Human resources section_8-textbook_on_public_health_and_community_medicine

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Human resources section_8-textbook_on_public_health_and_community_medicine

  1. 1. 10095752550
  2. 2. Section 8 : Entomology in Public Health Practice154 Introduction to Entomology Rina Tilak 903155 Principles of Vector Control Rina Tilak 906156 Housefly Rina Tilak 927157 Mosquitoes Rina Tilak 931158 Fleas Rina Tilak 940159 Human Lice Rina Tilak 944160 Sand Flies Rina Tilak 946161 Some Annoying Pests Rina Tilak 948162 Envenomizing Pests Rina Tilak 952163 Ticks and Mites Rina Tilak 955164 Rodents Rina Tilak 960166 Snakes Rina Tilak 966
  3. 3. (iv) Order Hemiptera : It contains the bedbugs and some other 154 Introduction to Entomology species like kissing or ‘assassin’ bugs, which act as vectors of ‘Chagas’ disease. Rina Tilak (b) Class Arachnida : It includes arthropods like ticks, mites, spiders and scorpions. The class is characterized by the presence of eight legs, body divided into two parts viz. cephalothoraxThe word ‘Entomology’ is derived from the Greek words (head and thorax are fused together) and abdomen and‘ENTOMON’ meaning an insect and ‘LOGOS’ meaning science, absence of antennae and wings. The cephalothorax bears sixthus ideally making Entomology ‘the branch of science which pairs of appendages, the first two pairs function as mouthpartsdeals with the study of insects’; however, the scope of the (chelicerae and pedipalps) and last four pairs as walking legs.subject has been broadened to include study of all Arthropods.Phylum Arthropoda constitutes all invertebrates with jointed (c) Class Crustacea : It includes lobsters, crabs, water fleasappendages and presence of chitinous exoskeleton besides and cyclops; some species of these are intermediate hosts ofother features. The word Arthropoda is derived from two words certain human helminths, e.g. Cyclops as intermediate host of‘ARTHRON’ meaning jointed and ‘PODA which means legs or ’, guinea worm infestation.appendages. The Phylum has many important classes of which (d) Class Myriapoda : It includes centipedes and millipedes.Class Insecta is the largest, constituting more than four million Modes of Disease Transmissioninsect species. The other important classes are Arachnida,Crustacea and Myriapoda. Arthropods transmit diseases to man through specialized modes of disease transmission. The modes of disease transmission byVector borne diseases are one of the leading causes of morbidity arthropods can be classified as under :and mortality the world over and pose a major public healthchallenge especially to the third world or developing countries. Direct Contact : When two hosts are in direct contact withOne of the important measures to combat these diseases is other, the arthropod vector itself gets transferred from one hostthrough control of vectors. To ensure effective vector control, to the other, e.g. pediculosis and scabies.the knowledge about their lifecycle, habits, habitat and Mechanical transmission : In this mode of transmission,diseases transmitted is essential. The chapters in this section the disease causing organism is transmitted on the outsidewill guide the reader on these aspects so that sound vector or inside the bodies of arthropods without undergoing anycontrol strategies can be formulated, wherever and whenever, development, propagation or any changes in the pathogenicityvector control is desired. e.g. diseases transmitted by houseflies - diarrhoea, dysentery,Classification of Arthropods cholera, hepatitis A & E etc.Diversity of structures amongst arthropods necessitates the Biological Transmission : The disease causing organismsub-division of the phylum Arthropoda into a number of undergoes certain biological changes inside the body of theclasses, orders, families, genera and species. The following vector. Depending on the type of biological changes, biologicalclasses include species of medical importance. transmission has been further classified as :(a) Class Insecta : It comprises about 70% of all the known Cyclo-developmental : In this mode of transmission, thespecies in the animal kingdom. The insects are characterized disease causing organism undergoes a part of its cycle in theby the presence of six legs, body divided into head, thorax and vector and simply develops or grows inside the body of theabdomen and presence of antennae besides other features. vector, e.g. Wuchereria bancrofti (Filariasis) transmitted byThe head bears the mouthparts, eyes in the form of compound Culex female.or simple eyes or at times may have no eyes and a pair of Cyclo-developmental-propagative or Cyclo-propagative :antennae. The thorax is subdivided into three segments with a In this mode of transmission, the disease causing organismpair of legs in each called the pro, meso and metathoracic legs. undergoes a part of its life cycle in the vector and also grows/The class is further subdivided into 29 orders of which only 4 develops and multiplies inside the body of the vector. Examplecontain species of medical importance. is Plasmodium sp (Malaria) transmitted by Anopheles female.(i) Order Diptera : It possesses one pair of wings and a pair Propagative : In this transmission mode, the disease organismof ‘halters’, which are vestigial wings. This is the largest order simply grows and multiplies in the body of the vector, e.g.comprising about seventy thousand described species with Yersinia pestis (Plague) transmitted by rat flea and allworld wide distribution. It contains such insects of medical bacterial, viral, spirochaetal or rickettsial diseases transmittedimportance as mosquitoes, sandflies, simulium flies and by arthropods.house-flies. Other Specialized Modes of Disease Transmission : These(ii) Order Anoplura : It comprises true or sucking lice, which specialized modes of disease transmission are generallyare parasitic on mammals and the chewing lice, which infest encountered in ticks and mites.birds as well as mammals. Lice of medical importance to man Trans-ovarian : The disease organism is transmitted to eggsare human lice. through ovary of infected female, e.g. Orientia tsutsugamushi,(iii) Order Siphonaptera : It contains many species of fleas the agent for Scrub typhus transmitted by trombiculid mite-including the rat flea, which is a vector of plague and endemic Leptotrombidium deliense.typhus. • 903 •
  4. 4. Table - 1 : Important arthropod borne diseases Disease Vector Causal organism Reservoir I Mosquito borne diseasesMalaria Anopheles species Plasmodium species ManFilariasis Culex quinquefasciatus W bancrofti (nocturnal, periodic) Man Aedes niveus group W. bancrofti (diurnal sub-periodic) Man Mansonoides species Brugia malayi Man, PrimateChikungunya Aedes species Arbovirus group A ManDengue fever & DHF Aedes species Arbovirus group B ManYellow fever Aedes species Arbovirus group B Man/ MonkeysJapanese Encephalitis Culex vishnui group Arbovirus group B Mammals/ Birds (C tritaeniorhynchus) II Sandfly borne diseasesLeishmaniasisVisceral (Kala azar) Phlebotomus argentipes Leishmania donovani Man/MammalsCutaneous (Oriental sore) P. papatasi L. tropica Man/MammalsEspundia P. sergenti L. braziliensis Man/MammalsSandfly fever P. sergenti, P. papatasi Virus Man III Fly borne diseasesBacillary dysentery M domestica Shigella ManAmoebic dysentery M domestica E. histolytica ManGastroenteritis M domestica Specific/Non specific organisms Man/animalsTyphoid M domestica Salmonella typhi ManParatyphoid M domestica Paratyphoid A&B ManCholera M domestica Vibrio cholera ManPoliomyelitis M domestica Virus ManViral hepatitis (Type A) M domestica HAV ManTrachoma M domestica C trachomatis ManYaws M domestica T pertenue Man IV Flea borne diseasesPlague (Bubonic) Xenopsylla species Yersinia pestis RodentsEndemic/Murine Typhus Xenopsylla species R. typhi Rodents/ Domestic animalChiggerosis (Jigger) - - Tunga penetrans (chigoe) Dogs, cats, wildDipylidium caninum Ctenocephalides. felis/canis Dipylidium caninumHymenolepis diminuta Hymenolepis diminuta Carnivores X cheopis / N fasciatusH nana X cheopis / C canis/ Pulex irritans H nana Rats, mice V Louse borne diseasesEpidemic typhus Pediculus humanus R. prowazeki ManEpidemic relapsing fever Pediculus humanus Borrelia recurrentis ManTrench fever Pediculus humanus Bartonella quintana Man/animalsDermatitis Pediculus humanus/ capitis Secondary organisms Man VI Tick borne diseasesKyasanur Forest Disease (KFD) Hard ticks species Arbovirus group B Monkeys/BirdsTick typhus Hard ticks species R conorii DogsTularaemia Hard ticks species P tularensis Rabbits/ Rodents/ cattleRelapsing fever Soft Tick B duttoni Rats VII Mite borne diseasesScrub typhus L. deliense Orientia tsutsugamushi RodentsRickettsial pox Allodermanyssus sanguineus1 R akari RodentsScabies S scabei - Man VIII Cyclops transmitted diseasesDracontiasis Cyclops species D medinensis ManFish tape worm Cyclops species D. latum Fish IX Reduviid bugsChagas disease Reduviid/Cone-nosed T cruzi Domestic animals/ man X Tsetse fliesTrypanosomiasis Glossina species T gambiense and T rhodesiense Wild animals/ cattle/ man • 904 •
  5. 5. Trans-stadial : The disease causing organism is transmitted Study Exercisesfrom one stage to another e.g. Tick typhus organism - Rickettsia Short Notes : Modes of disease transmission.conorii transmitted from infected larva to nymph to adult. MCQs & ExercisesArthropod Borne Diseases 1) Class Insecta is characterised by presence of how manyArthropods are responsible for transmission of innumerable legs? : (a) 4 (b) 5 (c) 6 (d) 8diseases. Some of the important arthropod borne diseases is 2) Mosquito belongs to the order a) Diptera (b) Anopluralisted in Table - 1 along with their vectors, causative organisms (c) Siphonoptera (d) Hemiptera.and reservoir hosts. 3) Mode of transmission of malaria by Anopheles is : (a) Cyclo - developmental (b) Cyclo - propogativeSummary (c) Propagative (d) Cyclo - developmental propagativeEntomology is the branch of science which deals with the 4) Orientia tsugtsugamushi is the causal organism for thestudy of insects, however, the scope of the subject has been diseases (a) Scrub typhus (b) Epidemic typhus (c) Endemicbroadened to include the study of all Arthropods. Amongst typhus (d) Tick typhus.the many important classes of the phylum, Insecta is the 5) Which of the following is not a mosquito borne disease :largest constituting more than 4 million species. Vector borne (a) Dengue (b) Filaria (c) Leishmaniasis (d) Yellow feverdiseases are one of the leading causes of morbidity & mortality 6) Aedes species cannot transmit : (a) Chickungunyaespecially in the developing countries. These diseases can (b) Dengue haemorrhagic fever (c) Japanese Encephalitisbe largely combated by effective vector control for which a (d) Yellow feversound knowledge of the bionomics of the vector is needed. The 7) Causal organism for bubonic plague : (a) R typhiimportant classes of Phylum Arthropoda are Insecta, Arachnida, (b) Y pestis (c) H nana (d) H diminutaCrustacea, Myriapoda. The class Insecta is characterized by 8) Murine Typhus is transmitted by : (a) Hard tick speciespresence of six legs, body divided into head, thorax & abdomen. (b) Soft tick species (c) Xenopsylla species (d) TrombiculidThe class has 4 orders of medical importance, Diptera, Anoplura, Mite speciesSiphonaptera & Hemiptera. The order Diptera has 1 pair of 9) Causal organism for epidemic Typhus : (a) B quintanawings and contains insects such as mosquitoes, sandflies, (b) R prowazeki (c) Borrelia recurrentis (d) R typhisimulium flies and houseflies. The order Anoplura comprises 10) KFD is transmitted by : (a) Soft Tick (b) Mite (c) Hard Ticktrue or sucking lice. Order siphonoptera includes the rat flea; (d) Licethe order hemiptera contains bed bugs. The class Arachnida 11) ___________ is the largest class of Phylum Arthropodaincludes ticks, mites, spiders and scorpions; body is divided constituting more than __________ insect speciesinto cephalothorax and abdomen and presence of eight legs. 12) Direct mode of transmission is seen in _______ & ______The class crustacea includes lobsters, crabs, water fleas and 13) Entomology is derived from the Greek word ENTOMONCyclops. Myriapoda includes millipedes and centipedes. meaning _________ & LOGOS meaning __________Arthropods transmit diseases to man by different modes of 14) Arthropoda is derived from two words ARTHRON meaningtransmission, mainly direct, mechanical & biological. In direct __________ & PODA meaning __________transmission, two hosts come in direct contact with each other 15) Leptotrombidium deliense is vector for __________e.g. pediculosis & scabies, mechanical transmission where Answers : (1) c; (2) a; (3) b; (4) a; (5) c; (6) c; (7) b; (8) c;disease causing organism is transmitted without undergoing (9) b; (10) c; (11) Insecta ; 4 Million; (12) Pediculosis;any change in pathogenecity or development e.g. diseases Scabies; (13) Insect, Science; (14) Jointed, Appendages;transmitted by houseflies. Biological transmission is further (15) Scrub Typhus.divided into cyclodevelopmental - the disease causing organismundergoes part of its life cycle in the vector e.g. Wuchereria Further Suggested Readingbancrofti; cyclopropogative - the disease causing agent 1. Gordon C cook, Alimuddin Zumla, Manson’s Tropical diseases, 21st Ed, 2003, Chapter 50, Rickettsial infections, p 900.undergoes part of the lifecycle in the vector & also multiplies 2. Service Mike. Medical Entomology for students. 3rd ed. Cambridge :inside the vector e.g. malaria transmitted by Anopheles female. Cambridge University Press, 2004.The other mode is propogative where disease causing organism 3. Kettle DS. Medical and Veterinary Entomology. 2nd ed. CAB International, 1995.simply grows & multiplies in the body of vector e.g. Yersinia 4. Hati AK. Medical Entomology. Allied Book Agency, Kolkata, 2001.pestis (plague) transmitted by rat flea, other specialized modesare transstadial & transovarian. • 905 •
  6. 6. stream flushing and regulation of the water level in reservoirs, 155 Principles of Vector Control vegetation removal, shading and exposure to sunlight. (c) Modification or Manipulation of Human Habitation or Rina Tilak Behaviour : This means “A form of environmental management that reduces man-vector - pathogen contact”. Examples of this approach are siting of settlements away from vector sources,Control of arthropods is one of the key strategies in the mosquito/rodent proofing, personal protection and hygienicmanagement of vector borne diseases. A strategist should measures against vectors and provision of mechanical barriers,have sound knowledge of the bionomics, distribution, seasonal providing facilities for water supply, disposal of waste waterprevalence, vectorial capacity, insecticide susceptibility status and excreta, laundry, bathing and recreation to prevent orand role of arthropods in diseases transmission coupled with discourage human contact with infested water.the knowledge of identification features of the incriminatedvectors for formulating effective control strategies. Once armed Chemical Controlwith this knowledge, the choice of effective vector management The new era of control of vector borne disease began with thetools may be exercised; the range and sophistication of control discovery of the insecticidal value of Dichloro Diphenyl Trichloromethods is impressive. The various control options available ethane (DDT). DDT was first synthesized by Othmar Zeidler inare as follows : 1874 at Strasbourg, Germany. In 1939, Paul Muller of the Geigy●● Environmental Control Company in Basle, Switzerland, discovered its remarkably long●● Chemical Control residual insecticidal property, earning him the Nobel Prize in●● Biological Control Medicine. The availability of several effective, safe and low●● Personal Protective measures cost pesticides, coupled with improvements in the techniques●● Mechanical control of their application, made it possible for many governments in●● Physical control the developed as well as developing countries to embark upon●● Genetic control extensive countrywide programmes for the control or eradication●● Legislative control of vector borne diseases. However, development of resistanceEnvironmental Control amongst vectors to insecticides has necessitated reassessment of the place of pesticides in vector control programmes. BesidesThe important environmental control measures which are the technical and financial difficulties, there is a growingincreasingly being used are described below : concern about the environmental contamination resulting fromEnvironmental Management the persistent use of insecticides.This has been defined as “The planning, organization, carrying Classification of Insecticidesout and monitoring of activities for the modification and/or Pesticides may be classified in many ways based on mode ofmanipulation of environmental factors or their interaction with entry, target stage, chemical composition and mode of action.man with a view to prevent or minimize vector propagation and However, the most common classification used is based onreducing man-vector-pathogen contact.” This is a naturalistic chemical composition. According to this classification, theapproach which attempts to extend and intensify natural insecticides are classified in the following categories asfactors which limit vector breeding, survival and contact with presented in Fig. - 1.man.(a) Environmental Modification : It is defined as “A formof environmental management consisting of any physicaltransformation that is permanent or long-lasting of land, water and vegetationaimed at preventing, eliminating or Fig. - 1 : Classification of insecticides as per chemical compositionreducing the habitats of vectors without Insecticidescausing unduly adverse effects on thequality of the human environment”. Natural SyntheticEnvironmental modification includesdrainage, filling, velocity alteration, Plant Based Inorganic Organicland levelling and transformation of Pyrethrum Mineral Oils Paris Greenimpoundment margins. Azadirachtin(b) Environmental Manipulation : Itis defined as “A form of environmental Organophosphates Syntheticmanagement consisting of any planned Malathion Pyrethroids Carbamatesrecurrent activity aimed at producing Temephos Deltamethrin Organochlorines Propoxurtemporary conditions unfavourable to Fenthion Cyfluthrin DDT Bendiocarbthe breeding of vectors in their habitats”. Dichlorvos Bifenthrin CarbarylExamples of environmental manipulation Fenitrothion Lambda-Cyhalothrinactivities are water salinity changes, Pirimiphos methyl Permethrin • 906 •
  7. 7. Natural Insecticides Chapter on Mosquitoes for further details on use). As per Govt.Plant based of India Gazette notification number S.O. 378(E) dt 26th May 1989, the use of DDT in Agriculture has been withdrawn andPyrethrum : Pyrethrum extract is obtained from the dried restricted to 10000 MT/ annum for Public Health programmeheads of the flower Chrysanthemum cinerariafolium and except in case of North East as Insecticidal Residual Spraycontains the active ingredients pyrethrins I and II, constituting (IRS).1 to 2% of the total weight of the raw pyrethrum. Pyrethrum ischaracterized by rapid knockdown action on arthropods even Organophosphorus Compounds : These insecticides arewhen used in very low dilution. It is very unstable in light and derivatives of phosphoric acid and act by inhibiting theair and has practically no residual effect. This makes repeated activity of cholinesterase. Many of the insects, which haveapplications necessary. Pyrethrum is available as 2% extract, become resistant to Organochlorines are still susceptible towhich needs 20 times dilution to make it 0.1% solution, which the members of this group. However, due to their extensiveis actually used for spraying. Using a 0.4 mm or lower calibre use in agricultural as well as public health field, more andnozzle, 50 to 100 ml of pyrethrum solution in kerosene oil is more insects are developing resistance to Organophosphorussprayed per 100 m3 of space. Addition of an Organophosphorus compounds. Some of the common compounds are Malathion,insecticide to pyrethrum formulation is a common commercial Temephos, Fenthion, Dichlorovos (DDVP) and Fenitrothion.practice for obtaining a better effect. It is one of the main Malathion : It is one of the least toxic Organophosphorusinsecticidal constituents in aerosol dispensers and also an compounds. Malathion is a broad spectrum insecticide, withinsecticide of choice for ULV sprays. Pyrethrum is perhaps the efficacy against a large number of pests ranging from mosquitoes,most acceptable insecticide for use in cook houses, dining halls houseflies, cockroaches, bedbugs, lice etc. It is available asand other food preparation areas. Malathion Technical (95%) for use as space spray, 50% WaterAzadirachtin : The active ingredient Azadirachtin is obtained Dispersible Powder (WDP) and Emulsifiable Concentrate (EC)from the seed kernels of neem plant Azadirachta indica. for residual control and 90% dust for use against fleas and lice.Azadirachtin has insecticidal, fungicidal, bactericidal, viricidal Malathion under the National Vector Borne Diseases Controlproperties including insect growth regulating qualities besides Programme of India is being used as Indoor Residual Spraydeterrent, anti-ovipositional, anti-feedant, fecundity and against mosquitoes in areas where the vectors have becomefitness-reducing properties on insects. It has been variously resistant to DDT. The dosage of its application is 2 g/m2 (Referformulated for mosquito larval and adult control in the form to Chapter on Mosquitoes for further details). As ULV spray itof liquid and cream formulations. Neem products contain up has been very widely used during outbreaks of Dengue and JEto 3% Azadiractin. as an anti adult mosquito measure. However, development of resistance has been reported in a large number of vectors toMineral Oils : Kerosene oil, diesel oil, petrol and crude engine Malathion.oil have been successfully used as mosquito larvicides. Theoil film cuts off the air supply, enters and blocks the trachea, Temephos : It is available as 50% EC. It is the only insecticidemay act as a stomach poison, and also lowers surface tension approved for use in potable water. Because of its low toxicity,which prevents larvae from floating. Malariol is the best and it has been successfully used for the control of Anopheleseasiest larvicidal oil to use for Anopheline and Culicine larvae. stephensi breeding in wells and domestic containers at aMalariol is used as it is @ 10 litres per 500 linear meters. dosage of 1ppm (Refer to Chapter on Mosquitoes for details). Sand impregnated with Temephos in 1% concentration has beenSynthetic Insecticides : These can be organic or inorganic. used in some countries against Aedes aegypti which breeds inThe only inorganic compound used in vector control (mosquito containers of clean and potable water. It has proved to be verylarvicide) was Paris green (Copper-aceto-arsenite). It acted as successful in Guinea worm eradication programme in India.stomach poison when ingested by mosquito larvae. However, itis not used any more for mosquito control. Fenthion : It is formulated as 82.5% EC and as granules containing 2% toxicant. It is a good mosquito larvicide but canThe Organic Insecticides fall into four major groups viz. not be used in potable water bodies. It is highly effective as aOrganochlorines, Organophosphates, Carbamates and Synthetic larvicide against Culex quinquefasciatus or any other vectorpyrethroids. found breeding in non potable water bodies at a dosage of 1Organochlorine Compounds : These compounds are contact ppm (Refer to Chapter on Mosquitoes for further details). Itpoisons and act on the nervous system. These or their can also be used for housefly control as a larvicide (Refer todegradation products are more or less stored in body fat and Chapter on Houseflies for details).may be demonstrated in milk, urine or sweat. They all have Pirimiphos methyl : This insecticide is being considered as anvariable residual action for variable periods and are toxic to alternative insecticide for Indoor residual spray. It is availableman and animals. The most important and the only member of as 25% WP; 2 kg is mixed in 10 litres of water and sprayed @ 10this group used in Public Health is DDT. litres/ 250 sq m area to give a deposit of 2g/sqm. Three roundsDichloro-diphenyl-trichloroethane (DDT) : Currently DDT is of spray are recommended as is followed in case of Malathion.being used for indoor residual spray in the North Eastern states Dichloro-dimethyl-dichlorvinyl-phosphate (DDVP orof India. A deposit of 1 g of DDT/m2 of surface area of walls Dichlorvos) : It differs from other organophosphorusand ceiling upto a height of 3.5 m in all dwellings applied at 8 compounds in that it possesses a much greater vapour pressureweeks’ interval, effectively controls majority of the mosquitoes at ordinary temperature which produces fatal insecticidaland also other arthropods resting on the treated wall (Refer to • 907 •
  8. 8. vapour. It is available as 72.6% EC. It can be combined with solid are available as Pretreated or Long Lasting Nets (LLNs).substances like wax and used as tablets or bricks thus allowing Other Synthetic pyrethroids used in Public health : Thereit to evaporate slowly. It is one of the common insecticides used is a large range of molecules used in the field of Public healthfor disinsecting aircraft. It is an effective housefly larvicide. besides the ones listed above. These molecules are Allethrin,Fenitrothion : It is available as Fenitrothion 40% water Resmethrin, Phenothrin, Cypermethrin, Imiprothrin, Bifenthrin,dispersible powder (WDP). The insecticide has shown promise Cyhalothrin, Cyphenothrin etc. These are all available as WP EC ,as an effective insecticide for control of bedbugs; however or Aerosol formulations for use against pests like cockroaches,toxicity constraints have limited its widespread use. houseflies and mosquitoes.Carbamates : These compounds are derivatives of carbamic Newer Group of Insecticidesacid and resemble Organophosphorus compounds in their Phenyl pyrazoles : Fipronil is the only member of this class ofmode of action. Some of the preparations produce a rapid insecticide. Fipronil acts by antagonizing the effect of GABA.knockdown effect like that of pyrethrum. The inhibition of It is available as 0.3% Gel for use against cockroach as a crackAcetylcholine esterase is reversible with Carbamates and hence and crevice treatment. It is a systemic material with contactthese compounds are less toxic. Some of the compounds in and stomach activity. It has a unique action called ‘cascadecommon use are Propoxur, Carbaryl and Bendiocarb. effect’ which is evident due to necrophagy seen in cockroaches.Propoxur : It is formulated as WDP as well as EC. It is considered When cockroaches consume the insecticide bait, they are killed;as the least toxic Carbamate compound for man and domestic these dead cockroaches when consumed by other cockroachesanimals. It has a flushing out effect and therefore is commonly bring about the death of these cockroaches and this goes on forused for cockroach and bedbug control. It is also used in bait about two months or so, thus obviating the need to retreat theformulations against houseflies and cockroaches. area at lesser intervals.Bendiocarb : Bendiocarb is an alternative insecticide for Indoor Neo Nicotinoids : Imidacloprid is the sole member from thisresidual Spraying. It is available as 80% WP For indoor residual . class. It acts by causing irreversible blockage of postsynapticspraying, it is recommended @ 200 mg/sqm. Two rounds of acetylcholine receptors. Imidacloprid is a systemic insecticide,spray are recommended for effective control against malaria. having notable contact and stomach action. Imidacloprid isSynthetic Pyrethroids : These are synthetic derivatives or available as 2.15% Gel for use against cockroaches and as Baitanalogues of natural Pyrethrum. These are broad spectrum, for use against houseflies, where it is formulated with houseflyhighly potent with quick knock down action and long residual pheromone - Muscalure.life. Synthetic pyrethroids are many times more effective than Biorational Insecticides : ‘Biorational’ means any substancethe previously available insecticides. Their relative safety of natural origin that has a detrimental or lethal effect onto man and higher animals, their efficient biodegradability specific target pest, e.g. insects. These insecticides are non-together with their higher target specific toxicity makes toxic to man, plants and animals and have little or no adversethem very attractive materials for integrated vector control. effects on the environment. An overview of the biorationalThe commonly available products are Permethrin, Allethrin, insecticides is presented in Fig. - 2.Phenothrin, Cypermethrin, Cyfluthrin, Deltamethrin andBifenthrin. The Synthetic pyrethroids are formulated as WDP , Fig. - 2 : Biorational Insecticides Used in Vector ControlEC, SC, Flow, EW and ULV formulations. Being broad spectrum,these insecticides are being used for vector control as residual Biorational Insecticidesspray, space spray and topical application as well as fortreatment of clothing. Pheromones BiocidesDeltamethrin : It is one of the most widely used Synthetic Insect Growthpyrethroid molecule in the field of vector control. It is available  Muscalure  Bacillus Regulatorsin many formulations for various vector control strategies viz.  Oviposition attractant thuringiensisSC 2.5% (Flow) formulation for treatment of bednet and routine var israelensishousehold pest control activity; 2.5% WP formulation for Indoor  BacillusResidual spray in Malathion resistant areas and 1.25 ULV for sphaericusspace spraying. The target dose (for Indoor Residual Spray) is Chitin Synthesis Juvenile Hormonegenerally 20 mg of a.i. (active ingredient) per sq m of surface Inhibitors Mimicsarea.  Diflubenzuron  Methoprene  Lufenuron  PyriproxyfenCyfluthrin : Besides Deltamethrin, this is the next most widely  Novaluron  Fenoxycarbused molecule. It is available as 0.5% EW formulation for  Triflumurontreatment of bednets; 5% EC for household use and 10% WP foruse as indoor residual spray in Malathion resistant areas.Permethrin : Widely used for control of lice, scabies and for Insect Growth Regulators : A new approach to vector controltreatment of clothing and bednets. The product is formulated in is the use of substances that adversely affect insect growthvarying concentration as Shampoo formulation for use as anti- and development. The enzymes and hormones that regulatelice treatment and 5% cream for use in scabies treatment. Bed developmental processes within an insect’s body can sometimesnets treated with Permethrin at the manufacturing stage itself be exploited as chemical control weapons. These compounds, • 908 •
  9. 9. often known as Insect Growth Regulators (IGRs) can be used houseflies) and oviposition attractant (Aedes control) haveto stimulate development at inappropriate times or inhibit it been exploited in the field of vector management.at other times. They are quite selective in their mode of action Biocides : The development of insecticide resistance amongstand potentially act only on target species. Most of the IGRs that the major pests and vectors coupled with the non target toxicity,have shown effectiveness against insect pests, cause the rapid necessitated development of safer alternatives to insecticides.death of the insect through failure of a key regulatory process This led to the screening, promotion and use of a large numberto operate or function. IGRs generally control insects either of biorational products of which biocides are one of the mostthrough inhibition of chitin synthesis or interference with important control options. The two biocides used in the fieldmetamorphosis by mimicking the action of juvenile hormone. of vector control are Bacillus thuringiensis var israelensis andThe major groups of IGR compounds include : Bacillus sphaericus. Both these products are widely used asChitin Synthesis Inhibitors : These chemicals inhibit the larvicides in Mosquito control programmes and act as stomachmoulting process by blocking the activity of chitin synthetase, poison.an enzyme needed by epidermal cells when constructing Bacillus thuringiensis var israelensis (Bti) : It was discovereda new exoskeleton. Because of this mode of action, Chitin in 1976 and has been found to be effective as mosquito larvicide.Synthesis Inhibitors (CSIs) are highly specific to arthropods. It is a gram positive spore forming bacteria. Bti produces toxinsThey act rather slowly (2-5 days), but eventually disrupt any which are present in parasporal body called the ‘protein crystal’.process that involves construction of new cuticle (e.g., molting, It primarily kills by the action of delta-endotoxin. When thehatching, pupation). They are most effective when used against mosquito larva ingests the protein crystal (inactive protoxin),the immature stages of a vector. Diflubenzuron, is used for it is activated inside its midgut by the action of proteases intocontrolling mosquitoes, houseflies etc. It is available as 25% active protoxin; these bind to the cell receptors present onEC, WP & 0.5% Granules and is used @ 1.0 g/ acre of surface midgut epithelium and cause disturbance in osmoregulatorywater as mosquito larvicide. Lufenuron, is a systemic CSI and mechanism which leads to swelling and eventual bursting ofis especially effective for flea and tick infestation control on the epithelium and finally death of the larvae. The product isanimals. Novaluron is a recent addition to the list, which has available as WP Granules, AS & Briquette. Bti 12 AS is used @ ,been found effective against the mosquitoes. It is a contact 20ml/m2 and has been found to be effective up to 15 days (forlarvicide and is available as 10% EC. It is used @ 20 μg a.i./ l details refer chapter on mosquito). Bti however, suffers fromand the efficacy lasts up to 3 months. the disadvantage that it can not be used in polluted watersJuvenile Hormone Analogues or Mimics : Juvenile hormone or where particulate matter is more; it also cannot recycle inanalogues or Juvenile Hormone Mimics (JHM’s) act by inhibiting nature. It is used in non potable water bodies.the developmental changes associated with embryogenesis, Bacillus sphaericus : A naturally occurring bacterium usedmorphogenesis, and reproduction. During normal development, against mosquito larvae. It is more effective in polluted waterJH levels are elevated in larvae (or nymphs) and decrease and can recycle and persist in nature. It is available in variousprior to pupation (or adult eclosion). Contact exposure to JH formulations like Bti viz. pellets, briquettes, granules & WP It .analogues during the egg stage or after the last larval molt is used @ 20ml/m2 and has been found to be effective up tocan inhibit development, delay maturation, and eventually three weeks.result in death. Since the onset of mortality is usually quite Fumigants : Some of the fumigants used as pesticides areslow (days to weeks), these chemicals are not used during carbon tetrachloride, methyl bromide, ethylene dibromide,epidemics; however, these chemicals are much in demand for chloropicrin, carbon disulphide and dichlorvos (DDVP).routine vector control due to their specificity and safety tonon-target organisms. Several compounds (e.g., Methoprene, Application TechniquesPyriproxyfen, Fenoxycarb, Triflumuron) have been successfully Control of arthropods in different habitats necessitates the useincorporated into vector management programmes especially of different types of spraying equipment as well as a variety ofDengue and Malaria and in products used for controlling ants, formulations such as liquids, granules and dusts. For examplefleas, and other household pests. Pyriproxyfen can cause control may involve treatment of small domestic or peridomesticsterilization and inhibition of growth of adult insects; it has a water collections which are ideal breeding places for Aedesresidual effect up to 3 to 6 month indoors and 30 days outdoors. mosquitoes; applications to stagnant waters in cesspools,It is widely used against mosquitoes @ 2gm a.i./ sq m. ditches and drains where Culex mosquitoes breed, large bodiesPheromones : Pheromones are semiochemicals (chemicals of standing water where certain Anopheles mosquito specieswhich mediate interactions between organisms) secreted by may be breeding; or aerosol spraying of extensive areas to haltan organism which provokes specific reaction in receiving epidemics. To meet with diverse situations, significant progressorganisms of the same species. These chemicals may further has been made in improving the spraying equipment. The Ultrabe classified based on the type of interaction mediated e.g. sex Low Volume (ULV) equipment for ground and aerial spray topheromone (muscalure secreted by houseflies), oviposition control mosquitoes and other haematophagous arthropods hasattractant (mosquito larvae), aggregation pheromone resulted in not only the elimination of several impediments(cockroach, bedbugs), alarm pheromones, trail pheromones like frequent mixing and reloading but helped in increasingetc. The scope of pheromones in vector control is promising, the speed of application and reducing the dosages and costs. Ithowever so far only two pheromones viz. Muscalure (in is specially recommended for control of an outbreak of vectorcombination with Imidacloprid insecticide as baits against borne disease. • 909 •
  10. 10. Formulations from 1 to 5%. These can be used in irrigation channels, irrigated or flooded lands, paddy fields and particularly whereManufacturers combine pesticides with other materials there is vegetation on the water surface. After sinking, theseto make usable concentrations called formulations. These formulations disintegrate slowly releasing small particles offormulations are designed to kill insects readily without insecticides. These can be effectively used also in small watercausing undue hazards to non-target organisms when diluted collections such as ornamental tanks and earthen pots, treeand applied correctly. Factors influencing application and holes and other domestic or peridomestic breeding places ofefficacy of an insecticide are its toxicity, size and shape of Aedes mosquitoes.its particles, concentration in formulation; type of solventused, type of surface to be sprayed, atmospheric temperature Wettable Powder : This formulation consists of the technicaland humidity, type of sprayer and its nozzle, training of the grade pesticide, an inert carrier and a wetting agent (usually aspraying personnel, the bionomics, morphology and physiology synthetic detergent) that helps it mix with water. These usuallyof the particular arthropod. No single preparation can meet the contain 50 to 75% of the toxicant. Most of these can be putrequirement of vector control in all spheres of human ecology. directly into water and require only slight agitation to makeSolutions, emulsions, suspensions, water dispersible powders, suspension; others may require mixing with a small amount ofdusts and granules to suit different conditions and problems water to form a paste or slurry. The required volume of waterare therefore, prepared and used. is then added to paste or slurry followed by thorough agitation of the mixture.Technical Grade Pesticide When water is added to a wettable powder it makes a suspension;This is the basic toxic agent in its purest commercial form. this enables the pesticide to stay on porous surfaces likeSome technical grade pesticides are liquids; others occur in concrete, plaster or unpainted wood. Water penetrates thesesolid form. Technical grade Malathion is used in ultra low surfaces, leaving the carrier and the maximum amount of thevolume space applications. pesticide on the surface available to kill pests. Suspensions haveTypes of Formulations other advantages, too. They have no solvent odour, and theyFormulations essentially are of three types : Solid or dry, liquid don’t tend to irritate or penetrate skin. However, they generallyand gaseous formulations. need agitation to keep pesticidal particles from settling out.Solid or Dry formulations Also, they tend to clog sprayer nozzles and strainers, especially when the wettable powder is stored for long periods in humidDusts : Dusts are normally ready-to-use formulations with a areas or when a high concentration is used.low percentage of active ingredient (usually 1 - 10%) plus a Liquid formulationsvery fine inert carrier such as talc, chalk, diatomaceous earth,clay or volcanic ash. These materials are usually low in cost, Emulsifiable Concentrates : Emulsifiable concentrates consisteasy to apply, non-staining and non-toxic to vegetation. Dusts of the technical grade pesticide (typically 45% to 75%), a solvent,are always used dry and can easily drift into non-target areas and an emulsifying agent, usually a synthetic detergent. Thisif they are not applied carefully. For this reason, outdoor agent is used to allow the concentrate to be diluted in water,applications should be made only when the wind is calm. A resulting in an emulsion.common use for dusts is in crack and crevice or spot treatments Emulsifiable concentrates are usually clear but emulsions lookindoors in out-of-sight areas (behind equipment, in wall voids similar to milk. Finished sprays are emulsions or solutionsand so on) which remain dry. The residual pesticidal activity diluted to field strength. Unlike solutions, most emulsionsof dust is normally fairly long, provided the dust stays dry, but need a little periodic agitation to keep the concentrate fromquickly loses it toxicity in the presence of moisture. They don’t separating out of the water. Emulsions are used for residualadhere well to vertical surfaces. treatments. Pests that contact these surfaces are killed byDusts are used on people during mass delousing operations to the pesticidal residue. Emulsions may damage aluminium,control outbreaks of lice borne diseases. Dusts are also used varnish, and painted surfaces due to the action of solvents suchfor flea control during plague outbreak. Dusts aren’t generally as Xylene. Emulsions may also be corrosive to metal sprayersabsorbed through the skin, but may be dangerous if inhaled and their fittings and hence sprayers made of stainless steel,into the respiratory tract. aluminium or other non-corrosive materials should be used.Granules : These are basically the same as dust formulation, Oil Solutions : These formulations consist of a technical gradeexcept the carrier particles are larger and thus don’t stick to pesticide dissolved in a solvent such as kerosene or dieselleaves allowing penetration in dense foliage. This is a real oil. Solutions are available as ready-to-use formulations (foradvantage when the pesticide must reach the water surface for example ordinary household fly and mosquito sprays with amosquito control in vegetated swamps, or if it must get to the low percentage of pesticide) and as solution concentrates. Theseground surface through trees and shrubs for chigger control. concentrates contain a high percentage of insecticide and mustGranules are also available in timed-release formulations that ordinarily be diluted in oil or another suitable solvent. Somerelease a dosage of the pesticide over an extended period of concentrates are used without dilution in Ultra Low Volumetime. Other advantages of using granules are that they provide (ULV) applications. Oil solutions applied as finished sprayslonger lasting effects and their use results in less drift than often kill insects on contact, since the oil helps the pesticidegenerally occurs with liquids or dusts. penetrate the insect’s waxy body wall.The percentage of insecticide in granules and pellets varies Ultra-Low Volume (ULV) : While most items of ULV pesticide • 910 •
  11. 11. dispersal equipment use the readily available solutions or Ticks depending on the formulation. Care should be takentechnical grade formulations, there are special ULV formulations while handling aerosol cans since they can explode if puncturedavailable for e.g. Deltamethrin 1.25 ULV etc. or overheated, even after the pesticide has been dispensed.Gaseous formulations : Gases are primarily used in Common insecticides used as aerosols are Pyrethroids,fumigation operations. They may be prepared as liquefied Malathion, DDVP and repellents like DEET and DEPA. Thesegases and packaged in pressure containers or in a material are used for disinfesting aircrafts, tents, rooms, other smallform that reacts with the moisture in the air to form a gas. enclosures, uniforms and for topical application. An emissionThe gas molecules can penetrate cracks, crevices and tightly of nearly 15 seconds is enough for a 100 m3 space.packed material. Gases are the most dangerous pesticides used Equipmentand hence special safety equipment and training are necessarywhen using gases and must never be attempted except by Equipment used for vector control can be broadly classified astrained pest management personnel operating in pairs. One ground equipment and equipment used for aerial applications.of the common gaseous formulations viz. Calcium cyanide (a) Ground Equipment(powder) and Aluminium phosphide (tablet) are used for rodent (i) Sprays for production of fine or coarse spray which may becontrol. either manually operated or power operated.Special formulations (ii) Sprayers for the production of mist which may be eitherResin Strips : Pesticide-impregnated resin strips release with gaseous energy nozzles (manual operated or powervapours as they are heated or exposed to normal room operated) or with centrifugal nozzles.temperatures. The use of resin strips in rooms occupied by (iii) Devises for the production of aerosols which maythe young, the elderly or in food preparation and food serving be mechanical, thermal or gaseous energy aerosolareas is strictly prohibited. generators. (iv) Dusting equipment which may be manually operated orBaits : Baits are commonly used to manage scavenging pests power operated.such as rodents, ants, flies, and cockroaches, which are (v) Applicators for granules and pellets, manually or powerparticularly difficult to manage with standard techniques. operated.Baits consist of the toxicant mixed with a food attractive to thetarget pest or with water. For this reason, baits made with local (b) Aerial Equipmentfoods are normally more effective than premixed formulations. Equipment for aerial sprays is essentially the same but withRecent development is the use of pheromone Muscalure with certain modifications. The equipment in common use is theImidacloprid as bait for houseflies. boom and nozzle system.Gel : One of the special formulations developed for use against Sprayerscockroaches is Gel formulation. Gels comprise some foodattractant mixed with the toxicant and some stabilizing agents. The equipment commonly used for spraying various insecticidalExamples are Fipronil and Imidacloprid Gels marketed against formulations are the hand operated sprayers, power operatedcockroaches. sprayers, aerosol dispensers, fog generators and dusters.Shampoo : This formulation has been specially developed (a) Hand Operatedfor use against head lice infestation. Permethrin is the most These are hand sprayers, knapsack sprayer and compressioncommon ingredient of the commercially available anti-lice sprayer.Shampoo formulations worldwide. (i) Hand Sprayer : The hand sprayer is used for space sprayingBeads / Pellets / Briquettes : Small floating beads, pellets or of small apartments. It is provided with a small can for holdingbriquettes incorporating biocides - Bti and B sphaericus have ½ to 1½ litres of spray fluid and a cylindrical plunger type airbeen developed against Anopheline larvae. These formulations pump. The nozzle size is less than 0.4 mm in order to produce acan be made as controlled release formulations as well. fine spray. The simplest form is the familiar ‘flit gun’ producingPaints and Lacquers : These can be used for incorporation intermittent spray. A number of other light hand sprayers haveof insecticides especially for control of pests on ships. These been designed, which can be pressurized in the manner ofpreparations remain effective for long periods. The new compression sprayers and are used to produce a mist or fineinsecticide, Imidacloprid is also available as a paint formulation droplet spray.against houseflies. (ii) Knapsack Sprayer : This is designed to fit on to the backMats / Coils : These are special formulations which have been of the operator and usually has a capacity of 15 to 20 litres.developed as controlled release formulation for indoor use It incorporates a light but powerful diaphragm pump actuatedagainst mosquitoes. These have synthetic pyrethroids such as by a lever carried forward to the operator’s hand where it isAllethrin, which acts as toxicant to knock down the mosquitoes worked by an up-and-down movement. These sprayers are usedwhen used indoors. both for larviciding and residual spraying. The nozzle size used for residual spraying varies between 0.78 to 1.0 mm so as toAerosols : Aerosols are pressurized cans containing a small produce a coarse spray.amount of pesticide driven through a small nozzle. They’recommonly used as space sprays for flying insects viz. (iii) Compression Pneumatic Sprayer : This is the commonestmosquitoes and houseflies and as residual sprays for Mites/ type of equipment used in National Vector Borne Diseases Control Programme for the application of insecticides. It has • 911 •
  12. 12. a hand operated pump incorporated to build up adequate (d) Wash your overalls and other protective clothing at thepressure. When the pressure is released by a trigger on the end of each working day in soap and water and keep themlance, the liquid is forced out from the tank to the nozzle by separate from the rest of the family’s clothes.the compressed air and a continuous spray of the insecticide (e) If the insecticide gets on your skin, wash off immediatelyformulation is produced. It is slung over the shoulder with with soap and water.one strap or may be carried on the back with two straps. It is (f) Change your clothes immediately if they becomeoperated by one person. contaminated with insecticides.(b) Power Operated Sprayers (g) Inform your supervisor immediately, if you do not feel well.These are useful for application of insecticides over large areas. (h) Wear protective clothing (Fig. - 3) :These are hydraulic sprayers in which the spray liquid is expelled - Broad rim hat (protects head, face and neck from sprayto the nozzle by positive displacement by the plunger pump. droplets).Insecticide tanks built into a truck or mounted over a hand - Goggles or face shield (protects face and eyes againsttrolley are connected directly to a power operated compressor. spray fall-out).By means of a long hose the spraying fluid is conveyed under - Face mask (protects nose and mouth from airbornepressure through the lance to the nozzle. particles of the spray fall-out).(c) Insecticidal Fog Generators - Long sleeved overalls (Keep overalls outside of boots).Several types of fog generators are now available for the - Rubber gloves.production of insecticidal fogs in the open on a large scale. - Boots.In these fogging machines the oily solution of the insecticide Preparationsis finely atomized by the powerful blast of hot exhaust gases The Household : Inform the householder of the sprayingfrom a petrol engine. schedule and the purpose of spraying, giving them time to(d) Aerosol Dispensers prepare and vacate the house. Occupants MUST leave housesThese are used for disinfestations of aircrafts, tents, rooms before spraying. Rooms occupied by sick people who cannotand similar small enclosures. It contains insecticide and a be moved must NOT be sprayed. Remove all household items,propellant. Common aerosols contain Synthetic pyrethroids including water, food, cooking utensils and toys from the house.or their combination, which are routinely used for mosquito, Move and cover, or take out the furniture to allow easy accesscockroaches and fly control. for spraying walls. Items that can not be removed should be well covered.(e) Dust Gun Equipment : Indoor residual spraying of insecticides isInsecticidal dusts are applied against lice and fleas in rat normally done using hand-operated compression sprayers.burrows or on water surfaces as dry powders diluted with inert Before starting a spray operation, the equipment must bedusts. Small light weight guns are used for mass delousing of checked. Faulty sprayers may result in poor control or over-infested people. treatment. Examine the sprayer visually to ensure that all partsResidual Spraying are present, assembled correctly and are in good condition (Fig. - 4).This is the application of insecticides to surfaces so that theinsecticide particles remain on the surface in the form, size and Fig. - 3 : Protective Fig. - 4 : Hand-operatedquantity suitable for insects to pick up on contact and sufficient clothing for spraying compression sprayerto exert a lethal effect over a long period. Organochlorine,Organophosphorus, Synthetic pyrethroids and Carbamate A: Hat H.Hosecompounds can thus be applied on the inside walls of houses B: Goggles G.Strainerand also on thick bushes in forests. The type of surface to C: Mask D.Pump (handle)which an insecticide is applied influences its toxicity againstinsects and its persistence. Solutions and emulsions quickly E.Pressure gaugeget soaked in the absorbent surfaces of soft bricks and mud D: Long J.Triggerwalls which take in a large portion of insecticidal material Sleeved Overalls C.Liddeposited on them; but when suspended in water it remainsover the surface after the water evaporates or gets absorbed. The B. A.Sprayer tanknozzles of sprayers used for residual spraying must conform to E: Rubber Shoulderthe need of having a droplet size which is neither too large nor Gloves strap F.Lancetoo small. Similarly, safety precautions should be observed, asfollows, while spraying as per standard WHO guidelines : F: Boots K. Foot rest(a) Do not eat, drink or smoke while working. I.Nozzle(b) Wash your hands and face with soap and water after Nozzle body spraying and before eating, smoking or drinking. Nozzle tip(c) Shower or bathe at the end of every day’s work and change Nozzle cap into clean clothes. • 912 •
  13. 13. A. Sprayer tank (c) Operate the pump using both hands and with foot onB. Shoulder strap the footrest. Pump to the working pressure of 55 psiC. Lid (Fig. - 7).D. Pump (handle)E. Pressure gauge Fig. - 7F. LanceG. StrainerH. HoseI. Nozzle - check correct type of nozzle is fitted and is not damaged or worn (flat fan nozzle with 55º to 60º swath and 0.75 l/min flow rate at 700 g/ sq cm).J. Trigger on/off valve. Is the strainer inside valve handle clean?K. FootrestBefore using an insecticide, use clean water to ensure that theequipment operates properly and does not leak. Wear protectiveclothing. To check, follow the steps below :(a) Pour clean water into the tank (never fill tank more than 3/4 full) (Fig. - 5). Fig. - 5 (d) Check tank is holding pressure. Listen for hissing sound of escaping air (Fig. - 8). Fig. - 8(b) Fit the lid. Turn the handle to lock the lid in position (Fig. - 6). (e) Check to make sure there are no leaks along lance and Fig. - 6 hose, especially where hose joins tank and trigger on/off valve (Fig. - 9). Fig. - 9 • 913 •
  14. 14. (f) Operate trigger on/off valve to make sure that spray is container with water for several hours before the blockage is emitted from the nozzle (Fig. - 10). removed by a very soft toothbrush. NEVER clean nozzle with a hard pin or piece of wire and NEVER put a nozzle to your Fig. - 10 mouth to blow through it. Mixing, Handling and Spray Techniques Prepare the insecticide spray according to the manufacturer’s instructions. The insecticide may be mixed separately in a bucket and poured into the sprayer. Water soluble sachets, tablets and insecticides granules are added directly to the water filled tank. These formulations mix readily with water and reduce the hazards associated with handling and mixing in a separate container. When the sprayer has been filled with water to the maximum level indicated on the tank, the lid of the tank is fitted and the sprayer pumped to a pressure of 55 psi by pumping 55 times (700 g/sq cm). The contents of the tank should be thoroughly mixed by shaking the tank before starting to spray (Fig. - 12). Fig. - 12(g) Check the spray pattern from the nozzle by spraying a dry wall surface. Look to see that the pattern is even and without streaks. Ensure nozzle does not drip when trigger on-off valve is released (Fig. - 11). Fig. - 11 Spraying in a room should commence from the backside of a door clockwise completing the plain surfaces of walls. Then the crevices on the walls and inside portion of windows etc. should be sprayed. Thereafter the pillars, under surfaces of furniture and lastly the ceilings should be taken for spray.(h) Calibrate the nozzle with water in the tank. Pump to 55 Spray is done from roof to floor, using downward motion, to psi (700 g/ sq cm). Open the trigger on-off valve for one complete one swath; then stepping sideways and spraying minute, collect the discharge and measure the amount in a upwards from floor to roof. Spray is applied in vertical swaths measuring jug. Empty the jug. Discharge for a further one 52-56 cm wide. Swaths should overlap by 5 cm and spraying minute and measure the amount. Repeat again and calculate should be undertaken as shown in Fig. - 13. Normal swath the average of the three, one-minute measurements. coverage will take 2.7 sec if height of wall is assumed to beWith the above procedure, the average discharge of an 8002 3 meters and hence in one minute 22-23 swaths will cover anozzle is about 750 ml per minute. If the discharge is incorrect, wall of 10-11 metres length and 3 metres height i.e. 30 - 33 sqcheck the nozzle and the screen filters to ensure they are not m. It takes about 5 minutes to spray a house with an averageclogged. If necessary replace nozzle. Repeat the calibration. surface area of 150 sq m.If the nozzle is clogged : The opening in a nozzle is very smalland must not be damaged. Clogged nozzles should be put in a • 914 •
  15. 15. Time your spray speed to cover one meter every 2.2 seconds, Fig. - 13 i.e. 4.5 seconds for a 2 m high wall. Timing may be aided by mentally counting “one thousand and one - one thousand and two - one thousand and three -…”. Adjust the mental counting procedure according to the local language (Fig. - 15). If spray stops due to a blockage in nozzle, unscrew the nozzle cap, remove blocked nozzle and replace with a new one. The blocked nozzle should be cleaned as explained above. Do not let spray drip on the floor. Re-pressurize the tank when the pressure falls. Fig. - 15To ensure the correct swath width, keep the spray tip about45 cm from the wall. Lean forwards as you spray from top ofthe wall and move back as you bring the nozzle downwards(Fig. - 14). Fig. - 14 Procedures after Spraying (a) Advise the occupants to stay outside until the spray is dry. (b) Instruct the householder to sweep or mop the floor before children or pets are allowed to re-enter. (c) Instruct the householder not to clean the sprayed surfaces. Disposal of Remains of Insecticides and Empty Packaging: At the end of the day’s work, put the washings from the sprayer into pit latrines, if available, or into pits dug especially for this purpose and away from sources of drinking water. Dilute any insecticide with more water before putting into pits. It is advisable to prepare only sufficient insecticidal solution to avoid disposal of remaining insecticidal solution. Never pour the remaining insecticide into rivers, pools or drinking water sources. All empty packaging should be returned to the supervisor for SAFE disposal. Never re-use empty insecticide containers. Empty insecticide containers should NOT be burned or buried. Maintenance of Equipment : After completing the day’s work, de-pressurize the tank and empty any remaining insecticide, following the instructions given in the previous section. Clean the tank as explained below :The flow of liquid from the nozzle tip at 700 g/sq cm pressure ●● De-pressurize the tank.is 750 ml/minute. Hence 30 sq m surface will be covered with ●● Fill the tank half-full with clean water.750 ml of the insecticide solution. ●● Replace the lid. • 915 •
  16. 16. ●● Shake the tank so all inside surfaces are washed Fig. - 19 (Fig. - 16). Fig. - 16 ●● With lid open, turn tank upside down, open the on/off valve and let all the water drain out of the hose and lance. ●● Ensure the lance is parked to protect nozzle when not in use. ●● When storing the sprayer for a long period, hang it upside down with lid open to allow air circulation. Allow lance to hang from D-ring on the tank with the trigger valve kept open (Fig. - 20). Fig. - 20●● Pump up to 700 g/ sq cm pressure. Spray water through nozzle (Fig. - 17). Fig. - 17●● De-pressurize the tank and pour out any remaining water into pit latrines or into a pit away from sources of water.●● Unscrew trigger on/off valve handle and check and clean the strainer.●● Reassemble the trigger on/off valve (Fig. - 18). Space Spraying Fig. - 18 It is an ideal method for bringing about rapid control of vectors in emergency or epidemic situations and may also be used for seasonal control of flying insect pests or vectors. An additional objective may be to reduce or interrupt the transmission cycle of insect-borne diseases. However, it may not be ideal for all vectors or situations and as such may not be an economical method of control. Among the disease vectors affecting public health, the most important and widespread are mosqui­ oes, t●● Remove the nozzle tip and wash houseflies, sandflies and other biting flies; some of these may●● Refit the nozzle be tar­ eted for space treatment. g●● Clean the outside of tank. Immediate killing of actively flying insects requires a cloud of insecticide droplets that they will encounter in flight. To • 916 •
  17. 17. be cost-effective and obtain good biological efficacy, space Cold Fogspraying requires : The cold fog is produced by a special device (cold fogger) that(a) Knowledge of the behaviour and biology of the target breaks up the chemical into microscopic droplets by mechanical species - to understand where and when space treatments means, basically with a high-pressure pump and an extremely will be effective; fine nozzle. The spray droplets are generated without any(b) Knowledge of insecticides and formulations most suitable external heat. With cold fogs, the volume of spray is kept to for space spraying; a minimum. Ultra-low-volume insecticide formulations are(c) Knowledge of pesticide application technology - to know commonly used for such applications. The cold fogger may which equip­ ent is needed and how to use it; and m dispense formulations in a very concentrated form and generate(d) Monitoring and surveillance of the target species and the droplets (usually in the 5-30 micron diameter range) in a vector-borne disease problem to evaluate the efficacy of precise manner. However, its ability to penetrate dense foliage the programme. or obstacles is not as good as that of the thermal fogging. ColdA space spray - technically a fog (sometimes referred to as an fogging is sometimes called Ultra Low Volume (ULV) treatmentaerosol) is a liquid insecticide dispersed into the air in the form as it allows the utilization of only a very small amount ofof hundreds of millions of tiny droplets less than 50 μm in chemical for coverage of a large area.diameter with a view to cause by contact, immediate knock Like thermal fogging, cold fogging also does not have lastingdown of the flying or resting insects in confined spaces. Space residual effects. It is, therefore, essential to carry out fogging atsprays, even when they settle on surfaces do not have much the time when the vectors are most active to hit them directly.residual action. It is only effective while the droplets remain Advantagesairborne. Therefore, they have to be repeated at frequentintervals. Space sprays are applied mainly as thermal fogs or ●● The amount of diluents is kept to a minimum, resulting incold fogs. lower appli­ ation cost and increased acceptability. Some c formulations are ready to use, thereby reducing operatorThermal Fog exposureThermal fog is produced by special devices known as thermal ●● Mostly water-based and water-diluted formulationsfoggers that use heat to break up the chemical into very small are used which pose a low fire hazard and are moredroplets (usually in 5-30 µm diameter range) which then environmental friendlydisperse in the air. When the chemical (usually diluted with ●● Application is more efficient because a lower volume ofoil-based carrier) is heated, it is vaporized in a combustion liquid is appliedchamber and then expelled via an outlet tube to form a dense ●● No traffic hazard as the spray cloud is nearly invisiblefog cloud when it condenses on contact with cool ambient air. DisadvantagesThe insecticide used in thermal fogs is diluted in a carrier ●● Dispersal of the spray cloud is difficult to observeliquid, which is usually oil-based. Hot gas is used to heat the ●● Higher technical skills and regular calibration are requiredpesticide spray, decreasing the viscosity of the oil carrier and for efficient operation of equipment.vaporizing it. When it leaves the nozzle, the vapour hits colder Space Spray Equipmentair and condenses to form a dense white cloud of fog. Most of Selection of appropriate equipment for space spraying dependsthe droplets are smaller than 20 µm. The droplet size is affected on the size and accessibility of the target area as well as theby the interaction between the formulation, the flow rate and human resources and operational capacity of the programme.the temperature at the nozzle (usually > 500°C). The volume Sometimes smaller machines may be needed in conjunctionof spray mix­ ure applied in vector control is usually 5-10 litres t with vehicle-mounted equipment to treat narrow pathways andper hectare, with an absolute maximum of 50 litres per hectare. other areas inaccessible to vehicles or sheltered from prevailingThe hot emission gas is obtained from engine exhaust, friction air movements. Cold fog equipment is recommended whereplate/engine exhaust or from a pulse jet engine. thermal fogs may cause a traffic hazard. Aerial applicationAdvantages of space sprays may be justified where access with ground●● Easily visible fog, so dispersal and penetration can be equipment is difficult and/or extensive areas need to be treated readily observed and monitored; very quickly.●● Good public relations in some circumstances as people can Equipment for Thermal Fogging see some­ hing being done about the problem; and t●● Low concentration of active ingredient in the spray mixture Hand-carried Thermal Foggers : These are used for treating and reduced operator exposure. houses and certain outdoor areas of limited size or accessibility,Disadvantages e.g. markets, hotel grounds and parks. There are two types of hand-carried thermal foggers; pulse jet and fric­ ion plate. t●● Large volumes of organic solvents are used as diluents, which may have bad odour and result in staining; Vehicle-mounted Thermal Foggers : Large thermal fog●● High cost of diluents and spray application; generators use an air-cooled motor to run an air blower, fuel●● Householders may object and obstruct penetration of fog pump and insecticide pump. Air from the “roots type air blower” into houses by closing windows and doors; is delivered into the combustion chamber. There it is mixed with●● Fire risk from machinery operating at very high gasoline vapour and ignited so that temperatures reach 426- temperatures with flam­ able solvents; and m 648°C. The diluted insecticide liquid is pumped via a simple flow●● Can cause traffic hazards in urban areas. delivery valve and injected into a cup in the fog head or directly • 917 •

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