Differential larvicidal efficacy of four species of <Emphasis Type="Italic">Vitex</Emphasis> against <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> larvae

The early fourth instar larvae of Culex quinquefasciatus, reared in the laboratory were used for larvicidal assay with leaf extracts of Vitex negundo, Vitex trifolia, Vitex peduncularis and Vitex altissima. The methanol extracts of the four species possessed varying levels of larvicidal nature. The highest larvicidal activity was found with the extract of V. trifolia (LC₅₀ = 41.41 ppm) followed by V. peduncularis (LC₅₀ = 76.28 ppm), V. altissima (LC₅₀ = 128.04 ppm) and V. negundo (LC₅₀ = 212.57 ppm).     

Efficacy of larvicidal botanical extracts against <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> Say (Diptera: Culicidae)

The present study explored the effects of crude leaf acetone, chloroform, hot water, methanol, petroleum ether (60–80°C), and water extracts of Calotropis procera (Ait) R. Br., Canna indica L., Hibiscus rosa-sinensis Linn., Ipomoea carnea Jacq. spp. fistulosa Choisy, and Sarcostemma brevistigma Wight that were selected for investigating larvicidal potential against second and fourth instar larvae of the laboratory-reared mosquito species, Culex quinquefasciatus Say, in which the major lymphatic filariasis was used. All plant extracts showed moderate larvicidal effects after 24 h of exposure at 1,000 ppm; however, the highest larval mortality was found in leaf acetone, chloroform, methanol, and petroleum ether of C. indica (LC₅₀ = 29.62, 59.18, 40.77, and 44.38 ppm; LC₉₀ = 148.55, 267.87, 165.00, and 171.91 ppm) against second instar larvae (LC₅₀ = 121.88, 118.25, 69.76, and 56.31 ppm; LC₉₀ = 624.35, 573.93, 304.27, and 248.24 ppm) and against fourth instar larvae and acetone, hot water, methanol, and petroleum ether extracts of I. carnea (LC₅₀ = 61.17, 41.07, 41.82, and 39.32 ppm; LC₉₀ = 252.91, 142.67, 423.76, and 176.39 ppm) against second instar larvae (LC₅₀ = 145.37, 58.00, 163.81, and 41.75 ppm; LC₉₀ = 573.30, 181.10, 627.38, and 162.63 ppm) and against fourth instar larvae of C. quinquefasciatus, respectively. These results suggest that the acetone, methanol extracts of C. indica and hot water, petroleum ether extracts of I. carnea have the potential to be used as an ideal eco-friendly approach for the control of the major lymphatic filariasis vector, C. quinquefasciatus.     

Evaluation of indigenous plant extracts against larvae of <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> Say (Diptera: Culicidae)

This study investigates the larvicidal potential of indigenous plant extracts from commonly used medicinal herbs as an environmentally safe measure to control the filarial vector, Culex quinquefasciatus Say (Diptera: Culicidae). The early fourth-instar larvae of C. quinquefasciatus, reared in the laboratory, were used for larvicidal assay with water, hot water, acetone, chloroform, and methanol leaf, stem-bark, and flower extracts of Acacia arabica Willd. Sans, Cedrus deodara Roxb, Hibiscus rosa-sinensis L., Mangifera indica L., Nerium indicum Mill., Nicotiana tabacum Linn., Pongamia pinnata (L.) Pierre, and Solanum nigrum Linn. All plant extracts showed moderate larvicidal effects after 24 h of exposure at 1,000 ppm; however, the highest larval mortality was found in stem-bark hot water, acetone, and methanol extracts of C. deodara (LC₅₀ = 133.85, 141.60, and 95.19 ppm, LC₉₀ = 583.14, 624.19, and 639.99 ppm) and leaf hot water, acetone, methanol, and chloroform extracts of N. tabacum (LC₅₀ = 76.27, 163.81, 83.38, and 105.85 ppm, LC₉₀ = 334.72, 627.38, 709.51, and 524.39 ppm) against the larvae of C. quinquefasciatus, respectively. This is an ideal ecofriendly approach for the control of lymphatic filariasis vector, C. quinquefasciatus.     

Evaluation of larvicidal and nymphicidal potential of plant extracts against <Emphasis Type="Italic">Anopheles subpictus</Emphasis> Grassi, <Emphasis Type="Italic">Culex tritaeniorhynchus</Emphasis> Giles and <Emphasis Type="Italic">Aphis gossypii</Emphasis> Glover

The acetone, chloroform, ethyl acetate, hexane and methanol extracts of peel and leaf extracts of Citrus sinensis, Ocimum canum, Ocimum sanctum and Rhinacanthus nasutus were tested against fourth instar larvae of malaria vector, Anopheles subpictus Grassi, Japanese encephalitis vector, Culex tritaeniorhynchus Giles (Diptera: Culicidae) and feeding deterrence to nymphs of cotton pest, Aphis gossypii Glover (Homoptera: Aphididae). The larval and nymph mortality were observed after 24 h of exposure. All extracts showed moderate larvicidal and nymphicidal effects; however, the highest mortality was found in peel chloroform extract of C. sinensis, leaf ethyl acetate extracts of O. canum and O. sanctum and leaf chloroform extract of R. nasutus against the larvae of A. subpictus (LC₅₀ = 58.25, 88.15, 21.67 and 40.46 ppm; LC₉₀ = 298.31, 528.70, 98.34 and 267.20 ppm), peel methanol extract of C. sinensis, leaf methanol extract of O. canum, ethyl acetate extracts of O. sanctum and R. nasutus against the larvae of C. tritaeniorhynchus (LC₅₀ = 38.15, 72.40, 109.12 and 39.32 ppm; LC₉₀ = 184.67, 268.93, 646.62 and 176.39 ppm), peel hexane extract of C. sinensis, leaf methanol extracts of O. canum and R. nasutus and leaf ethyl acetate extract of O. sanctum against the nymph of A. gossypii (LC₅₀ = 162.89, 80.99, 73.27 and 130.19 ppm; LC₉₀ = 595.40, 293.33, 338.74 and 450.90 ppm), respectively. These results suggest that the peel methanol extracts of C. sinensis and O. canum, ethyl acetate leaf extract of O. sanctum and leaf chloroform and ethyl acetate extract of R. nasutus have the potential to be used as an ideal eco-friendly approach for the control of the A. subpictus, C. tritaeniorhynchus and A. gossypii.     

Larvicidal activity of <Emphasis Type="Italic">Saraca indica,Nyctanthes arbor-tristis</Emphasis>, and <Emphasis Type="Italic">Clitoria ternatea</Emphasis> extracts against three mosquito vector species

Screening of natural products for mosquito larvicidal activity against three major mosquito vectors Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi resulted in the identification of three potential plant extracts viz., Saraca indica/asoca, Nyctanthes arbor-tristis, and Clitoria ternatea for mosquito larval control. In the case of S. indica/asoca, the petroleum ether extract of the leaves and the chloroform extract of the bark were effective against the larvae of C. quinquefasciatus with respective LC₅₀ values 228.9 and 291.5 ppm. The LC₅₀ values of chloroform extract of N. arbor-tristis leaves were 303.2, 518.2, and 420.2 ppm against A. aegypti, A. stephensi, and C. quinquefasciatus, respectively. The methanol and chloroform extracts of flowers of N. arbor-tristis showed larvicidal activity against larvae of A. stephensi with the respective LC₅₀ values of 244.4 and 747.7 ppm. Among the methanol extracts of C. ternatea leaves, roots, flowers, and seeds, the seed extract was effective against the larvae of all the three species with LC₅₀ values 65.2, 154.5, and 54.4 ppm, respectively, for A. stephensi, A. aegypti, and C. quinquefasciatus. Among the three plant species studied for mosquito larvicidal activity, C. ternatea was showing the most promising mosquito larvicidal activity. The phytochemical analysis of the promising methanolic extract of the seed extract was positive for carbohydrates, saponins, terpenoids, tannins, and proteins. In conclusion, bioassay-guided fractionation of effective extracts may result in identification of a useful molecule for the control of mosquito vectors.     

Larvicidal activity of micronized aqueous suspension of calcium hydroxide against <Emphasis Type="Italic">Aedes aegypti</Emphasis> and <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> (Diptera: Culicidae)

In the search of alternatives for the control of mosquitoes of medical importance, we evaluated the larvicidal activity of micronized suspensions of calcium hydroxide [Ca(OH)₂] against Aedes aegypti and Culex quinquefasciatus. Tests conducted under laboratory conditions determined a LC50 = 0.027% (LC90 = 0.096%) for A. aegypti and a LC50 = 0.092% (LC90 = 0.2%) for C. quinquefasciatus, at 24 h post-treatment. Considering that the LC50 for the less susceptible species killed 100% of larvae for both species at 48 h post-treatment, we decided to use the diagnostic concentration of 0.1% which eliminated 100% of larvae at 48 h under a simulated field trial. There was a residual effect for up to 84 and 70 days for A. aegypti and C. quinquefasciatus, respectively. Evaluation of Ca(OH)₂ on breeding sites showed a larvicidal activity of 100% for up to 56 days. When the micronized Ca(OH)₂ was incorporated at concentrations from 0.02% (w/v), a superficial film was formed which killed 100% of the larvae of both species after 24 h of contact, and the activity remains until the film broke apart due to stirring. The fact that Ca(OH)₂ is cheap and the people in rural areas of Mexico and other countries know the handling procedures for this compound led us to consider that 0.1% suspensions of Ca(OH)₂ could be used for mosquito control in deposits of water placed in human premises both in urban and rural areas.     

Laboratory study on larvicidal activity of indigenous plant extracts against <Emphasis Type="Italic">Anopheles subpictus</Emphasis> and <Emphasis Type="Italic">Culex tritaeniorhynchus</Emphasis>

Anopheles subpictus and Culex tritaeniorhynchus have developed resistance to various synthetic insecticides, making its control increasingly difficult. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. The leaf acetone, chloroform, ethyl acetate, hexane, and methanol extracts of Aegle marmelos (Linn.) Correa ex Roxb, Andrographis lineata Wallich ex Nees., Andrographis paniculata (Burm.f.) Wall. ex Nees., Cocculus hirsutus (L.) Diels, Eclipta prostrata L., and Tagetes erecta L. were tested against fourth-instar larvae of malaria vector, A. subpictus Grassi and Japanese encephalitis vector, C. tritaeniorhynchus Giles (Diptera: Culicidae). All plant extracts showed moderate larvicidal effects after 24 h of exposure at 1,000 ppm; however, the highest larval mortality was found in leaf ethyl acetate of A. marmelos, E. prostrata, hexane, methanol of A. paniculata and C. hirsutus against the larvae of A. subpictus (LC₅₀ = 167.00, 78.28, 67.24, 142.83 ppm; LC₉₀ = 588.31, 360.75, 371.91, and 830.01 ppm) and against the larvae of C. tritaeniorhynchus (LC₅₀ = 99.03, 119.89, 88.50, 105.19 ppm; LC₉₀ = 479.23, 564.85, 416.39, and 507.86 ppm), respectively. These results suggest that the leaf hexane extract of A. paniculata and ethyl acetate extract of E. prostrata have the potential to be used as an ideal eco-friendly approach for the control of the A. subpictus and C. tritaeniorhynchus. Therefore, this study provides first report on the mosquito larvicidal activity of plant extracts against vectors from Southern India.     

Efficacy of fungus mediated silver and gold nanoparticles against <Emphasis Type="Italic">Aedes aegypti</Emphasis> larvae

Chrysosporium tropicum is a pathogenic fungus. It is known to be an effective mosquito control agent. In the present study, we have synthesized the silver and gold nanoparticles using C. tropicum. These nanoparticles have been characterized through Microscan reader, X-ray diffractometer, transmission electron microscopy, and further confirmed by scanning electron microscopy. The characterization study confirmed the spherical shape and size (2–15 and 20–50 nm) of gold and silver nanoparticles. These silver and gold nanoparticles have been tested as a larvicide against the Aedes aegypti larvae. The larvicidal efficacy was noted when performed against all instars of A. aegypti at six different log concentrations, and significant results could be observed. The gold nanoparticles used as an efficacy enhancer have shown mortality at three times higher concentration than the silver nanoparticles. The larval mortality was observed after different time of exposures. The mortality values were obtained using the probit analysis. The larvae of A. aegypti were found to be highly susceptible for the silver nanoparticles. The second instar larvae have shown 100% mortality against the silver nanoparticles after 1 h, whereas the first, third, and fourth instars have shown efficacy (LC₅₀ = 3.47, 4, and 2; LC₉₀ = 12.30, 8.91, and 4; LC₉₉ = 13.18, 13.18, and 7.58, respectively) after 1 h. The results could suggest that the use of fungus C. tropicum, silver, and gold nanoparticles is a rapid, environmentally safer, and greener approach for mosquito control. This could lead us to a new possibility in vector control strategy.     

Larvicidal activity of oak <Emphasis Type="Italic">Quercus infectoria</Emphasis> Oliv. (Fagaceae) gall extracts against <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston

There is a growing interest in the use of botanical insecticides to reduce the use of synthetic pesticides in order to avoid environmental side effects. Anopheles stephensi is the primary vector of urban malaria, an endemic disease in India. So, an effort to assay An. stephensi larvae with gall extracts of Quercus infectoria was made under laboratory conditions at Mysore. Ethyl-acetate extract was found to be the most effective of all the five extracts tested for larvicidal activity against the fourth instar larvae, with LC₅₀ of 116.92 ppm followed by gallotannin, n-butanol, acetone, and methanol with LC₅₀ values of 124.62, 174.76, 299.26, and 364.61 ppm, respectively. The efficacy in killing mosquito larvae may make this plant promising for the development of new botanical larvicide.     

Bioactivity of essential oils of <Emphasis Type="BoldItalic">Zingiber officinalis</Emphasis> and <Emphasis Type="BoldItalic">Achyranthes aspera</Emphasis> against mosquitoes

Due to the global health problems associated with mosquito-borne diseases, over two million people primarily in the tropical countries are at risk. The widely and commonly used chemical method though effective, has some major disadvantages making insect control practically difficult. In view of the above, it is unavoidable to search for new molecules, which are eco-friendly, cheaper, and safer. The present study deals with evaluation of bioactive potential of two commonly occurring plants against mosquitoes presenting an alternative to the conventional chemical methods. Essential oils extracted by steam distillation from rhizome of Zingiber officinalis and leaf and stem of Achyranthes aspera were evaluated for larvicidal, attractant/repellent, and oviposition attractant/deterrent activity against two mosquito species viz. Aedes aegypti and Culex quinquefasciatus. The highest larvicidal activity, i.e., LC₅₀ = 154 ppm and LC₅₀ = 197 ppm for A. aegypti and C. quinquefasciatus, respectively was shown by Z. officinalis. This oil also offers 5-h protection at the concentration of 0.5 mg/cm2 from both mosquito species. The highest oviposition deterrence activity was exhibited by A. aspera stem oil, i.e., 100% and 85.71%, in case of A. aegypti and C. quinquefasciatus, respectively, at the concentration of 0.1%. These results reveal that both these oils have control potential against A. aegypti and C. quinquefasciatus.     

Efficacy of the <Emphasis Type="Italic">Trichophyton ajelloi</Emphasis> and <Emphasis Type="Italic">Lagenidium giganteum</Emphasis> metabolites against mosquitoes after flash chromatography

Entomopathogens are significant natural enemies for mosquitoes. We have investigated the adulticidal efficacies of metabolites of Trichophyton ajelloi and Lagenidium giganteum against Culex quinquefasciatus and Aedes aegypti simultaneously. The T. ajelloi was grown on Sabouraud’s dextrose broth medium at 25 ± 2°C and relative humidity at 75 ± 5% for 15 days. L. giganteum was grown in peptone yeast extract glucose broth at 25 ± 2°C and relative humidity 75 ± 5% for 15 days. The filtrations of metabolites have been made by using Whatman-1 filter paper then with the flash chromatograph. The bioassays were conducted as per the World Health Organization’s methods and protocols (2006). In this significant investigations, the metabolites of T. ajelloi have been found highly susceptible against A. aegypti with LC₉₉-7.24 ml after an exposure time of 24 h with a comparison, the LC₉₉-66 ml was observed against C. quinquefasciatus after exposure of 24 h. Moreover, the L. giganteum metabolites have shown higher pathogenicity against C. quinquefasciatus with LC₉₉-11.3 ml and A. aegypti with LC₉₉-15.49 ml. Although, the efficacy in adults could be achieved with higher concentration can be significant also. Their adulticidal activities in different climatic zones are plausible with metabolites which have better LT values of T. ajelloi.     

Larvicidal activity of silver nanoparticles synthesized using <Emphasis Type="Italic">Plumeria rubra</Emphasis> plant latex against <Emphasis Type="Italic">Aedes aegypti</Emphasis> and <Emphasis Type="Italic">Anopheles stephensi</Emphasis>

In the present study activity of silver nanoparticles (AgNPs) synthesized using Plumeria rubra plant latex against second and fourth larval instar of Aedes aegypti and Anopheles stephensi was determined. Range of concentrations of synthesized AgNps (10, 5, 2.5, 1.25, 0.625, 0.3125 ppm) and aqueous crude latex (1,000, 500, 250, 125, 62.50, 31.25 ppm) were tested against larvae of A. aegypti and A. Stephensi. The synthesized AgNps from P. rubra latex were highly toxic than crude latex extract in both mosquito species. The LC₅₀ values for second and fourth larval instars after 24 h of crude latex exposure were 1.49, 1.82 ppm against A. aegypti and 1.10, 1.74 ppm against A. stephensi respectively. These figures were 181.67, 287.49 ppm against A. aegypti and 143.69, 170.58 ppm against A. stephensi respectively for crude latex extract. The mortality rates were positively correlated with the concentration of AgNPs. The characterization studies of synthesized AgNPs by UV–Vis spectrophotometry, transmission electron microscopy (TEM), Particle size analysis (PSA) and zeta potential confirmed the spherical shape and size (32–200 nm) of silver nanoparticles alongwith stability. Toxicity studies carried out against non-target fish species Poecilia reticulata, the most common organism in the habitats of A. aegypti and A. stephensi showed no toxicity at LC₅₀ and LC₉₀ doses of the AgNPs. This is the first report on mosquito larvicidal activity of latex synthesized nanoparticles.     

<Emphasis Type="Italic">Amaranthus oleracea</Emphasis> and <Emphasis Type="Italic">Euphorbia hirta</Emphasis>: natural potential larvicidal agents against the urban Indian malaria vector, <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston (Diptera: Culicidae)

Malaria control in developing countries is based largely on vector eradication by the use of mosquito larvicides which is an ideal method for controlling mosquito and the related epidemics. On account of ecohazardous nature, nontarget specificity of chemical insecticides and evidences of developing resistance against them in the exposed species, currently, importance of secondary plant metabolites has been acknowledged. Insecticides of plant origin are environmentally safe, degradable, and target specific. In view of this fact, the present work highlights the larvicidal property of extracts of Amaranthus oleracea and Euphorbia hirta against the third instar larvae of Anopheles stephensi, the urban malaria vector. LC₅₀ values for the carbon tetrachloride fraction of A. oleracea against larvae are 17,768.00 and 13,780.00 ppm after 24 and 48 h of exposure accordingly. For the methanol extract of the same, LC₅₀ values are 15,541.00 and 10,174.00 ppm after 24 and 48 h of exposure. In the case of petroleum ether extract, LC₅₀ values after 24 and 48 h of exposure are 848.75 and 311.50 ppm. LC₅₀ values for carbon tetrachloride extracts of E. hirta against the larvae are 11,063.00 and 10,922.00 ppm after 24 and 48 h of exposure, respectively. For methanol extract of the same extract, the LC₅₀ values are 19,280.00 and 18,476.00 ppm after 24 and 48 h of exposure. In the case of petroleum ether extract, LC₅₀ values after a 24- and 48-h exposure period are 9,693.90 and 7,752.80 ppm. The results obtained for petroleum extracts of A. oleracea are encouraging and there are probabilities that the active principle contained in this extract may be more effective than its crude form and may serve as ecofriendly mosquito larvicide.     

Isolation and identification of mosquito larvicidal compound from <Emphasis Type="Italic">Abutilon indicum</Emphasis> (Linn.) Sweet

Larvicidal activity of crude hexane, ethyl acetate, petroleum ether, acetone and methanol extracts of five medicinal plants, Abutilon indicum, Aegle marmelos, Euphorbia thymifolia, Jatropha gossypifolia and Solanum torvum were assayed for their toxicity against the early fourth-instar larvae of Culex quinquefasciatus. The larval mortality was observed after 24 h exposure. All extracts showed moderate larvicidal effects; however, the highest larval mortality was found in petroleum ether extract of A. indicum. In the present study, bioassay-guided fractionation of A. indicum led to the separation and identification of a β-sitosterol as a potential new mosquito larvicidal compound with LC₅₀ value of 11.49, 3.58 and 26.67 ppm against Aedes aegypti L, Anopheles stephensi Liston and C. quinquefasciatus Say (Diptera: Culicidae), respectively. ¹H NMR, ¹³C NMR and mass spectral data confirmed the identification of the active compound. β-sitosterol has been recognized as the active ingredient of many medicinal plant extracts. All the crude extracts when screened for their larvicidal activities indicated toxicity against the larvae of C. quinquefasciatus. This article reports the isolation and identification of the β-sitosterol as well as bioassay data for the crude extracts. There are no reports of β-sitosterol in the genus A. indicum, and their larvicidal activities are being evaluated for the first time. Results of this study show that the petroleum ether extract of A. indicum may be considered as a potent source and β-sitosterol as a new natural mosquito larvicidal agent.     

The essential oil of <Emphasis Type="Italic">Zingiber officinalis</Emphasis> Linn (Zingiberaceae) as a mosquito larvicidal and repellent agent against the filarial vector <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> Say (Diptera: Culicidae)

Essential oils extracted by steam distillation from Zingiber officinalis was evaluated for larvicidal and repellent activity against the filarial mosquito Culex quinquefasciatus. The larval mortality was observed after 24 h treated for late third instar. The LC₅₀ value was 50.78 ppm. Skin repellent test at 1.0, 2.0, 3.0, and 4.0 mg/cm² concentration of Z. officinalis gave 100% protection up to 15, 30, 60, and 120 min. These results clearly reveal that the essential oil of Z. officinalis served as a potential larvicidal and repellent agent against filarial vector C. quinquefasciatus.     

Synthesis of silver nanoparticles using Nelumbo nucifera leaf extract and its larvicidal activity against malaria and filariasis vectors

The aim of this study was to investigate the larvicidal potential of the hexane, chloroform, ethyl acetate, acetone, methanol, and aqueous leaf extracts of Nelumbo nucifera Gaertn. (Nymphaeaceae) and synthesized silver nanoparticles using aqueous leaf extract against fourth instar larvae of Anopheles subpictus Grassi and Culex quinquefasciatus Say (Diptera: Culicidae). Nanoparticles are being used in many commercial applications. It was found that aqueous silver ions can be reduced by aqueous extract of plant parts to generate extremely stable silver nanoparticles in water. The results recorded from UV–vis spectrum, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared support the biosynthesis and characterization of silver nanoparticles. Larvae were exposed to varying concentrations of plant extracts and synthesized silver nanoparticles for 24 h. All extracts showed moderate larvicidal effects; however, the maximum efficacy was observed in crude methanol, aqueous, and synthesized silver nanoparticles against the larvae of A. subpictus (LC₅₀ = 8.89, 11.82, and 0.69 ppm; LC₉₀ = 28.65, 36.06, and 2.15 ppm) and against the larvae of C. quinquefasciatus (LC₅₀ = 9.51, 13.65, and 1.10 ppm; LC₉₀ = 28.13, 35.83, and 3.59 ppm), respectively. These results suggest that the leaf methanol, aqueous extracts of N. nucifera, and green synthesis of silver nanoparticles have the potential to be used as an ideal eco-friendly approach for the control of the A. subpictus and C. quinquefasciatus. This is the first report on the mosquito larvicidal activity of the plant extracts and synthesized nanoparticles.     

First report on susceptibility of wild <Emphasis Type="Italic">Aedes aegypti</Emphasis> (Diptera: Culicidae) using <Emphasis Type="Italic">Carapa guianensis</Emphasis> (Meliaceae) and <Emphasis Type="Italic">Copaifera</Emphasis> sp. (Leguminosae)

Oils of Carapa guianensis and Copaifera spp. are well known in the Amazonian region as natural insect repellent, and studies have reported their efficiency as larvicide against some laboratory mosquito species. However, in wild populations of mosquitoes, these oils have not yet been evaluated. Thus, the objective of this study was to investigate their efficiency as larvicide in wild populations of Aedes aegypti with a history of exposure to organophosphate. The susceptibility of larvae was determined under three different temperatures, 15°C, 20°C, and 30°C. For each test, 1,000 larvae were used (late third instar and early fourth instar—four replicates of 25 larvae per concentration). Statistical tests were used to identify significant differences. The results demonstrated that as the laboratory A. aegypti, the wild populations of A. aegypti were also susceptible to C. guianensis and Copaifera sp. oils. The lethal concentrations for Copaifera sp. ranged from LC₅₀ 47 to LC₉₀ 91 (milligrams per liter), and for C. guianensis, they were LC₅₀ 136 to LC₉₀ 551 (milligrams per liter). In relation to different temperature, the effectiveness of the oils on larvae mortality was directly related to the increase of temperature, and better results were observed for temperature at 25°C. The results presented here indicate the potential larvicidal activity of C. guianensis and species of Copaifera, in populations of A. aegypti from the wild. Therefore, the results presented here are very important since such populations are primarily responsible for transmitting the dengue virus in the environment.     

Chemical composition and larvicidal activity of essential oil from <Emphasis Type="Italic">Mentha spicata</Emphasis> (Linn.) against three mosquito species

Mosquitoes are blood-feeding insects and serve as the most important vectors for spreading human diseases such as malaria, yellow fever, dengue fever, and filariasis. The continued use of synthetic insecticides has resulted in resistance in mosquitoes. Synthetic insecticides are toxic and affect the environment by contaminating soil, water, and air, and then natural products may be an alternative to synthetic insecticides because they are effective, biodegradable, eco-friendly, and safe to environment. Botanical origin may serve as suitable alternative biocontrol techniques in the future. Mentha spicata, an edible and medicinal plant, is chiefly distributed in Southeast Asia and South Asia. In the present study, the toxicity of mosquito larvicidal activity of leaf essential oil (EO) and their major chemical constituents from Mentha spicata against Culex quinquefasciatus, Aedes aegypti, and Anopheles stephensi. The chemical composition of the leaf EO was analyzed using gas chromatography–mass spectroscopy (GC-MS). GC-MS revealed that the EO of M. spicata contained 18 compounds. The major chemical components identified were carvone (48.60%), cis-carveol (21.30%), and limonene (11.30%). The EO had a significant toxic effect against early third-stage larvae of C. quinquefasciatus, A. aegypti, and A. stephensi with LC₅₀ values of 62.62, 56.08, and 49.71 ppm and LC₉₀ values of 118.70, 110.28, and 100.99 ppm, respectively. The three major pure constituents extracted from the M. spicata leaf EO were also tested individually against three mosquito larvae. The LC₅₀ values of carvone, cis-carveol, and limonene appeared to be most effective against A. stephensi (LC₅₀ 19.33, 28.50, and 8.83 ppm) followed by A. aegypti (LC₅₀ 23.69, 32.88, and 12.01 ppm), and C. quinquefasciatus (LC₅₀ 25.47, 35.20, and 14.07 ppm). The results could be useful in search for newer, safer, and more effective natural larvicidal agents against C. quinquefasciatus, A. aegypti, and A. stephensi.     

Efficacy of female <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> with entomopathogenic fungus <Emphasis Type="Italic">Fusarium pallidoroseum</Emphasis>

This study was conducted to isolate and identify natural entomopathogenic fungi from female Culex quinquefasciatus and to test their adulticidal activity. Field-collected female C. quinquefasciatus died early and were placed on a Saboraud’s dextrose agar plates for growth and isolation of natural entomopathogenic fungi. The plates were maintained in an incubator at 24 ± 2°C for 3 days. Four fungal species were isolated in two genera namely, Aspergillus and Fusarium. The identified fungal species were A. niger, A. flavus, A. nidulans var acristatus (ITCC-6327.04), and F. pallidoroseum (ITCC-6324.06). Adult bioassays were carried out using spore-impregnated paper in WHO-holding tubes. F. pallidoroseum was found to be more effective than the others. Exposure of C. quinquefasciatus to spores of A. flavus and A. niger for 4 h caused 5.53% and 5.51% mortality in the mosquitoes within a week, respectively. All the female C. quinquefasciatus were killed within 4 days of exposure to F. pallidoroseum at a concentration of 1.11 × 10¹⁰ conidia per m². Significant difference of longevity was observed between the F. pallidoroseum-treated C. quinquefasciatus and control mosquitoes. The LT₅₀ of F. pallidoroseum was 2.08 days for 4 h exposure to C. quinquefasciatus. Results of the present study confirm that F. pallidoroseum is one of the alternative biological control agents of adult mosquitoes.     

Insecticidal Evaluation of essential oils of <Emphasis Type="BoldItalic">Citrus sinensis</Emphasis> L. (Myrtales: Myrtaceae) against housefly, <Emphasis Type="BoldItalic">Musca domestica</Emphasis> L. (Diptera: Muscidae)

The housefly, Musca domestica L., is one of the most common insects, associated with vectoring of various etiological agents. In order to search for effective control agent, the essential oil of sweet orange [Citrus sinensis (L.) Osbeck] was evaluated for its insecticidal activity against the larvae and pupae of housefly using contact toxicity and fumigation bioassays. In the contact toxicity assay, lethal concentration, LC₅₀ of C. sinensis essential oil against housefly larvae, varied between 3.93 and 0.71 μl/cm² for different observation days, while lethal time, LT₅₀, varied between 5.8 to 2.3 days. Mortality of larvae were significant with different concentrations (F = 2.79, df = 4, P < 0.05) and time (F = 6.69, df = 3, P < 0.01). In fumigant assay for housefly larvae, LC₅₀ of 71.2 and 52.6 μl/l was obtained in 24 and 48 h, respectively. Scanning electron microscopy of oil treated larvae revealed extreme dehydration and surface distortion while control larvae were free from any of the above symptoms and presented smooth surface, conforming effect of essential oil on housefly larvae. Percentage inhibition rate of oil against housefly pupae was 27.3–72.7% for contact toxicity and 46.4–100% for fumigation assay. Compositional analysis of C. sinensis essential oil using gas chromatography/mass spectrometry (GC-MS) revealed d-limonene (73.24%), α-pinene (5.86%) and myrcene (4.45%) as major components whereas its vapour profile (solid-phase micro extraction-GC/MS) was dominated by d-limonene at 92.57%. Significant activity of C. sinensis essential oil against larvae and pupae of housefly, pave the way for its use as eco-friendly housefly control measure.