Anopheles Subpictus Research Articles

GIS Mapping and Breeding Habitat Characterization of Anophelines Occurring in Malaria Endemic Areas of Hooghly, WB, India

The mosquitoes are small dipteran insect vectors responsible for various diseases like malaria as one of the major health problem that causes enormous mortality and morbidity in tropical and subtropical countries. The breeding habitat of mosquitoes is crucial for its population dynamics, since it is the location where many important life cycle processes occur such as oviposition, larval development, and emergence of the adult take place. The present study depicted the spatial distribution of anopheline larval (Anopheles subpictus) habitats using GIS mapping in malaria prone blocks of Hooghly district, West Bengal, India. Physico-chemical parameters like pH, dissolved oxygen content, turbidity, alkalinity, total dissolved solids and chloride content in relation to the larval prevalence of various breeding habitats were recorded during the study period (from Dec’2015 to Nov’2016). The present investigation showed the correlation between the physico-chemical parameters and anopheline larval abundance to be considered as a key factor for taking effective management programme to combat malaria .

Larvicidal efficacy of 4-Dodecene derived from marine Streptomyces sp. VITVSK1 on Blood-Sucking Parasites

The present study was aimed to assess the larvicidal activity of the lead compound 4-dodecene isolated from Streptomyces sp. VITVSK1 against cattle ticks, Haemaphysalis bispinosa and Rhipicephalus (Boophilus) microplus; Anopheles subpictus and Culex quinquefasciatus larvae. The compound was methanol extracted and purified by silica gel column chromatography and preparative thin layer chromatography using a solvent system of chloroform: methanol (9:1 v/v). The active fractions were concentrated and analyzed by mass spectroscopy (MS) and based on the similarity index with reference compounds available in the mass spectra library, National Institute of Standards and Technology (NIST) the structure of the pure compound was elucidated. The structure of the purified compound was further confirmed with the help of 1H-NMR and 13C-NMR spectra. In this study, the crude extract and the lead compound 4-dodecene extracted from Streptomyces sp. VITVSK1 were tested against the larvae of the selected parasites at varying concentrations. Based on the spectral studies the compound was identified as 4-dodecene and the molecular formula of the aliphatic compound was established as C14H20O2. The methanolic extract (1000 ppm) showed antiparasitic effects after 24 h of exposure and the mortality of the parasites was observed in the larvae of A. subpictus (LC50=116.1 ppm; r2=0.864); R. microplus (LC50=331.79 ppm; r2=0.948); C. quinquefasciatus (LC50=168.59 ppm; r2=0.425) and H. bispinosa (LC50=284.02 ppm; r2= 0.885). The maximum efficacy was observed with the extracted compound 4-dodecene and the LC50 and r2 values were calculated against the larvae of A. subpictus (82.65 ppm; 0.688), R. microplus (173.48 ppm; 0.857), C. quinquefasciatus (78.32 ppm; 0.769) and against H. bispinosa (126.59 ppm; 0.840) respectively. The active compound 4-dodecene from Streptomyces sp. VITVSK1 exhibited profound larvicidal activity against blood-sucking parasites, A. subpictus, R. microplus, C. quinquefasciatus and H. bispinosa. The results of this study suggest that the active compound 4-dodecene can be probed further to be developed as a larvicidal agent.

Toxicity studies of nanofabricated palladium against filariasis and malaria vectors

The present study was carried out to establish the biofabrication of palladium nanoparticles (PdNPs) using the plant leaf extract of Tinospora cordifolia Miers and its toxicity studies on the larvae of filariasis vector, Culex quinquefasciatus Say and malaria vector, Anopheles subpictus Grassi. The biofabricated PdNPs were characterized by using UV-visible spectrum, FTIR, XRD,FESEM, EDX and HRTEM. HRTEM confirmed the PdNPs were slightly agglomerated and spherical in shape and theaverage sizewas 16nm. Gas chromatography and mass spectrometry analysis result revealed that the major constituent present in the T. cordifolia leaf extract is 2,4-di-tert-butylphenol (31.79%) whereas the minor compounds are 1-hexadecanol (7.97%), 1-octadecanol (7.70%), 1-eicosanol (6.85%), behenic alcohol (5.36%), 1-tetradecene (6.22%), cyclotetradecane (6.23%), 1-hexadecene (7.97%), 1-octadecene (7.70%), 1-eicosene (6.85%), and 1-docosene (5.36%). T. cordifolia leaf extract exhibited the larvicidal activity against the fourth instar larvae of C. quinquefasciatus and A. subpictus with the values of LC50=59.857 and 54.536mg/L; LC90=113.445 and 108.940mg/L, respectively. The highest toxicity was observed in the biofabricated PdNPs against the fourth instar larvae of C. quinquefasciatus and A. subpictus with the values of LC50=6.090 and 6.454mg/L; LC90=13.689 and 13.849mg/L, respectively. Concerning non-target effects, Poecilia reticulata were exposed to PdNPs for 24h and did not exhibit any noticeable toxicity. Overall, our findings strongly suggest that PdNPs is a perfect ecological and inexpensive approach for the control of filariasis and malaria vectors.

Deforestation and vector-borne disease: Forest conversion favors important mosquito vectors of human pathogens

The global burden of vector-borne diseases accounts for more than 17% of infectious diseases in humans. Rapid global expansion of previously obscure pathogens, such as Zika and chikungunya viruses in recent years highlights the importance of understanding how anthropogenic changes influence emergence and spillover of vector-borne diseases. Deforestation has been identified as one anthropogenic change that influences vector-borne disease prevalence, although contrasting pictures of the effects of deforestation on vector-borne disease transmission have been reported. These conflicting findings are likely attributable to the inherent complexity of vector-borne disease systems, which involve diverse groups of vectors, hosts and pathogens, depending on geography. The current study represents a quantitative exploration of the link between deforestation and mosquitoes, the most important common constituents of vector-borne disease systems. Analysis of data compiled from published field studies for 87 mosquito species from 12 countries revealed that about half of the species (52.9%) were associated with deforested habitats. Of these species that are favored by deforestation, a much larger percentage (56.5%) are confirmed vectors of human pathogens, compared to those negatively impacted by deforestation (27.5%). Moreover, species that serve as vectors of multiple human pathogens were all favored by deforestation, including Anopheles bancroftii, Anopheles darlingi, Anopheles farauti, Anopheles funestus s.l., Anopheles gambiae s.l., Anopheles subpictus, Aedes aegypti, Aedes vigilax, Culex annulirostris, and Culex quinquefasciatus. Our quantitative analysis of vector and non-vector species, demonstrates that the net effect of deforestation favors mosquitoes that serve as vectors of human disease, while the obverse holds true for non-vectors species. These results begin to unify our understanding of the relationship between deforestation and vector mosquitoes, an important step in quantifying how land use change, specifically deforestation, affects human risk of vector-borne disease.

First record of Anopheles stephensi in Sri Lanka: a potential challenge for prevention of malaria reintroduction

BackgroundThe major malaria vector in Sri Lanka is reported to be Anopheles culicifacies with Anopheles subpictus, Anopheles annularis, and Anopheles varuna considered as potential vectors. The occurrence of Anopheles stephensi, which is the key vector of urban malaria in India and the Middle East, had never been reported from Sri Lanka.MethodsA series of entomological investigations were carried out by the Anti Malaria Campaign, Ministry of Health, Sri Lanka during December 2016 to April 2017 in two localities of the Mannar District in the Northern Province of the country. Adult mosquito collections were done through indoor and outdoor resting collections, animal and human biting collections and emergence traps. Potential mosquito breeding sites were investigated through larval surveys. The larvae and adults of An. stephensi were initially identified using morphological keys, and subsequently confirmed by sequencing the barcode region of the cytochrome c oxidase I (COI) gene.ResultsThis is the first report of the presence of An. stephensi in the island of Mannar in the Northern Province of Sri Lanka. Anopheles stephensi (36.65%) was the most abundant anopheline species in the larval habitats in Mannar. It was found breeding together with An. culicifacies (20.7%), An. subpictus (13.5%) and An. varuna (28.13%). Anopheles stephensi was found to be abundantly breeding in built wells used for domestic purposes. Adult females of An. stephensi were observed in emergence trap collections (93.9%), human landing catches all night (79.2%), pyrethrum spray sheet collections (38.6%), outdoor collections (8.3%), donkey-baited trap collections (14.3), and cattle-baited net trap collections (0.7%).ConclusionsSri Lanka was certified as malaria-free by the WHO in September 2016, however, this new finding may pose a serious challenge to the efforts of the Ministry of Health to prevent the re-introduction of malaria transmission in the country, considering the role that An. stephensi could play in urban and high vulnerability areas of Sri Lanka.

Molecular characterization of Anopheline (Diptera: Culicidae) mosquitoes from eight geographical locations of Sri Lanka

BackgroundGenus Anopheles is a major mosquito group of interest in Sri Lanka as it includes vectors of malaria and its members exist as species complexes. Taxonomy of the group is mainly based on morphological features, which are not conclusive and can be easily erased while handling the specimens. A combined effort, using morphology and DNA barcoding (using the markers cytochrome c oxidase subunit I (COI) gene and internal transcribed spacer 2 (ITS2) region, was made during the present study to recognize anophelines collected from eight districts of Sri Lanka for the first time.MethodsCytochrome c oxidase subunit I and ITS2 regions of morphologically identified anopheline mosquitoes from Sri Lanka were sequenced. These sequences together with GenBank sequences were used in phylogenetic tree construction and molecular characterization of mosquitoes.ResultsAccording to morphological identification, the field-collected adult mosquitoes belonged to 15 species, i.e., Anopheles aconitus, Anopheles annularis, Anopheles barbirostris, Anopheles culicifacies, Anopheles jamesii, Anopheles karwari, Anopheles maculatus, Anopheles nigerrimus, Anopheles pallidus, Anopheles peditaeniatus, Anopheles pseudojamesi, Anopheles subpictus, Anopheles tessellatus, Anopheles vagus, and Anopheles varuna. However, analysis of 123 COI sequences (445 bp) (16 clades supported by strong bootstrap value in the neighbour joining tree and inter-specific distances of >3%) showed that there are 16 distinct species. Identity of the morphologically identified species, except An. subpictus, was comparable with the DNA barcoding results. COI sequence analysis showed that morphologically identified An. subpictus is composed of two genetic entities: An. subpictus species A and species B (inter-specific K2P distance 0.128). All the four haplotypes of An. culicifacies discovered during the present study belonged to a single species. ITS2 sequences (542 bp) were obtained for all the species except for An. barbirostris, An. subpictus species B, An. tessellatus, and An. varuna. Each of these sequences was represented by a single species-specific haplotype.ConclusionsThe present study reflects the importance and feasibility of COI and ITS2 genetic markers in identifying anophelines and their sibling species, and the significance of integrated systematic approach in mosquito taxonomy. Wide distribution of malaria vectors in the country perhaps indicates the potential for re-emergence of malaria in the country.

Zingiber cernuum (Zingiberaceae) essential oil as effective larvicide and oviposition deterrent on six mosquito vectors, with little non-target toxicity on four aquatic mosquito predators.

Mosquitoes are responsible for the transmission of many pathogens and parasites, which cause serious diseases in humans and animals. Currently, botanical products have been suggested as alternative tools in the fight against arthropod vectors. In this study, the essential oil (EO) extracted from Zingiber cernuum was tested as larvicide and oviposition deterrent on six mosquito species of public health relevance, including malaria and Zika virus vectors. The EO showed high toxicity on third instar larvae of Anopheles stephensi (LC50=41.34μg/ml), Aedes aegypti (LC50=44.88μg/ml), Culex quinquefasciatus (LC50=48.44μg/ml), Anopheles subpictus (LC50=51.42μg/ml), Aedes albopictus (LC50=55.84μg/ml), and Culex tritaeniorhynchus (LC50=60.20μg/ml). In addition, low doses of Z. cernuum EO reduced oviposition rates in six mosquito species. The acute toxicity of Z. cernuum EO on four mosquito predators was scarce; LC50 ranged from 3119 to 11,233μg/ml. Overall, our results revealed that the Z. cernuum EO can be considered for the development of effective and environmental-friendly mosquito larvicides and oviposition deterrents.

Curzerene, trans-β-elemenone, and γ-elemene as effective larvicides against Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus: toxicity on non-target aquatic predators.

A wide number of studies dealing with mosquito control focus on toxicity screenings of whole plant essential oils, while limited efforts shed light on main molecules responsible of toxicity, as well as their mechanisms of action on non-target organisms. In this study, GC-MS shed light on main essential oil components extracted from leaves of the Suriname cherry Eugenia uniflora, i.e., curzerene (35.7%), trans-β-elemenone (11.5%), and γ-elemene (13.6%), testing them on Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus larvae. Non-target toxicity experiments were carried out on four species of aquatic larvivorous organisms, including fishes, backswimmers, and waterbugs. The essential oil from E. uniflora leaves tested on An. subpictus, Ae. Albopictus, and Cx. tritaeniorhynchus showed LC50 of 31.08, 33.50, and 36.35μg/ml, respectively. Curzerene, trans-β-elemenone, and γ-elemene were extremely toxic to An. subpictus (LC50=4.14, 6.13, and 10.53μg/ml), Ae. albopictus (LC50=4.57, 6.74, and 11.29μg/ml), and Cx. tritaeniorhynchus (LC50=5.01, 7.32, and 12.18μg/ml). The essential oil from E. uniflora leaves, curzerene, trans-β-elemenone, and γ-elemene showed low toxicity to larvivorous fishes, backswimmers, and waterbugs, with LC50 ranging from 303.77 to 6765.56μg/ml. Predator safety factor (PSF) ranged from 55.72 to 273.45. Overall, we believe that curzerene isolated from the essential oil from E. uniflora leaves can represent an ideal molecule to formulate novel mosquito larvicides, due to its extremely low LC50 on all tested mosquito vectors (4.14-5.01μg/ml), which far encompasses most of the botanical pesticides tested till now. Notably, the above-mentioned LC50 did not damage the four aquatic predators tested in this study.

Larvicidal activity of phytosteroid compounds from leaf extract of Solanum nigrum against Culex vishnui group and Anopheles subpictus

Background Vector control is facing a menace due to the appearance of resistance to synthetic insecticides. Insecticides of plant origin may provide appropriate substitute biocontrol techniques in the future. The present study was carried out to investigate the bio control potentiality of active ingredient isolated from chloroform: methanol (1:1 v/v) extract of mature leaves of Solanum nigrum L. (Solanaceae) against early 3rd instar larvae of Culex vishnui group (comprising of Cx. vishnui Theobald, Cx. pseudovishnui Colless and Cx. tritaeniorhynchus Giles) and Anopheles subpictus Grassi. S. nigrum is a common plant distributed in many parts of India with medicinal properties.Methods Bioactive compound isolated from chloroform: methanol (1:1 v/v) extract of mature leaves of S. nigrum was (25, 45, 60 mg/L) tested against early 3rd instar larvae of Cx. vishnui group and An. subpictus. The lethal concentration was determined by log probit analysis. The chemical nature of the active substance was also evaluated following gas chromatography–mass spectroscopy (GC–MS) and infrared (IR) analysis. The compound was also studied on non target organisms such as Daphnia sp. and Diplonychus annulatum.ResultsTLC spot having Rf value of 0.94 (Rf = 14.1/15 = 0.94) showed larvicidal activity. In a 72 h bioassay experiment, mortality rate at 60 mg/L was significantly higher (P < 0.05) than those at 25 and 45 mg/L against early 3rd instar. Result of log-probit analysis (at 95% confidence level) revealed that LC50 and LC90 values gradually decreased with the exposure period showing the lowest value at 72 h of exposure. A clear dose-dependent mortality was observed, as the rate of mortality (Y) was positively correlated with the concentration (X) having regression coefficient value close to one in each case. The compound was found to be eco-friendly as it did not show any adverse effect to the studied non target organisms. Chemical characterization (GC–MS and IR analyses) of the active ingredient revealed the presence of phytosteroid compounds responsible for mosquito larvicidal activity.ConclusionLeaf extract of S. nigrum has great potential as bio control agent against Cx. vishnui group and An. subpictus. In near future the isolated bioactive phytochemical could be used as a source of an effective mosquitocidal agent.

Boswellia ovalifoliolata (Burseraceae) essential oil as an eco-friendly larvicide? Toxicity against six mosquito vectors of public health importance, non-target mosquito fishes, backswimmers, and water bugs.

The use of synthetic pesticides to control vector populations is detrimental to human health and the environment and may lead to the development of resistant strains. Plants can be alternative sources of safer compounds effective on mosquito vectors. In this study, the mosquito larvicidal activity of Boswellia ovalifoliolata leaf essential oil (EO) was evaluated against Anopheles stephensi, Anopheles subpictus, Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Culex tritaeniorhynchus. GC-MS revealed that the B. ovalifoliolata EO contained at least 20 compounds. The main constituents were β-pinene, α-terpineol, and caryophyllene. In acute toxicity assays, the EO was toxic to larvae of An. stephensi, Ae. aegypti, Cx. quinquefasciatus, An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus with LC50 values of 61.84, 66.24, 72.47, 82.26, 89.80, and 97.95μg/ml, respectively. B. ovalifoliolata EO was scarcely toxic to mosquito fishes, backswimmers, and water bugs predating mosquito larvae with LC50 from 4186 to 14,783μg/ml. Overall, these results contribute to develop effective and affordable instruments to magnify the reliability of Culicidae control programs.

Resting and feeding preferences of Anopheles stephensi in an urban setting, perennial for malaria

BackgroundThe Indian city of Chennai is endemic for malaria and the known local malaria vector is Anopheles stephensi. Plasmodium vivax is the predominant malaria parasite species, though Plasmodium falciparum is present at low levels. The urban ecotype of malaria prevails in Chennai with perennial transmission despite vector surveillance by the Urban Malaria Scheme (UMS) of the National Vector Borne Disease Control Programme (NVBDCP). Understanding the feeding and resting preferences, together with the transmission potential of adult vectors in the area is essential in effective planning and execution of improved vector control measures.MethodsA yearlong survey was carried out in cattle sheds and human dwellings to check the resting, feeding preferences and transmission potential of An. stephensi. The gonotrophic status, age structure, resting and host seeking preferences were studied. The infection rate in An. stephensi and Anopheles subpictus were analysed by circumsporozoite ELISA (CS-ELISA).ResultsAdult vectors were found more frequently and at higher densities in cattle sheds than human dwellings. The overall Human Blood Index (HBI) was 0.009 indicating the vectors to be strongly zoophilic. Among the vectors collected from human dwellings, 94.2% were from thatched structures and the remaining 5.8% from tiled and asbestos structures. 57.75% of the dissected vectors were nulliparous whereas, 35.83% were monoparous and the rest 6.42% biparous. Sporozoite positivity rate was 0.55% (4/720) and 1.92% (1/52) for An. stephensi collected from cattle sheds and human dwellings, respectively. One adult An. subpictus (1/155) was also found to be infected with P. falciparum.ConclusionsControl of the adult vector populations can be successful only by understanding the resting and feeding preferences. The present study indicates that adult vectors predominantly feed on cattle and cattle sheds are the preferred resting place, possibly due to easy availability of blood meal source and lack of any insecticide or repellent pressure. Hence targeting these resting sites with cost effective, socially acceptable intervention tools, together with effective larval source management to reduce vector breeding, could provide an improved integrated vector management strategy to help drive down malaria transmission and assist in India’s plan to eliminate malaria by 2030.

Larvicidal activity of Blumea eriantha essential oil and its components against six mosquito species, including Zika virus vectors: the promising potential of (4E,6Z)-allo-ocimene, carvotanacetone and dodecyl acetate

The effective and environmentally sustainable control of mosquitoes is a challenge of essential importance. This is due to the fact that some invasive mosquitoes, with special reference to the Aedes genus, are particularly difficult to control, due to their high ecological plasticity. Moreover, the indiscriminate overuse of synthetic insecticides resulted in undesirable effects on human health and non-target organisms, as well as resistance development in targeted vectors. Here, the leaf essential oil (EO) extracted from a scarcely studied plant of ethno-medicinal interest, Blumea eriantha (Asteraceae), was tested on the larvae of six mosquitoes, including Zika virus vectors. The B. eriantha EO was analyzed by GC and GC-MS. The B. eriantha EO showed high toxicity against 3rd instar larvae of six important mosquito species: Anopheles stephensi (LC50=41.61 μg/ml), Aedes aegypti (LC50=44.82 μg/ml), Culex quinquefasciatus (LC50 =48.92 μg/ml), Anopheles subpictus (LC50=51.21 μg/ml), Ae. albopictus (LC50=56.33 μg/ml) and Culex tritaeniorhynchus (LC50=61.33 μg/ml). The major components found in B. eriantha EO were (4E,6Z)-allo-ocimene (12.8%), carvotanacetone (10.6%), and dodecyl acetate (8.9%). Interestingly, two of the main EO components, (4E,6Z)-allo-ocimene and carvotanacetone, achieved LC50 lower than 10 μg/ml on all tested mosquito species. The acute toxicity of B. eriantha EO and its major constituents on four aquatic predators of mosquito larval instars was limited, with LC50 ranging from 519 to 11.431 μg/ml. Overall, the larvicidal activity of (4E,6Z)-allo-ocimene and carvotanacetone far exceed most of the LC50 calculated in current literature on mosquito botanical larvicides, allowing us to propose both of them as potentially alternatives for developing eco-friendly mosquito control tools.

Biophysical characterization of Acacia caesia-fabricated silver nanoparticles: effectiveness on mosquito vectors of public health relevance and impact on non-target aquatic biocontrol agents.

Mosquito-borne diseases lead to serious public health concerns in tropical and sub-tropical countries worldwide, due to development of mosquito resistance to synthetic pesticides, non-target effects of pesticides, and socioeconomic reasons. Currently, green nanotechnology is a promising research field, showing a wide range of potential applications in vector control programs. The employ of natural products as reducing agents to fabricate insecticidal nanocomposites is gaining research attention worldwide, due to low costs and high effectiveness. Interestingly, biophysical features of green-synthesized nanoparticles strongly differ when different botanicals are employed for nanosynthesis. In this study, a cheap Acacia caesia leaf extract was employed to fabricate silver nanoparticles (Ag NPs) with ovicidal, larvicidal, and adulticidal toxicity against three mosquito vectors, Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus. Ag NPs were analyzed by various biophysical methods, including spectroscopy (UV-visible spectrophotometry, XRD, FTIR, EDX) and microscopy (SEM, TEM, AFM) techniques. High acute larvicidal potential was observed against larvae of An. subpictus (LC50=10.33μg/ml), Ae. albopictus (LC50=11.32μg/ml), and Cx. tritaeniorhynchus (LC50=12.35μg/ml). Ag NPs completely inhibited egg hatchability on three vectors at 60, 75, and 90μg/ml, respectively. In adulticidal assays, LD50 values were 18.66, 20.94, and 22.63μg/ml. If compared to mosquito larvae, Ag NPs were safer to threenon-target aquatic biocontrol agents, with LC50 ranging from 684 to 2245μg/ml. Overall, our study highlights the potential of A. caesia as an abundant and cheap bioresource to fabricate biogenic Ag NPs effective against mosquito young instars and adults, with moderate impact on non-target aquatic biocontrol agents.

Larvicidal activity of the essential oil from Amomum subulatum Roxb. (Zingiberaceae) against Anopheles subpictus, Aedes albopictus and Culex tritaeniorhynchus (Diptera: Culicidae), and non-target impact on four mosquito natural enemies

Mosquitoes (Diptera: Culicidae) are the primary vectors of several serious diseases that affect both animals and humans. Most of these diseases, especially the ones that are caused by arboviruses such as Zika, dengue and Japanese encephalitis, cannot be effectively prevented or treated, thereby rendering the discovery of alternative measures for the control of mosquito-borne diseases an absolute necessity. The current study evaluates the acute toxicity of Amomum subulatum-derived essential oil against Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus. We used gas chromatography–mass spectroscopy to analyze the chemical composition of A. subulatum EO. Analysis revealed thirty-three components. Primary constituents were 1,8- cineole (39.8%) and α-terpineol (11.5%). The essential oil from A. subulatum demonstrated a significant toxic effect against An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus third instar larvae, with LC50 values of 41.25, 44.11 and 48.12 μg/ml and LC90 values of 80.29, 85.6 and 89.30 μg/ml, respectively. Concerning non-target effects in the aquatic environment, we evaluated the acute toxicity of A. subulatum oil on 4 mosquito biocontrol agents, Anisops bouvieri, Diplonychus indicus, Poecilia reticulata and Gambusia affinis. We observed that the toxicity of this oil was extremely low, with LC50 ranging between 3123 and 9104 μg/ml. In conclusion, the A. subulatum essential oil is an interesting bioresource to develop environmental friendly mosquito larvicides. Indeed, it is effective against different Culicidae species with LC50 always lower than 50 μg/ml, while LC50 calculated for non-target organisms are about 100-fold higher.

Characterization of a Strain of &lt;i&gt;Bacillus sphaericus&lt;/i&gt; Isolated from Local Rice Field and its Virulence against Mosquito Larvae

Objective: Classical chemical control to mosquito is a preferable method. But it faces a problem for its increasing resistance against mosquito. To regulate the vector population as an alternative method, non-hazardous biocontrol methods would be the preeminent option to control mosquitoes. Objective of the present study is to examine the virulence of Bacillus sphaericus as an effective biocontrol agent against mosquitoes.Method: A strain of the bacteria Bacillus sphaericus was isolated from the gut of dead Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) larva collected from submerged rice fields, Burdwan, West Bengal, India. The strain was characterized following standard methodologies.Result: The bacterial strain formed crystals, tolerated 4% NaCl, produced protease and sensitive to different known antibiotics. An aqueous preparation of the bacteria revealed that 10ml/L (6.8x10 6 bacteria/ml) Bs formulation (bacterial broth) killed 100% larvae of Cx. quinquefasciatus , Anopheles subpictus, Armigeres subalbatus within 6 hours of exposure. Field tests showed that by the end of seventh day of application a total reduction of Cx. quinquefasciatus was achieved and 87% and 64% reduction of An. subpictus and Ar. subalbatus immatures were observed respectively. No larval emergence was observed up to tenth day in case of Cx. quinquefasciatus . The results indicate that the isolated strain of B. sphaericus can be a potential larvicide to regulate mosquito populations.Conclusion: Further tests need to be carried out to justify its use against different other mosquito species and insects.

What Kind of Reducing Botanical? High Mosquitocidal Efficacy of a Silver Nanocomposite Synthesized Using a Leaf Aqueous Extract of Fumaria indica

Mosquito vector control is a crucial challenge nowadays. Recently, the relevance of screening poorly studied plant products for green synthesis of nanopesticides was highlighted. Different plant products for nanosynthesis led to nano-composites with distinct biophysical features and toxicity. Here we fabricated silver nanoparticles capped with metabolites from Fumaria indica aqueous extract. Several biophysical methods were used to validate nanosynthesis F. indica-synthesized nanomaterial showed high efficacy as pesticide on Anopheles subpictus (LC50 = 10.34 µg/ml), Aedes albopictus (LC50 = 11.42 µg/ml) and Culex tritaeniorhynchus (LC50 = 12.50 µg/ml) larvae, allowing us to propose this easy to obtain nano-material as an effective source of novel mosquito pesticides.

Larvicidal and pediculicidal activity of synthesized TiO2 nanoparticles using Vitex negundo leaf extract against blood feeding parasites

Insecticide resistance and inadequate attention to the application instructions of topical pediculicides are common reasons for treatment failure. Essential oils or plant extracts are good and safe alternatives due to their low toxicity to mammals and easy biodegradability. The present study was carried out to establish the larvicidal and the pediculicidal activity of synthesized titanium dioxide nanoparticles (TiO2 NPs) using the leaf aqueous extract of Vitex negundo (Verbenaceae) against the fourth instar larvae of the malaria vector, Anopheles subpictus Grassi and filariasis vector, Culex quinquefasciatus Say (Diptera: Culicidae) and the head louse, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae). The synthesized TiO2 NPs were characterized by UV, XRD, FTIR and SEM-EDX. The SEM analyses were clearly indicated that the spherical shape of the synthesized TiO2 NPs. Mosquito larvae and head lice were exposed to varying concentrations of the synthesized TiO2 NPs, V. negundo leaf aqueous extract and titanium tetrachloride (TiCl4) for 24h. The maximum activity was observed in the synthesized TiO2 NPs against A. subpictus, C. quinquefasciatus and lice, (LC50=7.52, 7.23 and 24.32mg/L; χ2=0.161, 2.678 and 4.495; r2=0.663, 0.742 and 0.924), respectively. The TiO2 NPs did not exhibit any noticeable toxicity on Poecilia reticulata after 24h of exposure. The findings revealed that the synthesized TiO2 NPs possess excellent mosquito larvicidal and anti-lice activity. These results suggest that the green synthesis of TiO2 NPs has the potential to be used as an ideal eco-friendly approach for the control of vectors and head lice.

Artemisia absinthium-borne compounds as novel larvicides: effectiveness against six mosquito vectors and acute toxicity on non-target aquatic organisms

The eco-friendly control of mosquito vectors is a crucial challenge of public health importance. Here we evaluated the larvicidal potential of Artemisia absinthium essential oil (EO) and its three major chemical constituents against six mosquito vectors: Anopheles stephensi, Anopheles subpictus, Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Culex tritaeniorhynchus. The EO was obtained by leaf hydro-distillation. Its chemical composition was analyzed using gas chromatography-mass spectrometry. Major components were (E)-β-farnesene (31.6%), (Z)-en-yn-dicycloether (11.12%), and (Z)-β-ocimene (27.8%). The EO was toxic effect against larval populations of An. stephensi, An. subpictus, Ae. aegypti, Ae. albopictus, Cx. quinquefasciatus, and Cx. tritaeniorhynchus, with LC50 values of 41.85, 52.02, 46.33, 57.57, 50.57, and 62.16μg/ml. (E)-β-farnesene, (Z)-en-yn-dicycloether, and (Z)-β-ocimene were highly effective on An. stephensi (LC50 = 8.13, 16.24 and 25.84μg/ml) followed by An. subpictus (LC50 = 10.18, 20.99, and 30.86μg/ml), Ae. aegypti (LC50 = 8.83,17.66, and 28.35μg/ml), Ae. albopictus (LC50 = 11.38,23.47, and 33.72μg/ml), Cx. quinquefasciatus (LC50 = 9.66, 19.76, and 31.52μg/ml), and Cx. tritaeniorhynchus (LC50 = 12.51,25.88, and 37.13μg/ml). Notably, the EO and its major compounds were safer to the non-target organisms Chironomous circumdatus, Anisops bouvieri and Gambusia affinis, with LC50 values ranging from 207.22 to 4385μg/ml. Overall, our results highlight that (E)-β-farnesene, (Z)-en-yn-dicycloether, and (Z)-β-ocimene from the A. absinthium EO represent promising eco-friendly larvicides against six key mosquito vectors with moderate toxicity against non-target organisms.

Eco-friendly larvicides from Indian plants: Effectiveness of lavandulyl acetate and bicyclogermacrene on malaria, dengue and Japanese encephalitis mosquito vectors

Mosquitoes (Diptera: Culicidae) are a key threat for millions of people and animals worldwide, since they act as vectors for devastating pathogens and parasites, including malaria, dengue, Japanese encephalitis, filiariasis and Zika virus. Mosquito young instars are usually targeted using organophosphates, insect growth regulators and microbial agents. Indoor residual spraying and insecticide-treated bed nets are also employed. However, these chemicals have negative effects on human health and the environment and induce resistance in a number of vectors. In this scenario, newer and safer tools have been recently implemented to enhance mosquito control. The concrete potential of screening plant species as sources of metabolites for entomological and parasitological purposes is worthy of attention, as recently elucidated by the Y. Tu's example. Here we investigated the toxicity of Heracleum sprengelianum (Apiaceae) leaf essential oil and its major compounds toward third instar larvae of the malaria vector Anopheles subpictus, the arbovirus vector Aedes albopictus and the Japanese encephalitis vector Culex tritaeniorhynchus. GC–MS analysis showed that EO major components were lavandulyl acetate (17.8%) and bicyclogermacrene (12.9%). The EO was toxic to A. subpictus, A. albopictus, and C. tritaeniorhynchus, with LC50 of 33.4, 37.5 and 40.9µg/ml, respectively. Lavandulyl acetate was more toxic to mosquito larvae if compared to bicyclogermacrene. Their LC50 were 4.17 and 10.3µg/ml for A. subpictus, 4.60 and 11.1µg/ml for A. albopictus, 5.11 and 12.5µg/ml for C. tritaeniorhynchus. Notably, the EO and its major compounds were safer to three non-target mosquito predators, Anisops bouvieri, Diplonychus indicus and Gambusia affinis, with LC50 ranging from 206 to 4219µg/ml. Overall, this study highlights that H. sprengelianum EO is a promising source of eco-friendly larvicides against three important mosquito vectors with moderate toxicity against non-target aquatic organisms.

Observations on the pupal productivity of Culex tritaeniorhynchus in rice fields of West Bengal, India: implications for vector management (Diptera: Culicidae)

The mosquito &lt;em&gt;Culex&lt;/em&gt; &lt;em&gt;tritaeniorhychus&lt;/em&gt; is an established vector of Japanese encephalitis in India and many Asian countries. Entomological monitoring enables estimation of the abundance of the vector mosquitoes and therefore aids in vector management and disease control. In compliance with this proposition, an assessment of the pupal productivity of the mosquito &lt;em&gt;C. tritaeniorhynchus&lt;/em&gt; was made from selected rice fields of West Bengal, India. The results are expected to provide the present status of mosquitoes in an endemic region of Japanese encephalitis. In course of sampling of the rice fields, the mosquito &lt;em&gt;C. tritaeniorhyhchus&lt;/em&gt; was found in abundance with other mosquitoes like &lt;em&gt;Culex&lt;/em&gt; &lt;em&gt;bitaeniorhynchus&lt;/em&gt;, &lt;em&gt;Anopheles subpictus, Anopheles vagus, Anopheles barbirostris&lt;/em&gt;. Application of multivariate analysis indicated that the plant height, water depth and temperature could explain the variations in the pupal productivity of&lt;em&gt; C. tritaeniorhynchus&lt;/em&gt; in rice fields. The correspondence of the immature abundance of &lt;em&gt;C. tritaeniorhynchus&lt;/em&gt; with plant height suggests persistence of the population throughout the paddy rice cultivation period. Using the plant height as an indicator, the abundance of the mosquito &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;tritarniorhynchus&lt;/em&gt; can be predicted enabling application of appropriate strategies for population intervention and thus the possibility of the disease.