Larvicidal activity of Pseudocalymma alliaceum and Allium sativum against Culex quinquefasciatus (Say)

The larvicidal activity of the plant extracts Pseudocalymma alliaceum and Allium sativum were determined against Culex quinquefasciatus. The hexane extract of P. alliaceum and the petroleum ether extract of A. sativum exhibited larvicidal efficacy against Cx. quinquefasciatus larvae. Extracts of P. alliaceum resulted in concentrations that produced 50% mortality LC₅₀ and LC₉₀ values of 2.49 and 15.06 ppm, respectively, after 24 h and 1.16 and 8.45 ppm after 48 h. Extracts of A. sativum resulted in LC₅₀ and LC₉₀ values of 8.38 and 29.15 ppm after 24 h and 7.28 and 44.19 ppm after 48 h of exposure, respectively. The results indicate that the plant extract component(s) present in the hexane extract of P. alliaceum leaves demonstrated greater potential as an efficient larvicide than A. sativum against Cx. quinquefasciatus.     

Larvicidal Efficiency of Certain Seed Extracts Against Anopheles Stephensi,with Reference to Azadirachta indica

The toxicity of seed extracts of three Indian medicinal plants, Azadirachta indica, Momordica charantia and Ricinus communis, was evaluated for their larvicidal efficacy against Anopheles stephensi. The methanol extract of A. indica exhibited potent larvicidal activity with LC₅₀ 15.25 and 12.70 ppm and LC₉₀ 46.79 and 45.56 ppm after 24 and 48 hrs, respectively, followed by methanol extract of R. communis with LC₅₀ 54.95 and 23.06 ppm and LC₉₀ 251.03 and 144.54 ppm after 24 and 48 hrs of post treatment, respectively. In case of M. charantia, the carbon tetrachloride extract possess potential larvicidal efficacy with LC₅₀ values 87.00 and 57.53 ppm and LC₉₀ 301.20 and 262.21 ppm after 24 and 48 hrs of exposure period. The results indicate that A. indica methanol extract was most potential mosquito larvicide and can be use as alternate potential to synthetic insecticides.     

Purification,characterization and larvicidal activity of a potent bioactive compound asarone from leaves of Acorus calamus against the culician larval mosquitoes

Mosquitoes are potent vectors by serving as agents to life-threatening diseases in humans. Increasing resistance in mosquitoes against existing insecticides and repellents brings new challenges and an opportunity to explore sustainable compounds. We chose six medicinal plants to screen potential bioactive compounds that could act as an insecticide. Among these, crude hexane leaf extract of Acorus calamus showed higher mortality percentage against Aedes aegypti and Culex quinquefasciatus. The LC₅₀ and LC₉₀ values were 151.86 ppm and 536.36 ppm, respectively, for the third instar A. aegypti larvae, and 174.70 ppm and 696.73 ppm, respectively, for C. quinquefasciatus. The treated larvae of both species showed morphological and physiological variations when compared to control. The GC–MS profile of purified fractions showed a single peak. Further, FT-IR and NMR analyses confirmed the propensity of the purified compound as trans asarone (phenylpropanoid; C₁₂H₁₆O₃. LC₅₀ and LC₉₀ values of purified asasone-treated larvae were 2.35 ppm and 12.58 ppm, respectively, for A. aegypti and 2.15 ppm and 11.58 ppm, respectively, for C. quinquefasciatus. Treatment of different sub-lethal doses of asarone to mosquito larvae at various time intervals showed disruption of intestinal layers. By showing negligible toxicity to non-target organism, purified asarone has a great potential in vector management.     

Comparative study of three herbal formulations against dengue vectors Aedes aegypti

The efficacy of three formulations (i.e., natural lavender crude, essential oil, and gel) extracted from Lavender angustifolia was tested against vectors of the epidemic dengue virus, Aedesaegypti, to evaluate their larvicidal activity effect. The ethanolic extract of the lavender crude was prepared using a rotary evaporator, while the other extracts, such as essential oil and gel, were obtained from iHerb, a supplier of medicinal herbs in the US. The mortality rate of larvae was evaluated 24 h after exposure. Larvicidal activity of the lavender crude was 91% mortality at 150 ppm, 94% for essential oil at a concentration of 3000 ppm, and 97% for lavender gel at a 1000 ppm. Natural lavender crude was one of the most promising extracts tested against Ae.aegypti larvae, with lethal concentrations at LC₅₀ and LC₉₀ of 76.4 and 174.5 ppm post-treatment. The essential oil had the least effect on mosquito larvae, with LC₅₀ and LC₉₀ reaching 1814.8 and 3381.9 ppm, respectively. The lavender gel was moderately effective against Ae. aegypti larvae, with LC₅₀ and LC₉₀ values reaching 416.3 and 987.7 ppm after exposure. The occurrence of morphological abnormalities in the larvae treated with the three compounds, in turn, resulted in an incomplete life cycle. Therefore, our results indicated that natural lavender crude displayed the highest larvicidal activity against larvae, followed by gel and essential oil. Thus, this study concluded that lavender crude is an effective, eco-friendly compound that can be used as an alternative to chemical products to control vector-borne epidemic diseases.     

Evaluation of larvicidal potential of certain insect pathogenic fungi extracts against Anopheles stephensi and Culex quinquefasciatus

Fungal metabolites are attracting attention as potential microbial insecticides, and they are anticipated to overcome the problems of pesticide resistance and environmental pollution that are associated with the indiscriminate use of conventional synthetic insecticides. The relative bioefficacies of selected fungal pathogens, Aspergillus flavus, A. niger, A. parasiticus, Fusarium sporotrichoides and Penicillium verrucosum were observed against Anopheles stephensi and Culex quinquefasciatus larvae. A. flavus demonstrated the greatest bioefficacy with 50% lethal concentration (LC₅₀) values of 9.54 and 10.98 ppm against Anopheles stephensi and Culex quinquefasciatus larvae, respectively, after 24‐h exposure. The bioefficacy of A. flavus increased in both species with an exposure time of 48 h, with LC₅₀ values of 7.26 and 8.55 ppm, respectively.     

Impact Analysis of Neem Kernel Extracts on the Developmental Profile of Anopheles Stephensi

Laboratory evaluation of the larvicidal efficacy of Ageratum conyzoides, Argemone mexicana and Azadirachta indica was carried out against Anopheles stephensi to develop an effective ecofriendly insecticide of plant origin. The methanol extract of A. indica was observed remarkably active with LC₅₀ values 18.2 and 13.1 ppm after 24 and 48 hours of exposure. Petroleum ether extracts of Ag. conyzoides with LC₅₀ 425.6 and 267.9 ppm, carbon terra chloride extract of Ar. mexicana with LC₅₀ 313.2 and 240.3 ppm and petroleum ether extract of Az. indica with LC₅₀ 189.1 and 53. 5 ppm after 24 and 48 hours of exposure were also found effective. The impact of Az. indica methanol extract on the life cycle of malaria vector was further observed. Methanol extract of Az. indica causes deformities in different developmental stages of the malaria vector. Total developmental period was also extended from 10 to 15 It remarkably influenced hatching rates, larval-pupal transformation and development, adult emergence and growth index. Larval and pupal periods were also significantly prolonged.     

Fabrication and characterization of noble crystalline silver nanoparticles from Pimenta dioica leave extract and analysis of chemical constituents for larvicidal applications

The current works report the bio-efficacy of Pimenta dioica leaf derived silver nanoparticles (Pd@AgNPs) and leaf extract obtained trough different solvents against the larvae of malaria, filarial and dengue vectors. Synthesis of silver nanoparticles (AgNPs) was done by adding 10 ml of P. dioica leaf extract into 90 ml of 1 mM silver nitrate solution, a slow colour change was observed depicting the formation of AgNPs. Further, Pd@AgNPs was confirmed through Ultraviolet–visible spectroscopy which exhibited characteristic absorption peak at 422 nm wavelength. X-ray diffraction and selected area electron diffraction analysis confirmed monodispersed and crystalline nature of Pd@AgNPs with 32 nm an average size. Scanning electron microscopy and transmission electron microscopy showed the most of Pd@AgNPs were spherical and triangular in shape and energy-dispersive X-ray spectroscopy revealed silver elemental nature of nanoparticles. Zeta potential of Pd@AgNPs is highly negative which confirmed its stable nature. Pd@AgNPs showed prominent absorption peaks at 1015, 1047, 1243, 1634, 2347, 2373, 2697 and 3840 cm^?1 which are corresponding to following compounds polysaccharides, carboxylic acids, water, alcohols, esters, ethers, amines, amides and phenol, respectively as reported by Fourier-transform infrared spectroscopy analysis. Gas chromatography–mass spectrometry and Liquid chromatography–mass spectrometry analysis revealed 39 and 70 compounds, respectively, which might be contributed for bio-reduction, capping, stabilization and larvicidal behavior of AgNPs. A comparable lethality (LC₅₀ and LC₉₀) was observed in case of Pd@AgNPs over leaf extract alone. The potential larvicidal activity of Pd@AgNPs was observed against the larvae of Aedes aegypti,(LC_50, 2.605; LC_90, 5.084 ppm) Anopheles stephensi (LC_50, 3.269; LC_90, 7.790 ppm) and Culex quinquefasciatus (LC_50, 5.373; LC_90, 14.738 ppm without affecting non-targeted organism, Mesocyclops thermocyclopoides after 72 hr of exposure. This study entails green chemistry behind synthesis of AgNPs which offers effective technique for mosquito control and other therapeutic applications.     

Evaluation of Solanum xanthocarpum extract as a synergist for cypermethrin against larvae of the filarial vector Culex quinquefasciatus (Say)

Cypermethrin and crude extracts of Solanum xanthocarpum were both observed for their larvicidal activity against Culex quinquefasciatus. Petroleum ether extract with lethal concentration (LC)₅₀ and LC₉₀ of 41.28 and 111.16 p.p.m. after 24 h and LC₅₀ 38.48 and LC₉₀ 80.83 p.p.m. after 48 h, respectively, was found to be the most effective, followed by carbon tetrachloride and methanol extracts. LC₅₀ and LC₉₀ for cypermethrin were 0.0027 and 0.0097 p.p.m. after 24 h and 0.0013 and 0.0092 p.p.m. after 48 h of exposure, respectively. Combined formulations were evaluated for synergistic activity and a 1:1 ratio of cypermethrin and petroleum ether extract was observed to be more effective than 1:2 and 1:4 ratios. Combinations of S. xanthocarpum extracts and cypermethrin demonstrated higher larvicidal activity, indicating synergistic activity. These results demonstrate the need for further studies on the effectiveness and toxicity to humans and animals, particularly aquatic forms.     

Piperonyl butoxide synergizes the larvicidal activity of Origanum vulgare essential oil and its major constituents against the larvae of Aedes albopictus and Culex pipiens quinquefasciatus

Mosquitoes bite human beings and transmit many diseases, such as malaria, dengue fever, and Zika virus. Vector control of mosquitoes is an effective strategy for reducing the spread of disease. However, extensive use of insecticides (e.g. pyrethroids and organophosphorus) has caused resistance in mosquitoes, which weakens the effectiveness of mosquito control. Phytochemicals have been considered an alternative approach to mosquito control. Essential oil (EO) was obtained from the leaves and flowers of Origanum vulgare, and its synergistic activity with piperonyl butoxide (PBO) was tested against Aedes albopictus and Culex pipiens quinquefasciatus larvae. Thirty-seven compounds were identified, among which carvacrol and thymol were two major constituents (30.73 % and 18.81 %, respectively). O. vulgare EO had a significant toxic effect against fourth-stage larvae of Cx. p. quinquefasciatus and Ae. albopictus, with LC₅₀ values of 17.51 and 75.90 mg/L. Carvacrol and thymol also each appeared to be more effective against Cx. p. quinquefasciatus (LC₅₀ = 19.30 and 11.56 mg/L, respectively) than Ae. albopictus (LC₅₀ = 26.62 and 26.66 mg/L, respectively). PBO interacted synergistically with O. vulgare EO, carvacrol and thymol with 2.60–6.26 times as much of the active compound needed without PBO as against Cx. p. quinquefasciatus and Ae. albopictus larvae. Overall, our results contribute to the development of new natural mosquito insecticides.     

Ongoing challenges in the management of malaria

Background

Mosquitoes transmit serious human diseases, causing millions of deaths every year. Use of synthetic insecticides to control vector mosquitoes has caused physiological resistance and adverse environmental effects in addition to high operational cost. Insecticides of botanical origin have been reported as useful for control of mosquitoes. Azadirachta indica (Meliaceae) and its derived products have shown a variety of insecticidal properties. The present paper discusses the larvicidal activity of neem-based biopesticide for the control of mosquitoes.

Methods

Larvicidal efficacy of an emulsified concentrate of neem oil formulation (neem oil with polyoxyethylene ether, sorbitan dioleate and epichlorohydrin) developed by BMR & Company, Pune, India, was evaluated against late 3^rd and early 4^th instar larvae of different genera of mosquitoes. The larvae were exposed to different concentrations (0.5–5.0 ppm) of the formulation along with untreated control. Larvicidal activity of the formulation was also evaluated in field against Anopheles, Culex, and Aedes mosquitoes. The formulation was diluted with equal volumes of water and applied @ 140 mg a.i./m² to different mosquito breeding sites with the help of pre calibrated knapsack sprayer. Larval density was determined at pre and post application of the formulation using a standard dipper.

Results

Median lethal concentration (LC₅₀) of the formulation against Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti was found to be 1.6, 1.8 and 1.7 ppm respectively. LC₅₀ values of the formulation stored at 26°C, 40°C and 45°C for 48 hours against Ae. aegypti were 1.7, 1.7, 1.8 ppm while LC₉₀ values were 3.7, 3.7 and 3.8 ppm respectively. Further no significant difference in LC₅₀ and LC₉₀ values of the formulation was observed against Ae. aegypti during 18 months storage period at room temperature. An application of the formulation at the rate of 140 mg a.i./m² in different breeding sites under natural field conditions provided 98.1% reduction of Anopheles larvae on day 1; thereafter 100% reduction was recorded up to week 1 and more than 80% reduction up to week 3, while percent reduction against Culex larvae was 95.5% on day 1, and thereafter 80% reduction was achieved up to week 3. The formulation also showed 95.1% and, 99.7% reduction of Aedes larvae on day 1 and day 2 respectively; thereafter 100% larval control was observed up to day 7.

Conclusion

The neem oil formulation was found effective in controlling mosquito larvae in different breeding sites under natural field conditions. As neem trees are widely distributed in India, their formulations may prove to be an effective and eco-friendly larvicide, which could be used as an alternative for malaria control.     

Chicory (Cichorium intybus) and wormwood (Artemisia absinthium) extracts exhibit strong larvicidal activity against mosquito vectors of malaria,dengue fever,and filariasis

Vector-borne diseases transmitted by mosquitoes cause globally important diseases such as malaria, dengue fever, and filariasis. The incidence of these diseases can be reduced through mosquito control programs but these control programs currently rely on synthetic insecticides that can impact the environment, and has selected widespread mosquito resistance. Environment friendly and biodegradable natural insecticides discovered in plants offer an alternative approach to mosquito control. Here, we investigated extracts from root or aerial parts of Chicory (Cichorium intybus) and wormwood (Artemisia absinthium) against the early 4th instar larvae of Anopheles stephensi (malaria vector), Aedes aegypti (dengue fever vector), and Culex quinquefasciatus (filariasis vector). The root and aerial parts extracts of A. absinthium and C. intybus at 200, 100, 50, 25 and 12.5?ppm caused significant mortality of the tested mosquito species. Root extracts exhibited higher larvicidal activity that aerial part extracts. The highest larvicidal activity was recorded in methanol extract of roots of C. intybus with LC50?=?66.16, 18.88 and LC¬90?=?197.56, 107.16?ppm for An. stephensi; LC50?=?78.51, 40.15 and LC90?=?277.31, 231.28?ppm for Ae. aegypti and LC50?=?103.99, 64.56 and LC¬90?=?314.04, 247.54?ppm for Cx. quinquefasciatus. These results reveal potent mosquito larvicidal activity against vectors of malaria, dengue fever, and filariasis is present in extracts of chicory and wormwood.     

Mosquito larvicidal activity of Aloe vera (Family: Liliaceae) leaf extract and Bacillus sphaericus,against Chikungunya vector,Aedes aegypti

The bio-efficacy of Aloe vera leaf extract and bacterial insecticide, Bacillus sphaericus larvicidal activity was assessed against the first to fourth instars larvae of Aedes aegypti, under the laboratory conditions. The plant material was shade dried at room temperature and powdered coarsely. A. vera and B. sphaericus show varied degrees of larvicidal activity against various instars larvae of A. aegypti. The LC₅₀ of A. vera against the first to fourth instars larvae were 162.74, 201.43, 253.30 and 300.05 ppm and the LC₉₀ 442.98, 518.86, 563.18 and 612.96 ppm, respectively. B. sphaericus against the first to fourth instars larvae the LC₅₀ values were 68.21, 79.13, 93.48, and 107.05 ppm and the LC₉₀ values 149.15, 164.67, 183.84, and 201.09 ppm, respectively. However, the combined treatment of A. vera + B. sphaericus (1:2) material shows highest larvicidal activity of the LC₅₀ values 54.80, 63.11, 74.66 and 95.10 ppm; The LC₉₀ values of 145.29, 160.14, 179.74 and 209.98 ppm, against A. aegypti in all the tested concentrations than the individuals and clearly established that there is a substantial amount of synergist act. The present investigation clearly exhibits that both A. vera and B. sphaericus materials could serve as a potential larvicidal agent. Since, A. aegypti is a container breeder vector mosquito this user and eco-friendly and low-cost vector control strategy could be a viable solution to the existing dengue disease burden. Therefore, this study provides first report on the mosquito larvicidal activity the combined effect of A. vera leaf extract and B. sphaericus against as target species of A. aegypti.     

Induction of chymoelastase (Pr1) of <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> and its role in causing mortality to mosquito larvae

The efficacy of virulent strain Metarhizium anisopliae 892 obtained from Pyrausta nubilalis was evaluated against mosquito larvae. LC₅₀ values of M. anisopliae 892 for Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti were compared. Metarhizium anisopliae 892 could cause approximately 50% mortality of C. quinquefasciatus 4 days post inoculation in the concentration of 3.48 × 10³ conidia/ml. The production of cuticle degrading enzyme chymoelastase (Pr1) and trypsin like protease (Pr2) was compared in the presence of inducers. There were significant differences in the production of Pr1 and Pr2 after addition of inducers i.e. cuticles of the three mosquito. The cuticles of C. quinquefasciatus induced maximum Pr1 in the mycelia of M. anisopliae 892 than the rest of two mosquito cuticles during de-repression condition. The larvae of C. quinquefasciatus were more susceptible than the larvae of A. stephensi and A. aegypti against spores of M. anisopliae 892. The quantity of induction of Pr1 in the mycelia of M. anisopliae 892 was positively correlated with the mortality of mosquito larvae. Production of Pr1 and Pr2 was decreased when the inducers were de-proteinated cuticles. The Pr2 induction of M. anisopliae 892 did not correlate with the mortality of mosquito larvae. From the observations of the present study it can concluded that Pr1 is a responsible factor for the mortality of the mosquito larvae. This is the first report of Pr1 induction by mosquito cuticle and its role in mosquito mortality.     

Relative toxicity of different combinations of temephos and fenthion with Solanum xanthocarpum extract against anopheline larvae

The relative toxicity of different concentrations of temephos and fenthion with petroleum ether root extract of Solanum xanthocarpum (Schrader) at 1 : 1, 1 : 2 and 1 : 4 ratios was evaluated against Anopheles stephensi (Liston) larvae. All combinations exhibited antagonism at concentrations lower than LC₅₀ values and synergism at concentrations higher than their LC₉₀ values. A 1 : 1 product ratio was the most effective.     

Larvicidal activity of acetone extract and green synthesized silver nanoparticles from Allium sativum L. (Amaryllidaceae) against the dengue vector Aedes aegypti L. (Diptera: Culicidae)

Mosquito vectors of major human diseases are currently controlled using chemical and biological products. Extensive insecticide use has led to resistance development and human/environmental health risks, and alternative sustainable control options are needed; in this study, activity of an extract of garlic (Allium sativum; Amaryllidaceae), and silver nanoparticles (AgNPs) synthesized from the extract, were evaluated against 2nd and 3rd instar larvae of the yellow fever mosquito, Ae. aegypti (Diptera: Culicidae). Synthesis of AgNPs was confirmed using UV–Vis spectroscopy, and characterised using powdered X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Larvae were exposed to five concentrations (50, 100, 150, 200, 250 ppm) of garlic extract or synthesized AgNPs, with distilled water and silver nitrate solution (1 mM) as controls. The mortality of larvae was recorded after 6, 12, 24, 36, and 48 h following addition of the respective extracts.Dose- and time-dependent toxicity were recorded in both treatment groups with no mortality in control groups. Exposure to AgNPs at 250 ppm for 48 h yielded 100% mortality for both larval instars, with corresponding LC₅₀ values of 44.77 (2nd) and 62.82 ppm (3rd). Exposure to garlic extract resulted in similar 48-hour mortality (99 ± 0.77% (2nd) and 98 ± 1.10% (3rd), but consistently higher LC₅₀ values after all exposure times compared to AgNPs (e.g. 48-hour exposure: 108.42 ppm (2nd), 129.11 ppm (3rd), suggesting that AgNPs may potentially be used at lower concentrations for Ae. aegypti control.     

Efficacy of leaves extract of Calotropis procera Ait. (Asclepiadaceae) in controlling Anopheles arabiensis and Culex quinquefasciatus mosquitoes

The present study aimed to investigate, the larvicidal, adult emergence inhibition and oviposition deterrent activity of aqueous leaves extract of Calotropis procera against Anopheles arabiensis and Culex quinquefasciatus as natural mosquito larvicide. The larvicidal activity was monitored against 2nd, 3rd and 4th instar larvae of each mosquito species 24 h post-treatment. Adult emergence inhibition activity was tested by exposing 3rd instar larvae of each mosquito species to different concentrations of extracts (200, 400, 600, 800 and 1000 ppm for An. arabiensis and 100, 200, 300, 400, 500 and 600 ppm for Cx. quinquefasciatus). Probit analysis was used to analyze data from bioassay experiments. The oviposition deterrent activity was tested by using three different concentrations of extracts (1000, 500 and 200 for An. arabiensis, and 1000, 500 and 100 for Cx. quinquefasciatus) that caused high, moderate and low larval mortality in the larvicidal experiment against 3rd instar larvae. It was found that, LC50–LC90 values calculated were 273.53–783.43, 366.44–1018.59 and 454.99–1224.62 ppm for 2nd, 3rd and 4th larval instars, respectively, of An. arabiensis and 187.93–433.51, 218.27–538.27 and 264.85–769.13 ppm for 2nd, 3rd and 4th larval instars, respectively, of Cx. quinquefasciatus. Fifty percent of adult emergence inhibition (EI50) was shown at 277.90 and 183.65 ppm for An. arabiensis and Cx. quinquefasciatus, respectively. The pupal stage was not affected till a concentration of 5000 ppm. The extract showed oviposition deterrence and effective repellence against both mosquito species at different concentrations, with the observation on that maximal eggs were laid in low concentration of extract. These results suggest that the leaves extract of C. procera possess remarkable larvicidal, adult emergence inhibitor, repellent and oviposition deterrent effect against both An. arabiensis and Cx. quinquefasciatus, and might be used as natural biocides for mosquito control.     

Growth Inhibitory Nature of Artemisia annua Extract against Culex quinquefasciatus (Say)

Petroleum ether (Pee), carbon tetrachloride (Cte) and methanol extract (Mee) of Artemisia annua, Chenopodium album and Sonchus oleraceus were screened for their efficacy against Culex quinquefasciatus larvae. Pee of A. annua, Mee of A. annua and Ch. album, Cte of A. Annua were found effective in descending order after 24 and 48 hrs of treatment. Pee of A. annua, the most potent extract with LC₅₀ 78.2 ppm was selected to study its influence on the development and metamorphosis of the culicine mosquito. The extract significantly affected the hatching, larval development, pupal transformation and also lengthened the larval and pupal periods. Growth index was remarkably reduced. Treated culicine eggs, larvae and pupae showed deformities including disruption of the body wall, distorted alimentary canal, damaged tracheal network and arrested histogenesis. The extract has remarkable effect on the metamorphosis and high larvicidal potential, hence, can be used as an effective alternative to the existing synthetic pesticides for the control of Cx. quinquefasciatus.     

Chemical composition and larvicidal activity of Piper capense essential oil against the malaria vector,Anopheles gambiae

Hydro-distilled essential oil from Kenyan Piper capense (Piperaceae) was analysed by gas chromatography mass spectrometry (GC–MS) and evaluated for larvicidal activity against the malaria vector, Anopheles gambiae. The oil consisted mainly of sesquiterpene hydrocarbons which accounted for 43.9% of the oil. The major sesquiterpenes were δ-cadinene (16.82%), β-bisabolene (5.65%), and bicyclogermacrene (3.30%). The oil also had appreciable amounts of monoterpene hydrocarbons (30.64%), including β-pinene (7.24%) and α-phellandrene (4.76%), and arylpropanoids (8.64%), including myristicin (4.26%). The oil showed larvicidal activity against third instar larvae of A. gambiae, with LC₅₀ and LC₉₀ values of 34.9 and 85.0 ppm, respectively. Most of the larvae died within the first few hours. The high larvicidal activity of this oil was indicated by the fact that over 80% mortality was observed at a concentration of 100 ppm after 24 h. These results compared favourably with the commercial larvicide pylarvex® which had LC₅₀ and LC₉₀ values of 3.7 and 7.8 ppm, respectively. Application of this oil or of products derived from it to larval habitats may lead to promising results in malaria and mosquito management programmes.     

Larvicidal potential of gold and silver nanoparticles synthesized using Acalypha fruticosa leaf extracts against Culex pipiens (Culicidae: Diptera)

Plant secondary metabolites have been recently used for the synthesis of different nanoparticles. The present investigation aimed at evaluating the effect of gold (AuNPs) and silver (AgNPs) nanoparticles synthesized using Acalypha fruticosa leaf extracts to control the mosquito Culex pipiens. The A. fruticosa AuNPs and AgNPs spectra displayed their maximum absorption at 550 nm and 440 nm, respectively. The infrared spectra revealed different functional groups related to different chemical compounds. The larval mortality of aqueous leaf extract of A. fruticosa was 499.54 ppm (LC₅₀) and 1734.06 ppm (LC₉₀) after 24 h of treatment. This study revealed that AuNP (LC₅₀, 30.2 and LC₉₀, 104.83 ppm) and AgNP (LC₅₀, 52.86 and LC₉₀, 157.227 ppm) preparations were highly effective compared to the A. fruticosa extract alone and also more affordable, as a smaller amount was required. The present findings show the potential larvicidal effect of the synthesized AuNPs and AgNPs for the control of mosquito-mediated disease transmission.     

Larvicidal potentials of leaf and bark extracts of Eucalyptus camaldulensis (Schlect) and Eucalyptus citriodora (Hook) on Culex quinquefasciatus (Say) larvae

The larvicidal activity of leaf and bark extracts of Eucalyptus camaldulensis and Eucalyptus citriodora on juveniles of Culex quinquefasciatus was determined. Larvae were successfully bred in the laboratory to obtain a “pure” colony. One hundred and sixty‐two batches of 25 larvae each were treated with 3.90, 15.63, 62.50, 250 and 1000 mg/L of plant extract in three replicates, for 24 h to record mortality and for up to 96 h to record feeding and fecundity. There was an increase in percentage mortality with increase in concentration of the petroleum ether plant extracts. There was a statistically significant difference (P < 0.05) between extracts used in the bioassay and mortality of larvae, but there was no significant difference (P > 0.05) between the two plant species. Statistical analysis of average mortality figures using Probit analysis for the leaf extracts of E. citriodora and E. camaldulensis, respectively, had LC₅₀ of 245.47 (26.89 ± 10.13 [SE]) and 316.23 (22.89 ± 8.95) for the crude extracts; 97.72 (44.95 ± 12.89) and 223.87 (29.17 ± 9.56) for the petroleum ether extracts; and 162.18 (30.7 ± 11.16) and 257.04 (26.47 ± 9.28) for the methanol extracts. The bark extracts of E. citriodora and E. camaldulensis, respectively, had LC₅₀ of 251.19 (27.78 ± 8.39) and 398.11 (20.7 ± 7.17) for methanol; and 302.0 (21.56 ± 8.11) and 630.96 (13.56 ± 6.4) for hexane. Both plant species showed anti‐feeding properties against larvae of Culex quinquefasciatus.