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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]

BACKGROUND: Thymol is a known natural product with insecticidal activity against several insect species. A recent study on structural modifications of thymol to thymyl esters and their efficacy against Spodoptera litura suggested that such an approach could develop generalized novel insecticides/insect growth inhibitors and requires further studies to establish the efficacy against lepidopterans. RESULTS: Thymol and structurally modified eight esters were evaluated against beet armyworm, Spodoptera exigua using the topical application. Thymyl butanoate was the most toxic compound with a median lethal dose (LD50) of 2.33 and 1.62 μg/larva after 24 and 48 h posttreatment, respectively. All thymyl esters were potentially better than the parent compound thymol, except thymyl dibromoacetate, in their efficacy against Spodoptera exigua. Essentially, there were three levels of activity vis‐à‐vis the compounds used, that is, with the LD50 range of 1.5 to 5.0, 7.0 to 15.0, and > 20 μg/larva, respectively. Ovicidal activity and reduction in larval growth were also determined by treating third instars at sub‐lethal doses, that is, LD50 doses of second instars. Thymyl butanoate treated larvae inhibited glutathione S‐transferase, carboxylesterase, and acetylcholinesterase activities, whereas the other thymyl esters induced these enzymes. CONCLUSION: Thymyl butanoate exhibited higher toxicity against Spodoptera exigua and is the first to report about > 15.5× more toxicity than thymol and > 6.5× than thymyl cinnamate, which suggests that the efficacy was species‐specific versus the chemical structural variation of the esters. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

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 Spodoptera exigua. The highest acute toxicity was observed for ethyl acetate extract with an LD50 of 3.25 and 2.50 μg/larva and LD90 of 9.19 and 8.15 μg/larva after 24 and 48 h post-treatment after topical application. Piperine, methyl piperate, N-cinnamoyl-(2-phenylethyl) amine, pinostrobin, pinocembrin, cinnamic acid, lemairamin, N,N-Diphenylcinnamide, and methyl cinnamate were isolated from this extract that was toxic to S. exigua larvae. Cinnamic acid was the most active compound with a LD50 of 0.17 μg/larva after 48 h of topical treatment. Piperine was significantly similar in activity (LD50 = 0.19 μg/larva), but toxicity decreased with the change in structural configuration as observed with methyl piperate (LD50 = 0.73 μg/larva). Other compounds were 3 to 11-fold less toxic than cinnamic acid and piperine. Growth of survived S. exigua larvae until adult emergence after topical application was recorded and maximum inhibition of about 70% was observed after the application of cinnamic acid. Egg hatch was only 29.11% after cinnamic acid treatment, compared to 97.38% in controls. Neither induction nor inhibition of detoxification enzymes due to treatment of extracts were statistically significant, however, individual compounds like cinnamic acid, methyl cinnamate, piperine, pinostrobin, pinocembrin, and lemairamin did show a moderate impact on these enzymes. [ABSTRACT FROM AUTHOR]

Spodoptera exigua Hübner is one of the most important agricultural pests in Thailand. The present study investigated the toxicity of crude extracts and phenylpropanoid compounds of A. galanga (Zingiberaceae) against S. exigua. After 24 h of a topical application bioassay on secondary instar larvae, the ethyl acetate extract estimation of the LD50 of A. galanga (Zingiberaceae) showed toxicity toward secondary instar S. exigua larvae (LD50 ~ 2.44 µg/larva). Phenylpropanoid compounds were isolated from the ethyl acetate A. galanga crude extract which has [1'S]-1'-acetoxychavicol acetate as highest toxicity (LD50 of 1.93 µg/larvae). [1'S]-1'-acetoxychavicol acetate also showed carboxylesterase activity inhibition. Thus, the ethyl acetate extract of A. galanga may have [1'S]-1'-acetoxychavicol acetate as an active ingredient for controlling this pest, which could be used as an alternative to application of environmentally insecticides for controlling S. exigua. [ABSTRACT FROM AUTHOR]

The beet armyworm (Spodoptera exigua (Hübner)) is one of the most important vegetable pests in Thailand. After 24 hr of both dipping and sprayer bioassay, estimation of LC50 of the ethyl acetate extract of Jatropha gossypifolia senescent leaves demonstrated toxicity to secondary instar S. exigua larvae because in this stage most armyworm start to move to other plants and it is also the first susceptible stage for toxicity tests. Ricinine, the main alkaloid separated from ethyl acetate crude extract, showed toxicity on secondary instar larvae by the sprayer method with an LC50 of 3,215 ppm whereas the LC50 value for ethyl acetate crude extract is 8,644 ppm. Thus, the ethyl acetate crude extract of Jatropha gossypifolia senescent leaves may have ricinine as the active ingredient and may be used as an alternative choice for the minimal application of chemical insecticides for Spodoptera exigua. [ABSTRACT FROM AUTHOR]

Phytochemical investigation of the stem bark and leaf extract of Nauclea orientalis led to the isolation and identification of the three ursane-type triterpenoids rotundic acid, (3β)-3,19,23,24-tetrahydroxyurs-12-en-28-oic acid, 3-oxo-19,23,24-trihydroxyurs-12-en-28-oic acid, the two steroids β-sitosterol, β-sitostenone, the two megastigmane derivatives blumenol A and blumenol A glucoside, the isocoumarine trans -4-hydroxymellein, as well as the flavonole glycoside rutin. From the crude stem bark extract, we performed an anti-bacterial assay against four Gram positive and six Gram negative bacterial strains. An acetylcholinesterase inhibitory assay was performed from the crude extracts and rotundic acid, (3ß)-3,19,23,24-tetrahydroxyurs-12-en-28-oic acid and β-sitostenone. Both assays showed only weak effects. Contact toxicity determined via topical application revealed increased mortality of Spodoptera exigua caterpillars. The chemophenetic significance of ursane-type triterpenoids for the genus Nauclea is discussed briefly. [Display omitted] • Three ursane-type triterpenoids and six other compounds could be isolated from Nauclea orientalis. • 3-oxo-19α,23,24-trihydroxyurs-12-en-28-oic acid (3) was isolated the first time from a Rubiaceae species. • The lipophilic stem bark extract showed contact toxicity on Spodoptera exigua larvae. [ABSTRACT FROM AUTHOR]