Larvicidal activity of isolated compound 5-(2,4-dimethylbenzyl) pyrrolidin-2-one from marine Streptomyces VITSVK5 sp. against Rhipicephalus (Boophilus) microplus, Anopheles stephensi, and Culex tritaeniorhynchus

The aim of the present study was to assess the larvicidal property of marine actinobacterial compound 5-(2,4-dimethylbenzyl) pyrrolidin-2-one (DMBPO) extracted and isolated from Streptomyces VITSVK5 sp. tested against the larvae of Rhipicephalus (Boophilus) microplus Canestrini (Acari: Ixodidae), Anopheles stephensi Liston, and Culex tritaeniorhynchus Giles (Diptera: Culicidae). The isolate bacteria was taxonomically characterized, identified, and designated as Streptomyces VITSVK5 sp. The crude extract was loaded on silica gel column and eluted with chloroform:methanol. The isolated pure compound was analyzed by thin layer chromatography using chloroform and methanol as the solvent system and confirmed by high-performance liquid chromatography. The structure of the purified compound was established from infrared, ultraviolet, ¹H-nuclear magnetic resonance (NMR), ¹³C-NMR, and mass spectral data. The chemical shift assignments obtained for the aliphatic compound from ¹H-NMR corresponding to the molecular formula C₁₃H₁₇NO. Bioassay-guided fractionation led to the isolation of compound which was identified as DMBPO. In the present study, Streptomyces VITSVK5 sp. crude extract and different fractions were tested against the larvae of parasites at the concentration of 1,000 ppm. Those fractions showing 100% mortality in 24 h alone was selected for further column chromatographic separation. The purified compound, C₁₃H₁₇NO, was tested in the concentrations of 500, 250, 125, 62.5, and 31.25 ppm and observed the percent larval mortality of 100, 70, 64, 40, and 28 against R. microplus; 100, 79, 63, 36, and 22 against A. stephensi; and 100, 84, 67, 42, and 27 against C. tritaeniorhynchus, respectively. The crude extract showed parasitic effects after 24 h of exposure at 1,000 ppm, and parasite mortality was observed against the larvae of R. microplus (LC₅₀?=?210.39 ppm, r ²?=?0.873); A. stephensi (LC₅₀?=?169.38 ppm, r ²?=?0.840); and C. tritaeniorhynchus (LC₅₀?=?198.75 ppm, r ²?=?0.887). The maximum efficacy was observed in purified marine actinobacterial compound DMBPO with LC₅₀ and r ² values against the larvae of R. microplus (84.31 ppm, 0.889); A. stephensi (88.97 ppm, 0.817), and C. tritaeniorhynchus (74.95 ppm, 0.781), respectively. The control (distilled water) showed nil mortality in the concurrent assay.     

Mosquito larvicidal properties of silver nanoparticles synthesized using Heliotropium indicum (Boraginaceae) against Aedes aegypti,Anopheles stephensi,and Culex quinquefasciatus (Diptera: Culicidae)

Mosquitoes transmit dreadful diseases to human beings wherein biological control of these vectors using plant-derived molecules would be an alternative to reduce mosquito population. In the present study activity of aqueous leaf extract and silver nanoparticles (AgNPs) synthesized using Helitropium indicum plant leaves against late third instar larvae of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. The range of varying concentrations of synthesized AgNPs (8, 16, 24, 32, and 40 μg/mL) and aqueous leaf extract (30, 60, 90, 120, and 150 μg/mL) were tested against the larvae of Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus. The synthesized AgNPs from H. indicum were highly toxic than crude leaf aqueous extract in three important vector mosquito species. The results were recorded from UV–Vis spectrum, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis, transmission electron microscopy, and histogram. The synthesized AgNPs showed larvicidal effects after 24 h of exposure. Considerable mortality was evident after the treatment of H. indicum for all three important vector mosquitoes. The LC₅₀ and LC₉₀ values of H. indicum aqueous leaf extract appeared to be effective against A. stephensi (LC₅₀, 68.73 μg/mL; LC₉₀, 121.07 μg/mL) followed by A. aegypti (LC₅₀, 72.72 μg/mL; LC₉₀, 126.86 μg/mL) and C. quinquefasciatus (LC₅₀, 78.74 μg/mL; LC₉₀, 134.39 μg/mL). Synthesized AgNPs against the vector mosquitoes of A. stephensi, A. aegypti, and C. quinquefasciatus had the following LC₅₀ and LC₉₀ values: A. stephensi had LC₅₀ and LC₉₀ values of 18.40 and 32.45 μg/mL, A. aegypti had LC₅₀ and LC₉₀ values of 20.10 and 35.97 μg/mL, and C. quinquefasciatus had LC₅₀ and LC₉₀ values of 21.84 and 38.10 μg/mL. No mortality was observed in the control. These results suggest that the leaf aqueous extracts of H. indicum and green synthesis of silver nanoparticles have the potential to be used as an ideal ecofriendly approach for the control of A. stephensi, A. aegypti, and C. quinquefasciatus. This is the first report on the mosquito larvicidal activity of the plant extracts and synthesized nanoparticles.     

Evaluation of leaf aqueous extract and synthesized silver nanoparticles using Nerium oleander against Anopheles stephensi (Diptera: Culicidae)

Green nanoparticle synthesis has been achieved using environmentally acceptable plant extract and ecofriendly reducing and capping agents. The present study was carried out to establish the larvicidal activity of synthesized silver nanoparticles (AgNPs) using leaf extract of Nerium oleander (Apocynaceae) against the first to fourth instar larvae and pupae of malaria vector, Anopheles stephensi (Diptera: Culicidae). Nanoparticles are being used in many commercial applications. It was found that aqueous silver ions can be reduced by the aqueous extract of the plant parts to generate extremely stable silver nanoparticles in water. The results were recorded from UV–Vis spectrum, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy analysis. The production of the AgNPs synthesized using leaf extract of N. oleander was evaluated through a UV–Vis spectrophotometer in a wavelength range of 200 to 700 nm. This revealed a peak at 440 nm in N. oleander leaf extracts, indicating the production of AgNPs. The FTIR spectra of AgNPs exhibited prominent peaks at 509.12 cm^?1 (C–H bend alkenes), 1,077.05 cm^?1 (C–O stretch alcohols), 1,600.63 cm^?1 (N–H bend amines), 2,736.49 and 2,479.04 cm^?1 (O–H stretch carboxylic acids), and 3,415.31 cm^?1 (N–H stretching due to amines group). An SEM micrograph showed 20–35-nm-size aggregates of spherical- and cubic-shaped nanoparticles. EDX showed the complete chemical composition of the synthesized nanoparticles of silver. Larvicidal activity of aqueous leaf extract of N. oleander and synthesized AgNPs was carried out against Anopheles stephensi, and the results showed that the highest larval mortality was found in the synthesized AgNPs against the first to fourth instar larvae and pupae of Anopheles stephensi with the following values: LC₅₀ of instar larvae 20.60, 24.90, 28.22, and 33.99 ppm; LC₉₀ of instar larvae 41.62, 50.33, 57.78, and 68.41 ppm; and LC₅₀ and LC₉₀ of pupae 39.55 and 79.10 ppm, respectively. The aqueous leaf extract exhibited larval toxicity against the first to fourth instar larvae and pupae of Anopheles stephensi with the following values: LC₅₀ of instar larvae 232.90, 273.71, 318.94, and 369.96 ppm; LC₉₀ of instar larvae 455.95, 563.10, 639.86, and 730.30 ppm; and LC₅₀ and LC₉₀ of pupae 426.01 and 805.13 ppm, respectively. The chi-square value was significant at p?<?0.05 level. The possible larvicidal activity may be due to penetration of nanoparticles through a membrane. The results could suggest that the use of plant N. oleander to synthesize silver nanoparticles is a rapid, environmentally safer, and greener approach for mosquito control. This could lead us to a new possibility in vector-control strategy.     

Green synthesis of silver nanoparticles using Sida acuta (Malvaceae) leaf extract against Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti (Diptera: Culicidae)

Mosquitoes act as a vector for most of the life-threatening diseases like malaria, yellow fever, dengue fever, chikungunya fever, filariasis, encephalitis, West Nile Virus infection, etc. Under the Integrated Mosquito Management, emphasis was given on the application of alternative strategies in mosquito control. The continuous application of synthetic insecticides causes development of resistance in vector species, biological magnification of toxic substances through the food chain, and adverse effects on environmental quality and nontarget organisms including human health. Application of active toxic agents from plant extracts as an alternative mosquito control strategy was available from ancient times. These are nontoxic, easily available at affordable prices, biodegradable, and show broad-spectrum target-specific activities against different species of vector mosquitoes. In the present study, the larvicidal activity of silver nanoparticles (AgNPs) synthesized using Sida acuta plant leaf extract against late third instar larvae of Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti was determined. Range of concentrations of synthesized AgNPs (10, 20, 30, 40, and 50 μg/mL) and aqueous leaf extract (50, 100, 150, 200, and 250 μg/mL) were tested against the larvae of C. quinquefasciatus, A. stephensi and A. aegypti. The synthesized AgNPs from S. acuta leaf were highly toxic than crude leaf aqueous extract in three important vector mosquito species. The results were recorded from UV–Vis spectrum, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy analysis. Larvae were exposed to varying concentrations of aqueous crude extract and synthesized AgNPs for 24 h. Considerable mortality was evident after the treatment of S. acuta for all three important vector mosquitoes. The LC₅₀ and LC₉₀ values of S. acuta aqueous leaf extract appeared to be most effective against A. stephensi (LC₅₀, 109.94 μg/mL and LC₉₀, 202.42 μg/mL) followed by A. aegypti LC₅₀ (119.32 μg/mL and LC₉₀, 213.84 μg/mL) and C. quinquefasciatus (LC₅₀, 130.30 μg/mL and LC₉₀, 228.20 μg/mL). Synthesized AgNPs against the vector mosquitoes of A. stephensi, A. aegypti, and C. quinquefasciatus had the following LC₅₀ and LC₉₀ values: A. stephensi had LC₅₀ and LC₉₀ values of 21.92, and 41.07 μg/mL; A. aegypti had LC₅₀ and LC₉₀ values of 23.96, and 44.05 μg/mL; C. quinquefasciatus had LC₅₀ and LC₉₀ values of 26.13 and 47.52 μg/mL. These results suggest that the use of S. acuta synthesized silver nanoparticles can be a rapid, environmentally safer biopesticide which can form a novel approach to develop effective biocides for controlling the target vector mosquitoes. This is the first report on the mosquito larvicidal activity of the plant aqueous extract and synthesized nanoparticles.     

Ovicidal,larvicidal and adulticidal properties of Asparagus racemosus (Willd.) (Family: Asparagaceae) root extracts against filariasis (Culex quinquefasciatus), dengue (Aedes aegypti) and malaria (Anopheles stephensi) vector mosquitoes (Diptera: Culicidae)

Several diseases are associated to the mosquito–human interaction. Mosquitoes are the carriers of severe and well-known illnesses such as malaria, arboviral encephalitis, dengue fever, chikungunya fever, West Nile virus and yellow fever. These diseases produce significant morbidity and mortality in humans and livestock around the world. The present investigation was undertaken to study the ovicidal, larvicidal and adulticidal activities of crude hexane, ethyl acetate, benzene, chloroform and methanol extracts of root of Asparagus racemosus were assayed for their toxicity against three important vector mosquitoes, viz., Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi (Diptera: Culicidae). The mean percent hatchability of the eggs was observed after 48 h post-treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. All the five solvent extracts showed moderate ovicidal activity; however, the methanol extract showed the highest ovicidal activity. The methanol extract of Asparagus racemosus against Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi exerted 100 % mortality (zero hatchability) at 375, 300 and 225 ppm, respectively. Control eggs showed 99–100 % hatchability. The larval mortality was observed after 24 h of exposure. All extracts showed moderate larvicidal effects; however, the highest larval mortality was found in methanol extract of root of Asparagus racemosus against the larvae of Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi with the LC₅₀ and LC₉₀ values were 115.13, 97.71 and 90.97 ppm and 210.96, 179.92, and 168.82 ppm, respectively. The adult mortality was observed after 24 h recovery period. The plant crude extracts showed dose-dependent mortality. At higher concentrations, the adult showed restless movement for some times with abnormal wagging and then died. Among the extracts tested, the highest adulticidal activity was observed in methanol extract against Anopheles stephensi followed by Aedes aegypti and Culex quinquefasciatus with the LD₅₀ and LD₉₀ values were 120.44, 135.60, and 157.71 ppm and 214.65, 248.35, and 290.95 ppm, respectively. No mortality was recorded in the control. The finding of the present investigation revealed that the root extract of Asparagus racemosus possess remarkable ovicidal, larvicidal and adulticidal activity against medically important vector mosquitoes and this is the low cost and ideal eco-friendly approach for the control of mosquitoes. This is the first report on the mosquito ovicidal, larvicidal and adulticidal activities of the reported Asparagus racemosus root.     

Low-cost and eco-friendly green synthesis of silver nanoparticles using Feronia elephantum (Rutaceae) against Culex quinquefasciatus,Anopheles stephensi,and Aedes aegypti (Diptera: Culicidae)

Mosquitoes transmit serious human diseases, causing millions of deaths every year. The use of synthetic insecticides to control vector mosquitoes has caused physiological resistance and adverse environmental effects in addition to high operational cost. Insecticides of synthesized natural products for vector control have been a priority in this area. In the present study, the larvicidal activity of silver nanoparticles (AgNPs) synthesized using Feronia elephantum plant leaf extract against late third-instar larvae of Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus was determined. The range of concentrations of synthesized AgNPs (5, 10, 15, 20, and 25 μg mL^?1) and aqueous leaf extract (25, 50, 75, 100, and 125 μg mL^?1) were tested against the larvae of A. stephensi, A. aegypti, and C. quinquefasciatus. Larvae were exposed to varying concentrations of aqueous crude extract and synthesized AgNPs for 24 h. Considerable mortality was evident after the treatment of F. elephantum for all three important vector mosquitoes. The synthesized AgNPs from F. elephantum were highly toxic than crude leaf aqueous extract to three important vector mosquito species. The results were recorded from UV–visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy analysis (EDX). Synthesized AgNPs against the vector mosquitoes A. stephensi, A. aegypti, and C. quinquefasciatus had the following LC₅₀ and LC₉₀ values: A. stephensi had LC₅₀ and LC₉₀ values of 11.56 and 20.56 μg mL^?1; A. aegypti had LC₅₀ and LC₉₀ values of 13.13 and 23.12 μg mL^?1; and C. quinquefasciatus had LC₅₀ and LC₉₀ values of 14.19 and 24.30 μg mL^?1. No mortality was observed in the control. These results suggest that the green synthesis of silver nanoparticles using F. elephantum has the potential to be used as an ideal eco-friendly approach for the control of A. stephensi, A. aegypti, and C. quinquefasciatus. This is the first report on the mosquito larvicidal activity of the plant extracts and synthesized nanoparticles.     

Bioefficacy of Plumbago zeylanica (Plumbaginaceae) and Cestrum nocturnum (Solanaceae) plant extracts against Aedes aegypti (Diptera: Culicide) and nontarget fish Poecilia reticulata

In a search for natural products that could be used to control the vectors of tropical diseases, extracts of medicinal plants Plumbago zeylanica and Cestrum nocturnum have been tested for larvicidal activity against second, third, and fourth instar larvae of Aedes aegypti. The LC₅₀ values of all the extracts in different solvents of both the plants were less than 50 ppm (15.40–38.50 ppm) against all tested larval instars. Plant extracts also affected the life cycle of A. aegypti by inhibition of pupal development and adult emergence with increasing concentrations. The larvicidal stability of the extracts at five constant temperatures (19°C, 22°C, 25°C, 28°C, and 31°C) evaluated against fourth instar larvae revealed that toxicity of both plant extracts increases with increase in temperature. Toxicity studies carried out against fish species Poecilia reticulata, the most common nontarget organism in the habitats of A. aegypti, showed almost nil to meager toxicity at LC₅₀ and LC₉₀ doses of the plant extracts. The qualitative analysis of crude extracts of P. Zeylanica and C. nocturnum revealed the presence of bioactive phytochemicals with predominance of plumbagin in P. zeylanica and saponins in C. nocturnum. Partially purified plumbagin from P. zeylanica and saponins from C. nocturnum were obtained, and their presence was confirmed by thin-layer chromatography and biochemical tests. The bioassay experiment of partially purified secondary metabolites showed potent mosquito larvicidal activity against the fourth instar larval form. Therefore, this study explored the safer and effective potential of plant extracts against vector responsible for diseases of public health importance.     

Chemical constituents and larvicidal potential of Feronia limonia leaf essential oil against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus

In the present investigation, the leaf essential oil of Feronia limonia was evaluated for chemical constituents and mosquito larvicidal activity against the larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. GC and GC–MS analyses revealed that the essential oil contain 51 compounds. Estragole (34.69 %) and β-pinene(23.59 %) were identified as the major constituents followed by methyl (Z)-caryophyllene (11.05 %), eugenol (6.50 %), linalool (3.97 %), phytol (3.27 %), sabinene (2.41 %) and limonene (2.27 %). Larval mortality was observed after 12 and 24 h of exposure period. The oil showed remarkable larvicidal activity against A. stephensi (LC₅₀?=?38.93 and LC₉₀?=?108.64 ppm (after 12 h); LC₅₀?=?15.03 and LC₉₀?=?36.69 ppm (after 24 h)), A. aegypti (LC₅₀?=?37.60 and LC₉₀?=?104.69 ppm (after 12 h); LC₅₀?=?11.59 and LC₉₀?=?42.95 ppm (after 24 h)) and C. quinquefasciatus (LC₅₀?=?52.08 and LC₉₀?=?124.33 ppm (after 12 h); LC₅₀?=?22.49 and LC₉₀?=?60.90 ppm (after 24 h)). Based on the results, the essential oil of F. limonia can be considered as a new source of larvicide for the control of vector mosquitoes.     

Larvicidal and pupicidal activities of ecbolin A and ecbolin B isolated from Ecbolium viride (Forssk.) Alston against Culex quinquefasciatus Say (Diptera: Culicidae)

The mosquitocidal activity of different fractions and isolated compounds from the ethyl acetate extract of Ecbolium viride root was assessed on larvae and pupae of Culex quinquefasciatus Say (Diptera: Culicidae). The larvae and pupae were exposed to concentrations of 6.125, 12.5, 25 and 50 ppm for fractions and 1, 2.5, 5 and 10 ppm for compound. Among the 12 fractions screened, fraction 6 from the ethyl acetate extract of E. viride was recorded to have the highest larvicidal and pupicidal activities against C. quinquefasciatus. The lethal concentration (LC₅₀ and LC₉₀) values of fraction 6 were 4.26 and 9.0 ppm against C. quinquefasciatus larvae and 6.55 and 12.19 ppm against C. quinquefasciatus pupae, respectively, in 24 h. Fraction 7 was recorded to have moderate activity with LC₅₀ and LC₉₀ values of 11.25 and 25.02 ppm against C. quinquefasciatus larvae and 13.33 and 31.15 ppm against C. quinquefasciatus pupae, respectively, in 24 h. Ecbolin A and ecbolin B were identified from fractions 7 and 6, respectively. The structure of the isolated compounds was identified on the basis of spectral data (¹H NMR and ¹³C NMR) and compared with literature spectral data. Further, the isolated compound, ecbolin B, from fraction 6 was recorded to have strong larvicidal and pupicidal activities than ecbolin A. The LC₅₀ and LC₉₀ values of ecbolin B on C. quinquefasciatus larvae were 1.36 and 2.76 ppm, and on pupae, these were 1.54 and 3.51 ppm, respectively. The present results suggest that ecbolin B could be used as a mosquitocidal agent against C. quinquefasciatus.     

Chemical composition and larvicidal activity of plant extracts from Clausena dentata (Willd) (Rutaceae) against dengue,malaria, and filariasis vectors

Mosquitoes in the larval stage are attractive targets for pesticides because mosquitoes breed in water, and thus, it is easy to deal with them in this habitat. The use of conventional pesticides in the water sources, however, introduces many risks to people and/or the environment. Natural pesticides, especially those derived from plants, are more promising in this aspect. Aromatic plants and their essential oils are very important sources of many compounds that are used in different respects. Insecticides of botanical origin may serve as suitable alternative to chemical insecticides. Acetone, chloroform, ethyl acetate, methanol, and petroleum benzine leaf extracts of Clausena dentata were tested against the fourth instar larvae of Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera: Culicidae). Larval mortality was observed after 24 h of exposure. The highest larval mortality was found in acetone leaf extract, C. quinquefasciatus (LC₅₀?=?0.150278 mg/ml; LC₉₀?=?7.302613 mg/ml), A. aegypti (LC₅₀?=?0.169495 mg/ml; LC₉₀?=?1.10034 mg/ml), and A. stephensi (LC₅₀?=?0.045684 mg/ml; LC90?=?0.045684 mg/ml). GC–MS analysis of plant extracts of acetone solvent revealed 16 compounds, of which the major compounds were benzene,1,2,3-trimethoxy-5-(2-propenyl) (14.97 %), Z,Z-6,28-heptatriactontadien-2-one (6.81 %), 2-allyl-4-methylphenol (28.14 %), 2-allyl-4-methylphenol (17.34 %), and 2,6,10,14,18,22-tetracosahexaene, 2,6,10,15,19,23-hexamethyl (10.35 %). Our result shows acetone leaf extracts of C. dentata have the potential to be used as an ideal eco-friendly approach for mosquito control.     

Larvicidal,ovicidal, and adulticidal efficacy of Erythrina indica (Lam.) (Family: Fabaceae) against Anopheles stephensi,Aedes aegypti,and Culex quinquefasciatus (Diptera: Culicidae)

Mosquitoes are the major vector for the transmission of malaria, dengue fever, yellow fever, filariasis, schistosomiasis, and Japanese encephalitis. Mosquito control is facing a threat because of the emergence of resistance to synthetic insecticides. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. In view of the recently increased interest in developing plant origin insecticides as an alternative to chemical insecticide, this study was undertaken to assess the larvicidal, ovicidal, and adulticidal potential of the crude hexane, benzene, chloroform, ethyl acetate, and methanol solvent extracts from the medicinal plant Erythrina indica against the medically important mosquito vectors, Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus (Diptera: Culicidae). The larval mortality was observed after 24 h of exposure. All extracts showed moderate larvicidal effects; however, the highest larval mortality was found in methanol extract of leaf of E. indica against the larvae of A. stephensi, A. aegypti, and C. quinquefasciatus with the LC₅₀ and LC₉₀ values of 69.43, 75.13, and 91.41 ppm and 125.49, 134.31, and 167.14 ppm, respectively. The mean percent hatchability of the eggs was observed after 48 h post treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. All the five solvent extracts showed moderate ovicidal activity; however, the methanol extract showed the highest ovicidal activity. The methanol extract of E. indica against A. stephensi, A. aegypti, and C. quinquefasciatus exerted 100 % mortality (zero hatchability) at 150, 200, and 250 ppm, respectively. Control eggs showed above 99.3–100 % hatchability. The adult mortality was observed after 24 h recovery period. The plant crude extracts showed dose-dependent mortality. At higher concentrations, the adult showed restless movement for some times with abnormal wagging and then died. Among the extracts tested, the highest adulticidal activity was observed in methanol extract against A. stephensi followed by A. aegypti and C. quinquefasciatus with the LD₅₀ and LD₉₀ values of 88.76, 94.09, and 119.64 ppm and 160.83, 169.01, and 219.77 ppm, respectively. No mortality was recorded in the control. Our data suggest that the crude hexane, benzene, chloroform, ethyl acetate, and methanol solvent extracts of E. indica have the potential to be used as an eco-friendly approach for the control of the A. stephensi, A. aegypti, and C. quinquefasciatus.     

Studies on the impact of biosynthesized silver nanoparticles (AgNPs) in relation to malaria and filariasis vector control against Anopheles stephensi Liston and Culex quinquefasciatus Say (Diptera: Culicidae)

Biosynthesized nanoparticles have been achieved using environmentally acceptable plant extract and eco-friendly reducing and capping agents. The present study was based on assessments of the larvicidal activities to determine the efficacies of synthesized silver nanoparticles (AgNPs) using aqueous leaf extract of Vinca rosea (L.) (Apocynaceae) against the larvae of malaria vector Anopheles stephensi Liston and filariasis vector Culex quinquefasciatus Say (Diptera: Culicidae). Larvae were exposed to varying concentrations of aqueous extract of V. rosea and synthesized AgNPs for 24, 48, and 72 h. AgNPs were rapidly synthesized using the leaf extract of V. rosea, and the formation of nanoparticles was observed within 15 min. The results recorded from UV–Vis spectrum, Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) support the biosynthesis and characterization of AgNPs. The formation of the AgNPs synthesized from the XRD spectrum compared with the Bragg reflections at 2θ?=?29.36, 38.26, 44.51, 63.54, and 77.13° which can be indexed to the (121), (111), (200), (220), and (311) orientations, respectively, confirmed the presence of AgNPs. The FTIR spectra of AgNPs exhibited prominent peaks at the spectra showed sharp and strong absorption band at 3,406.71 to 3,431.90 cm^?1 double in case of NH₂ group of a primary amine (N–H stretch). The presence of the sharp peak at 2,926.54 to 2,925.80 cm^?1 very broad often looks like distorted baseline (O–H carboxylic acids). The band 1,633.26 to 1,625.81 cm^?1 was assigned to C?=?C alkenes, aromatic ring stretching vibration, respectively. SEM analysis of the synthesized AgNPs clearly showed the clustered and irregular shapes, mostly aggregated and having the size of 120 nm. TEM reveals spherical shape of synthesized AgNPs. Particle size analysis revealed that the size of particles ranges from 25 to 47 nm with average size of 34.61 nm. Energy-dispersive X-ray spectroscopy showed the complete chemical composition of the synthesized AgNPs. In larvicidal activity, the results showed that the maximum efficacy was observed in synthesized AgNPs against the fourth instar larvae of A. stephensi (LC₅₀?=?12.47 and 16.84 mg/mL and LC₉₀?=?36.33 and 68.62 mg/mL) on 48 and 72 h of exposure and against C. quinquefasciatus (LC₅₀?=?43.80 mg/mL and LC₉₀?=?120.54 mg/mL) on 72-h exposure, and aqueous extract showed 100 % mortality against A. stephensi and C. quinquefasciatus (LC₅₀?=?78.62 and 55.21 mg/mL and LC₉₀?=?184.85 and 112.72 mg/mL) on 72-h exposure at concentrations of 50 mg/mL, respectively. The AgNPs did not exhibit any noticeable toxicity on Poecilia reticulata after 24, 48, and 72 h of exposure. These results suggest that the synthesized AgNPs have the potential to be used as an ideal eco-friendly approach for the control of the A. stephensi and C. quinquefasciatus. This method is considered as a new approach to control vectors. Therefore, this study provides the first report on the mosquito larvicidal activity of V. rosea synthesized AgNPs against vectors.     

Integration of botanical and bacterial insecticide against Aedes aegypti and Anopheles stephensi

The present study evaluated the Orthosiphon thymiflorus leaf extract and the bacterial insecticide spinosad, testing the first to fourth instars larvae and pupae of two important vector mosquitoes, viz., Aedes aegypti, Anopheles stephensi. The fresh leaves of O. thymiflorus were washed thoroughly in tap water and shade-dried at room temperature (28?±?2 °C) for 5 to 8 days. The air-dried materials were powdered separately using a commercial electrical blender. From the plants, 500 g powder was macerated with 1.5 L organic solvents of petroleum ether sequentially for a period of 72 h each and then filtered. The larval and pupal mortality was observed after 24 h of exposure; no mortality was observed in the control group. The first- to fourth-instar larvae and pupae of A. stephensi had values of LC₅₀?=?309.16, 337.58, 390.42, 429.68, and 513.34 ppm, and A. aegypti had values of LC₅₀?=?334.78, 366.45, 422.97, 467.94, and 54.02 ppm, respectively. Spinosad against the A. stephensi had values of LC₅₀?=?384.19, 433.39, 479.17, 519.79, and 572.63 ppm, and A. aegypti had values of LC₅₀?=?210.68, 241.20, 264.93, 283.27, and 305.85 ppm, respectively. Moreover, in combined treatment, the A. stephensi had values of LC₅₀?=?202.36, 224.76, 250.84, 288.05, and 324.05 ppm, and A. aegypti had values of LC₅₀?=?217.70, 246.04, 275.36, 315.29, and 353.80 ppm, respectively. Results showed that the leaf extract of O. thymiflorus and bacterial insecticide spinosad are promising as a good larvicidal and pupicidal against dengue vector, A. aegypti and malarial vector, A. stephensi. This is an ideal eco-friendly approach for the control of target species of vector control programs.     

Green synthesis of silver nanoparticles using Murraya koenigii leaf extract against Anopheles stephensi and Aedes aegypti

Mosquitoes transmit serious human diseases, causing millions of deaths every year. The use of synthetic insecticides to control vector mosquitoes has caused physiological resistance and adverse environmental effects in addition to high operational cost. Insecticides of synthesized natural products for vector control have been a priority in this area. In the present study, the activity of silver nanoparticles (AgNPs) synthesized using Murraya koenigii plant leaf extract against first to fourth instars larvae and pupae of Anopheles stephensi and Aedes aegypti was determined. Range of concentrations of synthesized AgNPs (5, 10, 20, 30, and 40 ppm) and ethanol leaf extract (50, 200, 350, 500, and 650 ppm) were tested against the larvae of A. stephensi and A. aegypti. The synthesized AgNPs from M. koenigii leaf were highly toxic than crude leaf ethanol extract in both mosquito species. The results were recorded from UV–Vis spectrum, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis. Larvae were exposed to varying concentrations of aqueous extract of synthesized AgNPs for 24 h. The maximum mortality was observed in synthesized AgNPs, and ethanol leaf extract of M. koenigii against A. stephensi had LC₅₀ values of 10.82, 14.67, 19.13, 24.35, and 32.09 ppm and 279.33, 334.61, 406.95, 536.11, and 700.16 ppm and LC₉₀ values of 32.38, 42.52, 53.65, 63.51, and 75.26 ppm and 737.37, 843.84, 907.67, 1,187.62, and 1,421.13 ppm. A. aegypti had LC₅₀ values of 13.34, 17.19, 22.03, 27.57, and 34.84 ppm and 314.29, 374.95, 461.01, 606.50, and 774.01 ppm and LC₉₀ values of 36.98, 47.67, 55.95, 67.36, and 77.72 ppm and 777.32, 891.16, 1,021.90, 1,273.06, and 1,509.18 ppm, respectively. These results suggest that the use of M. koenigii synthesized silver nanoparticles can be a rapid, environmentally safer biopesticide which can form a novel approach to develop effective biocides for controlling the target vector mosquitoes.     

Silver nanoparticles: a possibility for malarial and filarial vector control technology

Green synthesis technology is one of the rapid, reliable and best routes for the synthesis of silver nanoparticles (AgNPs). There are bioactive compounds with enormous potential in Azadirachta indica (Neem). The extraordinary mosquitoes warrant nanotechnology to integrate with novel molecules. This will be sustainable technology for future. Here, we synthesized AgNPs using aqueous extracts of leaves and bark of Az. indica (Neem). We tested AgNPs as larvicides, pupicides and adulticides against the malaria vector Anopheles stephensi and filariasis vector Culex quinquefasciatus. The results were obtained using UV-visible spectrophotometer and the images were recorded with a transmission electron microscope (TEM). The efficacy tests were then performed at different concentrations varying many hours by probit analysis. The synthesized AgNPs were spherical in shape and with varied sizes (10.47-nm leaf and 19.22-nm bark). The larvae, pupae and adults of filariasis vector C. quinquefasciatus were found to be more susceptible to our AgNPs than the malaria vector An. stephensi. The first and the second instar larvae of C. quinquefasciatus show a mortality rate of 100 % after 30 min of exposure. The results against the pupa of C. quinquefasciatus were recorded as LC₅₀ 4 ppm, LC₉₀ 11 ppm and LC₉₉ 13 ppm after 3 h of exposure. In the case of adult mosquitoes, LC₅₀ 1.06 μL/cm², LC₉₀ 2.13 μL/cm² and LC₉₉ 2.4 μL/cm² were obtained after 4 h of exposure. These results suggest that our AgNPs are environment-friendly for controlling malarial and filarial vectors.     

Mosquito larvicidal activity of thymol from essential oil of Coleus aromaticus Benth. against Culex tritaeniorhynchus, Aedes albopictus, and Anopheles subpictus (Diptera: Culicidae)

Diseases transmitted by blood-feeding mosquitoes, such as dengue fever, dengue hemorrhagic fever, Japanese encephalitis, malaria, and filariasis, are increasing in prevalence, particularly in tropical and subtropical zones. To control mosquitoes and mosquito-borne diseases, which have a worldwide health and economic impacts, synthetic insecticide-based interventions are still necessary, particularly in situations of epidemic outbreak and sudden increases of adult mosquitoes. However, the indiscriminate use of conventional insecticides is fostering multifarious problems like widespread development of insecticide resistance, toxic hazards to mammals, undesirable effects on nontarget organisms, and environmental pollution. The aim of this research was to evaluate the toxicity of mosquito larvicidal activity of essential oil from Coleus aromaticus and its pure isolated constituent thymol against larvae of Culex tritaeniorhynchus, Aedes albopictus, and Anopheles subpictus. The chemical composition of the essential oil was analyzed using gas chromatography–mass spectroscopy. A total of 14 components of the essential oil of C. aromaticus were identified. The major chemical components identified were thymol (82.68 %), terpinen-4-ol (3.2 %), and trans-Caryophyllene (3.18 %). Twenty-five early third instar larvae of C. tritaeniorhynchus, A. albopictus, and A. subpictus were exposed and assayed in the laboratory. Thymol and essential oil were tested in concentrations of 10, 20, 30, 40, and 50 and 30, 60, 90, 120, and 150 ppm, respectively. The larval mortality was observed after 24 h of treatment. The thymol had a significant toxic effect against early third-stage larvae of C. tritaeniorhynchus, A. albopictus, and A. subpictus with an LC₅₀ values of 28.19, 24.83, and 22.06 μg/mL respectively, whereas the essential oil of C. aromaticus had an LC₅₀ values of 72.70, 67.98, and 60.31 μg/mL, respectively. No mortality was observed in controls. The Chi-square values were significant at p?<?0.05 level. The result indicated that the essential oil of C. aromaticus and the isolated constituent have a potential for use in control of C. tritaeniorhynchus, A. albopictus, and A. subpictus larvae and could be useful in search of newer, safer, and more effective natural compounds as larvicides.     

Housefly (Musca domestica L.) control potential of Cymbopogon citratus Stapf. (Poales: Poaceae) essential oil and monoterpenes (citral and 1,8-cineole)

In spite of being a major vector for several domestic, medical, and veterinary pests, the control aspect of the common housefly, Musca domestica L. (Diptera: Muscidae) is often neglected. In the present study, the essential oil of Cymbopogon citratus and its major components were evaluated for control of housefly. The chemical composition analysis of C. citratus oil by gas chromatographic mass spectrometry (GC–MS) revealed citral (47 %) and 1,8-cineole (7.5 %) as principal components. The analysis of oil vapor by solid phase microextraction (SPME/GC–MS) showed increase in citral (74.9 %) and 1,8-cineole (8.6 %) content. Assay of oil against housefly larvae and pupae through contact toxicity assay showed lethal concentration (LC)₅₀ value of 0.41 μl/cm² and of percentage inhibition rate (PIR) of 77.3 %, respectively. Fumigation assay was comparatively more effective with LC₅₀ of 48.6 μl/L against housefly larvae, and a PIR value of 100 % against housefly pupae. The monoterpenes, citral, and 1,8-cineole, when assessed for their insecticidal activity against housefly larvae, showed LC₅₀ of 0.002 and 0.01 μl/cm² (contact toxicity assay) and LC₅₀ of 3.3 and 2.4 μl/L (fumigation assay). For pupicidal assay, both citral and 1,8-cineole had a PIR value of 100 %. High efficacy of citral and 1,8-cineole against housefly, established them to be an active insecticidal agent of C. citratus oil. The study demonstrates potentiality of C. citratus oil as an excellent insecticide for housefly control, and the results open up the opportunity of oil/monoterpenes being developed into an eco-friendly, economical, and acceptable product.     

Larvicidal activity of lansiumamide B from the seeds of Clausena lansium against Aedes albopictus (Diptera: Culicidae)

The larvicidal activity of crude petroleum ether, toluene, n-butanol, ethyl acetate, acetone, and methanol extracts of the seeds of Clausena lansium was assayed for their toxicities against the early fourth instar larvae of Aedes albopictus. The larval mortality was observed after 24-h exposure. The LC₅₀ value of petroleum ether extract was 22.99 ppm, showing the best larvicidal activity among all six solvent extracts. A cinnamon amide compound lansiumamide B (N-methyl-N-cis-styrylcinnamamide) was isolated from the petroleum ether extract by column chromatographic method, which exhibited a strong larvicidal activity against the early fourth instar larvae of A. albopictus with LC₅₀ and LC₉₀ values of 0.45 and 2.19 ppm, respectively. The structure was elucidated by ¹H NMR, ¹³C NMR spectral data. The larvicidal activity against mosquito of lansiumamide B from the seed of C. lansium was evaluated for the first time.     

Larvicidal and repellent activity of the essential oil of Coriandrum sativum L. (Apiaceae) fruits against the filariasis vector Aedes albopictus Skuse (Diptera: Culicidae)

The essential oils of many Apiaceae species have been already studied for their insecticidal and repellent properties against insect pests. In this research, the essential oil (EO) extracted from the fruits of Coriandrum sativum L. (Apiaceae) was evaluated for the first time for its larvicidal and repellent activities against the most invasive mosquito worldwide, Aedes albopictus Skuse (Diptera: Culicidae). The chemical composition of C. sativum EO was investigated by gas chromatography with electron impact mass spectrometry analysis. Coriander EO was mainly composed by monoterpene hydrocarbons and oxygenated monoterpenes, with linalool (83.6 %) as the major constituent. C. sativum EO exerted toxic activity against A. albopictus larvae: LC₅₀ was 421 ppm, while LC₉₀ was 531.7 ppm. Repellence trials highlighted that C. sativum EO was a good repellent against A. albopictus, also at lower dosages: RD₅₀ was 0.0001565 μL/cm² of skin, while RD₉₀ was 0.002004 μL/cm². At the highest dosage (0.2 μL/cm² of skin), the protection time achieved with C. sativum essential oil was higher than 60 min. This study adds knowledge about the chemical composition of C. sativum EO as well as to the larvicidal and repellent activity exerted by this EO against A. albopictus. On this basis, we believe that our findings could be useful for the development of new and safer products against the Asian tiger mosquito.     

Larvicidal activities of Knema attenuata (Hook. f. & Thomson) Warb. (Myristicaceae) extracts against Aedes albopictus Skuse and Anopheles stephensi Liston

In recent years, uses of environment friendly and biodegradable natural insecticides of plant origin have received renewed attention as agents for vector control. The present study was undertaken to investigate the effect of aril and kernel extracts of Knema attenuata (Hook. f. & Thomson) Warb. (Myristicaceae) on larvae of Aedes albopictus Skuse and Anopheles stephensi Liston under laboratory conditions. The aril was extracted with chloroform and ethanol; the kernel was extracted with ethanol and hexane. The extracts were tested against the 3rd–4th instar larvae collected from Bunder area, Mangalore, India, which is a well-known fishing harbour, where several mosquito-borne diseases were reported. All the graded concentrations (100, 200, 300, 400 and 500 ppm) showed significant larval mortality after 24 h of observation. Chloroform extracts of aril showed 100% mortality against both larval forms of A. albopictus and A. stephensi at the concentration of 500 ppm. Among the extracts tested, chloroform extracts of aril and ethanol extracts of kernel exhibited higher toxicity against both A. albopictus (LC₅₀, 141 ppm and 159 ppm; LC₉₀, 290 ppm and 342 ppm) and A. stephensi (LC₅₀, 160 ppm and 162 ppm; LC90, 445 ppm and 458 ppm). Hexane extracts of kernel exhibited least toxicity against A. albopictus (LC50, 239 ppm; LC₉₀, 484 ppm), whereas ethanol extracts of aril showed the least toxicity against A. stephensi (LC₅₀, 290; LC₉₀, 498). A preliminary phytochemical assay revealed the presence of phenolics, tannins, steroids, terpenes, resins, and glycolipids in all the extracts. Alkaloids, flavonoids and saponins were absent. The lower LC₅₀ value of the chloroform extracts of K. attenuata aril indicates its potentiality as a larvicide against A. albopictus and A. stephensi mosquito larvae.