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

Metabolic detoxification and ace-1 target site mutations associated with acetamiprid resistance in Aedes aegypti L

Despite the continuous use of chemical interventions, Aedes-borne diseases remain on the rise. Neonicotinoids are new, safer, and relatively effective pharmacological interventions against mosquitoes. Neonicotinoids interact with the postsynaptic nicotinic acetylcholine receptors (nAChRs) of the insect central nervous system, but the absence of nAChR polymorphism in resistant phenotypes makes their involvement in neonicotinoid resistance uncertain. Thus, an investigation was carried out to understand the role of metabolic detoxification and target site insensitivity in imparting acetamiprid resistance in Aedes aegypti larvae. Studies were conducted on the parent susceptible strain (PS), acetamiprid-larval selected strain for five generations (ACSF-5; 8.83-fold resistance) and 10 generations (ACSF-10; 19.74-fold resistance) of Ae. aegypti. The larval selection raised α-esterase and β-esterase activities by 1.32-fold and 1.34-fold, respectively, in ACSF-10 as compared to PS, while the corresponding glutathione-S-transferase and acetylcholinesterase activity increased by 22.5 and 2%. The ace-1 gene in PS and ACSF-10 showed four mismatches in the 1312—1511 bp region due to mutations in the Y455C codon (tyrosine to cysteine) at the 1367th position (TAC→TGC); I457V codon (isoleucine to valine) at 1372 bp and 1374 bp (ATA→GTG); and R494M codon (arginine to methionine) at 1484 bp (AGG→ATG). The R494M mutation was the novel and dominant type, observed in 70% ACSF-10 population, and has not been reported so far. The studies evidenced the combination of metabolic detoxification and target site mutation in imparting acetamiprid resistance in Ae. aegypti.

Reversion of CYP450 monooxygenase-mediated acetamiprid larval resistance in dengue fever mosquito, Aedes aegypti L

Aedes-borne diseases are on the rampant rise despite continued application of chemical insecticide-based interventions. The appearance of high degree of insecticide resistance in Aedes species and noxious effects on environment and non-targets have raised further concerns. Among new chemical interventions, neonicotinoids are considered a safe and effective approach. The present study investigated the control potency of acetamiprid and development of resistance in Aedes aegypti larvae; and the involvement of CYP450 monooxygenases in inducing resistance. The early fourth instars of Ae. aegypti parent susceptible strain (PS) were selected with acetamiprid for 15 generations (ACSF strain) increasing the resistance to 19.74-fold in ACSF-10 and 36.71-fold in ACSF-15. The ACSF-10 larvae were assayed with acetamiprid combined with piperonyl butoxide (PBO) in three different ratios (1:1, 1:5 and 1:10) and selected for next five generations with 1:10 combination. Selection with synergized acetamiprid (APSF strains) reversed as well as reduced the rate of resistance development resulting in only 1.35-fold resistance in APSF-15. The APSF strains showed %monooxygenase dependency ranging from 86.71 to 96.72%. The estimation of the monooxygenases levels in parent and selected larvae showed increased monooxygenase level in the ACSF strains by 2.42-2.87-fold. The APSF-15 strains exhibited 57.95% lower enzyme production than ACSF-15 strain. The reduction and reversion of resistance by using PBO and the elevated levels of monooxygenases in ACSF and reduction in APSF strains recommend the involvement of CYP450-mediated mechanism in the development of acetamiprid resistance in Ae. aegypti. These studies could help in devising resistance management strategies in order to preserve the efficiency of pre-existing insecticides.

Target and non-target effects of Foeniculum vulgare and Matricaria chamomilla combined extract on Culex pipiens mosquitoes

The present study focused on extracting green larvicides from extracts of the combination of Foeniculum vulgare and Matricaria chamomilla using different solvents of increasing polarity in a Soxhlet extractor and evaluating their ovicidal, larvicidal, and cytotoxic activities. The most promising among all tested extracts was hexane extract. The ovicidal activity of the hexane PH2 extract resulted in a significant (p < 0.05) decrease in egg hatchability from 95.00 ± 6.16% to 15 ± 9.04% at doses ranging from 62.5 to 500 µg/mL. The larval mortality with the hexane extract ranged from 13.33 ± 3.3% to 93.33 ± 3.3% at doses ranging from 31.25 to 250 µg/mL, respectively. The LC₅₀ and LC₉₀ values of the larvicidal activity of the hexane extract were estimated to be 148.3 and 242.17 µg/mL, respectively, after 24 h of exposure. Similarly, the LC₅₀ values after 48 and 72 h of exposure were 124.93 and 100.3 µg/mL, respectively, against the third instar of Cx. pipiens. PH2 treatment of larvae resulted in histopathological changes such as degenerated epithelial cells and destruction of microvilli on the epithelial cells. The PH2 extract achieved a dose-dependent decrease in the rate of cell survival. The IC₅₀ value of PH2-treated HUVECs was 192.07 µg/mL after 24 h of incubation. The cells showed changes in cellular and nuclear morphology. In conclusion, the hexane extract of PH2 could be used in mosquito management programs.

Microencapsulation Preservation of the Stability and Efficacy of Citrus Grandis Oil-Based Repellent Formulation against Aedes aegypti during Storage

Essential oils have been widely used as an active ingredient in mosquito repellent products. However, essential oils are highly unstable and prone to degradation when exposed to the environment during storage. Microencapsulation techniques help to maintain the stability of molecules in essential oils that are sensitive to environmental stress, and therefore improve shelf life. In this study, the physical stability and efficacy of a repellent formulation consisting of encapsulated Citrus grandis essential oil (CGEO) were evaluated under different storage conditions over a 12-month period by comparing the formulation with a non-encapsulated formulation. The formulations were both stored under two different storage conditions, i.e., 25 ± 2 °C/60% ± 5% relative humidity (RH) and 40 ± 2 °C/75% RH ± 5%, for 12 months. Droplet size, zeta potential, and pH value were measured after 1, 6, and 12 months of storage to determine their stability. For the study of efficacy, each formulation was tested against Aedes aegypti under laboratory conditions. We found that the microencapsulated formulation’s physical characteristics showed insignificant changes as compared with the non-encapsulated formulation during storage. The microencapsulated formulation demonstrated better repellent effects, sustaining high protection (>80%) for 4 more hours of exposure after 12 months of storage as compared with the non-encapsulated formulation that demonstrated high protection for only an hour post application. Microencapsulation helped to preserve the stability of the formulation, which resulted in high protection being maintained for over 12 months of storage.

High larvicidal efficacy of yeast-encapsulated orange oil against Aedes aegypti strains from Brazil

Background

Botanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report.

Methods

Larvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC₅₀ and LC₉₀ values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions.

Results

YEOO was found to be a highly active larvicide (LC₅₀ < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC₅₀ = 8.1–24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC₅₀ = 20.0–49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC_90–95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months).

Conclusion

YEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04733-2.

Biocontrol of mosquito vectors through herbal-derived silver nanoparticles: prospects and challenges

Mosquitoes spread several life-threatening diseases such as malaria, filaria, dengue, Japanese encephalitis, West Nile fever, chikungunya, and yellow fever and are associated with millions of deaths every year across the world. However, insecticides of synthetic origin are conventionally used for controlling various vector-borne diseases but they have various associated drawbacks like impact on non-targeted species, negative effects on the environment, and development of resistance in vector species by alteration of the target site. Plant extracts, phytochemicals, and their nanoformulations can serve as ovipositional attractants, insect growth regulators, larvicides, and repellents with least effects on the environment. Such plant-derived products exhibit broad-spectrum resistance against various mosquito species and are relatively cheaper, environmentally safer, biodegradable, easily accessible, and are non-toxic to non-targeted organisms. Therefore, in this review article, the current knowledge of phytochemical sources exhibiting larvicidal activity and their variations in response to solvents used for their extraction is underlined. Also, different methods such as physical, chemical, and biological for silver nanoparticle (AgNPs) synthesis, their mechanism of synthesis using plant extract, their potent larvicidal activity, and the possible mechanism by which these particles kill mosquito larvae are discussed. In addition, constraints related to commercialization of nanoherbal products at government and academic or research level and barriers from laboratory experiments to field trial have also been discussed. This comprehensive information can be gainfully employed for the development of herbal larvicidal formulations and nanopesticides against insecticide-resistant vector species in the near future. Graphical abstract.

Yeast-encapsulated essential oils: a new perspective as an environmentally friendly larvicide

BACKGROUND

Effective mosquito control approaches incorporate both adult and larval stages. For the latter, physical, biological, and chemical control have been used with varying results. Successful control of larvae has been demonstrated using larvicides including insect growth regulators, e.g. the organophosphate temephos, as well as various entomopathogenic microbial species. However, a variety of health and environmental issues are associated with some of these. Laboratory trials of essential oils (EO) have established the larvicidal activity of these substances, but there are currently no commercially available EO-based larvicides. Here we report on the development of a new approach to mosquito larval control using a novel, yeast-based delivery system for EO.

METHODS

Food-grade orange oil (OO) was encapsulated into yeast cells following an established protocol. To prevent environmental contamination, a proprietary washing strategy was developed to remove excess EO that is adsorbed to the cell exterior during the encapsulation process. The OO-loaded yeast particles were then characterized for OO loading, and tested for efficacy against Aedes aegypti larvae.

RESULTS

The composition of encapsulated OO extracted from the yeast microparticles was demonstrated not to differ from that of un-encapsulated EO when analyzed by high performance liquid chromatography. After lyophilization, the oil in the larvicide comprised 26-30 percentage weight (wt%), and is consistent with the 60-65% reduction in weight observed after the drying process. Quantitative bioassays carried with Liverpool and Rockefeller Ae. aegypti strains in three different laboratories presented LD₅₀ of 5.1 (95% CI: 4.6-5.6) to 27.6 (95% CI: 26.4-28.8) mg/l, for L1 and L3/L4 mosquito larvae, respectively. LD₉₀ ranged between 18.9 (95% CI: 16.4-21.7) mg/l (L1 larvae) to 76.7 (95% CI: 69.7-84.3) mg/l (L3/L4 larvae).

CONCLUSIONS

The larvicide based on OO encapsulated in yeast was shown to be highly active (LD₅₀ < 50 mg/l) against all larval stages of Ae. aegypti. These results demonstrate its potential for incorporation in an integrated approach to larval source management of Ae. aegypti. This novel approach can enable development of affordable control strategies that may have significant impact on global health.

Larvicidal and Enzymatic Inhibition Effects of Annona muricata Seed Extract and Main Constituent Annonacin against Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

The mosquitoes Aedes aegypti and Aedes albopictus are vectors of arboviruses that cause dengue, zika and chikungunya. Bioactive compounds from plants are environmentally sustainable alternatives to control these vectors and thus the arboviruses transmitted by them. The present study evaluated the larvicidal activity of an acetogenin-rich fraction (ACERF) and its main constituent annonacin obtained from Annona muricata seeds on Ae. aegypti and Ae. albopictus. The larvicidal assays were performed using different concentrations to calculate the LC50 and LC90 values observed 24 h after exposure to the treatment. Annonacin was more active against Ae. aegypti (LC50 2.65 μg·mL-1) in comparison with Ae. albopictus (LC50 8.34 μg·mL-1). In contrast, the acetogenin-rich fraction was more active against Ae. albopictus (LC50 3.41 μg·mL-1) than Ae. aegypti (LC50 12.41 μg·mL-1). ACERF and annonacin treated larvae of Ae. aegypti and Ae. albopictus showed significant differences in the inhibition of their metabolic enzymes when compared to untreated larvae. The results demonstrate the relevant larvicidal action of the acetogenin-rich fraction and annonacin showing the potential to develop new products for the control of Ae. aegypti and Ae. albopictus.

Larvicidal activity of Hypoestes forskaolii (Vahl) R. Br root extracts against Anopheles gambiae Giless.s, Aedes aegypti L, and Culex quinquefasciatus Say

Aim: This study aimed to evaluate larvicidal activity of Hypoestes forskaolii R. Br root extract against 3rd instar Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus.

Methods: A protocol developed by the World Health Organization was adopted, with minor modification using chloroform and methanol extracts with concentrations ranging from 25–750 µg/mL.

Results: The H. forskaolii chloroform extract exhibited very high larvicidal activity after 72 hours of exposure, with LC₅₀ 2.0322, 3.8989, 6.0004 μg/mL against A. gambiae, A. aegypti, and C. quinquefasciatus, respectively.

Conclusion: The larvicidal activity of H. forskaolii is reported for the first time in this paper. The effectiveness of H. forskaolii chloroform extract warrants further research to develop botanical mosquito repellants from this source.

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Bio-Pesticides: New Tool for the Control of Aedes (Stegomyia) albopictus (Culicidae: Diptera) in Pakistan

BACKGROUND

Application of plant extracts as mosquito control strategy was practiced from centuries. These are easily available, non-toxic, biodegradable and exhibit broad-spectrum target specific activities against larval stages of mosquitoes.

METHODS

Different potential parts of locally grown plants, seeds of nutmeg (Myristica fragrans), peel of musambi (Citrus sinensis), leaves of babuna (Matricaria chamomilla), mint (Mentha spicata) and ginger rhizome (Zingiber officinale) selected and evaluated for their larvicidal properties against Aedes (Stegomyis) albopictus. Oils were extracted through steam distillation process and extracts were evaluated as per WHO 2005 guidelines for testing of insecticides against larvae of mosquitoes.

RESULTS

Among the five plant extracts, C. sinensis had the lowest LC₅₀ (400.81ppm) while M. fragrans had the highest LC₅₀ value (710.30ppm) respectively after 24h of exposure. In terms of % age mortality, a series of concentrations (300-800ppm) gave high % mortality in case of C. sinensis while M. fragrans gave low % age mortality.

CONCLUSION

All the five plant species have larvicidal effects to certain extant and C. sinensis had great potential. Further small-scale field trials with the extracts of the most promising one (C. sinensis) shall be conducted to determine operational feasibility.

Insecticidal and Repellent Activity of Several Plant-Derived Essential Oils Against Aedes aegypti

We examined the pupicidal, adulticidal, repellent, and oviposition-deterrent activities of essential oils (EOs) from Lippia alba, L. origanoides, Eucalyptus citriodora, Cymbopogon citratus, Cymbopogon flexuosus, Citrus sinensis , Cananga odorata , Swinglea glutinosa, and Tagetes lucida plants against Aedes aegypti under laboratory conditions. Pupicidal and adulticidal activities were assessed at exploratory concentrations of 250, 310, and 390 parts per million (ppm); and 30, 300, and 1,000 ppm, respectively. The greatest pupicidal activity was exhibited at 390 ppm with a 24-h exposure by L. origanoides, and 390 ppm with a 48-h exposure by Citrus sinensis . Lippia origanoides killed all adult mosquitoes at 300 ppm after 120 min of exposure. Only L. origanoides and E. citriodora EOs, applied at 1,000 ppm to human skin, produced the greatest repellency (100%) to host-seeking Ae. aegypti after 2 min of exposure; the repellency decreased between 12% and 10% after 15 min. Complete oviposition deterrence by gravid Ae. aegypti was observed for E. citriodora EOs at 200 ppm with an oviposition activity index of -1.00. These results confirm that the EOs assessed in this study have insecticidal, repellent, and oviposition-deterrent activities against the dengue vector, Ae. aegypti.

Larvicidal efficacy and chemical constituents of O. gratissimum L. (Lamiaceae) essential oil against Aedes albopictus Skuse (Diptera: Culicidae)

The current study accentuates the use of botanicals as an alternative to the chemical compounds in vector control by estimating the mosquito larvicidal potential of Ocimum gratissimum L. leaf essential oil against the fourth instar larvae of Aedes albopictus Skuse (Diptera: Culicidae). The chemical composition of essential oil from leaves was evaluated using gas chromatography-mass spectrometry (GC/MS) analysis. GC/MS revealed that the essential oil of O. gratissimum contained 51 compounds. The major chemical constituents identified were 3-allyl-6-methoxyphenol (19.30%), 4-(5-ethenyl-1-azabicyclo (2, 2, 2) octan-2) (16.82%), 1-(2, 5-dimethoxyphenyl)-propanol (12.23%) and 1-(1-hydroxybutyl)-2, 5-dimethoxybenzene (5.53%). The essential oil showed pertinent larvicidal effect, and the LC50 value in 24 h was 26.10 ppm (LC90 = 82.83 ppm). Aromatic plants and their essential oils are very important sources of many compounds that are used for different applications, and they are more promising pesticides or insecticides for control of mosquito populations than synthetic ones. The results of the present investigation justify the larvicidal potential of leaf essential oil of O. gratissimum as a safer and more effective larvicide against A. albopictus.

Larvicidal activity of Syzygium aromaticum (L.) Merr and Citrus sinensis (L.) Osbeck essential oils and their antagonistic effects with temephos in resistant populations of Aedes aegypti

Environmentally friendly botanical larvicides are commonly considered as an alternative to synthetic larvicides against Aedes aegypti Linn. In addition, mosquito resistance to currently used larvicides has motivated research to find new compounds acting via different mechanisms of action, with the goal of controlling the spread of mosquitos. Essential oils have been widely studied for this purpose. This work aims to evaluate the larvicidal potential of Syzygium aromaticum and Citrus sinensis essential oils, either alone or in combination with temephos, on Ae. aegypti populations having different levels of organophosphate resistance. The 50% lethal concentration (LC50) of the essential oils alone and in combination with temephos and the influence of essential oils on vector oviposition were evaluated. The results revealed that essential oils exhibited similar larvicidal activity in resistant populations and susceptible populations. However, S. aromaticum and C. sinensis essential oils in combination with temephos did not decrease resistance profiles. The presence of the evaluated essential oils in oviposition sites significantly decreased the number of eggs compared to sites with tap water. Therefore, the evaluated essential oils are suitable for use in mosquito resistance management, whereas their combinations with temephos are not recommended. Additionally, repellency should be considered during formulation development to avoid mosquito deterrence.

Chemistry and Pharmacology of Citrus sinensis

Presently the search for new drugs from natural resources is of growing interest to the pharmaceutical industry. Natural products have been the source of new drugs since ancient times. Plants are a good source of secondary metabolites which have been found to have beneficial properties. The present study is a review of the chemistry and pharmacology of Citrus sinensis. This review reveals the therapeutic potential of C. sinensis as a source of natural compounds with important activities that are beneficial for human health that could be used to develop new drugs.

Relative Toxicity of Leaf Extracts of Eucalyptus globulus and Centella asiatica against Mosquito Vectors Aedes aegypti and Anopheles stephensi

The larvicidal activity of different solvent leaf extracts (hexane, diethyl ether, dichloromethane, and methanol) of Eucalyptus globulus and Centella asiatica against two geographically different strains of Aedes aegypti and Anopheles stephensi was investigated. The extracts were tested against the late third instar larvae of Aedes aegypti and Anopheles stephensi, and larval mortality was observed after 24 hours of treatment. LC50 and LC90 were calculated. The LC50 values of hexane extract of Eucalyptus globulus against the late third instar larvae of the BSN and JPN strains of Aedes aegypti and the DLC and KNG strains of Anopheles stephensi were 225.2, 167.7, 118.8, and 192.8 ppm, while those of the hexane extract of Centella asiatica were 246.5, 268.7, 50.6, and 243.5 ppm, respectively. The LC50 values of diethyl ether extract of Centella asiatica were 339.6, 134.5, 241, and 14.7 ppm. The hexane extracts of both plants and the diethyl ether extract of C. asiatica presented the highest potential for the control of Aedes aegypti and Anopheles stephensi. The present findings also reveal the necessity of assaying multiple strains of a species to fully comprehend the larvicidal efficacy of a compound.

Essential oils with insecticidal activity against larvae of Aedes aegypti (Diptera: Culicidae)

Insecticidal activity of the essential oils (EOs) isolated from Tagetes lucida, Lippia alba, Lippia origanoides, Eucalyptus citriodora, Cymbopogon citratus, Cymbopogon flexuosus, Citrus sinensis, Swinglea glutinosa, and Cananga odorata aromatic plants, grown in Colombia (Bucaramanga, Santander), and of a mixture of L. alba and L. origanoides EOs were evaluated on Aedes (Stegomyia) aegypti Rockefeller larvae. The EOs were extracted by microwave-assisted hydrodistillation and characterized by gas chromatography-mass spectrometry (GC-MS). The main components of the EOs were identified using their linear retention indices and mass spectra. The lethal concentrations (LCs) of the EOs were determined between the third and fourth instar of A. aegypti. LC50 was determined by probit analysis using mortality rates of bioassays. All essential oils tested showed insecticidal activity. The following values were obtained for C. flexuosus (LC50 = 17.1 ppm); C. sinensis (LC50 = 20.6 ppm); the mixture of L. alba and L. origanoides (LC50 = 40.1 ppm); L. alba (LC50 = 42.2 ppm); C. odorata (LC50 = 52.9 ppm); L. origanoides (LC50 = 53.3 ppm); S. glutinosa (LC50 = 65.7 ppm); T. lucida (LC50 = 66.2 ppm); E. citriodora (LC50 = 71.2 ppm); and C. citratus (LC50 = 123.3 ppm). The EO from C. flexuosus, with citral (geranial + neral) as main component, showed the highest larvicidal activity.

Ovicidal, repellent, adulticidal and field evaluations of plant extract against dengue, malaria and filarial vectors

Mosquitoes are insect vectors responsible for the transmission of parasitic and viral infections to millions of people worldwide, with substantial morbidity and mortality. Infections transmitted by mosquitoes include malaria, yellow fever, chikungunya, filariasis and other arboviruses. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. The adulticidal activities of crude hexane, benzene, ethyl acetate, acetone and methanol leaf extracts of Acalypha alnifolia were assayed for their toxicity against three important vector mosquitoes, viz., Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. The adult mortality was observed after 24 h of exposure. All extracts showed moderate adulticide effects; however, the highest adult mortality was found in methanol extract were observed. The LC(50) values of A. alnifolia leaf extracts against adulticidal activity of (hexane, benzene, ethyl acetate, acetone and methanol) A. aegypti, A. stephensi and C. quinquefasciatus were the following: A. aegypti values were 371.87, 342.97, 320.17, 300.86 and 279.75 ppm; A. stephensi values were 358.35, 336.64, 306.10, 293.01 and 274.76 ppm; C. quinquefasciatus values were 383.59, 354.13, 327.74, 314.33 and 291.71 ppm. The results of the repellent activity of hexane, benzene, ethyl acetate, acetone and methanol extract of A. alnifolia plant at three different concentrations of 1.0, 3.0, and 5.0 mg/cm(2) were applied on skin of forearm in man and exposed against adult female mosquitoes. In this observation, this plant crude extracts gave protection against mosquito bites without any allergic reaction to the test person, and also, the repellent activity is dependent on the strength of the plant extracts. Mean percent hatchability of the ovicidal activity was observed 48 h post-treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. Mortality of 100 % with methanol extract of A. alnifolia was exerted at 125 and 300 ppm. The larval density was decreased after the treatment of plant extracts at the breeding sites (water bodies system) of vector mosquitoes, and hence, these plant extracts are suitable alternatives of synthetic insecticides for mosquito vector management.These results suggest that the leaf solvent plant extracts have the potential to be used as an ideal eco-friendly approach for the control of mosquitoes. This study provides first report on the mosquito ovicidal, repellent and adulticidal activities of these plant extracts against mosquito vector species from India.

Larvicidal, pupicidal, repellent and adulticidal activity of Citrus sinensis orange peel extract against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Mosquitoes are the carriers of severe and well-known illnesses such as malaria, arboviral encephalitis, dengue fever, chikunguniya fever, West Nile virus and yellow fever. These diseases produce significant morbidity and mortality in humans and livestock around the world. The present study explored the effects of orange peel ethanol extract of Citrus sinensis on larvicidal, pupicidal, repellent and adulticidal activity against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. The orange peel material was shade dried at room temperature and powdered coarsely. From orange peel, 300 g powdered was macerated with 1 L of ethanol sequentially for a period of 72 h each and filtered. The yields of the orange peel ethanol crude extract of C. sinensis 13.86 g, respectively. The extracts were concentrated at reduced temperature on a rotary vacuum evaporator and stored at a temperature of 4 °C. The larvicidal, pupicidal and adult mortality was observed after 24 h of exposure; no mortality was observed in the control group. For C. sinensis, the median lethal concentration values (LC(50)) observed for the larvicidal and pupicidal activities against mosquito vector species A. stephensi first to fourth larval instars and pupae were 182.24, 227.93, 291.69, 398.00 and 490.84 ppm; A. aegypti values were 92.27, 106.60, 204.87, 264.26, 342.45, 436.93 and 497.41 ppm; and C. quinquefasciatus values were 244.70, 324.04, 385.32, 452.78 and 530.97 ppm, respectively. The results of maximum repellent activity were observed at 450 ppm in ethanol extracts of C. sinensis and the mean complete protection time ranged from 150 to 180 min was tested. The ethanol extract of C. sinensis showed 100% repellency in 150 min and showed complete protection in 90 min at 350 ppm against A. stephensi, A. aegypti and C. quinquefasciatus, respectively. The adult mortality was found in ethanol extract of C. sinensis with the LC(50) and LC(90) values of 272.19 and 457.14 ppm, A. stephensi; 289.62 and 494.88 ppm, A. aegypti; and 320.38 and 524.57 ppm, respectively. These results suggest that the orange peel extracts of C. sinensis have the potential to be used as an ideal eco-friendly approach for the control of the vector control programmes.

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.