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  • Plantextractsaspotentialmosquitolarvicides

    AnupamGhosh,NanditaChowdhury*&GoutamChandra*

    Department of Zoology, Bankura Christian College, Bankura & *Mosquito & Microbiology Research Units, Parasitology Laboratory, Department of Zoology, The University of Burdwan, Burdwan, India

    ReceivedApril13,2011

    Mosquitoes act as a vector for most of the life threatening diseases like malaria, yellow fever, dengue fever, chikungunya ferver, filariasis, encephalitis, West Nile Virus infection, etc. Under the Integrated Mosquito Management (IMM), emphasis was given on the application of alternative strategies in mosquito control. The continuous application of synthetic insecticides causes development of resistance in vector species, biological magnification of toxic substances through the food chain and adverse effects on environmental quality and non target organisms including human health. Application of active toxic agents from plant extracts as an alternative mosquito control strategy was available from ancient times. These are non-toxic, easily available at affordable prices, biodegradable and show broad-spectrum target-specific activities against different species of vector mosquitoes. In this article, the current state of knowledge on phytochemical sources and mosquitocidal activity, their mechanism of action on target population, variation of their larvicidal activity according to mosquito species, instar specificity, polarity of solvents used during extraction, nature of active ingredient and promising advances made in biological control of mosquitoes by plant derived secondary metabolites have been reviewed.

    Key wordsInsecticides-integratedmosquitomanagement-larvicides-LC50-plantextracts

    581

    Review Article

    IndianJMedRes135,May2012,pp581-598

    Introduction

    Mosquitoes can transmit more diseases thanany other group of arthropods and affect million ofpeople throughout theworld.WHOhas declared themosquitoesaspublicenemynumberone1.Mosquitobornediseasesareprevalentinmorethan100countriesacross the world, infecting over 700,000,000 peopleevery year globally and 40,000,000 of the Indianpopulation.They act as a vector formost of the lifethreateningdiseaseslikemalaria,yellowfever,denguefever, chikungunya ferver, filariasis, encephalitis,WestNile virus infection, etc., in almost all tropicalandsubtropicalcountriesandmanyotherpartsoftheworld.

    To prevent proliferation of mosquito bornediseases and to improve quality of environment andpublichealth,mosquitocontrolisessential.Themajortool inmosquito control operation is the applicationof synthetic insecticides such as organochlorine andorganophosphate compounds. But this has not beenverysuccessfuldue tohuman, technical,operational,ecological, and economic factors. In recent years,use of many of the former synthetic insecticides inmosquito control programme has been limited. It isduetolackofnovelinsecticides,highcostofsyntheticinsecticides,concernforenvironmentalsustainability,harmfuleffectonhumanhealth,andothernon-targetpopulations,theirnonbiodegradablenature,higherrateof biological magnification through ecosystem, and

  • increasing insecticide resistance on a global scale2,3.Thus, the Environmental ProtectionAct in 1969 hasframedanumberofrulesandregulationstochecktheapplicationofchemicalcontrolagentsinnature4.Ithaspromptedresearcherstolookforalternativeapproachesranging fromprovisionoforpromoting theadoptionof effective and transparent mosquito managementstrategies that focus on public education,monitoringand surveillance, source reduction and environmentfriendly least-toxic larvalcontrol.These factorshaveresulted in an urge to look for environment friendly,cost-effective, biodegradable and target specificinsecticides against mosquito species. Consideringthese, theapplicationof eco-friedlyalternatives suchasbiologicalcontrolofvectorshasbecomethecentralfocusofthecontrolprogrammmeinlieuofthechemicalinsecticides.

    One of themost effective alternative approachesunder thebiologicalcontrolprogrammeis toexplorethe floral biodiversity and enter the field of usingsafer insecticidesofbotanicaloriginas a simpleandsustainablemethodofmosquitocontrol.Further,unlikeconventionalinsecticideswhicharebasedonasingleactive ingredient,plantderived insecticidescomprisebotanical blends of chemical compounds which actconcertedly on both behavourial and physiologicalprocesses. Thus there is very little chance of pestsdeveloping resistance to such substances. Identifyingbio-insecticides that are efficient, as well as beingsuitable and adaptive to ecological conditions, isimperative for continued effective vector controlmanagement.Botanicalshavewidespreadinsecticidalpropertiesandwillobviouslyworkasanewweaponin the arsenal of synthetic insecticides and in futuremayactassuitablealternativeproducttofightagainstmosquitobornediseases.

    Roark5 described approximately 1,200 plantspecies having potential insecticidal value, whileSukumaret al6listedanddiscussed344plantspeciesthat only exhibitedmosquitocidal activity.Shallanet alin20057reviewedthecurrentstateofknowledgeonlarvicidal plant species, extraction processes, growthandreproductioninhibitingphytochemicals,botanicalovicides, synergistic, additive and antagonistic jointaction effects of mixtures, residual capacity, effectson non-target organisms, resistance and screeningmethodologies, and discussed some promisingadvances made in phytochemical research. Table Isummarized the mosquitocidal activities of variousherbalproductsfromediblecrops,ornamentalplants,

    trees,shrubs,herbs,grassesandmarineplantsaccordingtotheexactionproceduredevelopedinelevendifferentsolvent systems and the nature of mosquitocidalactivitiesagainstdifferentlifestagesofdifferentvectorspeciesasareadyreferenceforfurtherstudies.

    Phytochemicals

    Phytochemicalsarebotanicalswhicharenaturallyoccurring insecticidesobtained fromfloral resources.Applications of phytochemicals in mosquito controlwere in use since the 1920s8, but the discovery ofsynthetic insecticides such as DDT in 1939 sidetrackedtheapplicationofphytochemicalsinmosquitocontrol programme. After facing several problemsdue to injudicious and over application of syntheticinsecticides in nature, re-focus on phytochemicalsthat are easily biodegradable and have no ill-effectsonnon-targetorganismswasappreciated.Sincethen,thesearchfornewbioactivecompoundsfromtheplantkingdomand an effort to determine its structure andcommercialproductionhasbeen initiated.Atpresentphytochemicals make upto 1 per cent of worldspesticidemarket9.

    Botanicalsarebasicallysecondarymetabolitesthatserveasameansofdefencemechanismoftheplantsto withstand the continuous selection pressure fromherbivore predators and other environmental factors.Several groups of phytochemicals such as alkaloids,steroids,terpenoids,essentialoilsandphenolicsfromdifferent plants have been reported previously fortheir insecticidal activities7. Insecticidal effects ofplantextractsvarynotonlyaccordingtoplantspecies,mosquitospecies,geographicalvaritiesandpartsused,but also due to extractionmethodology adopted andthepolarityof thesolventsusedduringextraction.Awideselectionofplantsfromherbs,shrubsandlargetrees was used for extraction of mosquito toxins.Phytochemicalswereextractedeitherfromthewholebody of little herbs or fromvarious parts like fruits,leaves, stems, barks, roots, etc., of larger plants ortrees.Inallcaseswherethemosttoxicsubstanceswereconcentratedupon, foundandextracted formosquitocontrol.

    Plants produce numerous chemicals, many ofwhichhavemedicinalandpesticidalproperties.Morethan2000plantspecieshavebeenknowntoproducechemical factors and metabolites of value in pestcontrol programmes.Members of the plant families-Solanaceae, Asteraceae, Cladophoraceae, Labiatae,Miliaceae, Oocystaceae and Rutaceae have various

    582 INDIANJMEDRES,May 2012

  • GHOSH et al: PLANT EXTRACTS AS MOSQUITO LARVICIDE 583

    Table I (A).Efficacyofbotanicalextractsincontrolling/reducingthepopulationofvectormosquitoesPlantspecies Family Plant

    partsused

    Targetmosquitospecies

    Lethalconcentrations/ biologicalactivity

    References

    Petroleum ether solvent extractArtemisia annua

    Asteraceae Leaf Anopheles stephensi

    LC50valuewas16.85ppmafter24hand11.45ppmafter48hofexposure

    Sharma et al (2006)12

    Acacia nilotica

    Fabaceae Leaf LC50valuewas55.72ppmandLC90valuewas194.58ppm

    Saktivadivel&Daniel(2008)13Argemone mexicana Papaveraceae Leaf,

    seedLC50valuewas30.47and24.17;LC90 valueswere246.33and184.99ppmforleavesandseedsrespectively

    Jatrophacurcas

    Euphorbiaceae Leaf LC50valuewas62.29andLC90valuewas454.18ppm

    Withania somnifera Solanaceae Leaf LC50valuewas65.08andLC90valuewas266.39ppm

    Citrullus colocynthis Cucurbitaceae Leaf LC50valueswere37.70andLC90valuewas52.62ppm

    Aloe barbadensi

    Liliaceae Leaf LC50valueswere29.06and22.59ppmfor24and48h

    Mauryaet al (2007)14

    Cannabissativa

    Moraceae Leaf LC50valueswere376.58and1316.09ppmfor24and48h

    Eucalyptus globulus Myrtaceae Seed,leaf

    Culex pipiens Boththeextractsatadoseof1000ppmcaused100and80%mortalitytothetestedlarvae

    Sheerenet al (2006)15

    Solanum xanthocarpum

    Solanaceae Root Cx. pipiens pallens

    LC50andLC90valueswere41.28and111.16ppmafter24hand38.48and80.83ppmafter48h,respectively

    Mohan et al (2006)16

    Thymus capitatus Lamiaceae Leaf Cx. pipiens Thevolatileoil,Thymol,andtheunsaponifiableportionprovedhighlarvicidalpotency(LC50valuewas49.0ppm)

    Mansouret al (2000)17

    Citrus aurantium17 Rutaceae Fruitpeel Cx. quinquefasciatus

    LC90valueswere53.80and32.52ppmafter24and48hoftreatment

    Kassir(1989)18

    Myrtus communis Myrtaceae FlowerandLeaf

    Cx. pipiens molestus

    LC50valuewas16mg/l.Thymol,carvacrol,(1R)-(+)--pineneand(1S)-(-)--pinenewerethemost