of 1.68 and 1.25 μg/larva after 24 and 48 h posttreatment, respectively. Among the seven phenylpropanoids separated from the ethyl acetate extract, 1′S-1′-acetoxychavicol acetate was identified as the most active compound with LD50 values of 1.63 and 1.40 μg/larva after 24 and 48 h posttreatment, respectively, followed by p-coumaryl diacetate. In addition, the two active compounds decreased glutathione S-transferase activity and increased acetylcholinesterase activity. p-Coumaryl diacetate also decreased carboxylesterase activity. [ABSTRACT FROM AUTHOR]

Terpenes and biogenically related phenols commonly found in plant essential oils are known to be toxic to insect pests. Accordingly thymol was tested for acute toxicity via topical application to diamondback moth,Plutella xylostellaL. (Lepidoptera: Plutellidae) and its parasitoid,Cotesia plutellae(Kurdjunov) (Hymenoptera: Braconidae under laboratory conditions. Topical application to adult female parasitoidsversussecond instars ofP. xylostellashowed that thymol was about 62 times less toxic to the parasitoid than to the host larvae with 24 h LD50of 0.052 and 0.0008M, respectively. Although thymol was less toxic to the parasitoid, some biological parameters of the progeny at sublethal doses of surviving parasitoids were impaired such as rate of emergence and development time of larvae and pupae. The impact on detoxification enzymes was also studied and there was no significant induction in cytochrome P450 and carboxylesterase activities in both treated male and female wasps. Results obtained suggest that parasitoid is able to withstand the impact of thymol significantly. [ABSTRACT FROM PUBLISHER]