ANNUAL PROGRESS REPORT

SE!~TO Medic Study 1'3'0. 50 Determination of Insecticide ToleranceLevel of Selected Mosquito Species inThailand

Project No. 3A 025601 A 811

.."-

Military l"Ieclical Research " PrograJitS.'E. Asia

Task 01: Military 1iedical Research ProgramS. E. Asia

l1u:itary' J:JIedical Rese;j.rch hogramSEAS III. (Tllailand)

Subtask 01:

Reporting Installation: US Army-SEATO Medicai Research LaboratoryAPO 146, Sa.l1 Francisco, California

Division of Medical Research laboratories

Department of Medical Entomology

1 April 1963 to 31 Mar~r 1964Period Covered by Report:

1/Lt. James }1. l~eely, MSCPrincipal Investigator:

Reports Control Symbol: lWDH-2BB

Security Classification: illJCLASS IFIED

318

ABSTRACT'.""-'

SEATO }iIedical Study No." 50'" '--Det;;e;ri1i::Liia:£ion of Ins8c;ti.ci'tl-e'-Tolerance

'- 'Level of;: Sele,cted l'4osquito Species in-~-'1'hiiilana~' _.~'-~-: ' .': -,\

l{tlitary Medical Research ProgramS. E. Asia

Project No. 3A 025601 A 811

Military Medical Research ProgramS. E. Asia

Task 01 :

Military lfudical Research ProgramSEASI!\. (Thailand)

Subtask 01:

US Army-SEATO ~Iedical Research LaboratoryAPO 146, San Francisco, California

Reporting Installation:

Division of l~dical Research Laboratories

Department of Medical Entomology

1 April 1963 to 31 ~mrch 1964Period Covered by Report:

1 /Lt. James }II. Neely, l'iSCPrincipal Investigator:

l'iEDDH-288Reports Control Symbol:

UNCLASSIFIEDSecurity Classification:

The objective of this study is the determination of the ofthe insecticide susceptibility status of some of the importantmosquitoes of Thailand. The increase in the number of insecticidesto which mosquitoes have become tolerant and/or resistant duringthe past few years, has emphasized the importance of determiningthe resistant. The insecticide tolerance levels of some importantspecies of mosquitoes in Thailand are being determined by means ofthe ~vorld Health Organization test kits; as recommended by the ArmedForces Pest Control Board. Initial emphasis has been placed on thestudy of the most important species in the Bangkok area, with aplanned later extension to other populations. Both larval and adultsare being tested. To date, tests of the tolerance of laboratory andwild strains of ~ pipiens QuinQuefasciatus and Aedes ae,gyptihave shown a high degree of tolerance to D.D.T. for same strains of

319

both species. Some \vild strains of ~ aegypti. collectedin the field, have shown very high resistance to D.D.T. BothAedes ~egypti and ~ Quinquefasciatl!s are susceptible todieldrin, and ?ayt~x, a coJIlInercial organic phosphate compound.Tests made with Anophele.s ba;1.abacensis. an important malariavector in Thailand, have shown it to be highly susceptible toD.p.T.

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320

BODY OF REPORT

SEATO 1-iedic Study No. 50 Determination of "Insecticide ToleranceLevel: of Selected l'IQsqui~o Species in.Thailand

Military l"ledical Research h'pgramS. E. Asia'

Project No. 3A 025601 A 811

Task 01: IvIilitary Medical Rese~ Programs~ E. Asia:

$ubtask 01: Military r-Iedical Re5e~rG~f;rogramSEASI~ (Thailand) ': :,

.;.

US. Army;;;;SEA'roMedica:l..R-e-search laboratoryArc 146, San Francisco,. California

----' "'.

.-, Reporting Installation:_.-;,-,-~.

---

Divi~ion of Medical Research laboratories

Q~;par~men~ ~t .Medic~l "El'lt~o,logy, '

.1~ Apr!l, 1963 to 31 r-fB.rch --1964,,' '

.1/Lt. James M. Nee;Ly, MSC

Period C,?vered by Report:; -.Principalfnvestigator:

Reports Control Symbol: };JEDPH7288

'liNCLASS!FIEDSecurity Classification: .-:.;

Ob.iect1ve: To determine. the' insecticide tolerance level of someof the more important mosqu,ito species in.. Thailand; ~ticularlyi;.hose of medical or p~st importance., '-To -condu-ct per:j,Odic surveil-

, .lance 0;1;1, the statu~~f these species. .';"

Description: Insecticide susceptibilJ;ty tests are perfQrmed, usingthe adult and larval mosquito test k~ts develop~d and qistributedby' the ..Wo~ld Health Qrga.ni~p.~ion. ..The m~thods' used are standardizedon a \:iorld':"wide basis arid theprecedures are also rec9mmeI1;ded bythe Arriied'FQrce~ Pest Control B6B;rd. The adult .test kit consistsof plastic tub~s containing paper impregna:ted wi. th graquated con-

I '.centrations of the 1nsecticide under test. Adult female mosqU1toesof similar physiological condition are placed in the tubes for one

321t

hour, then removed to plain plastic tubes for twenty-four hours.Mortality counts are made at that time, including counts froma control tube in which the mosquitoes are exposed to solventimpregnated paper, without insecticide. The larval test kitconsists of a graduated se~ies of conc,entrations of the testinsecticide, which are added to measure'dam6Unts of water con-taining the test larvae. Mortality counts are made after twenty-four hours. Replicate tests are performed to permit the calcu-lation of LC-50 values. In addition to the standard test insecti-cides supplies by \HiO, commercial iDsecticides available in Thailandare tested when possible.

Progress: Insecticide tssting was suspended in early 1963, due tothe assignment of the principal investigator to other duties inNorthern Thailand. Work was resumed in mid-December, but againsuspended until Janua,ry due to the principal investigator havingcontracted a serious case of falciparum malaria. Since resumptionof the testing program, the laboratory colonies of Aedes ae~iand ~ quinquefasciatus were again subjected to a complete seriesof tests. v.Jhen last tested, colony adults of Q. quinquefasciatushad yielded an LC-50 of 0.5.% for DDT, and A~~ aegypti yielded anLC-50 of 1.0%. During the year the colonies were moved to a newinsectary, and in the process all of the old stock was killed. New'specimens were obtained from the same areas of Bangkok as the oldcolonies, and retested. Tho new strain of ~ ~nquef.~~ciatusadUlts proved to be highly resistant to DDT, but the LC-50 fordieldrin was 1.2%. The larvae from the colony of Q. quinQuefasciatusshowed an LC-50 of 0.30 pJ:m. for DDT. The LC-50 for Q. q~inquefas-ciatus larvae from the c.olony when exposed to dieldrin was 0.02 pprn.

Because of its importance in the transmission of the virusof hemorrhagic fever, ~~ ~~ strains from several sourceswere tested during the period. Additional emphasis ~~s also placedon this species because of the developing interest on the ~rt ofThaj, authorities in controlling !. !~ii in Ba,ngkokw- :O£.f-icialsof the M1riistry of Health have reported finding several strains ofDDT tolerant !.. ~ef!YPti in',Ba~ok, a fact 1Iihich will considerablyinfluence the control program. The newly established laboratorycolony was tested agains~ DDT and dieldrin, and the adults andlarva,.e appeared to be normally susceptible to thes:e-:i~cticides'(Table 1) ~ It is planned to retest; the coiony at frequent intervals'to

Jprovide baseline data f'or evaluatmg changes in the wild populationsin the city as the control program progresses. One wild strain, fromthe S01 Plook Chit area of; Bangkok; was tested with DDT and dieldrinduring the period. As "shciwri iri~aqle 1 am figw."e 1, "-thj;s 'strain~ppeared to be markedlY resist~t to DDT, especially in the larval

--!'!

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TABLE 1

Insecticide Tolerance Levels of Selected MosquitoSpecies in Thailand

Insecticide

DDT 1.5%DDT 0.4% ppmDieldrin 0.6%Dieldrin 0.10 ppmDDT 3.5%DDT ResistantDieldrin 0.4%Dieldrin 0.40DDT ResistantDDT ResistantDieldrin 0.4%Dieldrin 0.40%DDT ResistantDDT 0.3 ppmDieldrin 1 .2%Dieldrin 0.02 ppmBaytex 6 Highly SusceptibleBaytex 6 Highly SusceptibleDDT 0.3%

Aedes aegypti (Lab strain) adultsAedes aegypti (Lab strain) larvaeAedes aegypti (Lab strain) adultsAedes aegypti (Lab strain) larvaeAedes aegypti (Soi Plook Chit) adults

* Aedes aegypti (Soi Plook Chit) larvae"" "adultsII II "larvae

Aedes aegypti (Pakchong) adultsII 'I II larvaeII II II adults" ,. II larvae

* Culex quinquefasciatus (Lab strain) adults"" "" larvaeII" "" adults"" II II larvae

1:~~ Aedes aegypti (Lab strain) adults1:~'(" Culex quinquefasciatus (Lab strain) adults

Anopheles balabacensis (Khao Mai Kaeo) adults

il-

{H',No mortality at any of the test concentrationsOnly preliminary test have been completed

323

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stage. Its response to dieldrin also differed from the laboratorycolony. This strain will be observed again as time permits. Thereis no history of an organized spraying campaign in the section ofBangkok where it was obtained. A strain of ~ aegypti was alsoobtained fram the city of Pakchong, approximately.150 Kilometers northof Bangkok. Unlike Bangkok, Pakchong is in a highly malarious zone,and has,be'en spI'f3.yed with"DDT and dieldrin for several y~a.r~, includingan application of DDT in 1963. It.has been observed in a number ofcountries with malaria control or eradication.campaigns that !. aegyptitendst'odisappear from sprayed areas. However, our virus collectionsin Pakchong (Study No. 42) showed, a large number of !. aegypti in thecity and surrounding villages. No satisfactory kill of !. aegyptifrom Pakc'hoiig could be obtained with DDT, even when the contf3.ct periodwas greatly extended, and it f3.ppears that the strain is extremelyresistant to DDT. However, an adult LC-50 of 0.4% with dieldrin indicatedthat the species was still susceptible to that insecticide in Pakchong.

Limited preliminary tests were made with papers impregnated withseveral concentrations of Baytex 6, an organic phosphate supplied bythe local representatives of the Bayer Co. Tests at all concentrationshave not been completed, but it appears to be highly effective against,8,. aef!YPti and Q. Qu.:!:!1quefasciatus adults fran the laboratory colonies.

Members of the malaria study group of the Laboratory conductedtests with WHO test kits against adults of Anopheles balabacensi$ atKhao l~i Kaeo. This species is a very important malaria vector inthat area. An 10,...;50 value of 0~3% .for DDT was obtained using wild-caught adults, indicating satisfactory susceptibility to the insecticideAn incomplete series with adult "Anopheles minimus in the same area in-dicated that this species was normally susceptible. These tests willbe resumed during the rainy season When additional mosquitoes becameavailable.

Summary: Insecticide susceptibility testing was resumed in early1964. Laboratory colonies of !. aegypti and Q. auinquefasciatu~ weretested to provide baseline data for DDT and dieldrin. The Q. a~inque-fasciatus colony exhibited signs of DDT resistance, while !. aegyptifrom the colony was susceptible to DDT. Both species were susceptibleto dieldrin, and to an organic phosphate. Several wild strains ofA. ae~ti appeared to be resistant to DDT.

Conclusions: The appearance of presumptive insecticide tolerance in!. aegypti may have a considerable effect on programs for control ofhemorrhagic fever. The situation warrants additional observationand study.

325