Melaleuca quinquinervia(Cav.) S.T. Blake(Myrtales:Myrtaceae):Natural alternative for mosquito control

Objective: To evaluate an essential oil with larvicide, adulticide and growth inhibitory activity against Aedes aegypti, Aedes albopictus and Culex quinquefasciatus mosquitoes, of medical importance. Methods: Standardized methodology by WHO was used to determine the levels of susceptibility of mosquito larvae exposed to the essential oil. To evaluate the adulticide activity with the essential oil at different doses, bottles were impregnated according to the methodology CDC. To determine the development inhibitory activity of Melaleuca quinquinervia(M. quinquinervia) oil in three mosquito species, third instar larvae were exposed to the LC_(50) and LC_(90) dose(calculated for each population) of M. quinquinervia oil in glass containers with a capacity of 500 mL. After 24 h exposure, the dead larvae were discarded. The mortality of larvae and pupae were recorded on a daily basis. Results: The calculated LC_(50) indicates an order of effectiveness of preferential oil for Culex quinquefasciatus(LC_(50)=0.002 1%), Aedes aegypti(LC_(50)=0.004 7%) and Aedes albopictus(LC_(50)=0.004 9%). Conclusions: The adulticide activity was achieved with impregnated bottles at 40 and 50 mg/mL with the three mosquitoes species. In larvae, a growth inhibition was detected when exposed to sublethal doses. The results indicate that M. quinquinervia is a plant with promising environmentally sustainable source for vector control.     

Efficacy of Limonia acidissima L. (Rutaceae) leaf extract on larval immatures of Culex quinquefasciatus Say 1823

ObjectiveTo investigate the role of leaf extract of Limonia acidissima L. (Rutaceae) as a biocontrol agent against the larval form of Culex quinquefasciatus, and characterization of bioactive component responsible for larvicidal activity.MethodsLarval mortality of mosquito species was observed after 24, 48 and 72 hours of exposure to different concentrations of aqueous extract, solvent extract and subsequently bioactive compound. The bioactive compound was subjected to IR and GC-MS analysis.ResultsMortality rate at 3% concentration of crude extract were highest (90%) amongst all concentrations tested and subsequently highest (95%) mortality was achieved in chloroform: methanol extract at 100 ppm concentrations. IR and GC-MS analysis of bioactive compound revealed the presence of steroid compound which may act as larvicide.ConclusionsThe chloroform: methanol extract of mature leaves of Limonia acidissima was found to exhibit considerable mosquito larvicidal activity against Culex quinquefasciatus.     

A comparative study of the ovicidal and larvicidal activities of aqueous and ethanolic extracts of pawpaw seeds Carica papaya (Caricaceae) on Heligmosomoides bakeri

ObjectiveTo assess the ovicidal and larvicidal activities of aqueous and ethanolic extracts of pawpaw seeds Carica papaya (Caricaceae) on the eggs and first stage larvae (L₁) of Heligmosomoides bakeri.MethodsEggs of this parasite were obtained from experimentally infested mice (Mus musculus) and larvae were from eggs after incubation at 25°C for about 72 hours. The eggs and larvae were exposed to ten different concentrations (0.125, 0.25, 0.375, 0.5, 0.75, 1.0, 1.25, 1.75, 2.25 and 2.75 mg/mL) of both aqueous and ethanolic extracts respectively for 72 hours. Distilled water and 0.05% ethanol used as placebo and negative control, respectively.ResultsPlacebo and negative control group all showed average 92% embryonnation, 98% egg hatching and 2% larval mortality, and did not affect development and larval survival. The extracts inhibited embryonic development, egg hatching and larval survival. In general, the ovicidal and larvicidal activities increased with increasing concentration of different extracts. The aqueous extract was found to be more potent on eggs than on larvae. At 2.75 mg/mL, only 8% of eggs embryonnated and 50% hatched to L₁ vs 57% embryonic development and 79% hatching occurred in the ethanolic extract. However, this later extract was more efficient in preventing larval development producing 96% mortality as against 68% with the aqueous extract.ConclusionsThese results shows the ovicidal and larvicidal properties of aqueous and ethanolic pawpaw seeds extracts.     

Larvicidal potential of Acorus calamus L. essential oil against filarial vector mosquito Culex quinquefasciatus (Diptera: Culicidae)

ObjectiveTo identify the chemical composition and larvicidal activity of Acorus calamus (A. calamus) rhizome essential oil against the filarial vector mosquito, Culex quinquefasciatus (Cx. quinquefasciatus).MethodsEssential oil was isolated by hydro-distillation and the chemical composition of the oil was analysed by gas chromatography and gas chromatography mass spectroscopy analysis. The larvicidal activity of the essential oil was analysed at different concentrations, viz., 12.5, 25.0, 50.0, 100.0 and 200.0 mL/L. Early 4th instar larvae were used for the larvicidal assay. The larval mortality was calculated after 24 h of the exposure.ResultsThe gas chromatography and gas chromatography mass spectroscopy analysis showed that the essential oil extracted from the rhizome of A. calamus contained 20 chemical compounds representing about 99.99% of the total oil. Beta-asarone (33.36%), cis-beta-terpineol (23.44%), limonene (13.08%), carvone (5.64%) and amyl isovalerate (4.92%) were identified as the major chemical compounds. The essential oil had promising larvicidal effect against the early 4th instar larvae of Cx. quinquefasciatus with LC₅₀ value of 63.43 mL/L and LC₉₀ value of 145.95 mL/L.ConclusionThe essential oil of A. calamus rhizome can be used as a natural larvicidal agent against the larvae of filarial vector mosquito, Cx. quinquefasciatus.     

Efficacy of larvicidal and pupicidal activity of Catharanthus roseus aqueous and solvent extracts against Anopheles stephensi Liston and Culex quinquefasciatus Say (Diptera: Culicidae)

ObjectiveTo investigate the larvicidal and pupicidal activities of aqueous, ethyl acetate and methanol extracts of Catharanthus roseus (C. roseus) against malaria and filariasis vectors.MethodsThe larvicidal and pupicidal activities of C. roseus leaf extracts were tested against the fourth instar larvae and pupae of Anopheles stephensi (An. stephensi) and Culex quinquefasciatus (Cx. quinquefasciatus). The mortality was observed after 24 and 48 h post the treatment. The data were subjected to probit analysis to determine the lethal concentrations (LC₅₀ and LC₉₀) at which 50% and 90% of the treated larvae or pupae of the tested species were killed.ResultsThe larval and pupal mortality were observed after 24 and 48 h of exposure of aqueous, ethyl acetate and methanol extracts of C. roseus; no mortality was observed in the control group. The LC₅₀ values against the fourth-instar larvae of An. stephensi were 68.62 and 72.04 mg/mL for the aqueous extract, 82.47 mg/mL for the ethyl acetate extract, and 78.80 and 86.64 mg/mL for the methanol extract, while the aqueous, ethyl acetate and methanol extracts had LC₅₀ values of 85.21, 76.84 and 94.20 mg/mL against the fourth-instar larvae of Cx. quinquefasciatus. The aqueous, ethyl acetate and methanol extracts had LC₅₀ values of 118.08, 182.47 and 143.80 mg/mL against the pupae of An. stephensi and 146.20, 226.84 and 156.62 mg/mL against the pupae of Cx. quinquefasciatus, respectively.ConclusionsThe aqueous and methanol extracts of C. roseus leaves had an excellent potential to control the malarial vector An. stephensi and filariasis vector Cx. quinquefasciatus.     

Larvicidal,ovicidal and repellent activities of marine sponge Cliona celata(Grant) extracts against Anopheles stephensi Liston(Diptera:Culicidae)

Obective:To evaluate the larvieidal.ovieidal and repellent properties of solvent extracts of marine sponge Cliona celala(C.celata)(Grant) against the malarial vector Anopheles stephensi(An.stephensi) Listen.Methods:Marine sponge C.celala was thoroughly washed with distilled water and shade dried for 48 h.Then the sponges were homogenized and extracted sequentially with hexane,ethyl acetate and methanol,Lanvicidal and ovicidal activities were tested at four different concentrations viz.,62.5.125.0.250.0 and 500.0 ppm.for repellent study extracts were taken in three different concentrations viz..5.0.2.5.1.0 mg/cm at.Results:Among the three solvent extracts of C.celata,methanol extract showed thc highest lanvieidal activity at 500 ppm against the fourth inslar larvae of An.stephensi.The LC_(50)and LC_(90) values of C.celata methanol extract were recorded as 80.61 and 220.81 ppm against An.stephensi larvae respectively.High ovieidal activity of 91.2%was recorded al 500 ppm concentration of methanol extract.The haxane extract was found to be the most effective protectant against the adult female mosquitoes of An.stephensi.The mean protection time recorded in hexane extract was up to 245 min at 5 mg/cm~2 dosage against An.Stephensi adults.Conclusions:The screening results suggest that the hexane and methanol extracts of C.celata arc promising in mosquito control.Considering these bioaclivitics.C.celata could the probed further to obtain some novel pesticidal molecules.     

Evaluation of larvicidal and pupicidal activity of Morinda citrifolia L. (Noni) (Family: Rubiaceae) against three mosquito vectors

ObjectiveTo evaluate the mosquito larvicidal and pupicidal activity against three important medically mosquito vector such as malarial vector, Anopheles stephensi (An. stephensi), dengue vector, Aedes aegypti (Ae. aegypti) and filarial vector Culex quinquefasciatus (Cx. quinquefasciatus).MethodsMorinda citrifolia (M. citrifolia) leaf was collected in and around Alleppy districts, Kerala, India. M. citrifolia leaf was washed with tap water and shade dried at room temperature. An electrical blender powdered the dried plant materials (leaves). From the leaf, 1 kg powdered was macerated with 3.0 L of methanol sequentially for a period 72 h and filtered. The crude plant extracts were evaporated to dryness in rotary vacuum evaporator. The larvicidal and pupicidal activity was assayed at various concentrations ranging from (100–500 ppm) under the laboratory as well as field conditions. The LC₅₀and LC₉₀value of the M. citrifolia leaf extract was determined by Probit analysis.ResultsThe plant extract showed larvicidal and pupicidal effects after 24 and 48 hrs of exposure; All larval instars and pupae have considerably moderate mortality; however, the highest larval and pupal mortality was methanolic extract of M. citrifolia observed in three mosquito vectors at 48 h. The LC₅₀and LC₉₀of M. citrifolia against the first to fourth instar larvae and pupae against mosquito vectors. An. stephensi had values of LC₅₀=146.08, 159.07, 172.16, 185.08 and 202.68 ppm and LC₉₀=322.12, 363.48, 388.56, 436.51 and 513.56 ppm, respectively. The Ae. aegypti had values of LC₅₀=181.27, 210.40, 229.80, 256.73 and 292.01 ppm and LC₉₀=407.99, 485.65, 534.14, 624.16 and 756.79 ppm, respectively. The Cx. quinquefasciatus had values of LC₅₀=226.70, 256.97, 290.05, 316.33 and 358.11 ppm and LC₉₀=560.35, 652.07, 733.03, 797.09 and 875.25 ppm, respectively at 24 h.ConclusionsThe results of the leaf extract of M. citrifolia are promising as good larvicidal and pupicidal activity against the mosquito vector, An. stephensi, Ae. aegypti, Cx. quinquefasciatus. This is a new eco-friendly approach for the control of vector control programs. Therefore, this study provides first report on the larvicidal and pupicidal activities against three species of mosquito vectors of this plant extract from India.     

Mosquito larvicidal activity of some common spices and vegetable waste on Culex quinquefasciatus and Anopheles stephensi

ObjectiveTo investigate the larvicidal activities of crude and chloroform: methanol (1:1 v/v) extracts of some common spices (Cuminum cyminum, Allium sativum, Zingiber offinale, Curcuma longa) and vegetable waste (Solanum tuberosum germinated tuber) against Anopheles stephensi and Culex quinquefasciatus mosquito larvae.MethodsLarval mortality of above mosquito species were observed after 24, 48 and 72 h of exposure to five concentrations of aqueous extract (0.1%, 0.2%, 0.3%, 0.4% and 0.5%) and four concentrations (25, 50, 75 ppm) of chloroform: methanol (1:1 v/v) extract. The lethal concentration of individual spices or vegetable waste was determined by log-probit analysis (at 95% confidence level) and effect of crude and chloroform: methanol (1:1 v/v) extracts were recorded on non target organisms.ResultsRelative mortality rate of both larval mosquito species were recorded in the following sequences: Cuminum cyminum > Allium sativum > Zingiber offinale, Curcuma longa > Solanum tuberosum germinated tuber for crude extract, and efficacy of chloroform: methanol (1:1 v/v) extract were as follows: Curcuma longa > Zingiber offinale > Solanum tuberosum germinated tuber > Cuminum cyminum > Allium sativum.ConclusionsCrude and chloroform: methanol (1:1 v/v) extract of Cuminum cyminum, Allium sativum, Zingiber offinale, Curcuma longa and Solanum tuberosum germinated tuber can be recommended effectively in mosquito control programmes at very low concentrations. No mortality and other abnormalities were noticed on non target organisms and further studies are needed to investigate the chemical structure of active principal which are responsible for larvicidal activity.     

Chemical composition and larvicidal activities of the essential oil of Zanthoxylum armatum DC (Rutaceae) against three mosquito vectors

BACKGROUND & OBJECTIVES: 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 potential of the essential oil from the seeds of Zanthoxylum armatum DC [syn. Z. alatum Roxb] (Rutaceae) against three medically important species of mosquito vectors, Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. METHODS: Essential oil was hydro distilled in the laboratory from the seeds obtained from the market and the chemical constituents of the oil were determined using GC/GC-MS. Bioefficacy of the essential oil was evaluated under laboratory conditions using III instar mosquito larvae. RESULTS: Among the three mosquito species tested, Cx. quinquefasciatus was the most sensitive (LC50 = 49 ppm) followed by Ae. aegypti (LC50 = 54 ppm) and An. stephensi (LC50 = 58 ppm). GC-MS analysis of the oil revealed at least 28 compounds, consisting mainly of oxygenated monoterpenes (75%) and monoterpenes (22%). Linalool though constituted a major part (57%), failed to produce any appreciable mortality when tested alone. INTERPRETATION & CONCLUSION: From the results it can be concluded that the larvae of the three mosquito species were susceptible to the essential oil composition. Such findings would be useful in promoting research aiming at the development of new agent for mosquito control based on bioactive chemical compounds from indigenous plant sources as an alternative to chemical larvicides.     

Mosquito larvicidal properties of Orthosiphon thymiflorus (Roth) Sleesen. (Family: Labiatae) against mosquito vectors, Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti (Diptera: Culicidae)

ObjectiveTo determine the mosquito larvicidal activities of hexane, chloroform, ethyl acetate, acetone and methanol leaf extract of Orthosiphon thymiflorus (O. thymiflorus) against Anopheles stephensi (An. stephensi), Culex quinquefasciatus (Cx. quinquefasciatus) and Aedes aegypti (Ae. aegypti).MethodsThe larvicidal activity was assayed against three mosquito species at various concentrations ranging from (50-450 ppm) under the laboratory conditions. The LC₅₀ and LC₉₀ value of the O. thymiflorus leaf extract was determined by Probit analysis.ResultsThe LC₅₀ values of hexane, chloroform, ethyl acetate, acetone and methanol extract of O. thymiflorus third instar larvae of An. stephensi were LC₅₀= 201.39, 178.76, 158.06, 139.22 and 118.74 ppm; Cx. quinquefasciatus were LC₅₀=228.13, 209.72, 183.35, 163.55 and 149.96 ppm and Ae. aegypti were LC₅₀=215.65, 197.91, 175.05, 154.80 and 137.26 ppm, respectively. Maximum larvicidal activity was observed in the methanolic extract followed by acetone, ethyl acetate chloroform and hexane extract. The larval mortality was observed after 24 h exposure. No mortality was observed in control.ConclusionsThe present results suggest that the effective plant crude extracts have potential to be used as an ideal eco-friendly approach for the control of mosquito vectors. This study provides the first report on the larvicidal activity of this plant crude solvent extract of against An. stephensi, Cx. quinquefasciatus and Ae. aegypti mosquitoes.     

Efficacy of neem oil-water emulsion against mosquito immatures.

Neem oil-water emulsion was used in mosquito breeding habitats to find out its larvicidal effect on immatures of different mosquito species. Application of 5% neem oil-water emulsion @ 50 ml/sq m in pools and @ 100 ml/sq m in tanks resulted in 100% reduction of III and IV instar larvae of An. stephensi after 24 h while, against Cx. quinquefasciatus it was 51.6 and 91.2% reduction in the larval density after Day 1 and 14 respectively. Similarly, application of 10% emulsion in desert coolers against Aedes aegypti @ 40 to 80 ml per cooler resulted in complete inhibition of pupal production.     

Mosquito larvicidal properties of various extract of leaves and fixed oil from the seeds of Caesalpinia bonduc (L) Roxb

A Preliminary laboratory trial was undertaken to determine the efficacies of petroleum ether, ethanolic, aqueous extracts of dried leaves and fixed oil from the seeds of Caesalpinia bonduc (L). Roxb (Family: Caesalpiniaceae) at various concentrations against the fourth instar larvae of Culex quinquefasciatus by following the WHO guidelines. Hundred per cent mortality was observed in 1% concentration of petroleum ether and ethanolic extract of leaf, whereas it was 55% in 2.5% concentration of aqueous extract and 92.6% in 2.5% concentration of fixed oil. The active constituent responsible for the mortality is to be isolated to come up with a promising larvicidal agent, which will be economic, non pollutant and ecofriendly.     

Potential larvicidal and pupacidal activities of herbal essential oils against Culex quinquefasciatus say and Anopheles minimus (Theobald)

The larvicidal and pupacidal effects of eight herbal essential oils were tested against third instar (L3), fourth instar (L4), and pupal stages of Culex quinquefasciatus and Anopheles minimus. Probit analysis was used to analyze the data. The larval mortality was recorded at 1, 5, 10, 30, and 60 minutes, and 24 hours. Pupal mortality was also recorded at 24 hours intervals for 96 hours when completed mortality was achieved. Citronella grass oil #2 (Cymbopogon nardus) proved to have the greatest toxicity against 3rd instar Cx. quinquefasciatus and An. minimus with LT50 at 1.2 and <0.2 minute, respectively. It exhibited a high level of effectiveness against 4th instar Cx. quinquefasciatus (LT50 at 5.1 minutes) and An. minimus (LT50 at 0.9 minute). Regarding pupacidal activity, Cx. quinquefasciatus and An. minimus pupae were susceptible to Lemon grass oil (LT50 at 1.2 hours) and Citronella grass oil #1 (LT50 at 0.6 hour), respectively. These oils had larvicidal and pupacidal activities with 100% mortality against L3, L4 and pupal stage Cx. quinquefasciatus at 10 minutes, 30 minutes and 24 hours. They also caused 100% mortality of An. minimus at 5 minutes (L3, L4), and 24 hours (pupal stage).     

Larvicidal activity of Wrightia tinctoria R. BR. (Apocynaceae) fruit and leaf extracts against the filarial vector Culex quinquefasciatus Say (Diptera: Culicidae)

ObjectiveTo determine the larvicidal activity of crude aqueous and petroleum ether extracts of Wrightia tinctoria fruits and leaves against the filarial vector, Culex quinquefasciatus.MethodsThe larvicidal activity was evaluated at concentrations of 0.06%, 0.12%, 0.25%, 0.50% and 1.00%. Larval mortality was observed for 24 and 48 h.ResultsAmong the plant parts tested, aqueous fruit extract exhibited highest larvicidal activity followed by aqueous leaf extract with LC₅₀ values of 0.17% and 0.09%; 0.21% and 0.11% after 24 and 48 h respectively.ConclusionsFurther investigations are needed to elucidate this activity against a wide range of all stages of mosquito species and also the active ingredient(s) of the extract responsible for larvicidal activity should be identified.     

Larvicidal activity of essential oil and methanol extract of Nepeta menthoides against malaria vector Anopheles stephensi

ObjectiveTo investigate the larvicidal activity of essential oil and methanol extract of the Nepeta menthoides (N. menthoides) against main malaria vector, Anopheles stephensi (An. stephensi).MethodsThe essential oil of plant was obtained by Clevenger type apparatus and the methanol extract was supplied with Percolation method. Larvicidal activity was tested by WHO method. Twenty five fourth-instar larvae of An. stephensi were used in the larvicidal assay and four replicates were tested for each concentration. Five different concentrations of the oil and extract were tested for calculation of LC₅₀ and LC₉₀ values.ResultsThe LC₅₀ and LC₉₀ values were determined by probit analysis. LC₅₀ was 69.5 and 234.3 ppm and LC₉₀ was 175.5 and 419.9 ppm for the extract and essential oil respectively.ConclusionsAccording to the results of this study methanolic extract of plant exhibited more larvicidal activity than essential oil. This could be useful for investigation of new natural larvicidal compounds.     

Mosquito larvicidal and pupicidal activity of Euphorbia hirta Linn. (Family: Euphorbiaceae) and Bacillus sphaericus against Anopheles stephensi Liston. (Diptera: Culicidae)

ObjectiveTo explore the larvicidal and pupicidal activity of Euphorbia hirta (E. hirta) leaf extract and Bacillus sphaericus (B. sphaericus) against the malarial vector, Anopheles stephensi (An. stephensi).MethodsThe larvicidal and pupicidal activity was assayed against An. stephensi at various concentrations ranging from (75-375 ppm) under the laboratory as well as field conditions. The LC₅₀ and LC₉₀ value of the E. hirta leaf extract was determined by probit analysis.ResultsThe plant extract showed larvicidal effects after 24 h of exposure; however, the highest larval mortality was found in the methanol extract of E. hirta against the first to fourth instars larvae and pupae of values LC₅₀= 137.40, 172.65, 217.81, 269.37 and 332.39 ppm; B. sphaericus against the first to fourth instars larvae and pupae of values LC₅₀= 44.29, 55.83, 68.51, 82.19 and 95.55 ppm, respectively. Moreover, combined treatment of values of LC₅₀= 79.13, 80.42, 86.01, 93.00 and 98.12 ppm, respectively. No mortality was observed in the control.ConclusionsThese results suggest methanol leaf extracts of E. hirta and B. sphaericus have potential to be used as an ideal eco-friendly approach for the control of the malarial vector, An. stephensi as target species of vector control programs. This study provides the first report on the combined mosquito larvicidal and pupicidal activity of this plant crude extract and bacterial toxin against An. stephensi mosquitoes.     

Laboratory evaluation of ethyl acetate and chloroform: methanol (1:1 v/v) extract of Swietenia mahagoni leaf against Japanese Encephalitis vector Culex vishuni group

ObjectiveTo study the larvicidal activity of a furniture tree Swietenia mahagoni L. (S. mahagoni) against mosquito Culex Vishnui group.MethodsDifferent concentrations of crude, chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts of S. mahagoni mature leaves were treated against Cx. vishnui group larvae.ResultsFive graded concentrations (0.05%, 0.10%, 0.20%, 0.30% and 0.40%) of crude extract of mature leaves and five graded concentrations (10 ppm, 20 ppm, 30 ppm, 40 ppm and 50 ppm) of chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts showed significant (P<0.05) larval mortalities. LC₅₀, LC₉₀ values were calculated at 24 h, 48 h and 72 h of exposures. Adult Cx. vishnui group mosquitoes exposed to burning coils prepared from S. mahagoni mature leaves showed smoke repellency and toxicity up to 4 h.ConclusionsThis study was a pioneer attempt to establish S. mahagoni as an effective mosquito larvicide.     

Larvicidal and repellent properties of some essential oils against Culex tritaeniorhynchus Giles and Anopheles subpictus Grassi (Diptera: Culicidae)

ObjectiveTo investigate the larvicidal and repellent properties of essential oils from various parts of four plant species Cymbopogan citrates, Cinnamomum zeylanicum, Rosmarinus officinalis and Zingiber officinale against Culex tritaeniorhynchus (Cx. tritaeniorhynchus) and Anopheles subpictus (An. subpictus).MethodsEssential oils were obtained by hydro-distillation method. The mosquitoes were reared in the vector control laboratory and twenty five late third instar larvae of Cx. tritaeniorhynchus and An. subpictus were exposed to based on the wide range and narrow range test, essential oil tested at various concentrations ranging from 25 to 250 ppm. The larval mortality was observed after 24 h under the laboratory conditions. The repellent efficacy was determined against two mosquito species at three concentrations viz., 1.0, 2.5 and 5.0 mg/cm² under laboratory conditions.ResultsResults showed all the four plant essential oil produced significant larval mortality against two mosquito species. However, the highest larvicidal activity was observed in the essential oil from Zingiber officinale against Cx. tritaeniorhynchus and An. subpictus with the LC₅₀ and LC₉₀ values as 98.83, 57.98 ppm and 186.55, 104.23 ppm, respectively. All the four essential oil shows significant repellency against Cx. tritaeniorhynchus than An. subpictus. Among four essential oil tested the highest repellency was observed in Zingiber officinale, a higher concentration of 5.0 mg/cm² provided 100% protection up to 150 and180 min against Cx. tritaeniorhynchus and An. subpictus, respectively.ConclusionsIn this work, it can be concluded that four essential oils which were distilled from Cymbopogan citrates, Cinnamomum zeylanicum, Rosmarinus officinalis and Zingiber officinale showed promising larvicidal and repellent agent against Cx. tritaeniorhynchus and An. subpictus.     

Mosquito larvicidal and ovicidal properties of Eclipta alba (L.) Hassk (Asteraceae) against chikungunya vector, Aedes aegypti (Linn.) (Diptera: Culicidae)

ObjectiveThe present study deals with the investigation of larvicidal and ovicidal activities of benzene, hexane, ethyl acetate, methanol and chloroform leaf extract of Eclipta alba (E. alba) against dengue vector, Aedes aegypti (Ae. Aegypti).MethodsTwenty five early III instar larvae of Ae. aegypti was exposed to various concentrations (50–300 ppm) and was assayed in the laboratory by using the protocol of WHO 2005; the 24 h LC₅₀ values of the E. alba leaf extract was determined by Probit analysis. For ovicidal activity, slightly modified method of Su and Mulla was performed. The ovicidal activity was determined against Ae. aegypti to various concentrations ranging from 100–350 ppm under the laboratory conditions. The egg hatch rates were assessed 48 h post treatment.ResultsThe LC₅₀ values of benzene, hexane, ethyl acetate, methanol and chloroform extract of E. alba against early third instar larvae of Ae. aegypti were 151.38, 165.10, 154.88, 127.64 and 146.28 ppm, respectively. Maximum larvicidal activity was observed in the methanol extract followed by chloroform, benzene, ethyl acetate and hexane extract. No mortality was observed in control. Among five solvent tested the methanol extract was found to be most effective for ovicidal activity against Ae. aegypti. The methanol extracts exerted 100% mortality (zero hatchability) at 300 ppm.ConclusionsFrom the results it can be concluded the crude extract of E. alba was an excellent potential for controlling Ae. aegypti mosquito.     

Formulation of tablets from the crude extract of Rhinacanthus nasutus (Thai local plant) against Aedes aegypti and Culex quinquefasciatus larvae: a preliminary study

Dried root powder of Rhinacanthus nasutus, Thong Phan Chang (Thai name) were extracted with methanol (MeOH) in a Soxhlet apparatus and made into 2 formulations of tablet containing the extract at 5% and 10% concentration. Due to the viscous and poor flow properties of the crude MeOH extract obtained, a wet granulation method was conducted in developing the tablets. Lactose was used as a filler. Polyvinyl pyrrolidone (PVP) K30 (15% w/w solution in alcohol) was used as the binding agent, while stearic acid (2% w/w) was used as a lubricant. Both formulas of prepared tablets had a smooth shiny surface with a round shape. Other physical properties of the tablets, such as weight variation, friability and disintegration time, met the requirements of the USP XX standard. The mosquito larvicidal activity of prepared tablets containing 5% and 10% R. nasutus extract against Aedes aegypti were not significantly different from each other (p > 0.05), with 48-hour LC50 values of 13.6 and 14.2 mg/I for the 5% and 10% tablets, respectively, while their activities against Culex quinquefasciatus were similar (p > 0.05) with LC50 values of 18.7 and 17.3, respectively. The larvicidal activity levels against Ae. aegypti and Cx. quinquefasciatus were also not significantly different from each other (p > 0.05). No larval mortality was observed in the two control groups: lactose solution and dechlorinated water. Toxicity to female and male fish (Poecilia reticulata) was tested with the prepared tablets. The toxicity of tablets containing 5% and 10% extracts were not significantly different from each other for the P. reticulata females with 48-hour LC50 values of 105.2 and 110.8 mg/I, respectively, and for P. reticulata males with LC50 values of 99.1 and 103.4 mg/I, respectively. Female and male P. reticulata were sensitive to the same dose of the extract. No fish died in the two control groups, with lactose solution and dechlorinated water. Acute-toxicity bioassay with fish showed that with an exposure of 48 hours the LC50 values of the tablets containing 5% and 10% were 5- to 10-fold higher than the LC50 of R. nasutus against mosquito larvae. These prepared tablets could possibly used to control mosquito vectors and be introduced into the mosquito control program.