Evaluation of mosquitocidal activity of essential oil and sesquiterpenes from leaves of Chloroxylon swietenia DC

The essential oil chemical composition of a sicilian (Italy) accession of Doronicum caucasicum M. Bieb

Doronicum is a relatively small genus belonging to the tribe Senecioneae (Fam. Asteraceae), distributed in Asia, Europe, and North Africa. Some of its species are considered toxic due to the presence of pyrrolizidine alkaloids whereas some other ones are largely utilised in the ethnopharmacology of several countries. In the present study, the essential oil composition of a Sicilian accession of Doronicum caucasicum M. Bieb (syn. D. orientale Hoffm.), not previously investigated, is particularly rich in sesquiterpene hydrocarbons (80.3%) with germacrene D (58.9%), α-humulene (8.8%), and β-caryophyllene (6.5%) as main metabolites. A comparison with all the essential oils from Doronicum taxa studied so far has been carried out.

GC-MS-based Metabolomics Unravels Metabolites across Larval Development and Diapause of a Specialist Insect

Plant-insect interactions are a driving force into ecosystem evolution and community dynamics. Many insect herbivores enter diapause, a developmental arrest stage in anticipation of adverse conditions, to survive and thrive through seasonal changes. Herein, we investigated the roles of medium- to non-polar metabolites during larval development and diapause in a specialist insect herbivore, Chlosyne lacinia, reared on Aldama robusta leaves. Varying metabolites were determined using gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Sesquiterpenes and steroids were the main metabolites putatively identified in A. robusta leaves, whereas C. lacinia caterpillars were characterized by triterpenes, steroids, fatty acids, and long-chain alkanes. We found out that C. lacinia caterpillars biosynthesized most of the identified steroids and fatty acids from plant-derived ingested metabolites, as well as all triterpenes and long-chain alkanes. Steroids, fatty acids, and long-chain alkanes were detected across all C. lacinia instars and in diapausing caterpillars. Sesquiterpenes and triterpenes were also detected across larval development, yet they were not detected in diapausing caterpillars, which suggested that these metabolites were converted to other molecules prior to the diapause stage. Our findings shed light on the chemical content variation across C. lacinia development and diapause, providing insights into the roles of metabolites in plant-insect interactions.

Phytochemical analysis and antibacterial/antifungal activity of the essential oil of Phlomis olivieri Benth in Iran

Phlomis olivieri Benth. is an aromatic plant endemic to Iran belonging to the Lamiaceae family. It is used to treat pain, stomach ache and common cold in Iranian traditional medicine. P. olivieri also has valuable biological properties including antioxidant, antimicrobial and analgesic ones. This was the first study designed to assess the quality, quantity and antimicrobial activity of Phlomis olivieri Benth. essential oil (POEO). Samples were randomly collected from flowering twigs of this species in three locations between Azeran and Kamoo in Kashan, Iran at peak flowering in June 2019. Water distillation extraction was used to obtain the POEO the quantity of which was calculated by weight. Gas chromatography coupled to mass spectrometry (GC/MS) was also used for POEO qualitative analysis, which revealed its chemical compounds and their percentages. Antimicrobial activity of POEO was also determined using the agar well diffusion method. Minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) were also measured using the broth microdilution method. The results of the quantitative and qualitative analysis showed that the POEO yield was ~ 0.2292% and its main chemical compounds included the sesquiterpenes germacrene D (26.43%), β-caryophyllene (20.72%), elixene (6.58%), β-trans-farnesene (6.17%), β-Cyclogermacrane (5.04%), germacrene B (4.73%), α-humulene (4.22%), and monoterpene α-pinene (3.22%). The agar diffusion method demonstrated the highest antimicrobial activity of POEO (MIC ~ 14.50 mm) was against the Gram-positive species Streptococcus pyogenes. The POEO also showed the strongest inhibitory and lethal activity against the gram-negative bacterial species Pseudomonas aeruginosa (MIC < 62.50 μg/mL) and S. paratyphi-A (MIC < 62.50 μg/mL and MBC = 125 μg/mL), and fungal species Candida albicans (MIC and MBC = 250 μg/mL) as compared to control-positive antibiotics. Therefore, POEO is a valuable natural alternative rich in sesquiterpenes with strong antimicrobial and antifungal activities against some fungal and bacterial strains. It can also be used in the pharmaceutical, food and cosmetic industries.

Challenges encountered by natural repellents: Since obtaining until the final product

Vector-borne diseases, particularly the arboviruses dengue, Zika, chikungunya, and yellow fever caused by the Aedes aegypti mosquito, have been driving the use of repellents worldwide. The most representative synthetic repellent, DEET stands out as the market's oldest and most efficient repellent. It is considered a reference standard but presents considerable toxicity, not recommended for children up to 6 months old and pregnant women. For this reason, alternatives have been sought, and natural repellents derived mainly from essential oils have been studied, highlighting the essential oils of lemon (Corymbia citriodora), citronella (Cympobogon sp.), Andiroba (Carapa guianensis). However, the development and commercialization of products containing natural repellents are significantly lower when compared to DEET and other synthetic repellents. In order to understand the reasons, aspects related to safety, mechanism of action, efficacy as well development and complexity of the products were evaluated. It is concluded that, as for safety, there is lacking information in the literature regarding the effects on non-target organisms and robust toxicity data. The mechanism of action is based on theories, with less information on the exact mode of action, molecular targets, and interaction with the olfactory and taste receptors of insects. Despite being a current trend to search for actives from natural sources highly present in essential oils, however they reduced action time because due to rapid evaporation after application to the skin, thus requiring repellent vehicles. The development and complexity related to these products bring challenging aspects, beginning on the plant cultivation and extraction processes to produce essential oils with a more homogeneous chemical composition towards the formulation stabilization processes due to fast evaporation and short action time, with the use of pharmaceutical technology such as encapsulation techniques.

Complete Genome of Rose Myrtle, Rhodomyrtus tomentosa, and Its Population Genetics in Thai Peninsula

Several parts of rose myrtle, Rhodomyrtus tomentosa, exhibited profound antibacterial and anti-inflammatory activities, suggesting its potential in healthcare and cosmetics applications. During the past few years, the demand for biologically active compounds in the industrial sectors increased. Therefore, gathering comprehensive information on all aspects of this plant species is essential. Here, the genome sequencing using short and long reads was used to understand the genome biology of R. tomentosa. Inter-simple sequence repeats (ISSR) and simple sequence repeats (SSR) markers, and geometric morphometrics of the leaves of R. tomentosa collected across Thai Peninsula, were determined for population differentiation analysis. The genome size of R. tomentosa was 442 Mb, and the divergence time between R. tomentosa and Rhodamnia argentea, the white myrtle of eastern Australia, was around 15 million years. No population structure was observed between R. tomentosa on the eastern and western sides of the Thai Peninsula using the ISSR and SSR markers. However, significant differences in leaf size and shape of R. tomentosa were observed in all locations.

Phytochemical Profiling, Biological Activities, and In Silico Molecular Docking Studies of Causonis trifolia (L.) Mabb. & J.Wen Shoot

Causonis trifolia (L.) Mabb. & J.Wen, commonly known as "fox grape", is an ethnomedicinally important twining herb of the Vitaceae family, and it is used by ethnic communities for its wide range of therapeutic properties. Our research aims to investigate the chemical composition; antioxidant, anti-inflammatory, and antidiabetic activities; and mechanisms of interaction between the identified selective chemical compounds and the target proteins associated with antioxidant, anti-inflammatory, and antidiabetic effects of the optimised phenolic extract of Causonis trifolia (L.) Mabb. & J.Wen, shoot (PECTS) to endorse the plant as a potential drug candidate for a future bioprospecting programme. Here, we employed the response surface methodology (RSM) with a Box-Behnken design to enrich the methanolic extract of C. trifolia shoot with phenolic ingredients by optimising three key parameters: solvent concentration (% v/v, methanol:water), extraction temperature (°C), and extraction duration (hours). From the quantitative phytochemical estimation, it was evident that the PECTS contained good amounts of phenolics, flavonoids, tannins, and alkaloids. During the HPLC analysis, we identified a total of eight phenolic and flavonoid compounds (gallic acid, catechin hydrate, chlorogenic acid, caffeic acid, p-coumaric acid, sinapic acid, coumarin, and kaempferol) and quantified their respective contents from the PECTS. The GC-MS analysis of the PECTS highlighted the presence of 19 phytochemicals. In addition, the bioactivity study of the PECTS showed remarkable potentiality as antioxidant, anti-inflammatory, and antidiabetic agents. In silico molecular docking and computational molecular modelling were employed to investigate the anti-inflammatory, antioxidant, and antidiabetic properties of the putative bioactive compounds derived from the PECTS using the GC-MS technique to understand the drug-receptor interactions, including their binding pattern. Out of the 19 phytocompounds identified by the GC-MS analysis, one compound, ergosta-5,22-dien-3-ol, acetate, (3β,22E), exhibited the best binding conformations with the target proteins involved in anti-inflammatory (e.g., Tnf-α and Cox-2), antioxidant (SOD), and antidiabetic (e.g., α-amylase and aldo reductase) activities. The nontoxic nature of this optimised extract was also evident during the in vitro cell toxicity assay against the Vero cell line and the in vivo acute toxicity study on BALB/c mice. We believe the results of the present study will pave the way for the invention of novel drugs efficacious for several ailments using the C. trifolia plant.

Mosquito-Borne Diseases and Their Control Strategies: An Overview Focused on Green Synthesized Plant-Based Metallic Nanoparticles

Mosquitoes act as vectors of pathogens that cause most life-threatening diseases, such as malaria, Dengue, Chikungunya, Yellow fever, Zika, West Nile, Lymphatic filariasis, etc. To reduce the transmission of these mosquito-borne diseases in humans, several chemical, biological, mechanical, and pharmaceutical methods of control are used. However, these different strategies are facing important and timely challenges that include the rapid spread of highly invasive mosquitoes worldwide, the development of resistance in several mosquito species, and the recent outbreaks of novel arthropod-borne viruses (e.g., Dengue, Rift Valley fever, tick-borne encephalitis, West Nile, yellow fever, etc.). Therefore, the development of novel and effective methods of control is urgently needed to manage mosquito vectors. Adapting the principles of nanobiotechnology to mosquito vector control is one of the current approaches. As a single-step, eco-friendly, and biodegradable method that does not require the use of toxic chemicals, the green synthesis of nanoparticles using active toxic agents from plant extracts available since ancient times exhibits antagonistic responses and broad-spectrum target-specific activities against different species of vector mosquitoes. In this article, the current state of knowledge on the different mosquito control strategies in general, and on repellent and mosquitocidal plant-mediated synthesis of nanoparticles in particular, has been reviewed. By doing so, this review may open new doors for research on mosquito-borne diseases.

Sesquiterpenoid-rich leaf, stem, and flower essential oil of the traditional herb Blumea paniculata (willd.) M.R.Almeida from India

The hydro-distillation essential oil was obtained from the leaf, stem, and flower of Blumea paniculata (Willd.) M.R.Almeida (Asteraceae) and analysed using gas chromatography equipped with a flame ionisation detector (GC-FID) and gas chromatography coupled with mass spectrometry (GC-MS). Fifty-eight, sixty-nine and, fifty-seven constituents were identified from leaf oil (LO), stem oil (SO) and flower oil (FO), representing 95.8%, 96.3% and 95.1% of the total oil constituents, respectively. The major constituents were identified as germacrene D (39.6-48.1%), α-humulene (4.9-8.9%), β-caryophyllene (4.8-7.7%), and α-cadinol (2.9-6.8%) from different parts of the plant B. paniculata. The oils were found to be rich in sesquiterpenoid-type constituents.

A Background Search on the Potential Role of Scutellaria and Its Essential Oils

Scutellaria (Lamiaceae), which contains over 350 species, usually known as skullcaps, is found throughout Europe, the United States, and East Asia. In traditional Chinese medicine, several species are used to wipe out heat-evil and remove surface ills (TCM). The current study examines the ethnopharmacology, biological activity, and chemical substances associated with Scutellaria species. More than 295 chemicals, including flavonoids and diterpenes, have been identified. Scutellaria and its active principles have been shown in studies to have a wide range of pharmacological activities, including antioxidant, antimicrobial, antifeedant, phytotoxic, acaricidal toxicity, antibacterial, anti-inflammatory, and antianalgesic activities. Currently, effective monomeric compounds or active components from Scutellaria have been evaluated for pharmacological action in vivo and in vitro. More data facilitates applications and exploitation of novel medication development.

Phospholipids modifications, genotoxic and anticholinesterase effects of pepper fruit (Dennettia tripetala G. Baker) extract in Swiss mice

The toxicity of D. tripetala fruit extract to mice was investigated using data obtained from lipidomic analyses, comet and Acetylcholinesterase (AChE) assays. Mice (n = 8) were exposed for 30 days via oral gavage to vehicle (5% Tween 80) (negative control), D. tripetala extract (100, 200 and 400 mg/kg) and 40 mg/kg methyl methanesulfonate (MMS) (positive control). The profile of compounds in the fruit extract was analyzed using gas chromatography-mass spectrometry. Out of the total of 32 compounds identified, considerable amount of established insecticidal compounds such as 2-phenylnitroethane, cis-vaccenic acid, linalool and linoleic acid were detected. Fruit extract did not induce DNA damage relative to negative control. Percentage gain in body weights differed significantly across the four weeks. Significantly highest and lowest brain AChE activity was observed in animals exposed to 200 and 400 mg/kg D. tripetala, respectively. Fruit extract modulated the brain phospholipid profile due to significant fold changes of 48 lipid species out of the total of 280 lipid species. High number of differentially expressed phosphatidylcholine (PC) species and significant levels of phosphatidylethanolamine (PE) at 400 mg/kg suggests that activation of inflammation and methylation pathways are the most plausible mechanisms of D. tripetala toxicity to mouse brain tissue.

Identification of the sesquiterpene synthase AcTPS1 and high production of (-)-germacrene D in metabolically engineered Saccharomyces cerevisiae

Background

The sesquiterpene germacrene D is a highly promising product due to its wide variety of insecticidal activities and ability to serve as a precursor for many other sesquiterpenes. Biosynthesis of high value compounds through genome mining for synthases and metabolic engineering of microbial factories, especially Saccharomyces cerevisiae, has been proven to be an effective strategy. However, there have been no studies on the de novo synthesis of germacrene D from carbon sources in microbes. Hence, the construction of the S. cerevisiae cell factory to achieve high production of germacrene D is highly desirable.

Results

We identified five putative sesquiterpene synthases (AcTPS1 to AcTPS5) from Acremonium chrysogenum and the major product of AcTPS1 characterized by in vivo, in vitro reaction and NMR detection was revealed to be (–)-germacrene D. After systematically comparing twenty-one germacrene D synthases, AcTPS1 was found to generate the highest amount of (–)-germacrene D and was integrated into the terpene precursor-enhancing yeast strain, achieving 376.2 mg/L of (–)-germacrene D. Iterative engineering was performed to improve the production of (–)-germacrene D, including increasing the copy numbers of AcTPS1, tHMG1 and ERG20, and downregulating or knocking out other inhibitory factors (such as erg9, rox1, dpp1). Finally, the optimal strain LSc81 achieved 1.94 g/L (–)-germacrene D in shake-flask fermentation and 7.9 g/L (–)-germacrene D in a 5-L bioreactor, which is the highest reported (–)-germacrene D titer achieved to date.

Conclusion

We successfully achieved high production of (–)-germacrene D in S. cerevisiae through terpene synthase mining and metabolic engineering, providing an impressive example of microbial overproduction of high-value compounds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01814-4.

Essential oils and their bioactive compounds as eco-friendly novel green pesticides for management of storage insect pests: prospects and retrospects

The control of storage insect pests is largely based on synthetic pesticides. However, due to fast growing resistance in the targeted insects, negative impact on humans and non-target organisms as well as the environment, there is an urgent need to search some safer alternatives of these xenobiotics. Many essential oils (EOs) and their bioactive compounds have received particular attention for application as botanical pesticides, since they exhibited high insecticidal efficacy, diverse mode of action, and favourable safety profiles on mammalian system as well as to the non-target organisms. Data collected from scientific articles show that these EOs and their bioactive compounds exhibited insecticidal activity via fumigant, contact, repellent, antifeedant, ovicidal, oviposition deterrent and larvicidal activity, and by inhibiting/altering important neurotransmitters such as acetylcholine esterase (AChE) and octopamine or neurotransmitter inhibitor γ-amino butyric acid (GABA), as well as by altering the enzymatic [superoxide dismutase (SOD), catalase (CAT), peroxidases (POx), glutathione-S-transferase (GST) and glutathione reductase (GR)] and non-enzymatic [glutathione (GSH)] antioxidant defence systems. However, in spite of promising pesticidal efficacy against storage pests, the practical application of EOs and their bioactive compounds in real food systems remain rather limited because of their high volatility, poor water solubility and susceptibility towards degradation. Nanoencapsulation/nanoemulsion of EOs is currently considered as a promising tool that improved water solubility, enhanced bio-efficacy, stability and controlled release, thereby expanding their applicability.

An approach to natural insect repellent formulations: from basic research to technological development

The incidence of dengue, Zika, chikungunya, yellow fever and malaria cases has increased significantly in the world. To avoid mosquito bites, one of the best strategies is the use of repellents. The interest in using plants as mosquito repellents has increased significantly. In this review, has been performed a bibliographic survey of the plants with repellent activity, evaluate the trends of natural repellent formulations in the scientific literature, those described in patents and commercially available products. Limonene, 1,8-cineole, geraniol, eugenol and citronellal are the active compounds that mostly appear in the essential oils of plants with repellent activity. The type of natural repellent formulation mostly widely marketed is the spray and lotion, respectively. In patents, classic formulation as emulsion was most frequently used, followed by lotions and sprays. Data collected from scientific articles and patents show that microparticles are the most widely used extended release systems nowadays for natural repellents. The citronella essential oil was the one mostly used among the classic commercially available formulations, as well as in the extended release systems described in the literature and patents. Future research must be conducted to the use of nanotechnology in the development of extended release systems containing essential oils with repellent activity produced from natural and biodegradable materials.

Chemical Compositions and Biological Activities of Scutellaria Genus Essential Oils (Lamiaceae)

Context: Essential oils are secondary metabolites with versatile organic structures that, due to their compounds, have useful medicinal properties. There are about 250 species of the genus of Scutellaria perennial flowering plants from the Lamiaceae family. Its application for the treatment of allergy, inflammatory, hyperlipidemia, arteriosclerosis, hypertension, and hepatitis has a long history. Evidence Acquisition: Various studies on the chemical compounds of the Scutellaria genus have identified several ‎compounds, especially essentials oils. The current review is based on the evidence found in Chemical Abstract, Science Direct, Scopus, PubMed, Web of Knowledge, and Google Scholar databases. Results: Many studies on the chemical components of essential oils from the Scutellaria genus have identified several compounds. We summarized the chemical compositions and biological activities of Scutellaria essential oils. Hexadecanoic acid, germacrene D, β-caryophyllene, linalool, β-farnesene, and eugenol are the main compounds in essential oils of this genus. Despite many reports about essential oils of Scutellaria species (more than 38), a large number of species have not been studied yet. Therefore, several studies should be conducted on the chemical compounds and biological activities of unstudied Scutellaria essential oils. Conclusions: This review has summarized reports on the chemistry and biological activities of Scutellaria essential oils,‎ such as antioxidant, antimicrobial, antifeedant, phytotoxic, and acaricidal toxicities, based on the recent literature.

Plant-based larvicidal agents: An overview from 2000 to 2018

Current review aims to systematically segregate, analyze and arrange the key findings of the scientific reports published on larvicidal plants including larvicidal formulations. The investigation was carried out by analyzing the published literature in various scientific databases, subsequently, the key findings of the selective scientific reports having larvicidal potency (LC₅₀) of extract or isolated oil<100 μg/mL were tabulated to provide the concise and crucial information. Special emphasis was given on reports in which LC₅₀ of extract or isolated oil was reported to be < 10 μg/mL, genus or species documented in multiple independent studies, advancement in larvicidal formulations and activity of isolated phytoconstituents. Extensive analysis of published literature revealed that the larvicidal potency of herbal resources varied from sub-microgram/ml to practically insignificant. Overall, this unprecedented summarized and arranged information can be utilized for design, development and optimization of herbal based formulation having potential larvicidal activity.

Chemical Diversity of Headspace and Volatile Oil Composition of Two Brown Algae (Taonia atomaria and Padina pavonica) from the Adriatic Sea

Two selected brown algae (Taonia atomaria and Padina pavonica from the family Dictyotaceae, order Dictyotales) growing in the same area (island Vis, central Adriatic Sea) were collected at the same time. Their phytochemical composition of the headspace volatile organic compounds (HS-VOCs; first time report) was determined by headspace solid-phase microextraction (HS-SPME). Hydrodistillation was applied for the isolation of their volatile oils (first report on T. atomaria volatile oil). The isolates were analyzed by gas chromatography (GC-FID) and mass spectrometry (GC-MS). The headspace and oil composition of T. atomaria were quite similar (containing germacrene D, epi-bicyclosesquiphellandrene, β-cubebene and gleenol as the major compounds). However, P. pavonica headspace and oil composition differed significantly (dimethyl sulfide, octan-1-ol and octanal dominated in the headspace, while the oil contained mainly higher aliphatic alcohols, trans-phytol and pachydictol A). Performed research contributes to the knowledge of the algae chemical biodiversity and reports an array of different compounds (mainly sesquiterpenes, diterpenes and aliphatic compounds); many of them were identified in both algae for the first time. Identified VOCs with distinctive chemical structures could be useful for taxonomic studies of related algae.

Larvicidal Activity of Synthesized Silver Nanoparticles from Curcuma zedoaria Essential Oil against Culex quinquefasciatus

Culex quinquefasciatus is the major vector of the bancroftian filarial parasite which causes human lymphatic filariasis and St. Louis encephalitis. The simple way to stop the transmission is to control the vector by using synthetic chemicals. However, herbal essential oils have biological properties, such as a larvicidal effect and are ecofriendly to use. In this study, we investigated the larvicidal activity of Curcuma zedoaria essential oil (ZEO) and biosynthesized silver nanoparticles using this essential oil (ZEO-AgNPs). The larvicidal activity against both insecticide-susceptible and -resistant strains of Cx. quinquefasciatus larvae of ZEO were investigated and compared with ZEO-AgNPs. The ZEO-AgNPs showed the utmost toxicity against both strains of Cx. quinquefasciatus. After 24 h of exposure, LC₅₀ and LC₉₉ of ZEO against susceptible strain were 36.32 and 85.11 ppm, respectively. While LC₅₀ and LC₉₉ of ZEO against the resistant strain were 37.29 and 76.79 ppm, respectively. Whereas ZEO-AgNPs offered complete larval mortality within 24 h of exposure, LC₅₀ and LC₉₉ of ZEO-AgNPs against the susceptible strain, were 0.57 and 8.54 ppm, respectively. For the resistant strain, LC₅₀ and LC₉₉ values were 0.64 and 8.88 ppm, respectively. The potency in killing Cx. quinquefasciatus and stability of ZEO-AgNPs have made this product a good candidate for the development of novel natural larvicides.

Insecticidal Activity of Local Plants Essential Oils Against Laboratory and Field Strains of Anopheles gambiae s. l. (Diptera: Culicidae) From Burkina Faso

The emergence and intensification of resistance to insecticides in malaria vector populations is the main obstacle to insecticide-based control efforts. The main objective of this study was to evaluate the larvicidal and adulticidal properties of the essential oils (EOs) of Ocimum canum, Hyptis suaveolens, Hyptis spicigera, and Lantana camara on field-collected, pyrethroids-resistant mosquitoes, local laboratory strains, and susceptible 'Kisumu' strain of Anopheles gambiae (Meigen) (Diptera: Culicidae) populations. Larvae and adults of these mosquitoes were challenged against four EOs. The mortality rates of larvae and adults were assessed 24 h after exposure to the EOs. Species identifications and detection of the L1014F and L1014S kdr mutations and the 1575Y super-kdr mutation were carried out using polymerase chain reaction on the pyrethroid-resistant mosquitoes from the field. EO compositions were analyzed by gas chromatography and mass spectrometry. Monoterpene hydrocarbons were the major components of H. suaveolens and H. spicigera EOs (49.8%) and (69.6%), respectively, whereas oxygenated monoterpenes (68.7%) were predominant in the O. canum EO. For L. camara, the component yields were variable, but it was the most effective EO against all strains. The LC50 values for the larvae were 7.73 and 25.63 ppm for the susceptible 'Kisumu' and resistant field strains, respectively. The LC50 for adults was 0.24% for the susceptible strain and 1.98% for the resistant strain. Molecular analysis confirmed the presence of L1014F and N1575Y mutations in resistant Anopheles arabiensis and Anopheles coluzzii mosquitoes from the field. Our results highlighted the potential of the EOs of local plants as insecticides against resistant and susceptible strains of An. gambiae populations.

Comparative multi-omics analysis reveals diverse latex-based defense strategies against pests among latex-producing organs of the fig tree (Ficus carica)

Latexes in immature fruit, young petioles and lignified trunks of fig trees protect the plant using toxic proteins and metabolites in various organ-dependent ways. Latexes from plants contain high amounts of toxic proteins and metabolites, which attack microbes and herbivores after exudation at pest-induced wound sites. The protein and metabolite constituents of latexes are highly variable, depending on the plant species and organ. To determine the diversity of latex-based defense strategies in fig tree (Ficus carica) organs, we conducted comparative proteomic, transcriptomic and metabolomic analyses on latexes isolated from immature fruit, young petioles and lignified trunks of F. carica after constructing a unigene sequence library using RNA-seq data. Trypsin inhibitors were the most abundant proteins in petiole latex, while cysteine proteases ("ficins") were the most abundant in immature fruit and trunk latexes. Galloylglycerol, a possible defense-related metabolite, appeared to be highly accumulated in all three latexes. The expression levels of pathogenesis-related proteins were highest in the latex of trunk, suggesting that this latex had adapted a defensive role against microbe attacks. Although young petioles and immature fruit are both unlignified soft organs, and potential food for herbivorous insects, unigenes for the sesquiterpenoid pathway, which likely produces defense-associated volatiles, and the phenylpropanoid pathway, which produces toxic furanocoumarins, were expressed less in immature fruit latex. This difference may indicate that while petioles and fruit protect the plant from attack by herbivores, the fruit must also attract insect pollinators at younger stages and animals after ripening. We also suggest possible candidate transcription factors and signal transduction proteins that are involved in the differential expression of the unigenes.

Isolation of eudesmane type sesquiterpene ketone from Prangos heyniae H.Duman & M.F.Watson essential oil and mosquitocidal activity of the essential oils

In the present work, an endemic species Prangos heyniae collected in four locations from Turkey was subjected to hydrodistillation in Clevenger type apparatus to obtain the essential oils (EO1-4). The gas-chromatography/mass spectrometry (GC/MS) and gas-chromatography-flame ionization detector (GC/FID) analyses showed that the EOs were rich in sesquiterpenes, germacrene D (10.3-12.1%), β-bisabolene (14.4%), kessane (26.9%), germacrene B (8.2%), elemol (3.4-46.9%), β-bisabolenal (1.4-70.7%), β-bisabolenol (8.4%) and an eudesmane type sesquiterpene (1) (16.1%) with [M+218]. This unidentified compound (1) was isolated in a rapid one-step manner with >95.0% purity using Preparative Capillary Gas Chromatography (PCGC) with an HP Innowax column connected to a Preparative Fraction Collector (PFC) system. Structure determination was accomplished from 1D- and 2D-NMR spectroscopic data which determined a new eudesmane type sesquiterpene, 3,7(11)-eudesmadien-2-one (1). Using a biting deterrent bioassay, the mean proportion not biting (PNB) values of the P. heyniae EO1-4 were 0.88 for EO1 and 0.80 for EO2 which were similar to the positive control DEET (N,N-diethyl-3-methylbenzamide). The EO3 and EO4 had lower PNB values of 0.64 and 0.44, respectively. P. heyniae EO1-4 showed good larvicidal activity at 125 and 62.5 ppm whereas EO1-3 were slightly less effective at the dose of 31.25 ppm and EO4 was not active at 31.25 ppm against 1st instar Aedes aegypti.

Trends in insect repellent formulations: A review

The use of natural and synthetic repellents, marketed in different pharmaceutical forms, is growing in the world due to the emerging vector-borne viral diseases as Dengue, Zika, Chikungunya, Yellow Fever and Malaria. The choice of the ideal formulation will depend on a series of factors to be analyzed: type of repellent active (natural or synthetic), pharmaceutical forms (spray, lotion, cream, gel), action time duration (short or long), environment of exposure and the user (adult, pregnant women, children, newborn). The most used repellents are DEET, IR3535 (Ethyl Butylacetylaminopropionate) (EB), Icaridin (Picaridin) and essential oils, each of them presenting advantages and disadvantages. DEET is the oldest and the most powerful repellent available in the market, thus being the reference standard. For this reason, there are many classic formulations available in the market containing the chemical component DEET in spray forms and lotions. However, due to its toxicity, DEET is not recommended for children up to 6 months and pregnant women. DEET has been an option along with other market-shared products as IR3535 and Icaridin (Picaridin), which present less toxicity in their composition. IR3535 is the less toxic and may be prescribed for children over 6 months of age and pregnant women so that they have been the best option because of the lower toxicity levels presented. IR3535 is the one that has the lowest toxicity level among the three options and may be prescribed for children above 6 months of age and pregnant women. Icaridin is as potent as DEET, but less toxic, and has the advantage of having the long-lasting action among the aforementioned repellents. The new formulations have been based on controlled release systems (CRS). The CRSs for repellents comprise polymer micro/nanocapsules, micro/solid lipid nanoparticles, nanoemulsions/microemulsions, liposomes/niosomes, nanostructured hydrogels and cyclodextrins. There are many formulations based on micro and nanocapsules containing DEET and essential oils to increase repellent action time duration and decrease permeation and consequently, systemic toxicity. The development of new formulations for the IR3535 and Icaridin is a research field yet to be explored. The current trend is the use of natural repellent actives such as essential oils, which present low toxicity, do not harm the environment, but present reduced repellent action time due to rapid evaporation after skin application. CRSs have been used as vehicle of natural repellents to improve long-lasting repellent action, reduce skin permeation and systemic effects.

Herbivory by leaf-cutter ants changes the glandular trichomes density and the volatile components in an aromatic plant model

Herbivory can induce several structural and functional alterations in the plant secretory system. Glandular trichomes are the main sites of production of volatile organic compounds (VOCs) with several chemical properties in Lamiaceae species. Ocimum species usually have three morphotypes of glandular trichomes (morphotype I is peltate and has a wide four-celled head; morphotype II is capitate and has a unicellular head; and morphotype III is capitate with a bicellular head) which produce a great amount of terpenes, although other chemical categories of substances are also produced. Despite the abundance of trichomes producing important anti-herbivory components in their leaves, the association between Ocimum species and leaf-cutter ants has been commonly registered in Brazil. We investigated the effect of leaf-cutter ant attack on the density of the glandular trichomes and on the chemistry of the VOCs released from leaves of O. gratissimum. Plants were subjected to Acromyrmex rugosus attack until 90 % of leaves were removed. After 40 days from the leaf-cutter attack, both treatments were sampled. The glandular trichome density was analysed by scanning electron microscopy. The VOCs were extracted utilizing headspace solid-phase microextraction (HS-SPME) technique and analysed by gas chromatography. Generally, the density of glandular trichomes increased in the adaxial leaf surface of the attacked plants. However, we bring novelties on this topic since we analysed the density of each morphotype separately. The morphotype I decreased in the abaxial leaf surface, and increased in the adaxial leaf surface; the morphotype II increased in both leaf surfaces; and the morphotype III decreased in the abaxial leaf surface and remained constant in the adaxial leaf surface of attacked plants. In leaves of attacked plants, the (Z)-β-ocimene increased by 50 %, the α-selinene by 13 % and the germacrene D by 126 %, whereas the eugenol decreased by 70 %. Our data point to a differential response of each glandular morphotype in O. gratissimum and are consistent with the idea of a compartmentalization of functions among the different glandular morphotypes in the plant defence against environmental factors.

Remarkable preservation of terpenoids and record of volatile signalling in plant-animal interactions from Miocene amber

Plants produce and release a large array of volatile organic compounds that play many ecological functions. These volatile plant metabolites serve as pollinator attractants, herbivore and pathogen repellents and protect plants from abiotic stresses. To date, the geological evolution of these organic compounds remains unknown. The preservation potential of these metabolites in the fossil record is very poor due to their low boiling points. Here we report a series of volatile sesquiterpenoids, including δ-elemene, α-copaene, β-elemene, β-caryophyllene, α-humulene, germacrene D, δ-cadiene and spathunenol, from early Miocene (~17 million year) amber from eastern India. The survival of these unaltered bioterpenoids can be attributed to the existence of extraordinary taphonomic conditions conducive to the preservation of volatile biomolecules through deep time. Furthermore, the occurrence of these volatiles in the early Miocene amber suggests that the plants from this period had evolved metabolic pathways to synthesize these organic molecules to play an active role in forest ecology, especially in plant-animal interactions.

Cytotoxic Essential Oils from Eryngium campestre and Eryngium amethystinum (Apiaceae) Growing in Central Italy

Eryngium campestre and E. amethystinum are thorny herbs belonging to the Apiaceae family and spontaneously growing in stony pastures and dry meadows, preferentially on calcareous substrates. In the Mediterranean countries, these plants have been used as a food or traditional remedies to treat various ailments. In the present work, we have analyzed the chemical composition of the essential oils distilled from the aerial parts by GC-FID and GC/MS, and evaluated their cytotoxic effects on a panel of human cancer cells, namely A375 (human malignant melanoma), MDA-MB 231 cells (human breast adenocarcinoma), and HCT116 cells (human colon carcinoma), by the MTT assay. Furthermore, the Eryngium essential oils were evaluated for antioxidant and acetylcholinesterase (AChE) activities. The two essential oils were rich in sesquiterpene hydrocarbons, with germacrene D as the major compound, accompanied by allo-aromadendrene, β-elemene, spathulenol, and ledol. They turned out to be highly cytotoxic on the tumor cells, with IC₅₀ values (1.65 - 5.32 and 1.57 - 2.99 μg/ml for E. amethystinum and E. campestre, respectively) comparable or close to those of the anticancer drug cisplatin. The E. amethystinum essential oil exhibited a moderate antioxidant activity, whereas that of E. campestre a weak AChE inhibition.

Lantana montevidensis Essential Oil: Chemical Composition and Mosquito Repellent Activity against Aedes aegypti

The essential oil (EO) of Lantana montevidensis (Spreng.) Briq. (L. sellowiana Link & Otto) was investigated for its chemical composition and mosquito repellent activity. The essential oil obtained by hydrodistillation of aerial plant parts was analyzed by GC-FID and GC-MS. The major constituents were β-elemene (22.0%), β-caryophyllene (20.1%), and germacrene D (9.4%). Sesquiterpene hydrocarbons were present in considerable quantities (78.9%) in the L. montevidensis EO, followed by oxygenated sesquiterpenes (8.9%), monoterpene hydrocarbons (7.7%), oxygenated monoterpenes (1.9%), diterpenes (1.2%) and other compounds (0.2%). The oil of L. montevidensis was repellent with a minimum effective dosage (MED) of 0.021 ± 0.013 mg/cm2 as compared with that of the positive control N,N-diethyl-3-methylbenzamide (DEET) with a MED of 0.006 ± 0.001 mg/cm2) against Aedes aegypti L. The major compound β-elemene was tested individually for its repellency and had a MED value of 0.23 ± 0.14 mg/cm2 (DEET was 0.008 ± 0.001 mg/cm2). This is the first report on the repellent activity of L. montevidensis EO and β-elemene using human-based in vivo assays against Ae. aegypti.

Variability, toxicity, and antioxidant activity of Eupatorium cannabinum (hemp agrimony) essential oils

CONTENT

Eupatorium cannabinum L. (Asteraceae) is as a potential source of biologically active compounds. The plant is used in traditional medicine for the treatment of diarrhea and livers diseases.

OBJECTIVE

The present study provides investigation on pharmacological properties (antioxidant and toxic activities) of essential oils of E. cannabinum, collected from 11 wild populations in Lithuania.

MATERIALS AND METHODS

Twenty-two hemp agrimony essential oil samples were prepared by hydrodistillation according to the European Pharmacopoeia, and their chemical composition was determined by GC-FID and GC-MS. Compositional data were subjected to principal components analysis (PCA). Instead of conventional spectrophotometric methods, cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were applied to determine antioxidant activity of hemp agrimony essential oils. Meanwhile, toxicity of the oils was determined using brine shrimp (Artemia sp.) assay.

RESULTS

Chemical profiles of E. cannabinum oils were described according to the first predominant components: germacrene D (≤22.0%), neryl acetate (≤20.0%), spathulenol (≤27.2%), and α-terpinene (11.5%). For the first time, α-zingiberene (≤7.8%) was found to be among three major constituents (as the second one) for hemp agrimony oils. SWV measurements revealed that oxidation potentials of compounds present in the oils are lower (below 0.1 V) compared with that of well-known antioxidant quercetin (0.15 V). Toxicity tests evaluated that hemp agrimony oils containing predominant amounts of germacrene D and neryl acetate were notably toxic (LC50 value 16.3-22.0 μg/mL).

CONCLUSION

The study provided some new data concerning chemical composition and pharmaceutical properties of E. cannabinum essential oils.

Effect of confertifolin from Polygonum hydropiper L. against dengue vector mosquitoes Aedes aegypti L

The essential oil from the leaves of Polygonum hydropiper L. (Polygonaceae) was tested against Aedes aegypti L. The LC50 values were 190.72 and 234.37 ppm against second and fourth instar larvae of A. aegypti, respectively. Confertifolin (6,6,9a-trimethy l-4,5,5a,6,7,8,9,9a-octahydronaphtho [1,2-c] furan-3 (1H)-one) was isolated from the essential oil of P. hydropiper leaves using silica gel column chromatography. The LC50 values were 2.90 and 2.96 ppm for second and fourth instar larvae of A. aegypti, respectively. At 10 ppm, the concentration of confertifolin showed ovicidal activity of 100, 100, and 77.6 % on 0-6, 6-12, and 12-18 h old eggs; the repellent activity was 323.2 min; and oviposition deterrent activity was 97.52 % and adulticidal activity was 100 % against A. aegypti. The results were statistically significant at P < 0.05 level. The results suggested that confertifolin as an effective major constituent against A. aegypti and might be considered as a potent source for the production of superior natural mosquitocides.

Repellent Effect and Metabolite Volatile Profile of the Essential Oil of Achillea millefolium Against Aegorhinus nodipennis (Hope) (Coleoptera: Curculionidae)

Aegorhinus nodipennis (Hope) (Coleoptera: Curculionidae) is an important native pest in fruit crops that is mainly found in European hazelnut fields in the south of Chile. We investigated the behavioral response of A. nodipennis to volatile compounds released from the essential oil of Achillea millefolium and its main constituent using olfactometric bioassays. Gas chromatographic and mass spectral analysis of the A. millefolium essential oil revealed the presence of 11 compounds. Monoterpene β-thujone (96.2%) was the main component of the oil. Other compounds identified were α-thujone, 1,8-cineole, p-cymene, and 4-terpineol, all with percentages below 1%. Both A. millefolium essential oil and thujone exhibited a repellent activity against this insect at the higher doses tested (285.7 ng/cm(2)), demonstrating their potential as repellents for this species.

Fumigant Activity of 6 Selected Essential Oil Compounds and Combined Effect of Methyl Salicylate And Trans-Cinnamaldehyde Against Culex pipiens pallens

We studied the knockdown activity and lethal toxicity of 6 essential oil compounds-methyl salicylate, linalool, 2-phenethyl alcohol, eugenol, β-citronellol, and trans-cinnamaldehyde-as fumigants against adult female Culex pipiens pallens in the laboratory. Of the 6 products tested, trans-cinnamaldehyde was the most toxic (LC50  =  0.26 µl/l air, 24 h) with a slow knockdown time (KT95  =  176.5 min at 0.5 µl/l air). Methyl salicylate displayed a lower toxicity (LC50  =  1.17 µl/l air, 24 h) but the fastest knockdown activity (KT95  =  16.8 min) at the sublethal concentration 0.5 µl/l air. Furthermore, the binary mixture of methyl salicylate and trans-cinnamaldehyde exhibited a combined effect of fast knockdown activity and high toxicity against Cx. p. pallens adults, showing potential for development as natural fumigants for mosquito control.

Chemogeography and antimicrobial activity of essential oils from Geijera parviflora and Geijera salicifolia (Rutaceae): two traditional Australian medicinal plants

Essential oils were hydrodistilled from 27 specimens of Geijera parviflora Lindl., (Rutaceae) and nine specimens of Geijera salicifolia Schott, collected over a wide geographic range in New South Wales, Queensland and South Australia. Essential oils were produced by traditional hydrodistillation and characterised using GC-MS. From one specimen a serendipitous discovery was made of bioactive coumarins dissolved in the hydrosol, which were the coumarins isopsoralen, xanthyletine and osthole. These coumarins were not present in the essential oil from that specimen. Using essential oil composition from all specimens, principal component analysis (PCA) demonstrated nine clusters for G. parviflora and three for G. salicifolia. Some clusters are representative of previously described chemotypes and some are reflective of possible chemotypes requiring more comprehensive sampling for confirmation. Thus, another three or four possible chemotypes of G. parviflora and one of G. salicifolia have been tentatively identified. Using micro-titre plate broth dilution assays, antibacterial and antifungal activity of all chemotypes was investigated. In this regard, the 'green oil' chemotype, restricted to G. parviflora, with major components linalool, geijerene/pregeijerene, 1,8-cineol and bicyclogermacrene, demonstrated the highest antimicrobial and free radical scavenging activity. Thus, in the light of traditional use reports of local analgaesia and bioactivity demonstrated in the current study, oils from select chemotypes of G. parviflora may be useful in suitably compounded lotions and creams designed for topical antimicrobial applications and local pain relief. In addition, because major components are known for insecticidal activities, such lotions may also be useful as topically applied insect repellents.

Plant based products: use and development as repellents against mosquitoes: A review

Global warming and deforestation have resulted in the relocation of many living creatures including insects during the recent years. This has affected the population balance of disease vectors including mosquitoes resulting in outbreaks. Traditionally, mankind has been using plants as means of protection from the mosquitoes which are considered to be environment friendly unlike the synthetic chemicals that cause major risk to human health and the ecosystem. Researchers explored mainly, essential oils and traditional plants using different testing methodologies to find out repellent molecules effective against mosquitoes which is the main focus of this review. Among the promising plant species, Eucalyptus spp., Ocimum spp. and Cymbopogon spp. are the most cited. Data of repellency produced from the bioassay systems is difficult to quantify because of different parameters, testing system and standards of material used against mosquitoes. Mainly, the human forearm based bioassays have been used with different sizes of treatment area in the laboratory and the results have not been tested in the field conditions for residual activity. In addition, effectiveness of essential oils and their protection time can be increased by using vanillin as synergist and formulation techniques like microencapsulation and nanoemulsion. There is a need to develop an alternate in vitro bioassay system that can address the problems of uniformity of the results.

Analysis of chemical constituents and antinociceptive potential of essential oil of Teucrium Stocksianum bioss collected from the North West of Pakistan

BACKGROUND

Medicinal plants are used for the treatment of different diseases in almost all cultures. Teucrium species grow wildly at different geographical locations around the world. Teucrium stocksianum is used in folk medicine for the treatment of diarrhea, cough, jaundice and abdominal pain. Scientific study on Teucrium stocksianum shows that it possesses anthelmintic, cytotoxic and antispasmodic activity. The aim of our present study is to identify the chemical composition and antinociceptive potential of the essential oil extracted from Teucrium stocksianum bioss.

METHOD

Essential oil (EO) from the aerial parts of Teucrium stocksianum were extracted by hydrodistillation process. The qualitative and quantitative composition of essential oil was determined with Gas chromatography/Mass spectrometer. Antinociceptive activity was determined by acetic acid induced writhing method. Percent inhibition of writhes of the test concentration was determined by comparing it with that of control. Tween-80 emulsion 2.5% (5 ml/kg b.w) was used as a control while Diclofenic sodium 50 mg/kg (b.w) was used as a standard drug.

RESULTS

The chromatogram of the essential oil of Teucrium stocksianum shows differences both qualitatively and quantatively from essential oil composition reported in other countries. Hydrodistillation of Teucrium stocksianum yielded 0.4% (v/w), pale yellowish oil on dry basis. A total of 26 chemicals were identified by GC-MS accounting for 90.28% of the oil. The major components of essential oil were δ-cadinene (12.92%), α-pinene (10.3%), myrcene (8.64%), β-caryophyllene (8.23%), germacrene D (5.18%) and limonene (2.36%). Essential oil of Teucrium stocksianum has shown outstanding antinociceptive activity. It has been observed that increase in percent writhe inhibition (PWI) occurred from 20-80 mg/kg (b.w) and maximum writhe inhibition has been noted at a concentration of 80 mg/kg (b.w), but PWI decreased at 160 mg/kg, which may be due to some toxic effect of higher dose. ED50 value for Teucrium stocksianum was calculated as 31.5 ± 1.72415 mg/kg (b.w).

CONCLUSION

Our results indicate that there is a lot of variation in the composition of essential oil of Teucrium stocksianum boiss, which may be due to different climatic and experimental conditions. Secondly, the essential oil possesses strong antinociceptive activity and could be used in analgesic preparations especially for topical use.

Headspace solid-phase microextraction combined with mass spectrometry as a powerful analytical tool for profiling the terpenoid metabolomic pattern of hop-essential oil derived from Saaz variety

Hop (Humulus lupulus L., Cannabaceae family) is prized for its essential oil contents, used in beer production and, more recently, in biological and pharmacological applications. In this work, a method involving headspace solid-phase microextraction and gas chromatography-mass spectrometry was developed and optimized to establish the terpenoid (monoterpenes and sesquiterpenes) metabolomic pattern of hop-essential oil derived from Saaz variety as a mean to explore this matrix as a powerful biological source for newer, more selective, biodegradable and naturally produced antimicrobial and antioxidant compounds. Different parameters affecting terpenoid metabolites extraction by headspace solid-phase microextraction were considered and optimized: type of fiber coatings, extraction temperature, extraction time, ionic strength, and sample agitation. In the optimized method, analytes were extracted for 30 min at 40°C in the sample headspace with a 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane coating fiber. The methodology allowed the identification of a total of 27 terpenoid metabolites, representing 92.5% of the total Saaz hop-essential oil volatile terpenoid composition. The headspace composition was dominated by monoterpenes (56.1%, 13 compounds), sesquiterpenes (34.9%, 10), oxygenated monoterpenes (1.41%, 3), and hemiterpenes (0.04%, 1) some of which can probably contribute to the hop of Saaz variety aroma. Mass spectrometry analysis revealed that the main metabolites are the monoterpene β-myrcene (53.0 ± 1.1% of the total volatile fraction), and the cyclic sesquiterpenes, α-humulene (16.6 ± 0.8%), and β-caryophyllene (14.7 ± 0.4%), which together represent about 80% of the total volatile fraction from the hop-essential oil. These findings suggest that this matrix can be explored as a powerful biosource of terpenoid metabolites.

Antioxidant and repellent activities of the essential oil from Colombian Triphasia trifolia (Burm. f.) P. Wilson

The chemical composition of essential oils isolated from aerial parts of Triphasia trifolia (Burm. f.) P. Wilson was analyzed using hydrodistillation by GC-MS. The main constituents found were β-pinene (64.36%), (+)-sabinene (8.75%), hexadecanoic acid (6.03%), α-limonene (4.24%) and p-cymene (2.73%). The essential oil from T. trifolia shows high antioxidant potential (94.53%), an effect that is comparable with ascorbic acid (96.40%), used as standard. In addition, these oils had high repellent effects on the insect Tribolium castaneum Herbst (99% ± 1) at 0.2 μL/cm(2) after 2 h of exposure.

Functional expression of an orchid fragrance gene in Lactococcus lactis

Vanda Mimi Palmer (VMP), an orchid hybrid of Vanda tesselata and Vanda Tan Chay Yan is a highly scented tropical orchid which blooms all year round. Previous studies revealed that VMP produces a variety of isoprenoid volatiles during daylight. Isoprenoids are well known to contribute significantly to the scent of most fragrant plants. They are a large group of secondary metabolites which may possess valuable characteristics such as flavor, fragrance and toxicity and are produced via two pathways, the mevalonate (MVA) pathway or/and the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. In this study, a sesquiterpene synthase gene denoted VMPSTS, previously isolated from a floral cDNA library of VMP was cloned and expressed in Lactococcus lactis to characterize the functionality of the protein. L. lactis, a food grade bacterium which utilizes the mevalonate pathway for isoprenoid production was found to be a suitable host for the characterization of plant terpene synthases. Through recombinant expression of VMPSTS, it was revealed that VMPSTS produced multiple sesquiterpenes and germacrene D dominates its profile.

Biolarvicidal compound gymnemagenol isolated from leaf extract of miracle fruit plant, Gymnema sylvestre (Retz) Schult against malaria and filariasis vectors

Owing to the fact that the application of synthetic larvicide has envenomed the surroundings as well as non-target organisms, natural products of plant origin with insecticidal properties have been tried as an indigenous method for the control of a variety of insect pests and vectors in the recent past. Insecticides of plant origin have been extensively used on agricultural pests and, to a very limited extent, against insect vectors of public health importance, which deserve careful and thorough screening. The use of plant extracts for insect control has several appealing features as these are generally more biodegradable, less hazardous and a rich storehouse of chemicals of diverse biological activities. Moreover, herbal sources give a lead for discovering new insecticides. Therefore, biologically active plant materials have attracted considerable interest in mosquito control study in recent times. The crude leaf extracts of Gymnema sylvestre (Retz) Schult (Asclepiadaceae) and purified gymnemagenol compound were studied against the early fourth-instar larvae of Anopheles subpictus Grassi and Culex quinquefasciatus Say (Diptera: Culicidae). In the present study, bioassay-guided fractionation of petroleum ether leaf extract of G. sylvestre led to the separation and identification of gymnemagenol as a potential new antiparasitic compound. Phytochemical analysis of G. sylvestre leaves revealed the presence of active constituents such as carbohydrates, saponins, phytosterols, phenols, flavonoids and tannins. However, cardiac glycosides and phlobatannins are absent in the plant extracts. Quantitative analysis results suggested that saponin (5%) was present in a high concentration followed by tannins (1.0%). The 50 g powder was loaded on silica gel column and eluted with chloroform-methanol-water as eluents. From that, 16 mg pure saponin compound was isolated and analysed by thin layer chromatography using chloroform and methanol as the solvent systems. The structure of the purified triterpenoid fraction was established from infrared (IR), ultraviolet (UV), (1)H nuclear magnetic resonance (NMR), (13)C NMR and mass spectral data. The carbon skeleton of the compound was obtained by (13)C NMR spectroscopy. The chemical shift assignments obtained for gymnemagenol from (1)H NMR correspond to the molecular formula C(30)H(50)O(4). The compound was identified as 3β, 16β, 28, 29-tetrahydroxyolean-12-ene (gymnemagenol sapogenin). Parasite larvae were exposed to varying concentrations of purified compound gymnemagenol for 24 h. The results suggested that the larval mortality effects of the compound were 28%, 69%, 100% and 31%, 63%, 100% at 6, 12 and 24 h against A. subpictus and C. quinquefasciatus, respectively. In the present study, the per cent mortality were 100, 86, 67, 36, 21 and 100, 78, 59, 38 and 19 observed in the concentrations of 1,000, 500, 250, 125 and 62.75 ppm against the fourth-instar larvae of A. subpitcus and C. quinquefasciatus, respectively. The purified compound gymnemagenol was tested in concentrations of 80, 40, 20, 10 and 5 ppm, and the per cent mortality were 100, 72, 53, 30 and 15 against A. subpitcus and 100, 89, 61, 42 and 30 against C. quinquefasciatus, respectively. The larvicidal crude leaf extract of G. sylvestre showed the highest mortality in the concentration of 1,000 ppm against the larvae of A. subpictus (LC(50) = 166.28 ppm, r (2) = 0.807) and against the larvae of C. quinquefasciatus (LC(50) = 186.55 ppm, r (2) = 0.884), respectively. The maximum efficacy was observed in gymnemagenol compound with LC(50) and r (2) values against the larvae of A. subpictus (22.99 ppm, 0.922) and against C. quinquefasciatus (15.92 ppm, 0.854), respectively. The control (distilled water) showed nil mortality in the concurrent assay.