Radhika Warikoo

Bioefficacy of Mentha piperita essential oil against dengue fever mosquito Aedes aegypti L.

OBJECTIVE To assess the larvicidal and repellent potential of the essential oil extracted from the leaves of peppermint plant, Mentha piperita (M. piperita) against the larval and adult stages of Aedes aegypti (Ae. Aegypti). METHODS The larvicidal potential of peppermint oil was evaluated against early fourth instar larvae of Ae. aegypti using WHO protocol. The mortality counts were made after 24 and 48 h, and LC50 and LC90 values were calculated. The efficacy of peppermint oil as mosquito repellent was assessed using the human-bait technique. The measured area of one arm of a human volunteer was applied with the oil and the other arm was applied with ethanol. The mosquito bites on both the arms were recorded for 3 min after every 15 min. The experiment continued for 3 h and the percent protection was calculated. RESULTS The essential oil extracted from M. piperita possessed excellent larvicidal efficiency against dengue vector. The bioassays showed an LC50 and LC90 value of 111.9 and 295.18 ppm, respectively after 24 h of exposure. The toxicity of the oil increased 11.8% when the larvae were exposed to the oil for 48 h. The remarkable repellent properties of M. piperita essential oil were established against adults Ae. aegypti. The application of oil resulted in 100% protection till 150 min. After next 30 min, only 1-2 bites were recorded as compared with 8-9 bites on the control arm. CONCLUSIONS The peppermint essential oil is proved to be efficient larvicide and repellent against dengue vector. Further studies are needed to identify the possible role of oil as adulticide, oviposition deterrent and ovicidal agent. The isolation of active ingredient from the oil could help in formulating strategies for mosquito control.

Larvicidal and irritant activities of hexane leaf extracts of Citrus sinensis against dengue vector Aedes aegypti L.

OBJECTIVE To assess the larvicidal and irritant activities of the hexane extracts of leaves of Citrus sinensis (C. sinensis) against the early fourth instars and female adults of Aedes aegypti (Ae. aegypti). METHODS The larvicidal potential of the prepared leaf extract was evaluated against early fourth instar larvae of Ae. aegypti using WHO protocol. The mortality counts were made after 24 h and LC50 and LC90 values were calculated. The efficacy of extract as mosquito irritant was assessed by contact irritancy assays. Extract-impregnated paper was placed on a glass plate over which a perspex funnel with a hole on the top was kept inverted. Single female adult, 3-day old unfed/blood-fed, was released inside the funnel. After 3 min of acclimatization time, the time taken for the first take-off and total number of flights undertaken during 15 min were scored. RESULTS The citrus leaf extracts from hexane possessed moderate larvicidal efficiency against dengue vector. The bioassays resulted in an LC50 and LC90 value of 446.84 and 1 370.96 ppm, respectively after 24 h of exposure. However, the extracts were proved to be remarkable irritant against adults Ae. aegypti, more pronounced effects being observed on blood-fed females than unfed females. The extract-impregnated paper was thus proved to be 7-11 times more irritable as compared with the control paper. CONCLUSIONS The hexane extracts from C. sinensis leaves are proved to be reasonably larvicidal but remarkably irritant against dengue vector. Further studies are needed to identify the possible role of extract as adulticide, oviposition deterrent and ovicidal agent. The isolation of active ingredient from the extract could help in formulating strategies for mosquito control.

Evaluation of 15 local plant species as larvicidal agents against an Indian strain of dengue fever mosquito, Aedes aegypti L. (Diptera: Culicidae)

The adverse effects of chemical insecticides-based intervention measures for the control of mosquito vectors have received wide public apprehension because of several problems like insecticide resistance, resurgence of pest species, environmental pollution, toxic hazards to humans, and non-target organisms. These problems have necessitated the need to explore and develop alternative strategies using eco-friendly, environmentally safe, bio-degradable plant products which are non-toxic to non-target organisms too. In view of this, 15 plant species were collected from local areas in New Delhi, India. Different parts of these plants were separated, dried, mechanically grinded, and sieved to get fine powder. The 200 g of each part was soaked in 1000 mL of different solvents separately and the crude extracts, thus formed, were concentrated using a vacuum evaporator at 45°C under low pressure. Each extract was screened to explore its potential as a mosquito larvicidal agent against early fourth instars of dengue vector, Aedes aegypti using WHO protocol. The preliminary screening showed that only 10 plants possessed larvicidal potential as they could result in 100% mortality at 1000 ppm. Further evaluation of the potential larvicidal extracts established the hexane leaf extract of Lantana camara to be most effective extract exhibiting a significant LC50 value of 30.71 ppm while the Phyllanthus emblica fruit extract was found to be least effective with an LC50 value of 298.93 ppm. The extracts made from different parts of other five plants; Achyranthes aspera, Zingiber officinalis, Ricinus communis, Trachyspermum ammi, and Cassia occidentalis also possessed significant larvicidal potential with LC50 values ranging from 55.0 to 74.67 ppm. Other three extracts showed moderate toxicity against A. aegypti larvae. Further investigations would be needed to isolate and identify the primary component responsible for the larvicidal efficiency of the effective plants.

Evaluation of the larvicidal efficiency of stem, roots and leaves of the weed, Parthenium hysterophorus (Family: Asteraceae) against Aedes aegypti L.

Abstract Objective To assess the larvicidal potential of various extracts prepared from the stem, roots and leaves of Parthenium hysterophorus ( P. hysterophorus ) against 3rd and 4th instars of Aedes aegypti (Ae. aegypti) . Methods The extracts from each part were prepared with four solvents; petroleum ether, hexane, acetone and diethyl ether. Each part was dried, powdered and soaked in different solvents, separately, for five days. The crude extracts thus formed were concentrated using rotary evaporator and stored as stock solution of 1 000 mg/L. Results All the extracts prepared from the leaves were found ineffective against both the instars causing only 10%-40% mortality. Against 3rd instars, the hexane and petroleum ether extracts prepared from the stem of P. hysterophorus were found effective exhibiting LC 50 values of 379.76 and 438.57 mg/L, respectively. Likewise the hexane and petroleum ether extracts from the Parthenium roots resulted in LC 50 values of 432.38 and 562.50 mg/L, respectively, against 4th instars of Ae. aegypti revealing their larvicidal potential. It was further found that the hexane extracts, whether from roots or stem, were 13-28% more effective than the petroleum ether extracts. The qualitative phytochemical study of the effective extracts from the stems and roots showed the presence of alkaloids, saponins, terpenoids and flavonoids in different combinations. Conclusions Our investigations demonstrated the potential of P. hysterophorus roots and stems against Ae. aegypti larvae and their benefits as new types of mosquito larvicides. Variety of types and levels of active constituents in each kind of extract may be responsible for the variability in their potential against Ae. aegypti . Further research is needed to identify these components.

Larvicidal, Repellent, and Irritant Potential of the Seed-Derived Essential oil of Apium graveolens Against Dengue Vector, Aedes aegypti L. (Diptera: Culicidae)

Aedes aegypti L. is one of the primary disease vectors spreading various dreadful diseases throughout the world, specifically over tropics and subtropics. Keeping in view the adverse effects of chemical insecticides-based intervention measures, the eco-friendly and bio-degradable essential oil extracted from the seeds of celery, Apium graveolens were investigated for its efficacy against Ae. aegypti. Larvicidal bioassay carried out with the seed oil against early fourth instars of Ae. aegypti caused an LC50 and LC90 values of 16.10 and 29.08 ppm, respectively, after an exposure to 24 h. The cidal effect of the celery seed oil augmented by 1.2-fold; after an exposure to 48 h; revealing an LC50 value of 13.22 ppm. Interestingly, the seed oil did not cause immediate larval mortality, suggesting a delayed toxicity against the larval stage. Present investigations also revealed remarkable effective repellency of the oil leading to 100% protection till 165 min as compared to control that did not result in any repellency against adult Ae. aegypti. Interestingly, only one bite was recorded in the 165th-min after which only two bites were scored until 180 min of exposure of the adult mosquitoes to the oil. An exciting observation was that the knocked-down effect in adults exposed to 10% oil-impregnated papers. The contact irritancy assays with paper impregnated with 1% celery seed oil caused first flight only after 4 s resulting in an average of 63.66 flights during 15 min of exposure revealing the relative irritability of 26.97. The qualitative phytochemical analysis of the seed oil showed the presence of flavonoids, lactones, and terpenoids as the major constituents suggesting their probable role in the toxicity. Our results confirmed that celery seed essential oil can be used as an efficient larvicide and repellent against Ae. aegypti. The identification of the bioactive components, their mode of action, and studying effects on non-target organisms and the environment would help in devising mosquito-management strategies.

Potential of Nardostachys jatamansi Extracts to Manage Indian Strain of Aedes aegypti: A Novel Approach for Vector Control

The antagonistic impacts of chemical toxicants-based intrusion measures for the control of mosquitoes have received extensive public apprehension because of numerous problems; including insecticide resistance, revival of pests, environmental contamination, lethal effects on humans and other non-target organisms. These complications have reasoned the requirement to explore and formulate the alternative plant-based strategies possessing eco-safety, bio-degradability and non-toxicity to nontarget organisms. Spikenard plant, Nardostachys jatamansi also known as the healing oil is grown in Northern India and China. Though earlier used as perfume and for healing purposes, it is not widely used today. In the current study, the efficacy of the roots of spikenard plant, Nardostachys jatamansi were explored against larvae of dengue vector, Aedes aegypti. The roots were separately extracted in two solvents; hexane and petroleum ether; which were then assessed against early fourth instars of Aedes aegypti as per procedure recommended by WHO. The larvae dead and in the moribund state were scored after 24 h of exposure and data was analysed statistically to calculate LC values. Both extracts proved to possess excellent larvicidal potential. The bioassays with hexane roots extracts resulted in LC50 and LC90 value of 140.64 and 302.54 ppm, respectively after 24 h of exposure, while the extracts prepared from petroleum ether showed LC50 and LC90 value of 84.50 and 214.12 ppm, respectively. The petroleum ether root extract exhibited 1.7–fold more larvicidal potential as compared to hexane root extract. The treated larvae that remained alive formed larvalpupal intermediates establishing the delayed toxic effects of the extracts. Further investigations are required to assess the impact of extracts on non-target organisms and explore the suitability of its use in the fields.

Impact of Ocimum Basilicum Leaf Essential Oil on TheSurvival and Behaviour of AnIndian Strain of Dengue Vector,Aedes aegypti (L.)

Objective: Aedes aegypti (L.) is a well-known widely spread disease vector transmitting several diseases of concern. Current investigations were undertaken to discover the larvicidal and repellent potential of essential oil from the basil plant, Ocimum basilicum leaves against Ae. aegypti as a suitable and eco-safe alternate to chemical insecticides. Methods: The larvicidal potential of basil oil was evaluated against Ae. aegypti early fourth instars using WHO protocol and LC50 and LC90 values were calculated. The efficacy of basil oil as mosquito repellent was assessed using the human-bait technique for 3 hours and the percent protection was calculated. Results: Exposure of early fourth instars of Ae. aegypti with various concentrations of O. basilicum essential oil for 24 h revealed a moderate LC50 and LC90 value of 141.95 ppm and 100.82 ppm, respectively. The investigations also showed that oil did not have any hormono-mimetic effects as it did not result in the formation of any larval-pupal intermediates. However, the basil essential oil exhibited significant effective repellency against adult Ae. aegypti. Introduction of the arms of human volunteers applied with basil oil in the cages of dengue vector resulted in 100% protection till 120 min as compared to control arm which experienced 3 to 8 bites. Remarkably, the experimental arm was bitten just once in every 15 minutes in next 45 minutes after which only 2 bites were recorded until 180 min of exposure. Conclusion: Our results recommended the efficient use of basil leaf essential oil as an efficient repellent and as a moderate larvicide agent against Ae. aegypti. Identification of bioactive components in the oil, their individual mode of action and synergistic effects, along with investigations on their impact on the environment and nontarget organisms would help in formulating strategies for mosquito management.

Utilization of Fruit Peel Wastes for the Management of Chikungunya Vector, Aedes aegypti

Chikungunya, a widely spread viral disease transmitted to human beings by Aedes aegyp‐ ti, is on rise in India, Africa and Asian subcontinent since last decade. Although chemical insecticides are used at a large scale for the control of Chikungunya vector, their applica‐ tions have led to several undesirable effects including insecticide resistance, revival of pests species, appearance of secondary pests, environmental pollution, noxious hazards to human beings and non-target organisms forcing investigators to explore unconven‐ tional alternate strategies. As an environment-friendly approach, there is increased atten‐ tion to devise and adopt suitable methods to utilize wastes as value-added products to reduce the problem of environmental pollution. Consequently, the larvicidal and adult ir‐ ritant potential of hexane and petroleum ether peel extracts of three different Citrus spe‐ cies, C. limetta, C. sinensis and C. Limon, were assessed against Ae. aegypti. The results showed the larvicidal potential of all the three peels, C. limetta peel extracts exhibiting the least activity. Furthermore, hexane extracts were more effective than petroleum ether ex‐ tracts, C. sinensis peels hexane extract being most effectual (LC50, 39.51 ppm) while petro‐ leum ether peels extract of C. limon was the most effective larvicide with LC50 value of 51.25 ppm. All the extracts also exhibited significant elicit response and irritant potential against adults signifying their potential role in reduced mosquito bites and disease trans‐ mission. The qualitative phytochemical analysis of the extracts showed presence of cer‐ tain components suggesting their probable role in bioefficacy of extracts. Further studies are needed to isolate and identify the active ingredient to formulate strategies for mosqui‐ to control.

Impact of the Argemone mexicana Stem Extracts on the Reproductive Fitness and Behavior of Adult Dengue Vector, Aedes aegypti L. (Diptera: Culicidae)

Present investigations evaluated the impact of Argemone mexicana stem extracts on the reproductive fitness of dengue vector, Aedes aegypti, assessed in terms of oviposition deterrent and ovicidal potential. The oviposition deterrent studies of the extracts, prepared using petroleum ether, hexane, benzene, acetone, and ethanol as the solvents, revealed the maximum deterrence potency of the petroleum ether extracts with a significant 15.6% ED at 60 ppm rising by 83.8% at 1000 ppm to 99.4% effective deterrence (ED). Other stem extracts were found to be ineffective at 60 ppm, though resulted in 85.3–96.2% ED and diminished fecundity in A. aegypti at 1000 ppm. Further, A. mexicana stem extracts exhibited moderate ovicidal potential against A. aegypti eggs causing only 42.65–67.85% egg mortality at 1000 ppm, the lowest hatch of 32.15% caused by the benzene extract. Other stem extracts also failed to express effective ovicidal potency with the percent egg hatch ranging between 96.6 and 99.0 at 400 ppm, and 78.8 and 99.0 at 600 ppm. Our results suggest the significant but variable efficacy of A. mexicana stem extracts causing reproductive disadvantage in A. aegypti.