Susceptibility of C~&V trittaeniow5ynch- and six other mosquitos to in Korea

L. S. SELF WHO Entomologist, WHO Japanese Encephalitis Vector Research Unit, Seoul, Korea. Present address: WHO, p.o. Box 302, Jakarta. lndonesia.

J. C. SHIM Entomologist, National Institute of Health, Seoul, Korea, seconded to WHO Japanese Encephalitis Yector Research seconded to WHO Japanese Encephalitis Vector Research Unit.

P. JOLIVET Aoject Leader, WHO Japanese Encephalitis Vectov Resemch Unit, Seoul, Korea.

RÉSUMÉ Presented herein are the results of 175 larval suscepti- bility tests and 132 adult tests obtained in Korea against Cette première étude détaillée de la sensibilité des seven species of mosquitos from August 1969 to Septem- moustiques aux insecticides en CoGe a montré clairement ber 1972. The test methods employed, using 13 organo- que Culex tritaeniorhynchus était Gsistant au DDT et au phosphorus insecticides, three chlorinated hydrocarbons Iindane. Dans les zones rurales, aucune résistance des and one , were those recommended by the World Culex, Anopheles et Aedes aux insecticides organophos- Health Organization (1970). Thèse results Will enable phorés n’est encore apparue, et cela en dépit de fréquentes comparisons to be made to susceptibility levels reported applications d’insecticides agricoles aux cultuses de riz. Le elsewhere and also provide base-lines for future work in produit de la concenfsation et du femps (CT), déduit de deux Korea. BROWNand PAL (1971) have reviewed the resist- sortes d’expériences de test d’adultes, monfr’e un même ance of mosquitos to insecticides on a world-wide basis. ordre de grandew de toxicité des insecticides envers Culex tritaeniorhynchus. SPECIES The vector of Japanese encephalitis, CU. tuitaeniorhyn- ABSTRACT. chus smzmo~osus was exposed in 33 ‘A of the 307 tests. Other speciestested of public health importance or interest This firsf detailed study on the susceptibility of mos- were CU. pipiens pallerts (31 y$, An. sineruis (11 %), quitos to insecticides in Korea has revealed the r’esistance of Ae. togoi (8 %) and Ae. vexans (7 %). A few tests included Culex tritaeniorhynchus fo DDT and . In rural CU. vagans and CU. orientalis. ar’eas, organophosphosus resistance in culex, anopheline and aedes species has net yet occuwed despite frequent pesticide LOCALITIES applications to rice. The pyoduct of concenfrafion and time (CT), derived from two ad& test pyocedures, gave the Specimens were obtained from 15 localities. There same order of toxicity for Culex tritaeniorhyn- provided adequate country-wide representation except for chus. the eastern region and areas north of Seoul. A species

Cah. O.R.S.T.O.M., sér. Ent. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. 81 L.-S. SELF, J.-C. SHIM, P. JOLIVET

was exposed to one of the standard WHO test procedures replacements (e. g. , trade name Dursban). when sufficient numbers had been collected. Since a Future tests should include difenphos (Abate). short time was spent in most localities, only a few insecti- The three con-mon chlorinated hydrocarbons were cides could normally be tested. used and also the carbamate, propoxur. Except for About 65 % of a11tests were made at the four study OMS-1424 (2-Diethylamino-6-methylpyrimidin-4-y1 dime- sites of the WHO Japanese Encephalitis Vector Research thyl phosphorothionate) a11 the insecticides tested are Unit (J.E.V.R.U.), which are described in an unpublished fait-ly well known. document (WHO/VBC/71.332). Briefly, Sintaein is locat- ed in an important rice growing area 215 km south of TEST PROCEDURES. Seoul, and 32 % of a11the tests occurred there. Sasang is a suburb of Pusan located near the Nak Tong river Al1 specimens were normally field-collected and imme- 330 km southeast of Seoul (15 % of tests). Another site diately tested, except for colony strains utilized during is Paju located in a small rice growing area 25 km north the cold months (November-March). The temperature of Seoul (10 %), whereas Banpo Dong is a suburb of Seoul during the tests normally ranged from 23 to 27 OCand the located 2 km south of the Han river (8 %). relative humidity from 65 to 55 O?. Data for many tests These 15 localities, as shown below, may be useful were forwarded to WHO headquarters in Geneva for in planning future tests. computer analysis, and the results are presented in various (1) Seoul suburbs south of Han river: Banpo Dong and issues of the WHO Information Circalar on Insecticide Kimpo. Resistance. The number of adults exposed are shown in (2) Seoul suburbs north of Han river: Rockbon Dong, Tables 5 and 6, and 300 or more specimens were normally Nokbun Dong and Soo Saik. used in each larval test. When the control mortalities (3) Pusan suburb near Nak Tong river: Sasang. exceeded 20 %, the tests were discarded. (4) Rice growing areasnear Seoul: Paju and Seiryu Dong (Suwon). Larvae. (5) Rice growing areasin Cholla Pukdo Province: Sintaein, Kim Je and Kwang Hwal. For each concentration, at least two replicates of (6) Coastal areas: Byon San (Cholla Pukdo) and Kajawa Dong (Inchon). 25 third and fourth instar larvae were exposed for 24 h (7) Offshore Islands: Cheju Do and Wi Do. in plastic containers. These held 249 ml of water to which 1 ml of toxicant in ethanol had been added. Stock solutions of , , , Dursban, INSECTICIDES bromophos, and the three chlorinated hydro- carbons were supplied by WHO. With the other com- When ample specimens had been obtained in breeding pounds, ethanol solutions were prepared from technical sites or from animal bait, fenitrothion was normally the material. Mortalities were recorded after 24 h exposures, first insecticide to be tested. It presently is the most and the regression lines were derived from at least three frequently applied pesticide in Korea. It is therefore the mortality points between 10 and 90 %. compound of choice, followed by malathion and fenthion, in screening for organophosphorus-resistance. About Adults. 20 % of a11tests were made with fenitrothion. (Dibrom) also has popular usage in Korea but The impregnated papers and standard test kits were for thermal fogging against mosquitos and for controlling supplied by WHO. Two methods of testing were employed caterpillars on pine trees. Aerial ULV applications are and two or more replicates of 26 engorged females were occasionally made. Although some mosquito larvae were normally used for each concentration or exposure period. tested against naled, the susceptibility levels of the adult The mosquitos were transferred to clean holding tubes populations have yet to be determined. One thermal after exposure to the toxicant, and the percentage morta- fogging experiment using caged CU. t~ifaelziol-ll~alchc~s lity determined 24 h later. adults has shown that naled cari provide good control at about one-third the effective malathion dosage (WHO/ MULTIPLE - CONCENTRATION EXPOSURE. The well , VBC 172.424). known WHO adult test for obtaining the percentage LC,, Some tests were made with rice materials, and percentage LC,, was used mainly in 1970. The namely EPN, (Cidial) and methyl . specimens were exposed for 60 minutes to the following Less toxic and less popular materials in this category are insecticides and concentrations : fenitrothion (. 025, . 1, trichlorfon (Dipterex) and diazinon. Several other organo- .4, 1.6 %), malathion (.4, .S, 1.6, 3.2, 6.4, 12.8 %), phosphorus materials were tested because they were used fenthion (.2, 14, lS, 1.6, 3.2 %), DDT (.25, .5, 1.0, in local vector control operations (e. g. ) or 2.0, 4.0 %), (.2, .4, .S, 1.6, 4.0 %> and pro- else they offered promise as improved vector control poxur (.025, .l, .4, 1.6 %).

82 Cah. O.R.S.T.O.M., s&. Eaf. viéd. et Payasitol., vol. XII, no 2, 1974 : 81-92. SLJSCEPTIBILITY OF C’ULEX TRZTAENIORHYNCHUS TO INSECTICIDES

MULTIPLE-TIME EXPOSURE. A relatively new, recom- RESULTS. mended WHO procedure for obtaining the LT,, and LT,, in minutes was used in 1971 and 1972. Here, the Larvae. regression lines were derived from the mortalities obtained FENITROTHION AND MALATHION. Table 1 shows the at different exposure times to the same concentration of results obtained with seven species; and no resistance is insecticide. indicated. With CU. tritaeiziorlzynchzzs, the highest LC,, values to fenitrothion and malathion are only .038 ppm CT PRODUCTS. Although both adult test procedures and .062 ppm, respectively. Moreover, the susceptibility could not be carried out simultaneously, the products levels in the two principal cities are similar to those in the of concentration and time (CT) are given for CI~. f&zerzio- rice growing and coastal areas. Apparently, there are ~l~y~zcht~s. ARIARATNA~~~ and BROWN (1969) show the not enough tests in each locality in each year to warrant calculation procedure for CI~. pipiuzs fatigatzs exposed a statistical analysis. In any case’ the results could not to DDT. provide a basis for concluding resistance.

TABLE 1. - Showing susceptibility levels of fourth instar larvae to fenitrothion and Malathion

1 toca1ity Date ESO L%a5 Locality Date LC50 w95 Ppra PV wm PP - -~Fenltrothion --F!lIllIi.hiOn CU. trltweniorhynchus CU. tritaoniorhynchus-- sesang 10.70 .0051 -0096 sesong 7.71 a14 .035 sasang 8.71 .012 ,029 sas-mg 9.72 .0096 .050 sasang 9.72 .0038 .023 Sintaoin 7.70 . 0024 .036 sintaein 8.70 .0080 .017 Sfnt.4oin 0.71 .017 .a46 Sintnoin 8.71 . cxxo -020 Sintnoin 6.72 .027 .C16' Sintnein 8.72 . oc-14 .011 Bnnpo DonK 9.71 .021 .OGF( Empo Dong 9.71 .OlO .03G Kimpo 9.72 .0030 -023 Kimpo 9.72 . 0038 .023 PSjU 9.G9 .021 .c-lR Mo0 Rcung Hi 10.70 , fK)58 .Oll Chido 1.0.70 .OlH . CG? Chidu 10.70 .0070 .Oll Knjawa Lmng 10.70 .0021 . 005G

Cu.pipiens pnllens --CU. &pif?ns-~- PS11 WIS sasang a.71 .0012 .039 Susnn~ 8.71 .079 .17 sesong 0.72 .aoGE .02G s1ntncin B.GR .0x .13 tiim Jo 4.70 .015 .032 Sint fiaj n 6.71 .075 .20 Sintnein 9.70 -0039 .OOGl SiTltROiIl 9.71 .wl7 .15 sintr.sin 6.71 ,012 .023 Kin Je 4.70 .Ml . ms Rockl>on Dong 3.70 .012 .022 Rockhon Done 2.70 .a41 .C69 Noktmn rmng 6.72 . ow6 .oOs4 Do0 :iüik 3.iO .060 .tti Chido 12,70 . 0058 . OOGE ChidO 12.70 .ORl .14

p. <&=tns ---L-._.-CU v n i: (: " .s; Beiq~o Don~ 6.71 .003G .OORO Pa ju 7.70 ,013 . l.126 Bmpo mng 6.72 .0012 .0032 Bim~m Dcne G.Tl . 01 2 .023

w--LCU «ri~ntalis -.-L.--.----..-CU orinntnlj s Pnju 7.70 .ooJLI .OlG 7.7cg .016 .a37 An. sinonsis _.----An. .sll&cl!sis Cl,ido lO.iO .17 .75 8.70 . C~E.1 -17 Slntaein 6.72 .035 .1% 0.72 .lII s . 1:72 lu. Ïcl .12 .CO

ho. tcqp1 .----*.-%2.-eAP. tcvvi. Byon San 5.70 .012 . 020 8.69 , cl::3 .x3 5.70 .Ol R ,052 Ac. vomns 13rnpo linng 5.72 .

Caiz. O.R.S. T.O.M., sh. Eut. nzkd. et Pavasitol., vol. XII, no 2, 1974 : 81-92. 83 * L.-S. SELF, J.-C. SHIM, P. JOLIVET

TABLE 2. - Showing susceptibility levels of fourth instar larvae to eleven organophosphorus insecticides w5 Loea:iEy Date X§O LC95 Locality Ltate KS0 mm wm rw Ppm

Fenihion tfûled-- Chlorpyritos ~-.CU. tritneniorhynchu5 CU, tritsuniorhvnchus 5~. tritaeniorhynchus - Sasnng 8.71 . OCJlH . vo53 Sasaz:g 8.71 -010 _ O?O sasang 7.71 . cKK355 .m19 sssartg 9.72 . xA6 .021 sflsanT' Y.72 .021 .095 SasnnK 9.72 .CO14 . CO42 Sintaein a.70 . (.U17 . «U3 3 Sintaein x.71 . ,704.l -010 stnraein a.71 . 00022 . OC072 Sintanin 8.71 . Or~~7 -010 Sint acin 9.71 .OZ7 .Od8 Sintsrin a.72 .cam ,a013 Skntnein a.72 .lK5%7 .097-l Sintaein 8.72 .0065 .037 Rmpo Dow ‘J.?l .ooO32 . Or472 R.illpo 1mrg 9.71 .0056 .022 &mpo Dons 9 , 7 1 . u0-x -043 Xi mpo 9.72 .00054 .oa5 Kimpo Y.72 . lJlJ3- .005é CU. pipons pallens CU. p i p ier.o pIllWS CU. pipiens pallens

Rockbon Don&, 3.70 .074 .13 SO» Srrik 12.70 .032 -0-15 Rockbon uwg I.îO . ooG44 .00076 Sao Snik 12.70 .w2a “W-IX Siniarin 7.71 .G13 .o.e7 Sao Saik 3.7rJ .

TABLE 2. - (Continued)

Locslity mite QD Le95 LucaI I ty D%?e LC50 LCSS L

--EPN ---PI:0nttlaa f e !&thyl pnrüthion CU. trlt.%miorhynchus CU. tritacniorhyrdms CU. tritseniorhynchus

SklSWK a.71 .cim75 . oO3i Sssan~ 8.71 . oOci72 .OO17 sa stmg a.71 .00054 .0019 Sznlaein 3.71 . wO55 .OOll Sintaein 9.71 . cQOR9 .0043 sintsein 8.72 .OO28 .OGGti Banpo Don&? 9.71 .ooll . Go34 tlanpo Dor:g Y.71 -0013 -Ix)32 CU. pipians pal1en.s CU. pipierxs pallens CU. plpic?n=i pallens Sao Snik 12.70 .OOlZ .GQ43 SO0 saili 12.70 -011 .023 Rockbon Dong 7.72 .@ozfl .ocm Sintaein 12.70 .cQPti ,0035 Sintnein 12.70 .om .028 Sintnein 12.70 .OO17 . CO4 2 Chido 12.70 .0012 .0026 CMS - 142.1 DiFlZiIIOIl Brozzoohoç CU. tritaeniorhynchus CU. triteeniorhynchus CII. 1 ieno nsllons sosnng a.72 .cQ65 .020 Sint min 8.72 -019 -038 R&kton Dong 2.70 .0x3 .OOE16 Soo Saik 3.70 .0051 .ooa7 sintaein 6.71 -CO79 .023 CU. pipiens pallens CU. pipiens pîllons A6. ?OCOi Nokbun Dong 6.72 .0034 .0095 Rockbon Dor.6 2.70 -030 .14 Byon Pan 5.70 .0047 .ooal Nokbun Dong 6.72 -016 .027 Kim Je 4.70 -041 .092 CU. vagans Ae. togoi Banpo Dong 5.72 . CO092 -0016 Byon San a.69 . ootïa -025 Byon snn 5.70 -010 _ 027 +

84 Cah. O.R.S.T.O.M., sér. Ent. méd. ef Parasitol., vol. XII, no 2, 1974 : 81-92. SUSCEPTIBILITY OF CULEX TRITAENIORHYNCHUS TO INSECTICIDES

Bath CU. frifaeniodtynchus and CU. pipiens pallens OTHER ORGANOPHOSPHORUS MATERIALS. Table 2 show a similar response to fenitrothion but not to mala- shows the results obtained with 11 compounds. With thion. The LC,, values of the latter species to malathion fenthion, the high LC,, value of .13 ppm was obtained normally fa11between . 1 ppm and .2 ppm in the cities in only one test with colonized CU.pipienspallens. This and elsewhere. high figure was not obtained in subsequent tests, using The limited data obtained with An. sinensis suggest field specimens. THOMAS (1970) however reported CU. tolerance to fenitrothion. However, the highest LC,, pipiens fatigans to be resistant to fenthion at two localities value (. 75 ppm) to fenitrothion was obtained late in the in Kuala Lumpur, in which case the LC,, values were season at Chido on the isiand of Wi Do, where organo- between .15 and .2 ppm. phosphorus pesticides are not extensively used.

TABLE 3. - Showing susceptibility levels of fourth instar larvae to DDT, Dieldrin and Lindane

Lwality Date w50 K95 Locnlity Data LC50 L-c95 PPm PP'" PPm wm

-DDT Lindanc CU. tritaaniorhynchus CU. tritaeniorhynchus snsang 8.71 .13 SaSallg 8.71 .099 .37 sintaein 8.69 1.2 sintnein 9.71 .19 1.3 Sihtaein 9.71 .18 .73 Sintaoin 8.72 -70 3.3 Sintaein 0.72 .45 3.4 L?anpo Don8 9.71 .17 .75 Banpo Don8 9.71 .lG .80 Pajll 9.G9 .11 .22 Paju 9.69 .11 -97 Chido 10.70 .061 .14 Chido 10.70 .w2 .19 CU. pipions pallens Cu, pipians pallehs - Rockbon Dong 2.70 .039 .ll Rockbon Don8 2.70 .26 .y sintaoin 8.69 .14 .49 Soo Saik 3.70 .OS7 .52 sint noin 9.71 .ffl6 .45 Sintaein 8.69 .090 .58 Kim JC 4.70 .080 .18 Sintaein 9.71 .DF4 .20 An. slnensis Kila Je 4.70 ‘095 .24 SintnBin 6.70 .13 .42 Chido 12.70 < 093 .20 Chido 10.70 .17 .99 ne. togoi -.--Ae. vex8ns 13yon snn 6.G9 ,012 .071 PtIjU 6.70 . CO38 .U3L ujjon Sfm 5.70 ,020 ,031 Ae. to@ - Dieldrin -- Byon Ssn 8.69 .015 .059 ~--_CU, tri tseniorhynchus^- Flyon San 5.70 .0069 .»23 sasnng 8.71 .25 .54 ~-CU. "Pye Sintoein 8.69 -22 .60 PiIjU 6.70 .OC93 .021 Si ntaein 9.71 .13 .44 SilltCOill 6.70 .018 .04s Uan~~o Don~ 9.71 .21 .58 Brnlpo Don& 6.71 .CO64 .017 Pmju 9.G9 .lQ .23 CU. orl ontn1is-- CU. pipions palIn!>---- POjU 7.70 .OCZl .CC67 Ilockbon u011L’ 2.70 . 00~0 ,032 Sintaoilt 8.69 .0357 .031 Kim Jo 4.70 . CU40 .017

.Ao.---- vcxiins P:t ju 6.70 .0012 .D034

-.-.-he. tonoi uvon San 5.70 .00097 .0045 CU. vagaz! Paju 7.70 , CO14 .0027

-_Cu. oriohtnlis sintnoin 6.70 .0062 .Oll

Cah. O.R.S.T.O.M., sér. Wt. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. 85 L.-S. SELF, J.-C. SHIM, P. JOLIVET

With trichlorfon, the LC,, values for CIL fritaenio- lindane is indicated. Moderate to highly developed organo- r&&~us and Ca. pipiens pallem range from .19 ppm to chlorine-resistance is not apparent among the different .82 ppm. There seems to be a natural refractoriness of species tested. CU. pipiens to this insecticide. For example, GAHAN and NOE (1956) reported a LC,, of .32 ppm for CI~. pipiens AVERAGE LC,, AND LC,, VALUES. These are shown fatigàm in the United States, whereas in the WHO stage 1 for six of the organophosphorus insecticides and the three insecticide tests at the Riverside Laboratory, the LC,, chlorinated hydrocarbons tested against Ca. fritaenior- for the same species exceeded 1 ppm trichlorfon. JzymJms (Table 4). Although these data are derived from EPN, phenthoate and methyl parathion were found tests in different localities and years, they should be useful to be very toxic to larvae, but less SO than chlorpyrifos. for comparing future test results. Shown also are the These results are consistent with previously reported highest values recorded in individual tests. (WHO/VBC/71.2701 field observations which showed With the organophosphorus materials, the average that the application rates used for rice pest control are values indicate that fenitrothion, malathion and naled presently about five to 10 times higher than required for have somewhat similar larvicidal activity. Dursban and mosquito larval control. EPN are the most toxic, followed by fenthion.

CHLORINATED HYDROCARBONS. TheresultsinTable 3 Adults. suggest DDT and lindane resistance in Ca. tritaenio- rJ~yr~chrrsat Sintaein. 0. pipiens pallens appears, except MULTIPLE-CONCENTRATION EXPOSURE. The results for at Rockbon Dong, to show only its natural tolerance to the 60-minute exposure are shown in Table 5. With these insecticides. The few tests made with dieldrin fenitrothion, additional LC,, values might have been suggest tolerance in CH. tr.itae~zio~Jz~lïrcJzzisbut susceptibility obtained if the impregnated papers included 3.2 ‘A as in in Ca. pipieru pallerrs. With AH. @ensis, tolerance to the fenthion series. Although Ca. t~itaalio~llyrlchlls and

TABLE 4. - Showing summary results of nine larvciides tested against CU. t~itacïliorl~~~ncJl~~sand CIL. pipiens pallens CU. tritnenlm-hynchus -- T CU. pipiens pa11ons -I Insecticide Avorago AWWCLgt? NO. Average AVerE.gO 1x50 NO. tests LC95 tests LC5O LCgg PPm PP= PPm PPD

Fenitrothion 11 .cxx4 .OlB 6 .0078 .020 (.ooZl-.012) (.ocm-.030) (.0026-.015) (.cw1-.039)

Malatilion 9 .015 ,017 8 ,062 .13 (.0024--027) (.023-.066) (.041-.OYl) (.088-.2O)

Fonthian G .cxn9 .017. 6 .015 .033 (.C017-.0066) (.0033-.022) (.0020-.074) ([email protected])

Naled 7 .012 .044 4 .024 .042 ( .0032-. 027) (.0X6-.OYS) (.022-.032) (.027-.048)

Chlorpyritos G .OOO55 .0017 5 . OXM6 . (WiK?D (.00022-.0014) (.OOO72-.OiM2) (.co031-.Ocml~ (.oGoô8-.oal3

EPN 3 .00080 .0025 3 .0015 .0033 (.cno55-.cml) ( . OOll-.0334) (.0012-.0020) (.C’J26-.OOl:i)

DDT 7 .33 1.4 6 .ll .45 c.Oâa-1.2) (,lY-3.4) (.0X-.26) (.20-.95)

DiC&drii2 5 .19 .48 .0(X2 .w7 (.13-.25) (.23-.60) ( .0040-. cmoj ( . OI 7- .- 03”)

Lindmr: G .22 .076 -31 (.061-.70) (.039-.14) (.ll-.4YJ

Range in parenthesis.

86 Cah. O.R.S.T.O.M., se?.. Ent. méd. et Parasitol., vol. XIT, nD 2, 1974 : Sl-9i. SUSCEPTIBILITY OF CULEX TRITAENIORHYNCHUS TO INSECTICIDES

CII. pipiem pallens larvae show a similar response to feni- are at present much higher than those of CU. frifaertior- trothion, the latter species is about three times more I~~~IC~IUSin the Cholla rice belt area. susceptible in the adult stage. With AII. si~zensis, the low With malathion, the October 1970 data deserve mortality to adults is consistent with the fenitrothion comment. The LC,, values for C~I. n’ifae~lio~l~y~lcl~Irs, tolerance indicated in larvae. In addition, unpublished CI~. pipiens pallens, and CI~. orieienfalis are 7.6, 6.6 % and JEVRU data show that adult densities of An. sinemis 8.7 % respectively. Here, the adults were reared from

TABLE 5. - Showing susceptibility levels of female adults exposedfor one hour to severalconcentrations of insecticides (multiple-concentration exposure)

NO. kPca1ity Dota I-C50 x95 exposed 7 con. a con. I I --; ?oni.trothion --Fenthion CU. tritnoniorhynchus CU. tritueniorhynchus - 3intaein 7.70 123 .4 1.2 sintac3in 6.70 67 .41 .96 jintacln 3.72 250 1.3 >l.G Chido 10.7” 103 1.5 2.5 iwant; Hwnl 6.70 73 .24 .Gl Cu. piplriis pw-sttt?ns Jasnng 10.70 1Wl >l.G :hido 10.70 117 .77 >1.6 .sinta?lin 6.69 2cc .31 30 sintr.ein 6.7~1 127 .39 .72 CU. pipiens pallens Sl"tC3i3i" 10.7u 1 IX) .G8 1.4 lockbon Don6 5.70 200 .20 .50 Rockbon D”“e 5.70 250 .31 ,59 jintaein 6.70 103 .45 .m Noktun DO”~ 6.72 4P.J .IO .77 jintseln 6.70 94 .17 .47 A". n1nons1s Sintsein 10.70 126 .53 .Gl ---.-- 'nju 10.70 60 .13 .40 Sintwi” 6.70 114 1.7 3.1 3.2 - A". si"c3"~ls AS. "ern"~ St ntaoi n 6.70 111 .60 >l.G jintaein 7.70 121 .24 1.4 Pnju 6.70 1x1 .56 .93 jintaain 6.70 66 .36 1.0 sintnc1n 6.70 153 .ti3 .Q ii"tGi~i" 9.70 59 >1.6 nanpo Dong 6.72 390 . GP 1 . 1 bju 6.70 lG0 1.0 .G Ab. toc‘>1 :wang IlVrïl Et.70 77 >1 .G _i_- :hido 10.70 50 >1.6 Rym 6s" R.69 %Ctii .22 . 17 JJyon Sa" 5.70 3CXI .35 .5Y no. Yc?l~"~

%jU 6.70 120 .34 1.1 Dieldri” jintp.eln 6.70 100 .40 1.5 s. tritaen: irl~yww 3n”po Do& 6.72 250 .27 .50 Kaen~ Hwal 6.70 lOr! >4.0 ne. ta& Chido 10.7CI 1711 >4.0 - tyon Sa" 5.70 180 .@s5 .14 CU. p i , ,ie”l_r.aJ- -_- 1<,“4 CU. Oii@“tolia - Rmkban DO”L< 4.70 3<%, .30 .8R %JU 7.70 150 -48 .e2 s1ntéel.n 6.70 218 .4i: 2.t ;elryu Don~ 10.70 RO .26 .9G Sintacin 111.70 tïs 2.6 > :.o ;l"tSl‘?l" X0.70 100 .oo >1.6 J'Mj" 1<1.71~ PO .14.0 CU. v*p;ans A". aincr~~l~ ‘CjU 6.70 100 .41 .06 sintaein 6.70 1 c4 2.0 ?4.0 Pztj” 7.70 20, 1.4 3‘l.u h!o* Rome Ri 10.70 55 X.1, Chido 10.70 55 >4.0

--h. YWP"5 J’RjU 6.70 150 .7G 1.4 SI"tRd" 6.70 120 .17 .62 Monpo DO”~ 6.72 350 .G2 1.55

he. tofwi "yo" Sa" 8.69 xx3 .67 1.5 II, on Sa." 5.70 350 .11!l6 .23

-_---CU. orl~?"

Cah O.R.S.T.O.M., sér.. Enf. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. 87 L.-S. SELF, J.-C. SHIM, P. JOLIVET

TABLE 5. - (Contimed)

Y”. No. Locallty nate ~50 m95 Lcca1ity Date G50 u95 expoçed J con. x con. exposed x con. a Cc>“.

Yal nttt1 on L?E

CL!!: trttanniorhynchus CU. trltaeniorhynchus Çintaetn 7.70 84 .a2 1.1 Sintaein 7.70 105 >4.0 *hIdo 10.70 164 4.1 7.6 Chido 10.70 icu P-4.0 CU pipif-nc: pallens Bnnpo Dong 9.71 105 .4.0 L- Sintsin 8.69 200 .95 1.5 CU. pipions pellens-- Si”tr\ei” fi.70 120 1.2 1.9 sintaein 8.69 1fQ ,4.0 Sintaeln 10.70 175 3.5 6.6 Rcckl>o” üong 4.70 375 74.0 P cwkbon Hong 5.70 240 1.0 2.0 Sintaei” 6.70 185 :4.0 N&bW t%“g 6.12 350 1.6 2.2 Nokbu” Don& 6.72 3x1 :4.0

An, sinrnais A”. sinensis

Sintaein G.70 15B 1.7 2.4 Sintaein 7.70 131 1.3 4.0 PBJU 6.70 180 1.4 2.9 Pdjlt 7.70 125 1.7 4.0 Ilanpo llong Y.71 120 1.7 >‘l.o At?. vl?xans ---- Sintaein 8.72 1cn 1.3 2.6 6.70 200 1.8 PaJu 2.3 J*O sintnein 7.70 94 1.7 3.2 hz. tcwJ1 --- Banpo no”.~ 6.72 250 2.6 >4.0

Byon sari 5.10 no0 , 51 .A3 An. togoi Cv. Ortenta is .----_-~ llyon San A.69 200 2.2 14.0 Seiryu Dang 10.70 120 3.6 G.7 l3yon San 5.70 225 1.5 3 , 0

CU. orientslis Propoxur CU. tri tar.nicrho”chus Paju 7.70 90 . 79 3.9

s1ntaein 7.70 91 .ORl .32 Chido 10. io 60 .14 .GO

CO. pipiwr- tulle”+

sintaein 7,ïo 170 .17 -56 Nokbun Done, 6.12 320 .035 .osa An. sinansi s

Sineanin 7.70 112 .c47 .17

--Ae. vexans Si”tar+i” 7.10 119 .M7 .17 Banpo Dcng 6.72 250 .050 .ll

--ne. tofoi Byon San 7.70 118 .03H .075

larvae collected in three widely separated localities. Ho- pallens show neglïgible mortality at the highest concen- wever, adult populations of these species in the spring and tration (4 %), but since the exposure time was not increased summer months never showed this lowlevel of suscepti- above one hour, these results are considered to be incon- bility to any organophosphorus material tested. PEN- clusive. The same pertains to CU. t~ifaalio~J~~~tcJ~Irs~sand NINGTON (1968) in Okinawa found malathion resistance An. sinensis exposed to dieldrin. Crossing experiments in CU. pipiens fatigans and CU. tlltaenio~l~~~ncl~w, but it in the laboratory, or longer exposure periods, are needed was expressed in adults as well as larvae that survived to clarify the type of adult response to the chlorinated concentrations of 1 ppm. Other results herein indicate hydrocarbons. On the other hand, An. sinensis shows susceptibility of An. sinensis to malathion but not to susceptibility to DDT and CIL pipiens pallem to dieldrin. fenthion. With propoxur, a11 the species tested were found With DDT, CU. fuitaeniorJzynchus and CU. pipiens to be susceptible.

88 Cah. O.R.S.T.O.M.. sW. Ent. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. SUSCEPTIBILITY OF CULEX TRITAENIORHYNCHUS TO INSECTICIDES

MULTIPLE-TIME EXPOSURE. The results of the expo- more tests are required to determine whether this increase sures to one concentration of insecticide are shown in in exposure time is due to resistance or tolerance. Table 6. Two of the concentrations of fenitrothion used The high LT,, values of 455 and 480 minutes for CI~. in 1972 were not made avaiiable in 1.971. This posed tritaeniorlzynchus to 1.6 ‘A fenitrothion occurred in two some minor difficulties in comparing the results. August 1972 tests. In West Africa, HAMON and SALES With CII. tr’itaeniorllyrzchus, the exposure times to (1970) reported LT,, values of 102 minutes for An. ganz- fenitrothion in 1972 normally had to be increased to biae and 178 minutes for CU. pipiem fatigans to only .4 % obtain the same mortalities achieved in 1971 on papers fenitrothion. This somewhat “ delayed ” response of having a lower percentage of active ingredient. However, CU. hitaeniorllywzluw to fenitrothion was detected simul-

TABLE 6. - Showing susceptibility levels of female adults exposedto one concentration of insecticide (multiple-time exposure)

concentratiun Nc. Ll LT of inaec tlclde L‘Xn1ity rAIte exposeci .2? ,“25 u$ed

----P«nl t.mtt11on 1.6 b 1.ç x 1.6 % 1.6 % 1.6 “6 1.0 x 1.0 % 1.0 % 0.4 % 0‘4 56 0.1 % 0.1 7.

5.0 % 7.71 .12ç 72 5s 5.0 % H.72 300 40 70 5.0 % fi.72 2w 15 225 5.0 % 8.71 200 9 27 5.0 !h a,,1 200 17 31 5.0 z 8.72 96 1G 83 5.0 ?d 8.72 199 11 85 0.5 % Ï.71 350 4 55 6.90 0.5 y48 8.71 390 165 1320

.lG% 8.72 150 12 21 .lO% 7.71 2m 12 26 .lng, 8.71 2CXl 16 27 .Ol% 7.71 300 38 59 .OlS 8.72 256 245 174

CaJz. O.R.S.T.O.M., s&. Ent. méd. et Parasitol., vol. XII, no 2, 1974 : 51-92. 89 L.-S. SELF, J.-C. SHIM, P. JOLIVET taneously in two widely separated and diverse localities; Moreover, both methods give the same order of insecticide namely, Sasang (Pusan) at the southeastern tip of the toxicity. The apparent superiority of fenitrothion over Korea peninsula and Sintaein located 200 km to the fenthion is interesting and not typical. With An. sinensis, northwest in the rice belt. However, in August 1972, malathion is superior to fenthion and also fenitrothion; wild adult females of CII. fritae~zio~l~y~zchw confined in and it may be recalled that these latter two compounds cages or loose in the natural environnemt, were susceptible have very popular usage in Korea. to fenitrothion ULV applied at 438 ml/ha from a C-46 In the multiple-time exposure tests, the results for aircraft at Sasang (.WHO /VX /72.406). fenthion and propoxur are somewhat constant regardless of the concentration used. But considerable variation CT PRODUCTS. Table 7 shows the results for CI~. occurs with fenitrothion and to a lesser extent with tritaelzio~lzyizclzus. Using data from the multiple-concen- malathion. The highest CT products for fenitrothion tration exposure tests, the product of percentage LC,, and pertain to the August 1972 tests previously discussed. In minutes exposure indicate the following order of insecticide one test made with DDT at Sasang, CII. tritaeniorhymhs toxicity: propoxur, fenitrothion, fenthion, malathion, is six times more susceptible than a DDT-tolerant strain dieldrin or DDT. By multiple-time exposure, the pro- of Ccl. pipiem fatigans from Rangoon (ARIARATNAM and duct of LT,, in minutes and percentage concentration BROWN, 1969), although the larvae of both species have also shows that fenitrothion is more toxic than fenthion. an identical response to DDT (LC,,, .13 ppm). How-

TABLE 7. - Showing concentration-time products (CT) derived from adult tests with CU. bitaerzio~lz~~zc~z~s

No. ivcrage CT: % x min. Insecticide teStS (range)

ultiple-concentration exposure Fenitrothion 60 .68(.24 - 1.3) 40 (14 - 48) hlalathion 60 2.5 t.82 - 4.1) 150 (49 - 246) Fenthion 60 .95(.41 - 1.5) 57 (25 - 90) Pl-CpXUr 60 ,11(.081 - .14) 7 ( 5 - 8) Dieldrin 60 94.0 >24O 1)DT 60 34.0 >.?4o

Multiple-time exposure - ilo Inscc ticide No. Avorage LTGo: min. tests (range 1

1.4 Z fenitrothion 3 74 ( 35 - 130) 118 c 61 - 2lJR) 1.0 % fenitrothion 1 16 18 0.4 x lon,itrothion 1 94 38 0.1 % fenitrothion 2 672 (325 - 1020) 67 f 33 - ICYL) 5.0 ommalethion 3 46 ( 22 - 75) 230 (110 - 375) 0.5 5 mnlathion 2 310 (165 - 4533 155 ( 83 - 228)

2.5 5 fenthion 3 60(35- 103) 190 ( 80 - 270)

0.25% Penthion 2 570 t5.10 - 600) 142 (135 - 150) *

0.16% propoxur 1 12 1 . 9 0.10% propoxur 1 12 1.2 0.01% propoxur 2 142 ( 38 - 245) 1.4 f.4 - 2.5) 4% DDT 1 174 69G 4 5 dieldrln 1 1108 432 90 Cah. O.R.S.T.O.M., sér. Ent. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. SUSCEPTIBILITY OF CULEX TRITAENIORHYNCHUS TO INSECTICIDES ever, data are lacking from the Sintaein area, where CI~. trations below 1 ppm, in which only a part of the popula- tritae~liorhy~~chra larvae have survived DDT concentra- tion is killed. But the organophosphorus materials now tions of 2.5 ppm. being applied to the rice fields are not persistent. If By multiple-concentration exposure, the CT products larvae survive a fresh pesticide application, such as one for fenitrothion, fenthion and malathion are lower than from fenthion, that could suggest highly developed organo- those derived from the multiple-time exposure tests. phosphorus resistance warranting prompt clarification and Conversely, the values for propoxur are higher, whereas testing. no meaningful comparisons are possible with the limited It should be noted that the larval populations in DDT and dieldrin data. By multiple-time exposure, Korea are often exposed to a variety of organophosphorus dieldrin has been shown to be more toxic than DDT, materials even during one rice growing season. Because whereas no distinction was possible by multiple concentra- these seasons are short, the present pesticide application tion exposures of only 60 minutes. shedules are probably frequent enough in many rural areas to account for the low adult densities of CI~. tri- DISCUSSION taeniorhynchm. Detailed studies might show that this species takes a longer time to complete its immature We believe that organophosphorus-resistance is not development than An. sinemis. clearly indicated in any Culex or Aedes species. An. TO sum up, the response of Ca. tritaeniorhynchus sitiensis may be naturally tolerant to fenitrothion, and CI~. larvae to DDT in two tests, and to lindane in one test, tritaeniorhynchus seems comparatively resistant to DDT appear to be the only probable cases of resistance revealed and lindane at only one locality. in this study. These test procedures are not always expected to be sensitive enough to clearly distinguish tolerance from low ACKNOWLEDGEMENTS. levels of resistance. The few inconclusive test situations We thank Dr T. TADANO for the tests carried out during may be followed up with more detailed experimentation. August 1969and also Dr. R. J. TONNformer project leader of With larvae, only Ca. tritaeniorhynchus at Sintaein JEVRU. has LC,, values to DDT and lindane above .3 ppm. The Mr. K. W. LEE,Mr. H. K. Star, Mr. H. 1. REEand other JEVRU personnel kindly assisted in the collection of field other larval species have even lower LC,, values to a11 specimens. During their visits to JEVRU, Dr. J. MOUCHET, three chlorinated hydrocarbons. Undoubtedly, a greater Dr. Y. H. BANGand Dr. C. Y. CHOWoffered valuable sugges- reliance is now being placed on the organophosphorus tions. materials in Korea. The susceptibility of An. sinensis Manuscrit reçu au S.C.D. le 4 décembre 1973. adults to DDT is noteworthy because vivax malaria sfill .occurs in certain areas. With the carbamate propoxur, a11 the species tested show considerable adult susceptibility. RÉFÉRENCES. The product of concentration and time (CT), derived ARIARATNAM (V.), BROWN (A. W. A.), 1969. - Exposure from two adult test procedures, gives the same order of time versus concentration in the WHO standart test insecticide toxicity for Ca. fritaerziorlz~l~zchrrs. Propoxur, a for Mosquito resistance to chlorohydrocarbon insecti- fast acting compound with a low LT,, value, was found to cides. Bull. Wld. Hlth. Org., 40, 4: 561-567. be superior to fenitrothion as a residual adulticide (WHO / BROWN (A. W. A.), PAL (R.), 1973. - Résistance des VBC/72.397), whereas fenitrothion was superior to mala- Arthropodes aux insecticides. 2e éd., Genève OMS, thion as a ULV aerial spray (WHO /VBC /72.406). These 541 p. field studies are consistent with the CT data. For non- GAHAN (J.), NOE (J. R.), 1966. - Control of Mosquito residual exterior space sprays, differences in the CT pro- larvae in rice fields with water-soluble phosphorus ducts could provide clues as to the dosage required for insecticides. J. econ. Ent., 48: 665-667. control’once the effective field dosage of one compound HAMON (J.), SALES (S.), 1970. - Étude de la relation has been established. existant, chez les moustiques adultes entre la durée These susceptibility test procedures are expected to d’exposition à un insecticide et la mortalité résultante. continue. Apart from the results obtained, any usually. Bull. Wld. Hlth. Org., 43, 5: 757-762. high CU. tritae?liorllyllchlrs density in a rice growing locality PENNINGTON (N. E.), 1968. - Resistance of Cnlex tri- might be an unwelcome but useful sign for resistance. taeniorhynchw Giles and Culex quinqaefaciatus Say On the other hand, the high organophosphorus dosagesat to malathion on Okinawa with notes on susceptibility present being applied clearly exceed the larval LC,,, to other insecticides. Mosqzrito New, 28, 2: 193-198. values. These dosages could even be lethal to some THOMAS(V. j, 1970. - Fenthion resistance in Calex pipiens individuals that eventually show resistance to one or fatigans Wiedemann in Kuala Lumpur, West Malaysia. more of the organophosphorus compounds. Sontheast Asian J. trop. Med. pub. Hlfh., 1, 1: 93-98. Some opportunity for the selection of resistance World Health Organisation, 1970. - Wld. Hlth. Org. might occur in previously treated water containing concen- techn. Rep. Ser., no 443.

Cah. O.R.S.T.O.M., sér. Ent. méd. et Parasitol., vol. XII, no 2, 1974 : 81-92. 91 **