Efficacy of bioactive compounds from Curcuma aromatica against mosquito larvae

Exploring the chemical characterization and insecticidal activities of Curcuma angustifolia roxb. leaf essential oils against three major stored product insects

Botanical pesticides are safe and widely used in pest management. Curcuma angustifolia belongs to the family Zingiberaceae and is a rhizomatous medicinal herb. Following rhizome harvesting, leaves are discarded as waste. However, they can be effectively utilized by extracting essential oils, which are potential biopesticides. The aim of the study is to evaluate the efficacy of the leaf essential oil of Curcuma angustifolia as a potential biopesticide against three stored grain pests, Lasioderma serricorne, Tribolium castaneum, and Callasobruchus chinensis, by their contact, fumigant, and repellent activities. The leaves yield 0.39 ± 0.02 % of oil by hydrodistillation. GC-MS/MS characterization identified curzerenone (18.37 %), geranyl-p-cymene (17.32 %), α-elemenone (13.59 %), eucalyptol (7.58 %) as the main constituents. When exposed to different concentrations of C. angustifolia oil, the test insect displayed noticeably high repellency rates. It also showed better contact toxicity at 24 h, LC50 = 0.22 mg/cm2 for cigarette beetle, LC50 = 0.64 mg/cm2 for red flour beetle, LC50 = 0.07 mg/cm2 for pulse beetle) and fumigation toxicities (LC50 = 10.8 mg/L air at 24 h, for cigarette, LC50 = 29.5 mg/L air for red flour beetle, LC50 = 7.9 mg/L air for pulse beetle). Additionally, a phytotoxicity study was done on paddy seeds, and the results showed no effect on seed germination or seedling growth. It was evident from this study that C. angustifolia oil from waste leaves can be utilized as a botanical pesticide to manage the adults of these storage pests.

Entomopathogenic Fungi: An Eco-Friendly Synthesis of Sustainable Nanoparticles and Their Nanopesticide Properties

The agricultural industry could undergo significant changes due to the revolutionary potential of nanotechnology. Nanotechnology has a broad range of possible applications and advantages, including insect pest management using treatments based on nanoparticle insecticides. Conventional techniques, such as integrated pest management, are inadequate, and using chemical pesticides has negative consequences. As a result, nanotechnology would provide ecologically beneficial and effective alternatives for insect pest control. Considering the remarkable traits they exhibit, silver nanoparticles (AgNPs) are recognized as potential prospects in agriculture. Due to their efficiency and great biocompatibility, the utilization of biologically synthesized nanosilver in insect pest control has significantly increased nowadays. Silver nanoparticles have been produced using a wide range of microbes and plants, which is considered an environmentally friendly method. However, among all, entomopathogenic fungi (EPF) have the most potential to be used in the biosynthesis of silver nanoparticles with a variety of properties. Therefore, in this review, different ways to get rid of agricultural pests have been discussed, with a focus on the importance and growing popularity of biosynthesized nanosilver, especially silver nanoparticles made from fungi that kill insects. Finally, the review highlights the need for further studies so that the efficiency of bio-nanosilver could be tested for field application and the exact mode of action of silver nanoparticles against pests can be elucidated, which will eventually be a boon to the agricultural industry for putting a check on pest populations.

Mosquito Larvicidal Activity and Cytotoxicity of the Extracts of Aromatic Plants from Malaysia

Despite ongoing control efforts, the mosquito population and diseases vectored by them continue to thrive worldwide, causing major health concerns. There has been growing interest in the use of botanicals as alternatives to insecticides due to their widespread insecticidal properties, biodegradability, and adaptability to ecological conditions. In this study, we investigated the larvicidal activity and cytotoxicity effects of solvent extracts from three aromatic plants-Curcuma longa (turmeric), Ocimum americanum (hoary basil), and Petroselinum crispum (parsley)-against Aedes albopictus. Subsequently, we examined the phytochemical composition of the extracts through gas chromatography-mass spectrometry (GC-MS) analysis. Results revealed that the hexane extracts of O. americanum and P. crispum exhibited the greatest larvicidal activity with the lowest median lethal concentration (LC₅₀) values (<30 µg/mL) at 24 h post-treatment, with the former found to be significantly less toxic towards African monkey kidney (Vero) cells. The GC-MS analysis of the said extract indicated the presence of different classes of metabolites, including phenylpropanoids, very long-chain alkanes, fatty acids and their derivatives, and terpenes, with the most abundant component being methyl eugenol (55.28%), most of which, have been documented for their larvicidal activities. These findings provide valuable insights into the potential use and development of bioinsecticides, particularly from O. americanum.

Euclasta condylotricha flowers essential oils: A new source of juvenile hormones and its larvicidal activity against Anopheles gambiae s.s. (Diptera: Culicidae)

The essential oil (EO) of plants of the Poaceae family has diverse chemical constituents with several biological properties. But, data on the chemical constituents and toxicity are still unavailable for some species belonging to this family, such as Euclasta condylotricha Steud (Eu. condylotricha). In this study, the chemical composition of the EOs of Eu. condylotricha flowers was evaluated by gas chromatography coupled with mass spectrometry (GC-MS). The EOs larvicidal property was assessed against third instar larvae of three Anopheles gambiae laboratory strains (Kisumu, Acerkis and Kiskdr) according to the WHO standard protocol. The percentage yields of the EOs obtained from hydro distillation of Eu. condylotricha flowers varied 0.070 to 0.097%. Gas Chromatography-Mass Spectrometry (GC-MS) applied to the EOs revealed fifty-five (55) chemical constituents, representing 94.95% to 97.78% of the total essential oils. Although different chemical profiles of the dominant terpenes were observed for each sample, EOs were generally dominated by sesquiterpenoids with juvenile hormones as the major compounds. The primary compounds were juvenile hormone C16 (JH III) (35.97-48.72%), Methyl farnesoate 10,11-diol (18.56-28.73%), tau-Cadinol (18.54%), and β-Eudesmene (12.75-13.46%). Eu. condylotricha EOs showed a strong larvicidal activity with LC50 values ranging from 35.21 to 52.34 ppm after 24 hours of exposition. This study showed that Eu. Condylotricha flowers essential oils are potent sources of juvenile hormones that could be a promising tool for developing an eco-friendly malaria vector control strategy.

Environmentally Safe Photodynamic Control of Aedes aegypti Using Sunlight-Activated Synthetic Curcumin: Photodegradation, Aquatic Ecotoxicity, and Field Trial

This study reports curcumin as an efficient photolarvicide against Aedes aegypti larvae under natural light illumination. Larval mortality and pupal formation were monitored daily for 21 days under simulated field conditions. In a sucrose-containing formulation, a lethal time 50 (LT50) of 3 days was found using curcumin at 4.6 mg L-1. This formulation promoted no larval toxicity in the absence of illumination, and sucrose alone did not induce larval phototoxicity. The photodegradation byproducts (intermediates) of curcumin were determined and the photodegradation mechanisms proposed. Intermediates with m/z 194, 278, and 370 were found and characterized using LC-MS. The ecotoxicity of the byproducts on non-target organisms (Daphnia, fish, and green algae) indicates that the intermediates do not exhibit any destructive potential for aquatic organisms. The results of photodegradation and ecotoxicity suggest that curcumin is environmentally safe for non-target organisms and, therefore, can be considered for population control of Ae. aegypti.

Mosquitocidal efficacy of embelin and its derivatives against Aedes aegypti L. and Culex quinquefasciatus Say. (Diptera: Culicidae) and computational analysis of acetylcholinesterase 1 (AChE1) inhibition

Embelin was isolated from the chloroform extract of Embelia ribes (Burm.f.) fruits; its derivative compounds 6-bromoembelin and vilangin were prepared, and they were evaluated for mosquitocidal activities against the third instar larvae and pupae of Aedes aegypti L. and Culex quinquefasciatus Say. (Diptera: Culicidae). The concentrations used were 0.5, 1.0, 1.5, and 2.0 ppm. Embelin recorded LC₅₀ values of 5.79 and 5.54 ppm against the larvae of Ae. aegypti and Cx. quinquefasciatus, respectively. Similarly, the LC₅₀ values of embelin were 10.23 and 6.93 ppm against the pupae of Ae. aegypti and Cx. quinquefasciatus, respectively. Of the two derivatives tested, vilangin showed the highest larvicidal activity with LC₅₀ values of 1.38 and 1.28 ppm against the larvae of Ae. aegypti and Cx. quinquefasciatus, respectively. Similarly, the LC₅₀ values of vilangin were 1.60 and 1.43 ppm against the pupae of Ae. aegypti and Cx. quinquefasciatus, respectively. The LC₅₀ values of 6-bromoembelin were 3.30 and 2.83 ppm against the larvae and 4.40 and 4.30 ppm against the pupae of Ae. aegypti and Cx. quinquefasciatus, respectively. The histopathological results displayed significant damage on cuboidal cells of the midgut (CU) in vilangin treated larvae of Ae. aegypti and Cx. quinquefasciatus at a concentration of 2.0 ppm. Similarly, peritrophic membrane (PM) was completely impaired in vilangin-treated larvae of Cx. quinquefasciatus and midgut content (MC) was very low in vilangin-treated larvae of Cx. quinquefasciatus. In addition, molecular docking and molecular dynamics studies demonstrated the efficacy of vilangin on the inhibition of acetylcholinesterase (AChE1) in Ae. aegypti and Cx. quinquefasciatus. The present results suggest that vilangin could be used to develop a natural active product against mosquito larvae.

Gradual reduction of susceptibility and enhanced detoxifying enzyme activities of laboratory-reared Aedes aegypti under exposure of temephos for 28 generations

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Aedes aegypti mosquitoes were exposed to temephos for 28 generations.

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This exposure led to a 7.83-fold decrease in temephos toxicity.

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With increase in generational time, Ae. aegypti exhibited increased detoxification.

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Increased detoxification correlated with increase in detoxifying enzymes.

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Repeated exposure of Ae. aegypti to temephos could lead to pesticide resistance.

Temephos, an organophosphate insecticide, is widely accepted for the control of Aedes aegypti, vector of infectious diseases such as dengue, chikungunya, yellow fever, and zika. However, there are claims that repeated and indiscriminate use of temephos has resulted in resistance development in exposed mosquito populations. The present study attempts to evaluate the continuous performance of temephos on the Ae. aegypti population, in laboratory conditions, in terms of toxicity and the effect on marker enzymes associated with metabolic resistance. Results of the toxicity bioassay showed that after the initial exposure, toxicity increased till F4 generation by 1.65 fold, and continuous exposure resulted in a 7.83 fold reduction in toxicity at F28 generation. Percent mortality result showed a marked reduction in mortality with the passage of generations while using the same series of concentrations, viz. 2 ppm, which was 100 % lethal at the initial nine generations, could kill only 22.66 % at F28. Resistance to organophosphates is mainly governed by metabolic detoxifying enzyme families of esterases, glutathione-s-transferase, and cytochrome P450. Analysis of these metabolic detoxifying enzymes showed an inverse trend to toxicity (i.e. toxicity increased in early generations as enzyme activity dropped and then dropped as enzyme activity increased). At the initial exposure, enzyme activity decreased in 2–4 generations, however, repeated exposure led to a significant increase in all the metabolic detoxifying enzymes. From the toxicity level as well as marker enzyme bioassay results, it can be inferred that mosquitoes showed increased detoxification in generational time with an increase in enzymes associated with metabolic detoxification. In conclusion, repeated application of temephos led to resistance development in Ae. aegypti which may be associated with the increase in metabolic detoxifying enzyme activities.

Curcumin Derivatives as Potential Mosquito Larvicidal Agents against Two Mosquito Vectors, Culex pipiens and Aedes albopictus

Vector-borne diseases have appeared or re-emerged in many Southern Europe countries making the transmission of infectious diseases by mosquitoes (vectors) one of the greatest worldwide health threats. Larvicides have been used extensively for the control of Aedes (Stegomyia) albopictus (Skuse, 1895) (Diptera: Culicidae) and Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) mosquitoes in urban and semi-urban environments, causing the increasing resistance of mosquitoes to commercial insecticides. In this study, 27 curcuminoids and monocarbonyl curcumin derivatives were synthesised and evaluated as potential larvicidal agents against Cx. pipiens and Ae. albopictus. Most of the compounds were more effective against larvae of both mosquito species. Four of the tested compounds, curcumin, demethoxycurcumin, curcumin-BF2 complex and a monocarbonyl tetramethoxy curcumin derivative exhibited high activity against both species. In Cx. pipiens the recorded LC50 values were 6.0, 9.4, 5.0 and 32.5 ppm, respectively, whereas in Ae. albopictus they exhibited LC50 values of 9.2, 36.0, 5.5 and 23.6 ppm, respectively. No conclusive structure activity relationship was evident from the results and the variety of descriptors values generated in silico provided some insight to this end.

Characterization of Ocimum basilicum synthesized silver nanoparticles and its relative toxicity to some insecticides against tobacco cutworm, Spodoptera litura Feb. (Lepidoptera; Noctuidae)

Tobacco cutworm, Spodoptera litura Feb. (Lepidoptera; Noctuidae) is a notorious cosmopolitan pest of numerous crops. Frequent evolution of insecticide resistance and polyphagous nature favors the survival of this voracious pest. Nanotechnology offers an alternative technique to overcome the limitations of existing pest management strategies. In the present study, the silver nanoparticles were synthesized from Ocimum basilicum leaf extract and UV-spectra at 464.17 nm confirmed their synthesis while crystalline nature of nanoparticles was evaluated by X-rays diffraction (XRD) pattern and scanning electron microscopy (SEM) revealed their octagonal to spherical shape. Insecticidal potential of O. basilicum synthesized silver nanoparticles (ObAgNPs) was evaluated in comparison with some synthetic insecticides owning different mode of actions, including Coragen®, Proclaim®, Tracer® and Talstar® against S. litura. Probit analysis of 2nd, 3rd, 4th and 5th instars of S. litura showed that lethal concentrations (LCs) of tested nanoparticles and pesticides were positively correlated with older instars. All values of LC50, LC90 and LC95 were statistically different from each other with maximum on the 4th instar and minimum on 2nd instar of S. litura. Tukey's HSD test revealed that ObAgNPs caused maximum mortality (21.67-96.67%) in 2nd instar larvae at the rate of 100-1500 mg/L followed by Coragen® (18.33-91.67%), Proclaim® (13.33-78.33%) and Talstar® (13.33-68.33%), while Tracer indicated the lowest larval mortality (11.67-66.67%) at the rate of 60-120 mg/L and a similar trend was assessed for all the successive instars of S. litura. Higher activity of carboxyl esterase and glutathione-s-transferases confirmed the development of insecticide resistance against the synthetic chemicals. Conclusively, ObAgNPs were found to be eco-friendly but the most effective biogenic compounds for the suppression of S. litura population as compared to the selected synthetic chemicals which may be hazardous for the environment as well as human health. This study will assist the pesticide industries to re-standardize the dose rates against Spodoptera litura.

An Insight into the Discovery of Potent Antifilarial Leads Against Lymphatic Filariasis

BACKGROUND AND OBJECTIVES

Lymphatic filariasis is a neglected tropical disease caused by infection with filarial worms that are transmitted through mosquito bites. Globally, 120 million people are infected, with nearly 40 million people disfigured and disabled by complications such as severe swelling of the legs (elephantiasis) or scrotum (hydrocele). Current treatments (ivermectin, diethylcarbamazine) have limited effects on adult parasites and produce side effects; therefore, there is an urgent to search for new antifilarial agents. Numerous studies on the antifilarial activity of pure molecules have been reported accross the recent literature. The present study describes the current standings of potent antifilarial compounds against lymphatic filariasis.

METHODS

A literature search was conducted for naturally occurring and synthetic antifilarial compounds by referencing textbooks and scientific databases (SciFinder, PubMed, Science Direct, Wiley, ACS, SciELO, Google Scholar, and Springer, among others) from their inception until September 2019.

RESULTS

Numerous compounds have been reported to exhibit antifilarial acitivity in adult and microfilariae forms of the parasites responsible for lymphatic filariasis. In silico studies of active antifilarial compounds (ligands) showed molecular interactions over the protein targets (trehalose-6-phosphate phosphatase, thymidylate synthase, among others) of lymphatic filariasis, and supported the in vitro results.

CONCLUSION

With reference to in vitro antifilarial studies, there is evidence that natural and synthetic products can serve as basic scaffolds for the development of antifilarial agents. The optimization of the most potent antifilarial compounds can be further performed, followed by their in vivo studies.

Effect of tiliamosine, a bis, benzylisoquinoline alkaloid isolated from Tiliacora acuminata (Lam.) Hook. f. & Thom on the immature stages of filarial mosquito Culex quinquefasciatus say (Diptera: Culicidae)

The present study was aimed to check the mosquitocidal activity of tiliamosine isolated from Tiliacora acuminata (Lam.) Hook. f. & Thom against immature stages of Culex quinquefasciatus. Eggs and larvae of Cx. quinquefasciatus were exposed to different concentrations of tiliamosine - 0.5, 1.0, 1.5 and 2.0 ppm - prepared using DMSO. The compound tiliamosine showed good larvicidal activity with LC₅₀ and LC₉₀ values of 1.13 and 2.85 ppm respectively, against third-instar larvae of Cx. quinquefasciatus at 24 h. In control, the larvae exhibited normal movement. Tiliamosine exhibited 91% ovicidal activity at 2.0 ppm concentration after 120 h post-treatment. Lowest concentration of tiliamosine (0.5 ppm) showed 19% egg mortality. Histopathology study of the compound-treated larvae showed serious damage on the larval midgut cells. The treated larvae showed restless movement which was different from that of the control larvae. The larvae exhibited malformation in development. The compound tiliamosine was harmless to non-target organisms P. reticulata and Dragon fly nymph at tested concentrations. The compound was highly active and inhibited AChE in a concentration-dependent manner. Computational analysis of the tiliamosine had strong interaction with AChE1 of Cx. quinquefasciatus. This report clearly suggests that the isolated compound can be used as an insecticide to control mosquito population and thus prevent the spread of vector-borne diseases.

Toxicity and possible mechanisms of action of honokiol from Magnolia denudata seeds against four mosquito species

This study was performed to determine the toxicity and possible mechanism of the larvicidal action of honokiol, extracted from Magnolia denudata seeds, and its 10 related compounds against third-instar larvae of insecticide-susceptible Culex pipiens pallens, Aedes aegypti, and Aedes albopictus and Anopheles sinensis resistant to deltamethrin and temephos. Honokiol (LC₅₀, 6.13–7.37 mg/L) was highly effective against larvae of all of the four mosquito species, although the toxicity of the compound was lower than that of the synthetic larvicide temephos. Structure–activity relationship analyses indicated that electron donor and/or bulky groups at the ortho or para positions of the phenol were required for toxicity. Honokiol moderately inhibited acetylcholinesterase and caused a considerable increase in cyclic AMP levels, indicating that it might act on both acetylcholinesterase and octopaminergic receptors. Microscopy analysis clearly indicated that honokiol was mainly targeted to the midgut epithelium and anal gills, resulting in variably dramatic degenerative responses of the midgut through sequential epithelial disorganization. Honokiol did not affect the AeCS1 mRNA expression level in Ae. aegypti larvae, but did enhance expression of the genes encoding vacuolar-type H⁺-ATPase and aquaporin 4, indicating that it may disturb the Na⁺, Cl⁻ and K⁺ co-transport systems. These results demonstrate that honokiol merits further study as a potential larvicide, with a specific target site, and as a lead molecule for the control of mosquito populations.

Finding the bad actor: Challenges in identifying toxic constituents in botanical dietary supplements

Botanical-derived dietary supplements have widespread use in the general population. The complex and variable nature of botanical ingredients and reports of adverse responses have led to concern for negative human health impacts following consumption of these products. Toxicity testing of the vast number of available products, formulations, and combinations is not feasible due to the time and resource intensive nature of comprehensive testing. Methods are needed to assess the safety of a large number of products via more efficient frameworks. Identification of toxicologically-active constituents is one approach being used, with many advantages toward product regulation. Bioassay-guided fractionation (BGF) is the leading approach used to identify biologically-active constituents. Most BGF studies with botanicals focus on identifying pharmacologically-active constituents for drug discovery or botanical efficacy research. Here, we explore BGF in a toxicological context, drawing from both efficacy and poisonous plant research. Limitations of BGF, including loss of mixture activity and bias toward abundant constituents, and recent advancements in the field (e.g., biochemometrics) are discussed from a toxicological perspective. Identification of active constituents will allow better monitoring of market products for known toxicologically-active constituents, as well as surveying human exposure, two important steps to ensuring the safety of botanical dietary supplements.

Biocontrol and non-target effect of fractions and compound isolated from Streptomyces rimosus on the immature stages of filarial vector Culex quinquefasciatus Say (Diptera: Culicidae) and the compound interaction with Acetylcholinesterase (AChE1)

The present study was aimed to check the mosquitocidal activity of intracellular methanol extract fractions and the compound di (2-ethylhexyl) phthalate isolated from Streptomyces rimosus. The isolated compound was also analyzed for its interaction with Acetylcholinesterase (AChE1). The larvae and eggs of Culex quinquefasciatus were exposed to four different concentrations such as 2.5, 5.0, 7.5 and 10 ppm for fractions and 0.5, 1.0, 1.5 and 2.0 ppm for compound. After 24 and 120 h post treatment, the larval mortality and ovicidal activity were recorded. Fractions collected from the intracellular methanol extract were tested for larvicidal activity; among them Fraction 4 was found to be the active fraction. Fraction 4 showed 74% larvicidal activity with LC₅₀ and LC₉₀ values of 6.9 and 17.2 ppm, respectively, in 24 h against the larvae of Cx. quinquefasciatus. Fraction 4 showed 95% ovicidal activity at 10 ppm concentration after 120 h post treatment. The eluted compound di(2-ethylhexyl) phthalate was highly toxic and exhibited promising activity against the eggs of Cx. quinquefasciatus. The compound presented 94% ovicidal activity at 2.0 ppm concentration after 120 h post treatment. The larvae of Cx. quinquefasciatus were exposed to di(2-ethylhexyl) phthalate which showed good activity in a concentration-dependent manner. The compound showed 76% larvicidal activity against the larvae of Cx. quinquefasciatus with LC₅₀ and LC₉₀ values of 1.22 and 3.28 ppm, respectively, at 2 ppm concentration in 24 h. Fraction 4 and the compound were subjected to toxicity study against non-target organism and were found to be nontoxic. The present studies revealed that the treated larvae showed serious damage in the midgut cells. Growth disruption and larval deformities were observed in compound-treated larvae. The compound was highly active and inhibited AChE in a concentration-dependent manner. Computational analysis of the compound had strong interaction with AChE1 of Cx. quinquefasciatus. These results clearly showed that Fraction 4 and the compound isolated from S. rimosus can be used to control the life stages of Cx. quinquefasciatus; it will be a good alternative to synthetic insecticides.

Chemical Constituents and Bioactivities of Several Indonesian Plants Typically Used in Jamu

This article reviews the chemical constituents and bioactivities of several Indonesian plants typically used in Jamu prescriptions in Indonesia. Jamu is Indonesia traditional medicine: it consists of either a single ingredient or a mixture of several medicinal plants. One plant family always used in Jamu is Zingiberaceae (ginger), such as Curcuma domestica/C. longa, C. xanthorrhizae, C. heyneana, C. zedoaria, C. aeruginosa, Zingiber aromaticum, Alpinia galanga. We also report other commonly used plant families such as Justicia gendarussa and Cassia siamea, whose activities have been extensively explored by our department.

Chemical constituents and biological research on plants in the genus Curcuma

Curcuma, a valuable genus in the family Zingiberaceae, includes approximately 110 species. These plants are native to Southeast Asia and are extensively cultivated in India, China, Sri Lanka, Indonesia, Peru, Australia, and the West Indies. The plants have long been used in folk medicine to treat stomach ailments, stimulate digestion, and protect the digestive organs, including the intestines, stomach, and liver. In recent years, substantial progress has been achieved in investigations regarding the chemical and pharmacological properties, as well as in clinical trials of certain Curcuma species. This review comprehensively summarizes the current knowledge on the chemistry and briefly discusses the biological activities of Curcuma species. A total of 720 compounds, including 102 diphenylalkanoids, 19 phenylpropene derivatives, 529 terpenoids, 15 flavonoids, 7 steroids, 3 alkaloids, and 44 compounds of other types isolated or identified from 32 species, have been phytochemically investigated. The biological activities of plant extracts and pure compounds are classified into 15 groups in detail, with emphasis on anti-inflammatory and antitumor activities.

Larvicidal and Pupicidal Activities of Alizarin Isolated from Roots of Rubia cordifolia Against Culex quinquefasciatus Say and Aedes aegypti (L.) (Diptera: Culicidae)

The mosquitocidal activities of different fractions and a compound alizarin from the methanol extract of Rubia cordifolia roots were evaluated on larvae and pupae of Culex quinquefasciatus Say and Aedes aegypti (L.) (Diptera: Culicidae). Larvae and pupae were exposed to concentrations of 2.5, 5.0, 7.5 and 10 ppm for fractions and 0.5, 1.0, 1.5 and 2.0 ppm for compound. After 24 h, the mortality was assessed and the LC50 and LC90 values were estimated for larvae and pupae. Among the 23 fractions screened, fraction 2 from the methanol extract of R. cordifolia showed good mosquitocidal activity against C. quinquefasciatus and A. aegypti. LC50 and LC90 values of fraction 2 were 3.53 and 7.26 ppm for C. quinquefasciatus and 3.86 and 8.28 ppm for A. aegypti larvae, and 3.76 and 7.50 ppm for C. quinquefasciatus and 3.92 and 8.05 ppm for A. aegypti pupae, respectively. Further, the isolated compound alizarin presented good larvicidal and pupicidal activities. LC50 and LC90 values of alizarin for larvae were 0.81 and 3.86 ppm against C. quinquefasciatus and 1.31 and 6.04 ppm for A. aegypti larvae, respectively. Similarly, the LC50 and LC90 values of alizarin for pupae were 1.97 and 4.79 ppm for C. quinquefasciatus and 2.05 and 5.59 ppm for A. aegypti pupae, respectively. The structure of the isolated compound was identified on the basis of spectroscopic analysis and compared with reported spectral data. The results indicated that alizarin could be used as a potential larvicide and pupicide.

Bioefficacy of ecbolin A and ecbolin B isolated from Ecbolium viride (Forsk.) Alston on dengue vector Aedes aegypti L. (Diptera: Culicidae)

Ecbolin A and ecbolin B were isolated from ethyl acetate extract of Ecbolium viride (Forsk.) Alston root and evaluated for larvicidal and growth disturbance activities against Aedes aegypti L. (Diptera: Culicidae). For larvicidal activity, the third instar larvae of A. aegypti were exposed to different concentrations viz., 1.0, 2.5, 5.0 and 10 ppm for each compound. Among the two compounds screened, ecbolin B recorded highest larvicidal activity with LC50 and LC90 values of 0.70 and 1.42 ppm, respectively. In control, the larval behaviour was normal. The active compound ecbolin B was tested for growth disruption activity at sub lethal concentrations viz., 0.5, 1.0 ppm and observed for malformation like larval gut elongation, larval longevity, intermediates, malformed adults, failed adult emergence and compared with methoprene. The results showed significant level of larva-pupa intermediates, pupa-adult intermediates, malformed adult emergence and less adult formation against A. aegypti. The histopathological results revealed a severe damage on the midgut epithelial columnar cells (CC) and cuboidal cells (CU) in ecbolin B treated larvae of A. aegypti. Similarly peritrophic membrane (pM) was also observed to be damaged in the treated larvae. The present results suggest that, ecbolin B could be used as a larvicidal agent against dengue vector A. aegypti.

Effect of niloticin, a protolimonoid isolated from Limonia acidissima L. (Rutaceae) on the immature stages of dengue vector Aedes aegypti L. (Diptera: Culicidae)

The aim of the present study was to evaluate the mosquitocidal activity of fractions and a compound niloticin from the hexane extract of Limonia acidissima L. leaves on eggs, larvae and pupae of Aedes aegypti L. (Diptera: Culicidae). In these bioassays, the eggs, larvae and pupae were exposed to concentrations of 2.5, 5.0, 7.5 and 10.0ppm for fractions and 0.5, 1.0, 1.5 and 2.0ppm for compound. After 24h, the mortality was assessed and the LC50 and LC90 values were calculated for larvae and pupae. Per cent ovicidal activity was calculated for eggs after 120h post treatment. Among the sixteen fractions screened, fraction 8 from the hexane extract of L. acidissima generated good mosquitocidal activity against Ae. aegypti. The LC50 and LC90 values of fraction 8 were 4.11, 8.04ppm against Ae. aegypti larvae and 4.19, 8.10ppm against Ae. aegypti pupae, respectively. Further, the isolated compound, niloticin recorded strong larvicidal and pupicidal activities. The 2ppm concentration of niloticin showed 100% larvicidal and pupicidal activities in 24h. The LC50 and LC90 values of niloticin on Ae. aegypti larvae were 0.44, 1.17ppm and on pupae were 0.62, 1.45ppm, respectively. Niloticin presented 83.2% ovicidal activity at 2ppm concentration after 120h post treatment and niloticin exhibited significant growth disruption and morphological deformities at sub lethal concentrations against Ae. aegypti. The structure of the isolated compound was identified on the basis of single XRD and spectral data ((1)H NMR and (13)C NMR) and compared with literature spectral data. The results indicate that niloticin could be used as a potential natural mosquitocide.

Larvicidal, ovicidal, and oviposition-deterrent activities of four plant extracts against three mosquito species

In mosquito control programs, insecticides of botanical origin have the potential to eliminate eggs, larvae, and adults. So, the larvicidal, ovicidal, and oviposition-deterrent activities of petroleum ether and ethyl acetate extracts of the leaves of Eugenia jambolana, Solidago canadensis, Euodia ridleyi, and Spilanthes mauritiana were assayed against the three vector mosquito species, namely Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus. The larval bioassay was conducted following the World Health Organization method. The maximum larval mortality was found with ethyl acetate extract of S. mauritiana against the larvae of A. stephensi, A. aegypti, and C. quinquefasciatus with LC50 values of 11.51, 28.1, 14.10 ppm, respectively. The mean percent hatchability of the ovicidal activity was observed at 48-h post-treatment. The percent hatchability was found to be inversely proportional to the concentration of the extract and directly proportional to the number of eggs. The flower head extract of S. mauritiana gave 100% mortality followed by E. ridleyi, S. canadensis, and E. jambolana against the eggs of the three mosquito vectors. For oviposition-deterrent effect, out of the five concentrations tested (20, 40, 60, 80, and 100 ppm), the concentration of 100 ppm showed a significant egg laying-deterrent capacity. The oviposition activity index value of E. jambolana, E. ridleyi, S. canadensis, and S. mauritiana against A. aegypti, A. stephensi, C. quinquefasciatus at 100 ppm were -0.71, -0.71, -0.90, -0.93, -0.85, -0.91, -1, -1, -0.71, -0.85, -1, and -1, respectively. These results suggest that the leaf/flower extracts of certain local plants have the potential to be developed as possible eco-friendly means for the control of mosquitoes.

Evaluation of naturally occurring curcuminoids and related compounds against mosquito larvae

The three curcuminoid components commonly isolated from Curcuma longa, curcumin (1), demethoxycurcumin (2), and bis-demethoxycurcumin (3) were separated and isolated from a commercially available turmeric extract product in high purity and sufficient amounts. Three more derivatives of curcumin, the di-O-demethylcurcumin (4), di-O-methylcurcumin (5) and the di-O-acetylcurcumin (6) were also synthesized and characterized. All six compounds were evaluated for their larvicidal effect against the mosquito Culex pipiens. Curcumin (1) exhibited highly potent larvicidal activity with LC(50) value of 19.07mgL(-1). Moreover, di-O-demethylcurcumin (4), was found to be equally active with LC(50) value of 12.42mgL(-1). Based on the LC(90) values of the two compounds, di-O-demethylcurcumin (4) was the most active of all, resulting in an LC(90) value of 29.40mgL(-1), almost half of the LC(90) value 61.63mgL(-1) found for compound 1. The rest of the compounds were inactive at concentrations even as high as 150mgL(-1) indicating a dependence of the larvicidal activity upon the substitution patent and the presence of aromatic hydroxyl and methoxy moieties. These results show for the first time the potential of this valuable natural product regarding its use as vector control agent.

Mosquito larvicidal activity of methyl-p-hydroxybenzoate isolated from the leaves of Vitex trifolia Linn

The vector-borne diseases caused by mosquitoes are one of the major health problems in many countries especially in tropical and sub-tropical countries. The resistance of mosquitoes to synthetic chemicals and environmental toxicity created by the chemicals raised the demand for finding of alternate natural molecules that control mosquito. In the present study, a crystalline compound methyl-p-hydroxybenzoate was isolated from the methanol extract of Vitex trifolia leaves and it was identified by (1)H and (13)C NMR and single crystal X-ray diffractometer. The larvicidal potential of the isolated compound was evaluated against early 4th instar larvae of Culex quinquefasciatus and Aedes aegypti. The compound exhibited 100% larval mortality of both the mosquitoes at 20 ppm with LC(50) values of 5.77 and 4.74 ppm against C. quinquefasciatus and A. aegypti, respectively. The methyl-p-hydroxybenzoate, which is reported for the first time to our best of knowledge from V. trifolia can be better explored for the control of mosquito population.

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.

Oviposition deterrent activity from the ethanolic extract of Pongamia pinnata, Coleus forskohlii, and Datura stramonium leaves against Aedes aegypti and Culex quinquefaciatus

Mosquitoes are responsible for spread of many diseases than any other group of arthropods. Diseases such as malaria, filariasis, dengue hemorrhagic fever (DHF), and chikunguinya are real threat to mankind. In the present study, ethanolic extracts of leaves of Pongamia pinnata, Coleus forskohlii, and Datura stramonium were evaluated for oviposition deterrent activity against Aedes aegypti and Culex quinquefasciatus. The oviposition deterrent tests of ethanolic extract of Pongamia pinnata, Coleus forskohlii, and Datura stramonium leaves reduced egg laying by 97.62%, 77.3%, 100% against Aedes aegypti and 59.10%, 39.22%, 82% against Culex quinquefasciatus at higher concentration (0.1%).

Ethnomedical uses of Zingiberaceous plants of Northeast India

AIM OF THE STUDY

Family Zingiberaceae consists of large number of medicinal plants and is well known for its use in ethnomedicine. The objective of this study is to systematically analyse and document the traditional knowledge regarding the use of Zingiberaceous plants for the treatment of various human ailments from NE India, adding information to the valuation of biodiversity and, to forward suggestions for its sustainable use, conservation and for future pharmacological studies.

MATERIALS AND METHODS

A survey on the utilization of medicinal plants belonging to Zingibereceae of North-eastern states was carried out by interviewing herbalists followed by collecting plant specimens and identifying the specimen. Ethnobotanical information on traditional plants was catalogued through structured questionnaires in consultations with traditional healers.

RESULTS

A total of 34 species were documented belonging to 9 genera of Zingiberaceae for about 25 types of ailments, 67.6% of which were used in curing multiple disorders. Arunachal Pradesh hosts maximum number of Zingiberaceous plant (88%). Rhizomes were found to be the primary plant material as a source for medication and poultices as the predominant mode of preparation. Gastrointestinal conditions (58%) and chest and lungs (41%) related ailments were the main categories for which these plants are used.

CONCLUSIONS

The study establishes Zingiberaceae as a medicinal family since 41% of all the available Zingiberaceous plant species in NE were found to possess medicinal value. Some new use of herbs also appeared in this study for the first time.