Natural Insecticidal Agents Research Articles

Design, Synthesis, and Biological Evaluation of Novel Osthole-Based Isoxazoline Derivatives as Insecticide Candidates.

Natural products are an abundant and environmentally friendly source for controlling plant pathogens and insect pests. Toward the development of new natural product-based pesticides, here, a series of osthole-based isoxazoline derivatives were prepared by [3 + 2] annulation and evaluated for their insecticidal activities and toxicities. The structures of all osthole-based isoxazoline derivatives were characterized by various spectral analyses, and derivative B13 was further confirmed by X-ray crystallography. Among all the osthole derivatives, B2 displayed the most promising growth inhibitory effect on Mythimna separata with a final corrected mortality rate of 96.4% ± 3.3, which was 1.80 times higher than those of both osthole and toosendanin. Derivative B13 displayed the most promising larvicidal activity against Plutella xylostella with an LC50 value of 0.220 mg/mL, which was superior to rotenone. Furthermore, both B13 and B21 also exhibited better control efficacy against P. xylostella than rotenone in the pot experiments. Additionally, the toxicity evaluation suggested that these osthole-based isoxazoline derivatives showed relatively low toxicity toward nontarget organisms. Given these results, osthole derivatives B2, B13, and B21 could be deeply developed as natural insecticidal agents in agriculture.

Ceanothane and oleanane-type triterpenes from Talguenea quinquenervia have insecticidal activity against Cydia pomonella, Tenebrio molitor and Drosophila melanogaster

Many secondary metabolites from plants are constitutive and/or induced chemical defenses that play a role in protection against phytopathogenic attack. Talguenea quinquenervia (Rhamnaceae) is a notorious weed that possesses several medicinal applications such as American taxa of Rhamnaceae species are toxic to insects, fungi and several bacteria strains. These effects have been associated with the presence of alkaloids, phenolics and terpenes. A methanolic extract from the roots afforded 9 triterpenes belonging to lupane, oleanane, ursane, sterol and ceanothane groups. Our results indicate that these compounds are involved in interference of sclerotization and moulting. They showed selective effects on pre-emergence metabolism of selected insects including lepidoptera and diptera, but not to coleoptera. The results were fully comparable to known natural insect growth inhibitors such as azadirachtin, gedunin and Cedrela extract and have a possible role as natural insecticidal agents. To the best our knowledge, this is the first report of the isolation of ceanothane-type triterpenes from this plant species. The level of activity achieved by the assayed compounds indicated inhibition in a concentration dependent manner with LD50 values between 41 and 17μg/mL.

Insect growth regulatory effects by diterpenes from Calceolaria talcana Grau & Ehrhart (Calceolariaceae: Scrophulariaceae) against Spodoptera frugiperda and Drosophila melanogaster

The n-hexane extract from aerial parts of Calceolaria talcana (Calceolariaceae, formerly Scrophulariaceae) afforded 1,10-α-cyclopropyl-4,13-dimethyl-19-α-hydroxy-9-epi-ent-7,15-isopimaradiene (1,10-cyclopropyl-9-epi-ent-isopimarol) 1, and 19α-hydroxy-8,11,13-abietatriene 2 together with other known triterpenes and naphthoquinones. These natural products together with n-hexane extract and several fractions showed insecticidal and insect growth regulatory activity against fall armyworm (Spodoptera frugiperda, Lepidoptera: Noctuidae), and fruit fly (Drosophila melanogaster, Diptera: Drosophilidae), insect pests of corn and fruits, respectively. The most active samples were a mixture (M1) of the diterpenes 1+2 (6:4) that showed insecticidal activity between 10 and 20ppm. Additionally, a mixture of triterpenes 3–5 (M2), fraction 5 (F-5), a mixture of two naphthoquinones 6, 7 (M3), and the n-hexane extract, which had significant effects between 20.0 and 35.0μg/mL in diets. Almost all samples were insecticidal with lethal doses between 35 and 50μg/mL. Our results indicate that these compounds at low concentrations appear to have selective effects on the pre-emergence metabolism of the insect. The results were fully comparable to known natural insect growth inhibitors such as gedunin, MeOH-Cedrela and MeOH-Yucca extracts, suggesting a possible role as natural insecticidal agents.

Insect growth regulatory effects of some extracts and sterols from Myrtillocactus geometrizans (Cactaceae) against Spodoptera frugiperda and Tenebrio molitor

A methanol extract from the roots and aerial parts of Myrtillocactus geometrizans (Cactaceae) yielded peniocerol 1, macdougallin 2, and chichipegenin 3. The natural products 1, 2 their mixtures, MeOH and CH 2Cl 2 extracts showed insecticidal and insect growth regulatory activity against fall armyworm [ Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae)], an important insect pest of corn, and [ Tenebrio molitor (Coleoptera)], a pest of stored grains in Mexico. The most active compounds were 1, 2, and a mixture ( M 2 ) of 1 and 2 (6:4). All these extracts, compounds and the mixture had insect growth regulating (IGR) activity between 5.0 and 50.0 ppm and insecticidal effects between 50 and 300 ppm in diets. The extracts were insecticidal to larvae, with lethal doses between 100 and 200 ppm. These compounds appear to have selective effects on the pre-emergence metabolism of Coleoptera, because in all treatments of the larvae of T. molitor, pupation were shortened and this process show precociousness in relation to controls. In contrast to S. frugiperda larvae, onset of pupation was noticeably delayed. Emergence in both cases was drastically diminished. In both pupae and in the few adults that were able to emerge, many deformations were observed. The results of these assays indicated that the compounds were more active than other known natural insect growth inhibitors such as gedunin and methanol extracts of Cedrela salvadorensis and Yucca periculosa. Peniocerol, macdougallin and chichipegenin, as well as mixtures of these substances, may be useful as natural insecticidal agents.

Insect growth inhibition by tocotrienols and hydroquinones from Roldana barba-johannis

The methanol extract from the aerial parts of Roldana barba-johannis (Asteraceae) afforded sargachromenol, sargahydroquinoic acid, and sargaquinoic acid. These natural products and their corresponding acetylated and methylated derivatives showed insecticidal and insect growth regulatory activities against the Fall Armyworm [ Spodoptera frugiperda J.E. Smith, (Lepidoptera: Noctuidae)], an important insect pest of corn. The most active compounds were sargachromenol and its acetylated derivative; sargahydroquinoic acid and its acetylated derivative; and a mixture of sargachromenol, sargahydroquinoic acid, and sargaquinoic acid (6:3:1) and the acetylated form of this mixture. All these compounds and mixtures had significant inhibitory effects between 5.0 and 20.0 ppm in diets. Most compounds were insecticidal to larvae, with lethal doses between 20 and 35 ppm. In addition, these substances also demonstrated scavenging properties toward 2,2-diphenyl-1-picrylhydrazyl radical in TLC autographic and spectrophotometric assays. These compounds appear to have selective effects on the pre-emergence metabolism of the insect. The results from these compounds were fully comparable in activity to those known natural insect growth inhibitors such as gedunin and methanol extracts of Cedrela salvadorensis and Yucca periculosa. These substances may be useful as natural insecticidal agents.

Antioxidant and insect growth regulatory activities of stilbenes and extracts from Yucca periculosa

The methanol extract from the bark of Yucca periculosa F. Baker afforded 4,4′-dihydroxstilbene, resveratrol and 3,3′,5,5′-tetrahydroxy-4-methoxystilbene and had growth regulatory activity against the Fall Army worm ( Spodoptera frugiperda J.E. Smith, Lepidoptera:Noctuidae) an insect pest of corn. The most active compound was 3,3′,5,5′-tetrahydroxy-4-methoxystilbene which had significant effects at 3 μg/g in diets. In addition to the inhibitory activity on bleaching of crocin induced by alkoxyl radicals, these compounds also demonstrated scavenging properties toward 2,2-diphenyl-1-picrylhydrazyl in TLC autographic and spectrophotometric assays. Our results indicate that these compounds could be involved in interference of sclerotization and moulting. These compounds appear to have selective effects on the pre-emergence metabolism of the insect. The results were fully comparable to known natural insect growth inhibitors such as gedunin and Cedrela extracts and have had a possible role as natural insecticidal agents.