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

Exploring the antiviral inhibitory activity of Niloticin against the NS2B/NS3 protease of Dengue virus (DENV2)

Dengue virus (DENV2) is the cause of dengue disease and a worldwide health problem. DENV2 replicates in the host cell using polyproteins such as NS3 protease in conjugation with NS2B cofactor, making NS3 protease a promising antiviral drug-target. This study investigated the efficacy of 'Niloticin' against NS2B/NS3-protease. In silico and in vitro analyses were performed which included interaction of niloticin with NS2B/NS3-protease, protein stability and flexibility, mutation effect, betweenness centrality of residues and analysis of cytotoxicity, protein expression and WNV NS3-protease activity. Similar like acyclovir, niloticin forms strong H-bonds and hydrophobic interactions with residues LEU149, ASN152, LYS74, GLY148 and ALA164. The stability of the niloticin-NS2B/NS3-protease complex was found to be stable compared to the apo NS2B/NS3-protease in structural deviation, PCA, compactness and FEL analysis. The IC50 value of niloticin was 0.14 μM in BHK cells based on in vitro cytotoxicity analysis and showed significant activity at 2.5 μM in a concentration-dependent manner. Western blotting and qRT-PCR analyses showed that niloticin reduced DENV2 protein transcription in a dose-dependent manner. Besides, niloticin confirmed the inhibition of NS3-protease by the SensoLyte 440 WNV protease detection kit. These promising results suggest that niloticin could be an effective antiviral drug against DENV2 and other flaviviruses.

A comprehensive apoptotic assessment of niloticin in cervical cancer cells: a tirucallane-type triterpenoid from Aphanamixis polystachya (Wall.) Parker

Pharmacologically active small organic molecules derived from natural resources are prominent drug candidates due to their inherent structural diversity. Herein, we explored one such bioactive molecule, niloticin, which is a tirucallane-type triterpenoid isolated from the stem barks of Aphanamixis polystachya (Wall.) Parker. After initial screening with other isolated compounds from the same plant, niloticin demonstrated selective cytotoxicity against cervical cancer cells (HeLa) with an IC50 value of 11.64 μM. Whereas the compound exhibited minimal cytotoxicity in normal epithelial cell line MCF-10A, with an IC50 value of 83.31 μM. Subsequently, in silico molecular docking studies of niloticin based on key apoptotic proteins such as p53, Fas, FasL, and TNF β revealed striking binding affinity, reflecting docking scores of -7.2, -7.1, -6.8, and -7.2. Thus, the binding stability was evaluated through molecular dynamic simulation. In a downstream process, the apoptotic capability of niloticin was effectively validated through in vitro fluorimetric assays, encompassing nuclear fragmentation. Additionally, an insightful approach involving surface-enhanced Raman spectroscopy (SERS) re-establishes the occurrence of DNA cleavage during cellular apoptosis. Furthermore, niloticin was observed to induce apoptosis through both intrinsic and extrinsic pathways. This was evidenced by the upregulation of upstream regulatory molecules such as CD40 and TNF, which facilitate the activation of caspase 8. Concurrently, niloticin-induced p53 activation augmented the expression of proapoptotic proteins Bax and Bcl-2 and downregulation of IAPs, leading to the release of cytochrome C and subsequent activation of caspase 9. Therefore, the reflection of mitochondrial-mediated apoptosis is in good agreement with molecular docking studies. Furthermore, the anti-metastatic potential was evidenced by wound area closure and Ki67 expression patterns. This pivotal in vitro assessment confirms the possibility of niloticin being a potent anti-cancer drug candidate, and to the best of our knowledge, this is the first comprehensive anticancer assessment of niloticin in HeLa cells.

Essential oil from Piper tuberculatum Jacq. (Piperaceae) and its majority compound β-caryophyllene: mechanism of larvicidal action against Aedes aegypti (Diptera: Culicidae) and selective toxicity

Synthetic insecticides have been the primary approach in controlling Aedes aegypti; however, their indiscriminate use has led to the development of resistance and toxicity to non-target animals. In contrast, essential oils (EOs) are alternatives for vector control. This study investigated the mechanism of larvicidal action of the EO and β-caryophyllene from Piper tuberculatum against A. aegypti larvae, as well as evaluated the toxicity of both on non-target animals. The EO extracted from P. tuberculatum leaves was majority constituted of β-caryophyllene (54.8%). Both demonstrated larvicidal activity (LC50 of 48.61 and 57.20 ppm, p < 0.05), acetylcholinesterase inhibition (IC50 of 57.78 and 71.97 ppm), and an increase in the production of reactive oxygen and nitrogen species in larvae after exposure to the EO and β-caryophyllene. Furthermore, EO and β-caryophyllene demonstrate no toxicity to non-target animals Toxorhynchites haemorrhoidalis, Anisops bouvieri, and Diplonychus indicus (100% of survival rate), while the insecticide α-cypermethrin was highly toxic (100% of death). The results demonstrate that the EO from P. tuberculatum and β-caryophyllene are important larvicidal agents.

Bioactive Molecules Derived from Plants in Managing Dengue Vector Aedes aegypti (Linn.)

Mosquitoes are the potential vectors of several viral diseases such as filariasis, malaria, dengue, yellow fever, Zika fever and encephalitis in humans as well as other species. Dengue, the most common mosquito-borne disease in humans caused by the dengue virus is transmitted by the vector Ae. aegypti. Fever, chills, nausea and neurological disorders are the frequent symptoms of Zika and dengue. Thanks to various anthropogenic activities such as deforestation, industrialized farming and poor drainage facilities there has been a significant rise in mosquitoes and vector-borne diseases. Control measures such as the destruction of mosquito breeding places, a reduction in global warming, as well as the use of natural and chemical repellents, mainly DEET, picaridin, temephos and IR-3535 have proven to be effective in many instances. Although potent, these chemicals cause swelling, rashes, and eye irritation in adults and children, and are also toxic to the skin and nervous system. Due to their shorter protection period and harmful nature towards non-target organisms, the use of chemical repellents is greatly reduced, and more research and development is taking place in the field of plant-derived repellents, which are found to be selective, biodegradable and harmless to non-target species. Many tribal and rural communities across the world have been using plant-based extracts since ancient times for various traditional and medical purposes, and to ward off mosquitoes and various other insects. In this regard, new species of plants are being identified through ethnobotanical surveys and tested for their repellency against Ae. aegypti. This review aims to provide insight into many such plant extracts, essential oils and their metabolites, which have been tested for their mosquitocidal activity against different life cycle forms of Ae. Aegypti, as well as for their efficacy in controlling mosquitoes.

Docking studies and thiourea-mediated reduced graphene oxide nanosheets' larvicidal efficacy against Culexquinquefasciatus

The larvicidalproperty of graphene oxide (GO) and thiourea-reduced graphene oxide (T-rGO)was assessed against Culexquinquefasciatuslarvae. A simple water-soluble material synthesis method was used. The transformation of graphene into graphene oxide was accomplished in a single step. Under mild conditions, grapheneoxidewasdissolved in water to form a solution. Structure, optical, and microstructural features of the synthesized samples wereevaluatedusing a variety of analytical tools to compare the samples. Both GO and RGO, as well as GO, showed strong larvicidal potential when used against the third instar larvae of the Culexquinquefasciatus mosquito, with LC₅₀and LC₉₀values of 1.71 and 5.17 ppm and 1.89 and 5.00 ppm, respectively. As a result, our study showed that all of the GO and T-rGO under investigation create larvicidal compounds that could be employed to support efforts to control mosquito populations. It also offers an alternative method for producing GO and rGO on a big scale, which may be used in the future for a variety of biomedical applications.The binding efficacy of the active compounds against AChE1 was studied using Auto dock and the results were observed to be highly promising.

Essential oil of Piper purusanum C.DC (Piperaceae) and its main sesquiterpenes: biodefensives against malaria and dengue vectors, without lethal effect on non-target aquatic fauna

The mosquito vectors of the genera Aedes and Anopheles present resistance to several commercial insecticides, which are also toxic to non-predator targets. On the other hand, essential oils are a promising source of insecticides. Thus, in this work, the essential oil from the leaves of Piper purusanum was characterized by gas chromatography-based approaches and evaluated as biodefensive against malaria and dengue vectors. The main compounds of P. purusanum essential oil were β-caryophyllene (57.05%), α-humulene (14.50%), and germacrene D (8.20%). The essential oil inhibited egg hatching (7.6 ± 1.5 to 95.6 ± 4.5%), caused larval death (LC₅₀ from 49.84 to 51.60 ppm), and inhibited the action of acetylcholinesterase (IC₅₀ of 2.29 µg/mL), which can be related to the mechanisms of action. On the other hand, the biological activities of β-caryophyllene, α-humulene, and germacrene D were higher than that of essential oil. In addition, these sesquiterpenes and essential oil did not show a lethal effect on Toxorhynchites splendens, Anisops bouvieri, Gambusia affinis, and Diplonychus indicus (LC₅₀ from 2098.80 to 7707.13 ppm), although D. indicus is more sensitive (SI/PSF from 48.56 to 252.02 ppm) to essential oil, representing a natural alternative against these relevant vectors.

Niloticin inhibits osteoclastogenesis by blocking RANKL-RANK interaction and suppressing the AKT, MAPK, and NF-κB signaling pathways

Dysregulation of osteoclasts or excessive osteoclastogenesis significantly -contributes to the occurrence and development of osteolytic diseases, including osteoporosis, inflammatory bone erosion, and tumor-induced osteolysis. The protein-protein interaction between the receptor activator of nuclear factor (NF)-κB (RANK) and its ligand (RANKL) mediates the differentiation and activation of osteoclasts, making it a key therapeutic target for osteoclastogenesis inhibition. However, very few natural compounds exerting anti-osteoclastogenesis activity by inhibiting the RANKL-RANK interaction have been found. Niloticin is a natural tetracyclic triterpenoid compound with anti-viral, antioxidative, and mosquitocidal activities. However, its role in osteoclastogenesis remains unknown. The present study found that niloticin directly binds to RANK with an equilibrium dissociation constant of 5.8 μM, blocking RANKL-RANK interaction, thereby inhibiting RANKL-induced AKT, MAPK (p38, JNK, and ERK1/2), and NF-κB (IKKα/β, IκBα, and p65) pathways activation, and reducing the expression of key osteoclast differentiation-related regulatory factors (NFATc1, c-Fos, TRAP, c-Src, β3-Integrin, and cathepsin K) in osteoclast precursors, ultimately negatively regulating osteoclastogenesis. These findings suggest that niloticin could serve as a novel osteoclastogenesis inhibitor and might have beneficial effects on bone health.

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.

Bio-efficacy of Soil Actinomycetes and an Isolated Molecule 1,2-Benzenedicarboxylic Acid from Nonomuraea sp. Against Culex quinquefasciatus Say and Aedes aegypti L. Mosquitoes (Diptera: Culicidae)

Vector-borne diseases such as filariasis and dengue that contribute significantly to disease burden, death, poverty, and social frailty are still a major public healthcare problem worldwide. Currently, synthetic chemicals have been used in mosquito control programs. However, repeated use of chemical insecticides causes environmental pollution and harmful effects on non-target organisms. Therefore, alternative ecofriendly sources from biological source are urgently needed to manage mosquitoes. In this respect, the present study was aimed to evaluate mosquito larvicidal and pupicidal activities of 22 crude extracts of soil actinomycetes on Culex quinquefasciatus and Aedes aegypti and to identify the active molecule. Briefly, the crude ethyl acetate extract and fractions were tested at 62.5, 125, 250, and 500 ppm and 2.5, 5.0, 7.5, and 10.0 ppm concentrations on larval and pupal stages of Cx. quinquefasciatus and Ae. aegypti. The larval and pupal mortality was assessed after 24 h of treatment. Among the 22 isolates screened, Nonomuraea sp. VAS-16 exhibited significant larvicidal and pupicidal activities against the tested mosquito species. Among the 18 fractions screened, fraction-6 showed strong larvicidal and pupicidal activities with the LC₅₀ and LC₉₀ values of 9.1, 18.7, 9.82, and 22.85 ppm against the larvae and LC₅₀ and LC₉₀ values of 10.5, 23.1, 12.3, and 24.13 ppm against the pupae of Cx. quinquefasciatus and Ae. aegypti, respectively. Fascinatingly, the isolated compound 1,2-benzenedicarboxylic acid from fraction-6 at 0.5, 1.0, 1.5, and 2.0 ppm concentration recorded lower LC₅₀ and LC₉₀ values of 4.27, 14.90, 4.67, and 11.90 ppm against the larvae and LC₅₀ and LC₉₀ values of 4.58, 12.06, 5.36, and 13.07 ppm against the pupae of Cx. quinquefasciatus and Ae. aegypti, respectively. On the other hand, the compound recorded less ovicidal activity of 11.0% and 10.3% at 2 ppm against the eggs of Cx. quinquefasciatus and Ae. aegypti, respectively. The present study clearly shows that the crude extract and the compound from Nonomuraea sp. VAS-16 can be used as an effective biopesticide in integrated mosquito management program.

Synthesis, molecular docking and mosquitocidal efficacy of lawsone and its derivatives against the dengue vector Aedes aegypti L. (Diptera: Culicidae)

BACKGROUND

Aedes aegypti is the primary dengue vector, a significant public health problem in many countries. Controlling the growth of Ae. aegypti is the biggest challenge in the mosquito control program, and there is a need for finding bioactive molecules to control Ae. aegypti in order to prevent dengue virus transmission.

OBJECTIVE

To assess the mosquitocidal property of lawsone and its 3-methyl-4H-chromen-3-yl-1-phenylbenzo[6,7]chromeno[2,3,c]pyrazole-dione derivatives (6a-6h) against various life stages of Ae. aegypti. Besides, to study the mode of action of the active compound by molecular docking and histopathological analysis.

METHODS

All derivatives were synthesized from the reaction between 2-hydroxy-1,4-naphthoquinone, chromene-3-carbaldehyde, and 1-phenyl-3-methyl-pyrazol-5-one by using one pot sequential multicomponent reaction. The mosquito life stages were subjected to diverse concentrations ranging from 1.25, 2.5, 5.0, and 10 ppm for lawsone and its derivatives. The structure of all synthesized compounds was characterized by spectroscopic analysis. Docking analysis was performed using autodock tools. Midgut sections of Ae. aegypti larvae were analyzed for histopathological effects.

RESULTS

Among the nine compounds screened, derivative 6e showed the highest mortality on Ae. aegypti life stages. The analyzed LC50 and LC90 results of derivative 6e were 3.01, 5.87 ppm, and 3.41, 6.28 ppm on larvae and pupae of Ae. aegypti, respectively. In the ovicidal assay, the derivative 6e recorded 47.2% egg mortality after 96-hour post-exposure to 10 ppm concentration. In molecular docking analysis, the derivative 6e confirmed strong binding interaction (-9.09 kcal/mol and -10.17 kcal/mol) with VAL 60 and HIS 62 of acetylcholinesterase 1 (AChE1) model and LYS 255, LYS 263 of kynurenine aminotransferase of Ae. aegypti, respectively. The histopathological results showed that the derivative 6e affected the columnar epithelial cells (CC) and peritrophic membrane (pM).

CONCLUSION

The derivative 6e is highly effective in the life stages of Ae. aegypti mosquito and it could be used in the integrated mosquito management programme.

Larvicidal and ovicidal activities of phenyl acetic acid isolated from Streptomyces collinus against Culex quinquefasciatus Say and Aedes aegypti L. (Diptera: Culicidae)

The bio-efficacy of crude ethyl acetate extract, fractions and a compound phenyl acetic acid from the ethyl acetate extract of Streptomyces collinus was evaluated on Culex quinquefasciatus Say and Aedes aegypti L. mosquitoes (Diptera: Culicidae). The larvae were exposed to concentrations of 2.5, 5.0, 7.5 and 10.0 ppm for fractions and 0.5, 1.0, 1.5 and 2.0 ppm for compound. After 24 h, the larval mortality was assessed and the LC₅₀ and LC₉₀ values were calculated. Similarly, per cent ovicidal activity was calculated for eggs after 120 h post treatment for phenyl acetic acid. Among the eleven fractions screened, fraction 7 from the ethyl acetate extract of Streptomyces collinus exhibited good larvicidal activity against both mosquito species. The LC₅₀ and LC₉₀ values of fraction 7 were 4.42, 6.23 ppm against Cx. quinquefasciatus larvae and 5.13, 14.51 ppm against Ae. aegypti larvae, respectively. Further, the isolated compound, phenyl acetic acid from fraction 7 recorded 100% larvicidal activity at 2 ppm concentration with LC₅₀ and LC₉₀ values of 2.07, 4.87 ppm on Cx. quinquefasciatus larvae and 3.81, 9.87 ppm on Ae. aegypti larvae, respectively. Phenyl acetic acid presented 50.3% and 42.0% ovicidal activity against Cx. quinquefasciatus and Ae. aegypti eggs at 2 ppm concentration after 120 h post treatment. The compound, phenyl acetic acid could be used in mosquito control programme.

Ovicidal, pupicidal, adulticidal, and repellent activity of Helicteres velutina K. Schum against Aedes aegypti L. (Diptera: Culicidae)

Aedes aegypti is a vector of emerging and neglected diseases, such as dengue, chikungunya, and Zika. Helicteres velutina, known as "pitó" in Brazil, is traditionally used as an insect repellent, and several studies have demonstrated its larvicidal activity. The aim of this study was to investigate this species and evaluate its potential ovicidal, pupicidal, adulticidal, and repellent activity. The viability of the eggs was evaluated using different concentrations of the test substances for 25 days. The hexane fraction killed 72.7% of the eggs, while dichloromethane killed 67.7%. The survival of the pupae and adults was verified after 72 h and 48 h, respectively. The LC₅₀ for the hexane and dichloromethane fractions was 0.12 mg/mL and 8.85 mg/mL for pupae, 8.01 mg/mL and 0.74 mg/mL for adults (tarsal test), and 0.05 mg/mL and 0.23 mg/mL for adults (body test), respectively. Repellency was assessed for 240 min using neonatal Wistar rats on a Y-tube olfactometer. The hexane fraction attracted mosquitoes to the test chamber, while the dichloromethane fraction had a repellent action. The 7,4'-di-O-methyl-8-O-sulfate flavone provides greater repellency, and this finding is similar to the results of the in silico studies that have shown the potential of this substance against adult mosquitoes. This suggests that 7,4'-di-O-methyl-8-O-sulfate flavone may be one of the substances present in the extract from aerial parts of H. velutina that is responsible for the repellent activity mentioned in traditional medicine. These findings provide a better understanding of the insecticidal and repellent activity of the extract, fraction, and compounds isolated from H. velutina against Ae. aegypti, thereby revealing its potential in the development of a more effective botanical insecticide.

Plant Natural Products for the Control of Aedes aegypti: The Main Vector of Important Arboviruses

The mosquito species Aedes aegypti is one of the main vectors of arboviruses, including dengue, Zika and chikungunya. Considering the deficiency or absence of vaccines to prevent these diseases, vector control remains an important strategy. The use of plant natural product-based insecticides constitutes an alternative to chemical insecticides as they are degraded more easily and are less harmful to the environment, not to mention their lower toxicity to non-target insects. This review details plant species and their secondary metabolites that have demonstrated insecticidal properties (ovicidal, larvicidal, pupicidal, adulticidal, repellent and ovipositional effects) against the mosquito, together with their mechanisms of action. In particular, essential oils and some of their chemical constituents such as terpenoids and phenylpropanoids offer distinct advantages. Thiophenes, amides and alkaloids also possess high larvicidal and adulticidal activities, adding to the wealth of plant natural products with potential in vector control applications.

Insights on the Larvicidal Mechanism of Action of Fractions and Compounds from Aerial Parts of Helicteres velutina K. Schum against Aedes aegypti L

Viral diseases transmitted by the female Aedes aegypti L. are considered a major public health problem. The aerial parts of Helicteres velutina K. Schum (Sterculiaceae) have demonstrated potential insecticidal and larvicidal activity against this vector. The objective of this research was to investigate the mechanisms of action involved in the larvicidal activity of this species. The cytotoxicity activity of H. velutina fractions and compounds of crude ethanolic extract of the aerial parts of this species was assessed by using fluorescence microscopy and propidium iodide staining. In addition, the production of nitric oxide (NO) and hemocyte recruitment were checked after different periods of exposure. The fluorescence microscopy revealed an increasing in larvae cell necrosis for the dichloromethane fraction, 7,4′-di-O-methyl-8-O-sulphate flavone and hexane fraction (15.4, 11.0, and 7.0%, respectively). The tiliroside did not show necrotic cells, which showed the same result as that seen in the negative control. The NO concentration in hemolymph after 24 h exposure was significantly greater for the dichloromethane fraction and the 7,4′-di-O-methyl-8-O-sulphate flavone (123.8 and 56.2 µM, respectively) when compared to the hexane fraction and tiliroside (10.8 and 8.3 µM, respectively). The presence of plasmocytes only in the dichloromethane fraction and 7,4′-di-O-methyl-8-O-sulphate flavone treatments suggest that these would be the hemocytes responsible for the highest NO production, acting as a defense agent. Our results showed that the larvicidal activity developed by H. velutina compounds is related to its hemocyte necrotizing activity and alteration in NO production.

Enzymology, Histological and Ultrastructural Effects of Ar-Turmerone on Culex pipiens pallens Larvae

Our previous article demonstrated that ar-turmerone ((6S)-2-methyl-6-(4-methylphenyl)-2-hepten-4-one) extracted from Curcuma longa L. has a significant larvicidal activity against the fourth instar larvae of Culex pipiens pallens. To reveal the effects of ar-turmerone on C. pipiens pallens larvae, light microscopy and transmission electron microscopy were used to observe the histological and ultrastructure changes in muscle and digestive tissues of fourth instar larvae. It was also revealed by detecting the activity of the acetylcholinesterase (AChE) enzyme and three detoxifying enzymes, including carboxylesterase (CarE), glutathione-S-transferase (GST) and Cytochrome P450 monooxidases (P450). The observation under the light microscope showed that the larvae displayed a disruption of myofibril in ventral muscle cells, the disappearance of nucleolus in the malpighian tubule cells, and the exfoliation of the brush border in midgut epithelial cells, 24 h after treatment. The observation under the transmission electron microscope displayed disorganized Z-lines in the ventral muscle cells, and dissolved membrane of mitochondria, nuclear and endoplasmic reticulum in abdominal cells. The enzymatic activity results showed that ar-turmerone significantly increased the level of detoxifying enzymes, while the activity of AChE was not obviously affected. All the results suggest that the larvicidal mechanism of ar-turmerone is estimated to be stomach poison and the active sites might be the muscle and digestive tissues, and the mode of action of ar-turmerone may be unrelated to AChE.

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.

Larvicidal Compounds Extracted from Helicteres velutina K. Schum (Sterculiaceae) Evaluated against Aedes aegypti L

Helicteres velutina K. Schum (Sterculiaceae), a member of Malvaceae sensu lato, is a Brazilian endemic plant that has been used by the indigenous tribe Pankarare as an insect repellent. A previous study has reported the isolation of terpenoids, flavonoids and pheophytins, in addition to the larvicidal activity of crude H. velutina extracts derived from the aerial components (leaves, branches/twigs, and flowers). The present study reports the biomonitoring of the effects of fractions and isolated compounds derived from H. velutina against A. aegypti fourth instar larvae. A crude ethanol extract was submitted to liquid–liquid extraction with hexane, dichloromethane, ethyl acetate and n-butanol to obtain their respective fractions. Larvicidal evaluations of the fractions were performed, and the hexane and dichloromethane fractions exhibited greater activities than the other fractions, with LC₅₀ (50% lethal concentration) values of 3.88 and 5.80 mg/mL, respectively. The phytochemical study of these fractions resulted in the isolation and identification of 17 compounds. The molecules were subjected to a virtual screening protocol, and five molecules presented potential larvicidal activity after analyses of their applicability domains. When molecular docking was analysed, only three of these compounds showed an ability to bind with sterol carrier protein-2 (1PZ4), a protein found in the larval intestine. The compounds tiliroside and 7,4′-di-O-methyl-8-O-sulphate flavone showed in vitro larvicidal activity, with LC₅₀ values of 0.275 mg/mL after 72 h and 0.182 mg/mL after 24 h of exposure, respectively. This is the first study to demonstrate the larvicidal activity of sulphated flavonoids against A. aegypti. Our results showed that the presence of the OSO₃H group attached to C-8 of the flavonoid was crucial to the larvicidal activity. This research supports the traditional use of H. velutina as an alternative insecticide for the control of A. aegypti, which is a vector for severe arboviruses, such as dengue and chikungunya.

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.

Molecular Targets for Components of Essential Oils in the Insect Nervous System-A Review

Essential oils (EOs) are lipophilic secondary metabolites obtained from plants; terpenoids represent the main components of them. A lot of studies showed neurotoxic actions of EOs. In insects, they cause paralysis followed by death. This feature let us consider components of EOs as potential bioinsecticides. The inhibition of acetylcholinesterase (AChE) is the one of the most investigated mechanisms of action in EOs. However, EOs are rather weak inhibitors of AChE. Another proposed mechanism of EO action is a positive allosteric modulation of GABA receptors (GABArs). There are several papers that prove the potentiation of GABA effect on mammalian receptors induced by EOs. In contrast, there is lack of any data concerning the binding of EO components in insects GABArs. In insects, EOs act also via the octopaminergic system. Available data show that EOs can increase the level of both cAMP and calcium in nervous cells. Moreover, some EO components compete with octopamine in binding to its receptor. Electrophysiological experiments performed on Periplaneta americana have shown similarity in the action of EO components and octopamine. This suggests that EOs can modify neuron activity by octopamine receptors. A multitude of potential targets in the insect nervous system makes EO components interesting candidates for bio-insecticides.

Isolation of limonoid compound (Hamisonine) from endophytic fungi Penicillium oxalicum LA-1 (KX622790) of Limonia acidissima L. for its larvicidal efficacy against LF vector, Culex quinquefasciatus (Diptera: Culicidae)

Upon screening for novel and potential biocompounds with larvicidal activities, we successfully isolated hamisonine (HMSN) a limonoid compound from endophytic fungi Penicillium oxalicum LA-1 of Limonia acidissima. The extracted compound structure was elucidated by spectral studies such as UV-vis spectroscopy, thin-layer chromatography, FTIR, LC-ESI-MS, ¹H NMR, and ¹³C NMR upon comparing with the spectral data available in the literature. Further, the isolated HMSN was tested against III and IV instar Culex quinquefasciatus larvae. The outcome of this study clearly emphasize that the extracted compound HMSN possesses a stupendous larvicidal activity in a dose-dependent manner with the LC₅₀ and LC₉₀ values of 1.779 and 7.685 ppm against III instar larvae and 3.031 and 28.498 ppm against IV instar larvae of C. quinquefasciatus, respectively. Interestingly, the histological studies evidently showing the damage of peritrophic membrane and epithelial cells of testing mosquito larvae.

Larvicidal efficacies of plants from Midwestern Brazil: melianodiol from Guarea kunthiana as a potential biopesticide against Aedes aegypti

A total of 36 ethanol extracts from different anatomical parts of 27 plant species (18 families), native to the Pantanal and Cerrado biomes in Midwest Brazil, was assessed for their effect against Aedes aegypti larvae, the vector of dengue, hemorrhagic dengue, Zika and chikungunya fevers. Only the extract obtained from seeds of Guarea kunthiana (Meliaceae) proved active (LC50 = 169.93 μg/mL). A bioassay-guided investigation of this extract led to the isolation and identification of melianodiol, a protolimonoid, as the active constituent (LC50 = 14.44 mg/mL). Meliantriol, which was also obtained from the bioactive fraction, was nevertheless devoid of any larval toxicity, even at the highest concentration tested (LC50 > 100.0 mg/mL). These results indicate that the larvicidal activity of melianodiol stems from the presence of the carbonyl moiety at C-3 in the 21,23-epoxy-21,24,25-trihydroxy-tirucall-7-ene-type skeleton. The structures of both protolimonoids were established on the basis of spectral methods (1H and 13C NMR and MS). This is the first report on the toxicity of melianodiol against Ae. aegypti larvae. Based on the results, melianodiol can be regarded as a potential candidate for use as an ecologically sound biocontrol agent for reducing the larval population of this vector.

A biodegradable device for the controlled release of Piper nigrum (Piperaceae) standardized extract to control Aedes aegypti (Diptera, Culicidae) larvae

INTRODUCTION:

The significant increase in dengue, Zika, and chikungunya and the resistance of the Aedes aegypti mosquito to major insecticides emphasize the importance of studying alternatives to control this vector. The aim of this study was to develop a controlled-release device containing Piper nigrum extract and to study its larvicidal activity against Aedes aegypti.

METHODS:

Piper nigrum extract was produced by maceration, standardized in piperine, and incorporated into cotton threads, which were inserted into hydrogel cylinders manufactured by the extrusion of carrageenan and carob. The piperine content of the extract and thread reservoirs was quantified by chromatography. The release profile from the device was assessed in aqueous medium and the larvicidal and residual activities of the standardized extract as well as of the controlled-release device were examined in Aedes aegypti larvae.

RESULTS

The standardized extract contained 580mg/g of piperine and an LC50 value of 5.35ppm (24h) and the 3 cm thread reservoirs contained 13.83 ± 1.81mg of piperine. The device showed zero-order release of piperine for 16 days. The P. nigrum extract (25ppm) showed maximum residual larvicidal activity for 10 days, decreasing progressively thereafter. The device had a residual larvicidal activity for up to 37 days.

CONCLUSIONS:

The device provided controlled release of Piper nigrum extract with residual activity for 37 days. The device is easy to manufacture and may represent an effective alternative for the control of Aedes aegypti larvae in small water containers.

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.