Insecticide Susceptibility Status of Culex Tritaeniorhynchus Giles

Jpn. J. Infect. Dis., 53, ll-14, 2000

Original Article Insecticide SusceptibilityStatusof Culex tritaeniorhynchus Giles,

Ⅵctor of J叩aneSe Encephalitis in Delhi

Thekkevilayil George Thomas*, Sushil KumarSharma, Anand PrakashI , Jotna Sokheyand Brij Raj Shama2 National Institute of Communicable Diseases, 22-Shamnath Marg, Delhi- ll 0054, 1DA V (P G) College, MuzaHarnagar-251001, Uttar Pradesh and 2National Zoological Park, Mathura road, Delhi, India

(Received October 19, 1999. Accepted January 3 1, 2000)

StJMMARY: Laboratory studies were camied out to ascertainthe current susceptibility status ofadultand laJVal stages of the Culex tritaeniorhynchus mosquito, vector of Japanese encephalitis, to variousinsecticides used under public healthprogramSinhdia･ The present study revealedthat exposure of adult mosquitoes to diagnostic concentrations of DDT - 4･0%, malathion - 5･0%, fenitrothion - l･0%,and propoxur - 0･1% couldinduce only 50･0, 10･0, 1 5･0,and 5･0% mortality, respectively,indicatingthatthe species was resistant toall oftheseinsecdcides･ The LT50and LT,5 Values calculated using diagnostic concentrations of DDT, mahthion,fenitrothion,and propoxur were found to be 56･4and 136, 138and 272, 1 85and 258,and I 87and 249 min, respectively･ However, when adult mosquitoes were exposed tothe diagnostic concentration of synthetic pyrethroids, viz･, deltamethrin-0･025%, permethrin- 0･25%,and lambdacyhalothrin - 0. 1%, loo.0% mortalitywas observed,indicatingthatthe species was highly susceptible tothese adulticides･ Larval susceptibility tests carried out using diagnostic dosages of DDT- 0･00i, temephos- 0･02, fenthion- 0･008, fenitrothion- 0･ 125,and malathion- 0･005 mg/I failed toinduce any mortality, indicating that laJVae Were resistant tothese larvicides. The LC,.and LC,. values calculated for commonly used lamicides, viz･, temephosand fenthion, were O･151 land l･9098,and O･6151and 2･395 mgn, respectively･ Increaseintolerance level were estimated at 95･5-and 299･4-fold whenthese LC,. values were ･compared withdiagnostic dosages of temephosand fenthion, respectively･

INTRODUC TION Zoological Park, Delhi丘om various channels and moats aroundanimal enclosures, where stagnant water collects with Cula tritaeniorJwnchzLS Giles is one of the vector mosquito free waterflOating vegetation favorable for the breeding of species largelyinvolved in the transmission of Japanese Cx. tritaenior句/nchus mosquitoes. Mosquitoes at immature encephalitisinSoutheastAsia, notablyinIndia. It has been stages were collected from different breeding sitesand reported to be a widely distributed speciesinthe IndianSub- transported tothe laboratory, where samples were separated continent･ This vector mosquito species has not only been by genus. Late thirdinstar larvae of Cx. tritaenior勿/nchus exposed to the larvicides/adulticides usedunder public health were used for larval susceptibilitytests. Fourthinstarlarvae programs but to theinsecticides used for the control ofagn- were keptuntil emergence, for purposes of adult susceptibility cultural pests, particularly in the case of the paddy crop, as tests. the mosquitoes have outdoor restingand feeding habits･ Adult Bioassay: The Cx. tritaeniorb/nchus adults emerged Therefore, it is essential, before contemplating use of any from the field-collected materialina mosquito cage (12 by insecticide either as an indoor residual spray, application 12 by 12in.)and were allowed to feed on 10%glucose solution through ULV (ultra low value) Spray or thermal fogging, or soakedinto a cotton pad. Therea鮎r, three day-Old female implementation as a laJVicide, that the susceptibilitystatus adult mosquitoes were exposed to a diagnostic concentration of adultand larval stages of the vector mosquito species be (concentrationthat has a highprobabilityofkilling all suscep- ascertainedinorder to ensure the effectiveness of vector tible populations ll]) of DDT- 4.0%, malathion -5.0%, control measures. fenitrothion - I.0%, propoxur - 0. 1%, deltamethrin- 0.025%, The present report deals with the results of laboratory permethrin- 0.25%,and lambdacyhalothrin- 0. 1%, respec- bioassay tests camied out during 1 999 to ascertainthe current tively. Control experiments were runinparallel. For eachrun susceptibilitystatus of larvaeand adults of Cx.かitaeniwb7nChw of insecticide, four replicates wererun, eachrun containing mosquito to variousinsecticides commonly usedunder public 20female glucose-fed mosquitoes. A鮎r the recommended healthprograms in India for purposes of controlling vector exposure period ( 1 -3 h) toinsecticide-impregnated papers ( 12 mosquito species. by 1 5 cm), mosquitoes were transferred to recovery chambers provided withcotton pads soakedin1 0%glucose solution as food. Mortalitycounts were made after a 24-h recovery A4ATERIALS AND METHODS period (2). The experiments were conducted at anambient The biological material was collected at the National temperature of27土loCand relative humidityof75 to 80% under laboratory conditions (3,4). *Corresponding author: Mailing address: Dy.Asstt. Director, To determine the lethal time (LT) inducing 50and 95% Medical Entomology Division, National Institute of Communi- (LT50and LT95) mortality, respectively, adult mosquitoes were cable Diseases, 22-Shamnath Marg, Delhi 1 10054, INDIA exposed atintervals of 15 min(ranging 80m 15 minto 4 h 45

ll min) tothe diagnostic concentration ofthoseinsecticides to RE SUIJS which they had shown resistance; viz., DDT, malathion, propoxur,and fenitrothion. Adult Bioassay: The results of the susceptibilitytests Larval Bioassay: Field-collectedthirdinstar laJVae Of Cx. carried out using the adult Cx. tritaeniorJwnchus mosquito tritaeniorhynchus were identified, separated, washedintap are glVeninThble 1. In adult mosquitoes exposed to diagnostic water to remove debris,and kept for observation for 2 h to concentrations of DDT, malathion, fenitrothion,and propoxur, weed outthe deadand moribund larvae. Healthy laJVae Were 50%, 10%, 15%,and 5% mortalityrates, respectively, were then exposed to the diagnostic dosages of DDT - 0.008, induced,indicatingthatthe species has developed resistance temephos - 0.02, fenthion - 0.008,fenitrothion - 0.125,and to all four oftheseinSecticides. However,inthe mosquitoes malathion - 0･005 ppm, respectively. Tests were camied out exposed to diagnostic concentrations of deltamethrin, by placing 25 laJVaeina 5001ml capacitybeaker containing pemethrin, and lambdacyhalothrin, 100% mortality was 250 ml of water and the required dosage of larvicide. For induced, which showedthat the species is highly susceptible dosage of each larvicide, four replicates were runand control to synthetic pyrethroids. experiments were runinparallel. Mortalitycounts were made In order to determine the LT50and LT95 Values, the adult after a 24-h exposure period. To determine LC5.and LC,. mosquitoes were exposed to diagnostic concentrations of (lethal concentration) values,the teclmical form of temephos DDT, malathion, fenitrothion,and propoxur, respectively, for (50% emulsion concentrate)作C)andthat offenthion (82.6% a range of expostweperiods. The data obtained were subjected EC), obtained from Cyanamid Ltd., Mumbai, hdiaand Bayer to probitanalysis to calculatethe regression equation, LT50, Ltd･, Mumbai, India, respectively, wereused. LT,5 Values, and heterogeneity(5)･ The resultsare given i.n Bioassay tests showing more than20% control mortality Table 2. The LT5.and LT95 Values calculatedusing diagnostlC were discardedand repeated, although,inthe control case concentrations of DDT, malathion,fenitrothion,and propoxur mortalityranged between 5 to 20%,the corrected mortality were foundto be 56.4and 136, 138and272, 185and258, was calculated using Abbot's formula (2). and 1 87and 249 min, respectively. The heterogeneibT (刑.05) was found to be signiflCant, implyingthatthe adult popula-

Table 1 ･ Results of susceptibilitytests exposing Culex LritqenjorJynchus adult mosquitoes to variotwinsecticidcs at diagnostic conccntraltions

Concen ExpostJTe No. of adults No. dead Mortality Susceptibility/ Insecti ci de tration time (h) exposed (aRer 24 h) (%) Resistant status+ (%)

丘V ′0 ′hV ′8 6 ′〇人V 00 1 つ一 ′0 ′b 6 DDT 4 5 L o o o o 0 0 0 1 0 つ▲ 1 L L 2 2 L 3 L 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 ′b 4 00 0 0 0 5 1 1 0 0 00 0 5 5 0 0 0 0 0 0 0 0 0 0 良良良良 s s s Mat adlion Femitrothion

Propoxur

日‖一 = = Deltamethrin 2 5 5 1 1 1 Permethrin Lambdacyhalothrin

+S: susceptible (> 9名% mortality), VR: veriGcahon required (80-9i% mortality), R: resistant (< 80% mortality) (2).

Td)le 2. Dosage mortality response of adult CuLex Lrilaeniorbmchus mosquitoes, used to determine LT5｡ and lJ95 Values and heterogeneity

Insecticide REeqEIst諾onn LT;omvi:)ueS LT;Lvhd)ues Het;:o(gdeP;iサ

∠U 3 8 8 ′0 2 00 9 DDT4.0% -7.4997土1. 8596x 5 1 1 1 . 4 8 5 7 1 つ一 2 つ一 3 7 5 4 20.3 12(6)

Malathion15. 0% 1. i883土2.4 1 65x 29. 1912(5)

Fenitrothion- 1.0% 25.93 89土4.965x 1 7.0607(4)

Propoxur･0. 1 % 3. 8087土3. 8682X 1 2.2598(4) +df: degrees of Beedom.

Table 3･ Results of susceptibility tests carried out using Culex LritaeniorbJnchus larvae agalnst different larvicides at diagnostic dosages

L-icides doDsILg蒜,蓋sifd (nOe･,d2C.add, "o(T%.r RSeSs"itti:禁書

●l ●l ■l ● - ■l一l一 l 1 1 1 00 各 5 5 醐mmmm 0 0 0 0 0 〇 0 0 1 00 2 0 つ一〇 2 つ】 2 2 2 0 0 0 0 00 0 0 0 0 N N N N N 0 0 0 0 0 0 0 0 0 0 氏良良氏良

'S: suspeptible (> 98% mortality), VR: veriGcation required (80-98% mortality), R: resIStant (<80% mortality) (2).

12 Table 4. Dosage-mortality response of Culex Lrilaeniorhynchus larvae to various dosages oftemephos and fenthion, used to deterTnine the LCS.and LC,. values, and heterogeneity

Insecticide 琵慧15.Sion LC(5Avgnd)ues LC("mvgnd)ues "eT(gS;iサ

Tcmephos 0.9547土0.5052x 0. 15 1 1 1.9098 25.5986(5)

Fenthion 0.4582土0.9427x 0.6 1 5 1 2.395 26.93 87(4)

+df:degrees of Beedom.

tion tested was heterogeneous. has been reported Bom Japanand Korea (13). Susceptibility Larval Bioassay: The results of the larval susceptibility tests carried out earlierinDelhi againstthe larvae of the Cx. tests camied out using respective diagnostic dosages of DDT, tritaeniorJwnchus mosquito recorded LC5｡and LC9｡ Values temephos, fenthion, fenitrothion,and malathion revealedthat for temephosandfenthion ofO.0383 land 0.2214,and 0.02939 these larvicides failed toinduce any larval mortalityaRer a and 0.1614, respectively (14). In the present study, LC50and 24-h exposure period,indicating that larvae were resistant to LC90 Values recorded for temephosand fenthion were found these laJVicides (Table 3). to be 0.1511and 1.9098,andO.6151and2.395, respectively; The results of larvae exposed to various dilutions of the much higher thapthose previously reported･ Comparatively, teclmical formof larvicides revealed that the LC50and LC,. LC90 Values found in the present study indicate a 95.5-and values estimated for temephosandfenthion were 0. 15 I land 299.4-fold increase against the diagnostic dosages of 1 ･9098and O･615 land 2.395 mg/1, respectively (Table 4). The temephosandfenthion, respectively. heterogeneity(P=0･05) was found to be significant, implying The development of DDT and malathion resistance in that the larval population tested was heterogeneous･ adults,and temephosandfenthion resistancein1arvae, of Cx. tritaeniorhynchus mosquitoes warrants strict monitoring of the susceptibilitystatus of this species to variousinsecticides DISCtJS S ION inJapanese encephalitis proneareas before contemplating During 1958,the flrSt report Onthe development of DDT the use of these substances for ULV spray/thermal fogglng, resistanceinCx･ tritaenL'orJwnchus mosquito appeared from as a residual spray, or as a laJIVicide. Okinawa Island, Japan (6). In India, DDT and dieldrin resistance were reported from different parts of the country ACKNOWLEDGMENT by severalresearchers (7,8). DDT resistance in the Cx. tritaeniorkynchus mosquito has also been reported from The audlOrS Wish tothank Shri. Rai馳ddinKhan, Techmician, additional countries, including Bangladesh, Benin, China, for providing teclmical assistance. Nigeria, Korea, Sri Lanka, and Thailand (4). During the present study, this species was also found to be resistant to DDT,and the highLT95 Values estimated for DDT- 4.0% (136 REFERENCES min) is indicative of development of a highlevel of DDT I. World HealthOrganiZation (1976): Criteriaand meaning resistanceinadult Cx･ tritaeniorkynchus･ It appears likely of tests for determiningthe susceptibilityor resistance that the use of DDT creates a DDT-Containing dustinand of insects to insecticides. WrHO∧rBC/76.2. around animal enclosures erected to protect the captive 2. World HealthOrganiZZLtion ( 1 970): hsecticide resistance animalsfrom other crawling Insects at National Zoological and vector control. 17threport of the WHO expert Park,andthis dust has contributed significantlyinprecipitat- committee on insecticide. WHO Tech. Rep. Ser., no. 443, lng the DDT resistance evident inincreased LT5.and LT95 p. 47-73. values. 3. World Heal血OrganiZation (1 986): Resistance of vectors Malathion resistanceinthe Cx. Lritaeniorhynchw mosquito and reservoirs of diseases to pesticides. loth report of was reported from Japanduring 1987 (9). In India, malathion the WHO expert cornmitbee on vector biologyand control. resistanceinlaJValand adult stages of Cx. tritaeniorhynchus WHO Tech. Rep. Ser., no. 737. mosquito has been reported from Arthala, Uttar hadesh,and 4. World HealthOrganization (1992): Vector resistance to Kota, Rajasthan(10,1 1). Pennington (12) reported a 48.4- pesticide. 1 5threport of the WHO expert committee on fo1dincrease ofmal姐Iion resistanceinthe Cx. Lritaeniov1秒nChzm vector biologyand control. WHO Tech. Rep. Ser･, no･ mosquito larvae within 5 years after the introduction of 818. malathion･ Malathion resistanceinthe Cx. tritaeniorhynchus 5. Fimey, D. J. (1981): Probitanalysis. Cambridge Univer- mosquito has been reported from severalcountries,including sityPress, London. China, Japan, Korea,and SriLanka (4). The LT95 Values for 6. Brown,A. W. A.and Pal, R. (1971): Insecticide resistance malathion, fenthion, and propoxur reported from Kota inarthropods. WHO Monograph Ser･, no･ 38･ (RQjasthan) were 123 min, 132 min,and 168 min, respectively, 7. Kulkarni, S. M.and Naik, P. S. (1991): Susceptibility at diagnostic concentrations ( I 1). In the present study, the studies on Cx. tritaenior砂nchus Giles, 1901, toinsecti- LT,5 Values recorded for malathion, fenthion,and propoxur cides in the state ofGoa. 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