The impact of climatic variables on the population dynamics of the main malaria vector, Anopheles stephensi Liston(Diptera: Culicidae), in southern Iran

Objective:To determine the significance of temperature,rainfall and humidity in the seasonal abundance of Anopheles stephensi in southern Iran.Methods:Data on the monthly abundance of Anopheles stephensi larvae and adults were gathered from earlier studies conducted between 2002 and 2019 in malaria prone areas of southeastern Iran.Climatic data for the studied counties were obtained from climatology stations.Generalized estimating equations method was used for cluster correlation of data for each study site in different years.Results:A significant relationship was found between monthly density of adult and larvae of Anopheles stephensi and precipitation,max temperature and mean temperature,both with simple and multiple generalized estimating equations analysis(P<0.05).But when analysis was done with one month lag,only relationship between monthly density of adults and larvae of Anopheles stephensi and max temperature was significant(P<0.05).Conclusions:This study provides a basis for developing multivariate time series models,which can be used to develop improved appropriate epidemic prediction systems for these areas.Long-term entomological study in the studied sites by expert teams is recommended to compare the abundance of malaria vectors in the different areas and their association with climatic variables.

Astrodaucus persicus as a new source of bioinsectisides against malaria vector, Anopheles stephensi

Objective: To determine the larvicidal activities of petroleum ether, chloroform, ethyl acetate and methanol fractions of roots and fruits extracts of Astrodaucus persicus from Apiaceae family against malaria vector, Anopheles stephensi(An. stephensi).Methods: Twenty five third instar larvae of An. stephensi were exposed to various concentrations(10–160 g/L) of fractions and were assayed according to World Health Organization protocol. The larval mortality was calculated after 24 h treatment.Results: Among tested fractions, the highest larvicidal efficacy was observed from ethyl acetate fraction of fruits extract with 50% and 90% mortality values(LC_(50) and LC_(90)) of34.49 g/L and 108.61 g/L, respectively. Chloroform fraction of fruits extract was the second larvicidal sample with LC_(50) of 45.11 g/L and LC_(90) of 139.36 g/L. Petroleum ether fractions of fruits and roots and methanol fraction of fruits showed moderate toxicity against An. stephensi.Conclusions: Astrodaucus persicus is a potential source of valuable and natural larvicidal compounds against malaria vector, An. stephensi and can be used in mosquitoes control programs as an alternative to synthetic insecticides.

Wash resistance and bio-efficacy of Olyset~? Plus, a long-lasting insecticide-treated mosquito net with synergist against malaria vector, Anopheles stephensi

Objective: To determine the wash resistance of Olyset~? Plus using World Health Organization Pesticide Evaluation Scheme standard washing procedure and to assess the value of knock down and mortality rates of Anopheles stephensi at different regimens of long lasting insecticide treated nets washings.Methods: The study was conducted at the Bioassay Laboratory of Culicidae Insectary,School of Public Health, Tehran University of Medical Sciences, Iran. The net was made of polyester impregnated with permethrin and piperonyl butoxide at a ratio of 2:1. The washing resistance was assessed using Le Chat?soap and a shaker incubator set at a speed of 155 r/min, 30℃ for 10 min. The cone bioassay test was carried out according to World Health Organization recommended guideline with tolerant field strain of female Anopheles stephensi to pyrethroids.Results: The knockdown and mortality rates of female mosquitoes exposed to Olyset~? Plus from un-washed nets to 2 washings were 79.7% and 88.8% respectively. Mortality was dropped to zero while active ingredient estimated 0.532 mg/100 cm^2 to 0.481 mg/100 cm^2 after 15 washings. A positive correlation was seen between residues of permethrin on nets, knockdown rate and mortality rate of female Anopheles stephensi exposed to different regimes of washed Olyset~? Plus(r = 0.954, P = 0.001).Conclusions: It is recommended that a preliminary survey conducted on resistance level of Anopheles vectors before the distribution of Olyset~? Plus in malaria endemic communities.

Indication of pyrethroid resistance in the main malaria vector Anopheles stephensi from Iran

ObjectiveTo investiagte insecticide resistance in target species for better insecticide resistance managemnet in malaria control programs.MethodsThe status of insecticide resistance to different imagicides in Anopheles stephensi (An. stephensi) including DDT 4%, lambdacyhalothrin 0.50%, deltamethrin 0.05%, permethrin 0.75%, cyfluthrin 0.15% and etofenprox 0.50% was performed according to WHO standard method.ResultsThe mortality rate to lambdacyhalothrin, permethrin, cyfluthrin, deltamethrin, etofenprox and DDT was (88.0±3.2), (92.0±2.7), (52.0±5.0), (96.0±2.2), (90.0±3.0) and (41.0±5.7) percent, respectively at diagnostic dose for one hour exposure time followed by 24 h recovery period.ConclusionsThese results showed first indication of pyrethroid resistance in An. stephensi in a malarious area, from southern Iran. There is widespread, multiple resistances in the country in An. stephensi to organochlorine and some report of tolerance to organophosphate insecticides and recently to pyrethroids. However, results of this paper will provide a clue for monitoring and mapping of insecticide resistance in the main malaria vector for implementation of any vector control.

Genetic differentiation between three ecological variants （‘type’, ＇mysorensis＇ and ‘intermediate’） of malaria vector Anopheles stephensi （Diptera： Culicidae）

Anopheles stephensi is the main vector of urban malaria in South Asia. Three ecological variants （‘type’, ‘mysorensis’ and ‘intermediate’） of An. stephensi have been reported on the basis of ecology and egg morphology. However, it is unclear if there is any genetic isolation between the three variants. We analyzed the three variants of An. stephensi using eight microsatellite loci and found that large and significant genetic differentiation exists between them （mean FST = 0.393 and mean RST = 0.422）. Pairwise estimates of genetic differentiation between the variants were ‘type’ versus ‘mysorensis’ （mean FsT = 0.411 and mean RST = 0.308）, ‘type’ versus‘intermediate’ （mean FsT = 0.388 and mean RST = 0.518） and ‘intermediate’versus ＇mysorensis＇ （mean FST = 0.387 and mean RST = 0.398） and all were statistically significant （P 〈 0.05）. The greater sensitivity of RST in differentiation indicated that mutations and not genetic drift had generated the differences between three variants of An. stephensi. The present study indicated large genetic differentiation and presence of non-significant low level ofgene flow between the three variants （‘type’,‘ mysorensis’ and ‘intermediate’） of An. stephensi.

Mosquito larvicidal properties of Impatiens balsamina(Balsaminaceae)against Anopheles stephensi,Aedes aegypti and Culex quinquefasciatus(Diptera:Culicidae)

Objective:To assess the larvicidal potential of the crude benzene,chloroform,ethyl acetate and methanol solvent extracts of the medicinal plant Impatiens balsamina against Anopheles stephensi(An.stephensi),Aedes aegypti(Ae.aegypti)and Culex quinquefasciatus(Cx.quinquefasciatus).Methods:Twenty five third instar larvae of An.stephensi,Ae.aegypti and Cx.quinquefasciatus were exposed to various concentrations and were assayed in the laboratory by using the protocol recommended by WHO.The larval mortality was observed after 24 h of treatment.Results:Among extracts tested,the highest larvicidal activity was observed in leaf methanol extract of Impatiens balsamina against An.stephensi,Ae.aegypti and Cx.quinquefasciatus with the LC_(50)and LC_(90)values 98.04,119.68,125.06 and 172.93,210.14,220.60 mg/L,respectively.Conclusions:From the results it can be concluded that the larvicidal effect of Impatiens balsamina against An.stephensi,Ae.aegypti and Cx.quinquefasciatus make this plant product promising as an alternative to synthetic insecticide in mosquito control programs.

Mosquitocidal activity of indigenenous plants of Western Ghats,Achras sapota Linn.(Sapotaceae)and Cassia auriculata L.(Fabaceae)against a common malarial vector,Anopheles stephensi Liston(Culicidae:Diptera)

Objective:To evaluate the mosquito larvicidal,ovicidal,pupicidal and repellent activities of hexane,diethyl ether,dichloromethane,acetone and methanol extracts of Indian medicinal plants,Achras sapota(A.sapota)and Cassia auriculata(C.auriculata)at different concentrations against Anopheles stephensi(An.stephensi),a malarial vector.Methods:Twenty five early third instar larvae of An.stephensi were exposed to various concentrations(30-210 mg/L)of plants extracts and were assayed in the laboratory by using the protocol of WHO 2005;then after 24 h LC_(50) values of the A.sapota and C.auriculata leaf extract was determined by probit analysis.The ovicidal activity was tested with the extracts ranging from 50-350 mg/L.The pupicidal activity was recorded after 24 h of exposure to the extract.The repellent efficacy was determined against mosquito species at two different concentrations 1.5 and 3.0 mg/cm^(2) under laboratory conditions.Results:Among the five different extracts tested against the An.stephensi,methanol extract of A.sapota proved to be an more effective solvent extract in almost all the parameters studied than C.auriculata.Conclusions:It is inferred that the leaf extract of A.sapota and C.auriculata could be used in vector control programme.

Mosquito repellent potential of Pithecellobium dulce leaf and seed against malaria vector Anopheles stephensi(Diptera:Culicidae)

Objective:To determine the repellent properties of hexane,benzene,ethyl acetate,chloroform and methanol extract of Pithecellobium dulce(P.dulce)leaf and seed against Anopheles stephensi(An.stephensi).Methods:Repellent activity assay was carried out in a net cage(45 cm×30 cm×25 cm)containing 100 blood starved female mosquitoes of An.stephensi.This assay was carried out in the laboratory conditions according to the WHO 2009 protocol.Plant crude extracts of P.dulce were applied at 1.0,2.5,and 5.0 mg/cm^(2) separately in the exposed fore arm of study subjects.Ethanol was used as the sole control.Results:In this study,the applied plant crude extracts were observed to protect against mosquito bites.There were no allergic reactions experienced by the study subjects.The repellent activity of the extract was dependent on the concentration of the extract.Among the tested solvents,the leaf and seed methanol extract showed the maximum efficacy.The highest concentration of 5.0 mg/cm^(2) leaf and seed methanol extract of P.dulce provided over 180 min and 150 min protection,respectively.Conclusions:Crude extracts of P.dulce exhibit the potential for controlling malaria vector mosquito An.stephensi.

Mosquito larvicidal properties of volatile oil from salt marsh mangrove plant of Sesuvium portulacastrum against Anopheles stephensi and Aedes aegypti

Objective:To identify the larvicidal activity of the volatile oil from Sesuvium portulacastrum(S.portulacastrum)against Anopheles stephensi and Aedes aegypti.Methods:Volatile oil extract of S.portulacastrum was prepared in a graded series of concentration.The test for the larvicidal effect of volatile oil against mosquitos larvae was conducted in accordance with the WHO standard method.Batches of 25 early 4th instar larvae of two mosquitoes were transferred to 250 mL enamel bowl containing 199 mL of distilled water and 1 mL of plant extracts.Each experiment was conducted with triplicate with concurrent a control group.Results:Volatile oil extract of S.portulacastrum showed toxicity against 4th instar larvae of Aedes aegypti and Anopheles stephensi with equivalent LC50 value[(63±7.8)μL/mL,LCL-UCL=55.2-64.0]and LC90 value[(94.2±3.9)μL/mL]in maximum activity with minimum concentration(200μL/mL)of volatile oil and followed by maximum activity of 250μL concentration showed LC50 value=(68.0±8.2)μL/mL,LCL-UCL=66.26-69.2 and LC50 value of(55.2±2.8)μL/mL,LCL-UCL=53.7-56.9,LC90=(95.2±1.25)μL/mL and followed by 250μL of oil extract against 4th instar larvae of Aedes aegypti respectively.Conclusions:It is inferred from the present study that,the extracts from salt marsh mangrove plan of S.portulacastum are identified as a potential source of safe and efficacious mosquito control agents for the management of vector borne diseases of malaria and dengue.

Chemical composition and laboratory investigation of Melissa officinalis essential oil against human malarial vector mosquito,Anopheles stephensi L.(Diptera:Culicidae)

Objective:To decide the larvicides,ovicidal,pupicidal and repellent activity of Melissa officinalis(M.officinalis)chemical compositions against important mosquito Anopheles stephensi(An.stephensi)(Diptera:Culicidae).Methods:A chemical constituent of 24 compounds was identified in the oils of M.officinalis compounds representing to 98.73%.A total of 253rd instar larvae of An.stephensi were showed to a variety of concentrations(30-300 mg/L)in laboratory by means of utilizing the standard procedure portrayed by World Health Organization(2005).The larvae were exposed for 24 h and mortalities were subjected to probit analysis.The ovicidal activity was strong-minded against An.stephensi mosquito to a variety of concentrations ranging from 15-90 mg/L under the laboratory circumstances.The repellent activity of M.officinalis chemical compositions tested at concentrations of 0.75 and 1.50 mg/cm^(2)was evaluated in a net cage(45 cm×45 cm×40 cm)including 100 blood starving female mosquitoes of An.stephensi using the methods of World Health Organization(1996).Results:The LC_(50)and LC_(90)values of citronellal compound against An.stephensi larvae were 85.44 and 159.73 mg/L,respectively.Mean percent hatchability of the ovicidal action was observed 48 h post-treatment.Similarly,the citronellal compound and other compositions were found to be mainly effective against eggs of An.stephensi.Citronellal compound exerted 45,60,75 and 90 mg/L against An.stephensi,respectively.The repellent activity of citronellal compound was contained to be mainly effective and the maximum action was observed at 0.75 and 1.50 mg/cm^(2)concentrations giving 100%protection up to 210 min against An.stephensi.Conclusions:This current study was undertaken to evaluate the larvicidal,ovicidal,repellent potential of compounds from the M.officinalis essential oil against An.stephensi.This is initial statement on the mosquito larvicidal,ovicidal and repellent activity of M.officinalis chemical compositions.

The Influence of Portulaca Oleracea L. Leaves Extracts on the Histoarchitecture of Culex Quinquefasciatus and Anopheles Stephensi Larvae

Background:Mosquito is a big threat to the human health.Mosquito-borne diseases cause millions of death to the human beings.Hence,a permanent solution is eagerly to be established to control its excessive growth in stagnant water.Portulaca oleracea Linn is a natural larvicidal agent,which contains active ingredients such as linolenic acid,linoleic acid(omega-3 fatty acids).These bioactive compounds may be responsible for its larvicidal properties on mosquito.Objective:The present study is focussed on identifying the bioactive compounds,such as linolenic acid,through GC-MS,and analyzing the larvicidal efficacy of Portulaca oleracea L.against Culex quinquefasciatus and Anopheles stephensi larvae.Methods:Preliminary phytochemical analysis,total protein content,total carbohydrate content,total phenol content,total flavonoid content and GC-MS analysis exhibited the presence of rich phytoconstituents in Portulaca oleracea.DPPH analysis was carried out to analyze the antioxidant potential of plant extract.Larvicidal activity and histological change were detected to evaluate the efficacy of Portulaca oleracea L.on the Culex quinquefasciatus and Anopheles stephensi larvae.Results:Aqueous and ethanol leaf extracts of Portulaca oleracea L.against both Culex quinquefasciatus and Anophe-les stephensi larvae,showed a very good larvicidal activity at 500μg/mL among the various concentrations.His-tological damages of mosquito larvae were observed when treated with the Portulaca oleracea L.extract,and provided further evidence for its larvicidal activity.Conclusion:This study concluded that the plant Portulaca oleracea L.contained many useful bioactive compounds,can be a strong larvicidal agent against both Culex quinquefasciatus and Anopheles stephensi larvae.The molecular mechanism for the larvicidal activity will be identified in future studies.

UP REGULATION OF UBIQUITIN C TERMINAL HYDROLASE IN THE RESPONSE OF THE MOSQUITO ANOPHELES STEPHENSI TO PLASMODIUM YOELII INFECTION

The isolation and study of genes that are differentially expressed in malaria infected mosquitoes is important for the elucidation of basic molecular mechanisms underlying vector parasite interactions. When screening against a previously established cDNAs pool representing specifically expressed genes in the mosquito Anopheles stephensi infected by Plasmodium yoelii, it was found that one of these encodes a protein with extensive sequence similarity to the Drosophila melanogaster ubiquitin C terminal hydrolase(UCTH). Similarity alignment showed that the fragment is 89% identical at amino acid level to the corresponding region of the known An. gambiae EST sequence, as well as 63% identical to that of both the fruitfly and human sequence. Virtual Northern blot expression dynamics of the gene indicated that it was up regulated significantly in the mosquito at least 1 7 days post infection, consistent with the critical transition stages of midgut invasion and relocation of sporozoites from the oocysts to the salivary glands during parasite development. Rather little is known about the role of the ubiquitin pathway in the activation of the mosquito innate immune system. The results indicate that the gene is related to malaria infection in mosquito. The cloning and expression profile analysis of As UCTH enables us to make predictions as to the roles it may play during malaria infection.