Oviposition attractancy of dodecanoic, hexadecanoic and tetradecanoic acids against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae).

OBJECTIVE: Vector control is facing a threat due to emergence of resistance to synthetic insecticides. Compounds that mediate the oviposition of mosquitoes: a possible sustainable tool for the control and monitoring of Culicidae. The present study to evaluate oviposition attractancy of dodecanoic, hexadecanoic and tetradecanoic acid (isolated from conspecific eggs) against gravid female Aedes (Ae.) aegypti and Culex (Cx.) quinquefasciatus mosquitoes. MATERIALS AND METHODS: The oviposition attractancy was determined against two mosquito species to various concentrations viz., 1, 10, and 50 ppm. The attractancy was assessed after 24 h experiment in laboratory condition. After 24 h, the number of eggs laid in treated and control bowls were counted under the stereo microscope. RESULTS: Significant level of concentration-dependent positive oviposition response of mosquitoes to dodecanoic acid, hexadecanoic acid and tetradecanoic acid were observed. Dodecanoic acid have more attractancy in higher concentrations. The oviposition active index (OAI) values of dodecanoic acid against Ae. aegypti and Cx. quinquefasciatus at the concentration of 50 ppm were 0.52 and 0.50 respectively. Whereas hexadecanoic acid shows more attractancy in lower concentration (1 ppm) for both Ae. aegypti and Cx. quinquefasciatus and the values were 0.40 and 0.36 respectively. The result of tetradecanoic acid provides positive response in all concentrations of both mosquitoes. The higher OAI value 0.65 was observed in 10 ppm for Ae. aegypti and 0.55 in 1 ppm for Cx. quinquefasciatus. Among the three compounds tested tetradecanoic acid shows more attractancy to Ae. aegypti and Cx. quinquefasciatus. CONCLUSIONS: In this result it can be concluded that the three compounds possess remarkable oviposition attractancy against Ae. aegypti and Cx. quinquefasciatus.

Prevention of Dengue fever through plant based mosquito repellent Clausena dentata (Willd.) M. Roem (Family: Rutaceae) essential oil against Aedes aegypti l. (Diptera: Culicidae) mosquito.

BACKGROUND: Plant based repellent against mosquito borne diseases are used recently because synthetic repellents cause side effects like breathing problem, eye irritation, head ache, cough, etc. The use of natural products for dengue control would protect the environment, reduce dependence on expensive synthetic repellents and also generate local employment. MATERIAL AND METHODS: Essential oil was isolated by steam distillation which was used against the bites of Aedes aegypti and duration of protection period was assessed. Skin-irritant potential test was also conducted on 25 healthy volunteers by using four-point scale. RESULTS: The increase in the concentrations of essential oil increased the mean protection time against the bites of Aedes aegypti. The lowest mean protection time was 180.0 min for 2.5% and highest time of 255.0 min for 10%. The mean score of zero for skin-irritant potential test for all the concentrations indicated that the essential oil did not cause irritation to human skin. CONCLUSIONS: Results indicated that the use of plant based repellent for the control of dengue fever would replace the currently used synthetic repellents which causes many side effects.

Mosquitocidal and repellent activity of the leaf extract of Citrullus vulgaris (cucurbitaceae) against the malarial vector, Anopheles stephensi liston (diptera culicidae).

The efficacy of the Cucurbitaceous plant Citrullus vulgaris against the Anopheles stephensi was assessed in the present study. The leaf extract of Citrullus vulgaris with different solvents viz, benzene, petroleum ether, ethyl acetate and methanol were tested for larvicidial, ovicidal, repellent and insect growth regulatory activities against Anopheles stephensi. The larval mortality was observed after 24 h exposure. The LC50 values are 18.56, 48.51, 49.57 and 50.32 ppm respectively. The mean percent hatchability of the egg of Anopheles stephensi were observed after 48 h. 100 per cent mortality was exerted at 250 ppm with benzene extract and the other extracts exerted 100 percent mortality at 300 ppm. Skin repellent test at 1.0, 2.5 and 5.0 mg per cm2 concentration gave the mean complete protection time ranged from 119.17 to 387.83 minutes with the four different extracts tested. The Citrullus vulgaris plant extract have shown insect growth regulatory activity against Anopheles stephensi at five different test concentrations ranging from 10 to 150 ppm with different solvents and they exhibit the following EI50 values 28.99, 70.02, 106.33 and 84.25 ppm respectively.

Antibacterial activity of Acalypha indica L.

Hexane, chloroform, ethyl acetate and methanol extracts from the leaves of Acalypha indica were tested against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Streptococcus faecalis) and Gram-negative (Klebsiella pneumoniae, Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa) bacteria. All the extracts exhibited antibacterial activity against Gram-positive organisms with minimum inhibitory concentrations (MIC) between 0.156 to 2.5 mg/ml. Among the Gram-negative bacteria, only the Pseudomonas aeruginosa was susceptible to the extracts.

Entomofaunal diversity of tree hole mosquitoes in Western and Eastern Ghats hill ranges of Tamilnadu, India.

The distribution and abundance of various mosquito vectors is important in the determination of disease prevalence in disease endemic areas. The aim of the present study was to conduct regular entomological surveillance and to determine the relative abundance of tree hole mosquito species in Tamilnadu, India. In addition to this, the impact of weather-conditions on tree hole mosquito population were evaluated between June, 2014 and May, 2015. Six hills ranges viz., Anaimalai hills, Kodaikanal hills, Sitheri hills, Kolli hills, Yercaud hills, and Megamalai were selected, the immatures collected from tree holes by the help of suction tube. Collections were made at dusk and dawn at randomly selected 15 different tree species. The collected samples were stored and morphologically identified to species level in the laboratory. Mosquito diversity was calculated by Simpson's and Shannon-Weiner diversity indicies with spatial and temporal aspects. Over 2642 mosquitoes comprising the primary vectors of dengue, chickungunya, malaria, filariasis were identified. Other species collected from the fifteen sites in each hill during the study included Christophersiomyia annularis, Christophersiomyia thomsoni, Downsiomyia albolateralis, Downsiomyia nivea and Toxorhynchites splendens, etc. Study revealed high species diversity and relative density associated with different study sites. Based on the Shannon diversity index high number of species was recorded with Aedes pseudoalbopicta (0.0829) followed by Ae. aegypti (0.0805) and least species was recorded as Anopheles elegans (0.0059). The distribution of the primary vectors of DF along the high occurrence was evident with most study sites representing proportions of this vector population. This showed the high risk level associated with the livestock movement in amplification and circulation of the virus during the outbreaks. The findings of this study, therefore, demonstrated the potential vulnerability of nomadic communities to infection by arboviral diseases transmitted by mosquito vectors.

Oviposition deterrent and skin repellent activities of Solanum trilobatum leaf extract against the malarial vector Anopheles stephensi.

The leaf extract of Solanum trilobatum (Solanaceae) was tested under laboratory conditions for oviposition deterrent and skin repellent activities against the adult mosquito Anopheles stephensi. Concentrations of 0.01, 0.025, 0.05, 0.075 and 0.1% reduced egg laying by gravid females from 18 to 99% compared to ethanol-treated controls. In skin repellent tests, concentrations of 0.001, 0.005, 0.01, 0.015, and 0.02 % provided 70 to 120 minutes protection against mosquito bites, whereas the ethanol control provided only 2.2 minutes of protection. Both oviposition deterrent and skin repellent activity were dose dependent. The results suggest that the leaf extract of S. trilobatum is an effective oviposition deterrent and skin repellent against An. stephensi.

Larvicidal efficacy of some Cucurbitacious plant leaf extracts against Culex quinquefasciatus (Say).

Larvicidal efficacies of extracts of five species of Cucurbitacious plants, Momordica charantia, Trichosanthes anguina, Luffa acutangula, Benincasa cerifera and Citrullus vulgaris were tested against the late third larval age group of Culex quinquefasciatus. The larval mortality was observed after 24 h exposure. The LC50 values of M. charantia, T. anguina, L. acutangula, B. cerifera and C. vulgaris were 465.85, 567.81, 839.81, 1189.30 and 1636.04 ppm respectively.

Repellent activity of Ferronia elephantum Corr. (Rutaceae) leaf extract against Aedes aegypti (L.).

The repellent activity of a methanol extract of Ferronia elephantum leaves against Aedes aegypti was studied in the laboratory. The percentage protection in relation to the dose method was used. The repellent activity at 1.0 and 2.5 mg/cm2 concentrations gave 100% protection up to 2.14 +/- 0.16 h and 4.00 +/- 0.24 h, respectively. The total percentage protection of Ferronia elephantum was 45.8% at 1.0 mg/cm2 and 59.0% at 2.5 mg/cm2 for 10 h.

Larvicidal efficacy of Pavonia zeylanica L. and Acacia ferruginea D.C. against Culex quinquefasciatus Say.

Larvicidal efficacy of leaf extracts of Pavonia zeylanica and Acacia ferruginea were tested against the late third instar larvae of Culex quinquefasciatus. The larval mortality was observed after 24 h of treatment. The LC50 values of P. zeylanica and A. ferruginea were 2214.7 and 5362.6 ppm, respectively.

Mosquitocidal activities of octacosane from Moschosma polystachyum Linn (lamiaceae).

The toxicity of the plant Moschosma polystachyum was evaluated against mosquito Culex quinquefasciatus. The crude leaf extract and active compound octacosane showed negligible mortality against early third instar larvae of Culex quinquefasciatus. The 24 h LC(50) value was observed at 153.2+/-1.3 mg/l and 7.2+/-1.7 mg/l for crude leaf extract and active compound octacosane, respectively. The repellent activity of active compound octacosane at 1.0 and 2.5 mg/cm(2) concentration gave 85.2+/-1.7 min and 54.6+/-2.3 min protection, respectively. The total percentage protection of octacosane was 96.2+/-0.9 at 2.5 mg/cm(2) and 86.4+/-1.3 at 1.0 mg/cm(2) concentration.

Larvicidal and repellent activity of tetradecanoic acid against Aedes aegypti (Linn.) and Culex quinquefasciatus (Say.) (Diptera:Culicidae).

OBJECTIVE: To investigate the larvicidal and repellent efficacy of tetradecanoic acid against Aedes aegypti (Ae. aegypti) L. and Culex quinquefasciatus (Cx. quinquefasciatus) Say (Diptera: Culicidae). METHODS: Larvicidal efficacy of tetradecanoic acid was tested at various concentrations against the early third instar larvae of Ae. aegypti and Cx. quinquefasciatus. The repellent activity was determined against two mosquito species at three concentrations viz., 1.0,2.5 and 5.0 ppm under the laboratory conditions. RESULTS: The tetradecanoic acid was found to be more effective against Cx. quinquefasciatus than Ae. aegypti larvae. The LC(50) values were 14.08 ppm and 25.10 ppm, respectively. Tetradecanoic acid showed lesser repellency against Ae. aegypti and Cx. quinquefasciatus. The highest repellency was observed in higher concentration of 5.0 mg/cm(2) provided 100% protection up to 60 and 90 min against Ae. aegypti and Cx. quinquefasciatus respectively. CONCLUSIONS: From the results it can be concluded the tetradecanoic acid is a potential for controlling Cx. quinquefasciatus and Ae. aegypti mosquitoes.

Larvicidal and oviposition activity of Cassia obtusifolia Linn (Family: Leguminosae) leaf extract against malarial vector, Anopheles stephensi Liston (Diptera: Culicidae).

The ethanolic leaf extract of Cassia obtusifolia was investigated for their larvicidal and oviposition deterrence effects against Anopheles stephensi. Concentrations ranging from 25 to 125 mg/l were assessed at 24 h post-treatment against late third instar larvae. The leaf extract had significant larvicidal effect with LC(50) and LC(90) values were 52.2 and 108.7 mg/l, respectively. In oviposition behaviour study, four different concentrations ranging from 100 to 400 mg/l were studied against gravid female mosquitoes. The results of oviposition study indicated that the leaf extract showed concentration dependent oviposition deterrent activity. At higher concentration (400 mg/l) showed 92.5% effective repellency against oviposition, followed by 300, 200 and 100 mg/l showed 87.2%, 83.0% and 75.5%, respectively. The larvicidal and oviposition deterrent effect of C. obtusifolia against A. stephensi make this plant product promising as an alternative to synthetic insecticide in mosquito control programs.

Bioactivity of flavonoid compounds from Poncirus trifoliata L. (Family: Rutaceae) against the dengue vector, Aedes aegypti L. (Diptera: Culicidae).

The bioactivity of four flavonoid compounds, namely poncirin, rhoifolin, naringin and marmesin, from Poncirus trifoliata was studied against the Aedes aegypti. Larvicidal assays were conducted to evaluate the 24 h LC(50) and LC(90) values of the flavonoid compounds. The lethal concentration (LC(50) and LC(90)) values ranged from 0.082 to 0.122 mg/l and 0.152 to 0.223 mg/l, respectively. The result of ovicidal test suggests that the ovicidal activity of the flavonoid compounds was influenced by the concentration of flavonoid compounds and age of the eggs. The result of oviposition test showed that the four flavonoid compounds exhibited oviposition-deterrent activity against gravid female mosquitoes. Oviposition decreased with an increase in concentration of flavonoid compounds. A laboratory test was carried out to evaluate protection period and percentage of repellency of four compounds diluted in ethanol (10 mg/l). The compound rhoifolin provided maximum 365.0 +/- 12.0 min protection and also 100.0% +/- 0.0 repellency against mosquito bite followed by poncirin, marmesin and naringin. None of the 25 volunteers of either sex exposed to 10% (w/v) flavonoid compounds (4-h patch test) showed a positive skin irritant reaction. All of the tested compounds proved to have various activities against different life stages of A. aegypti. Therefore, flavonoid compounds from P. trifoliata can be a potential candidate for use in the development of commercial mosquitocidal products that may be an alternative to conventional synthetic chemicals, particularly in integrated vector control applications.

Effect of bioactive fractions of Citrullus vulgaris Schrad. leaf extract against Anopheles stephensi and Aedes aegypti.

The benzene extract of Citrullus vulgaris was tested against Anopheles stephensi and Aedes aegypti for the larvicidal activity and ovicidal properties. The crude benzene extract was found to be more effective against A. stephensi than A. aegypti. The LC50 values were 18.56 and 42.76 ppm respectively. The LC50 values for silica gel fractions (bioactive fractions I, II, III and IV) were 11.32, 14.12, 14.53 and 16.02 ppm respectively. The mean per cent hatchability of the egg rafts were observed after 48 h post treatment. The crude extract of benzene exerted 100% mortality at 250 ppm against A. stephensi and at 300 ppm against A. aegypti. The silica gel fractions I and II afforded 100% mortality at 100 ppm and III and IV exerted the hatchability rate of 4.9 and 5.3% at the same concentration against A. stephensi.

Studies on effect of Acalypha indica L. (Euphorbiaceae) leaf extracts on the malarial vector, Anopheles stephensi Liston (Diptera:Culicidae).

The leaf extract of Acalypha indica with different solvents viz, benzene, chloroform, ethyl acetate and methanol were tested for larvicidal, ovicidal activity and oviposition attractancy against Anopheles stephensi. The larval mortality was observed after 24 h exposure. The LC(50) values are 19.25, 27.76, 23.26 and 15.03 ppm, respectively. Mean percent hatchability of the ovicidal activity was observed 120 h after treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. The highest effective attractancy of 90.09%, 94.20%, 85.43% and 95.75% were observed at 100 ppm concentration viz, benzene, chloroform, ethyl acetate and methanol, respectively. The lowest effective attractancy of 47.17%, 61.94%, 49.28% and 68.12% were observed at 25 ppm concentration viz, benzene, chloroform, ethyl acetate and methanol, respectively. The results that the leaf extract of A. indica is promising as larvicidal and ovicidal activity and oviposition attractancy against malaria vector A. stephensi.

Larvicidal and ovicidal activity of Cassia fistula Linn. leaf extract against filarial and malarial vector mosquitoes.

Methanolic leaf extract of Cassia fistula was tested for larvicidal and ovicidal activity against Culex quinquefasciatus and Anopheles stephensi. The extract was found to be more lethal to the larvae of A. stephensi than C. quinquefasciatus with LC(50) values of 17.97 and 20.57 mg/l, respectively. Mean percent hatchability of the ovicidal activity was observed 120 h after treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. The egg raft of C. quinquefasciatus was found to be more hatchable than A. stephensi. The results show that the leaf extract of C. fistula is promising as a larvicidal and ovicidal agent against C. quinquefasciatus and A. stephensi.

Larvicidal, ovicidal and repellent activities of the leaf extract of two cucurbitacious plants against filarial vector Culex quinquefasciatus (Say) (Diptera : Culicidae).

The leaf extract of two cucurbitacious plants Citrullus colocynthis and Cucurbita maxima with different solvents viz., benzene, ethylacetate, petroleum ether and methanol were tested for larvicidal, ovicidal and repellent activities against the mosquito Culex quinquefasciatus. Larval mortality was observed and recorded after 24 h exposure period. The LC50 values of C. colocynthis were 61.72, 47.58, 66.92 and 118.74 ppm respectively. C. maxima shows the LC50 values of 123.02, 75.91, 117.73 and 171.64 ppm respectively. The mean percent hatchability of the egg rafts were observed after 48 h treatment. 100% mortality was observed at 450 ppm for C. colocynthis and 600 ppm for C. maxima. Skin repellent test at 1.0, 2.5 and 5.0 mg/cm2 concentration of C. colocynthis gives the complete protection time ranges from 107 to 271 minutes. C. maxima exerted the complete protection time of 78 to 215 minutes. The leaf extract of these two plants shows the larvicidal and ovicidal properties and they can also be applied as an effective personal protection measure against mosquito bites.

Repellent activity of selected plant essential oils against the malarial fever mosquito Anopheles stephensi.

In recent years, use of environment friendly and biodegradable natural insecticides of plant origin have received renewed attention as agents for vector control. In this study, essential oils extracted by steam distillation from leaves of five plant species Centella asiatica L., Ipomoea cairica L., Momordica charantia L., Psidium guajava L. and Tridax procumbens L. were evaluated for their topical repellency effects against malarial vector Anopheles stephensi in mosquito cages. All essential oils were tested at three different concentrations (2, 4 and 6%). Of these, the essential oils of I. cairica, M. charantia and T. procumbens exhibited relatively high repellency effect (>300 minutes at 6% concentration), followed by C. asiatica and P. guajava which showed less effective (< 150 minutes at 6 % concentration). However, the ethanol applied arm served as control provided maximum 8.0 minutes repellency in this study. In general, clear dose-response relationships were established in all essential oils, with the highest concentration of 6% provided high repellency effect. The results obtained from this study suggest that essential oils of I. cairica, M. charantia and T. procumbens are promising as repellents at 6% concentration against An. stephensi and could be useful in the search for new natural repellent compounds.

Larvicidal, ovicidal and repellent activities of Cymbopogan citratus Stapf (Graminae) essential oil against the filarial mosquito Culex quinquefasciatus (Say) (Diptera : Culicidae).

Essential oils extracted by steam distillation from Cymbopogan citratus were evaluated for larvicidal, ovicidal and repellent activities against the filarial mosquito Culex quinquefasciatus. The larval mortality was observed after 24 hours treatment. The LC(50) values calculated for the 2nd, 3rd and 4th larval instar were 144.54 +/- 2.3, 165.70 +/- 1.2 and 184.18 +/- 0.8 ppm respectively. Hundred percent ovicidal activity was observed at 300 ppm. Skin repellent test at 1.0, 2.5 and 5.0 mg/cm(2) concentration of C. citratus gave 100% protection up to 3.00, 4.00 and 5.00 hours respectively. The total percentage of protection of this essential oil was 49.64% at 1.0 mg/cm(2), 62.19% at 2.5 mg/cm(2) and 74.03% at 5.0 mg/cm(2) for 12 hours.

Repellency of volatile oils from Moschosma polystachyum and Solanum xanthocarpum against filarial vector Culex quinquefasciatus say.

Volatile oils extracted by steam distillation from leaves of two plant species Moschosma polystachyum and Solanum xanthocarpum were evaluated in mosquito cages for their topical repellency effects against filarial vector Culex quinquefasciatus. The oil from M. polystachyum was tested at four different concentrations ranging from 1 to 4%. The 4% concentration gave 332.2 minutes protection whereas control gave only 4.4 minutes protection against mosquito bites. However, the volatile oil of S.xanthocarpum was tested from 2 to 8% concentration. The 8% concentration gave 311.4 minutes protection whereas control gave only 4.4 minutes protection against mosquito bites. The results suggest that the volatile oils of these two plant species were effective as repellents and gave more than 300 minutes of (>5 hour) protection against the bite of Cx. quinquefasciatus bite. Both volatile oils did not cause dermal irritation when applied to human skin. No adverse effects on human volunteers were observed after application. Therefore, both volatile oils can be applied as an effective personal protection measure against mosquito bites.