Journal of the American Mosquito Control Association,9(3\:285-293, 1993Copyright @ 1993 by the American Mosquito Control Association, Inc.

LABORATORY EVALUATION OF THE IRRITANCY OFBENDIOCARB. LAMBDA-CYHALOTHRIN AND DDT TO

ANOPHELES GAMBIAE

R. G. EVANS

CAMCO, Chesterford Park, Safron Walden, Essex, CB10 [XL, United Kingdom

ABSTRACT. In a laboratory study, the irritancy of bendiocarb, lambda-cyhalothrin and DDT toAnopheles gambiaewas evahrated at field, Yr field and No field rates using WHO conical exposure chambersand excito-repellency t€st boxes. Bendiocarb was the least irritant insecticide at all rates, inducing levelsof takeofr flight and exiting behavior similar to those of a distilled water control treatment. Of thosemosquitoes introduced to the bendiocarb-treated boxes, not more than l% exited and survived at anydose rate. Lambda-cyhalothrin and DDT were highly irrit^ntto An. gambiae, indrcrnga strong stimulationto take offand fly and also a high level ofexiting. Exiting-survival rates associated with lambda-cyhalothrinand DDT were between I 5 and 5 l0l0. The relevance of these findings to the control of mosquito populationsand the prevention of malaria transmission is discussed.

INTRODUCTION

Irritancy of insecticides to adults of mosquitovector species has long been recognized (Metcalfetal. 1945, Kennedy 1947). Insecticide irritancyis important because it is a factor governing thenumber and duration of contacts between themosquito and the insecticide deposit, and henceis a critical determinant of the probability ofmosquitoes acquiring lethal doses (Trapid o 19 52).Most data so far have been generated for irri-tancy to DDT, often to the neglect of studies onother insecticides. No method of studying irri-tancy is yet widely accepted, thus preventing thegeneration of strictly comparable data (Robertset al. 1984).

In 1970, the World Health Organization(WHO) proposed their latest methodology forassessing insecticide irritancy to mosquitoes inan attempt to standardize techniques. This con-sists of observations of mosquitoes placed insidetransparent conical exposure chambers held overimpregnated papers. With modifications, thismethod has been used to show a high irritancyof DDT to several lnopheles spp. (Bondareva etal. 1986, Quinones and Suarez 1989), a high ir-ritancy of permethrin to 2 anophelines and oneculicine (Ree and Loong 1989) and a high irri-tancy of cyfluthrin, deltamethrin and lambda-cyhalothrin to Anopheles gambiae Giles (Pell etal. 1989). More realistic and less time-consumingdata on the behavioral effects ofinsecticides onmosquitoes may be obtained from the use of theexcito-repellency (ER) test box (Rachou et al.1973). In this apparatus, mosquitoes are able toescape completely from perceived unfavorableconditions by movement from a treated box intoan untreated location, usually a smaller exit box.Marked escape responses ofanophelines to DDThave been reported using this technique (Charl-wood and Paraluppi 1 978, Rozendaal et al. 1 989).

This study reports a laboratory investigationof the irritancy of 3 insecticides currently spec-ified by the WHO for mosquito control: bendio-carb (a carbamate), lambda-cyhalothrin (a py-rethroid) and DDT. Irritancy was assessed usingboth conical exposure chambers and ER test box-es.

MATERIALS AND METHODS

Mosquitoes: The mosquitoes used in the studywere 4-5-day-old, freshly bloodfed, An. gambiaesensu stricto (G, strain). This strain was colo-nized from The Gambia and had been held inlaboratory culture, with no insecticidal pressure,s ince 1975.

WHO conical exposure chambers: Sheets ofglass (10 crn2 x 2 mm thick) were covered withglass microfiber paper (Whatman GF/A) andtreated with bendiocarb, lambda-cyhalothrin orDDT. A distilled water control treatment wasalso included. The insecticide formulations anqdoses applied are shown in Table l. Glass mi-crofiber paper was chosen because ofits lack ofinteraction with insecticides (Barlow and Had-away 1968). The treatment procedure involveduse of an automated spraying device fitted witha Tee-jet 8004-E nozzle, which moved at a speedof I m sec-r and a height of 29.5 cm above thetargets. This produced an application rate of40ml m-2.

Approximately 18 h later, mosquitoes wereplaced individually in adaptation tubes (trans-parent plastic cylinders 2 cm diam x 7.5 cmheight), and a stopper fitted to each tube. Thebase of each tube contained a 2-cm-wide disc ofglass microfiber paper that had been soaked indistilled water 24 h earlier. Tubes were placedin an aluminium rack and held horizontally. Thebases of all tubes were illuminated by a uniform

285

286 JounN,c,L or rHs ANrEnrceN Mosquno CoNtnol AssocnrroN Vol. 9, No. 3

Table l. Insecticide formulations and dosesevaluated.

and 3) total time in flight. If a mosquito landedon the paper prior to the 7-min observation pe-riod, but did not take offfrom the paper duringthe course ofthis period, a score of 42O sec wasgiven for time to first take ofl, Similarly, if amosquito landed on the paper during the obser-vation period and had not taken offby the endof this period, a score equal to the length of timespent on the paper was given. Mosquitoes main-taining contact with either the exposure chamberor the cotton wool plug for a period > 30 sec wereinduced to move by gentle tapping of the ap-paratus. Any immediate flight induced was notrecorded in (3). Each treatment was replicated20 times and the order in which treatments wereobserved was randomized to control for effectsof circadian rhythm on mosquito behavior, ex-perimenter fatigue, etc. All observations tookplace between 0830 and 1900 h at 23-25t and55-650/o RH.

ER test boxes: Light-proof test boxes, eachconsisting of 6 plates of aluminium (30 cmr) thatcould easily be assembled and dismantled, wereconstructed (Fie. l). Adjacent plates could beattached by means of 2 screws positioned throughflanges running along the edges of the plates. Oneplate ofeach box had a circular exit hole (10 cmdiam) cut into it. The plates, on the sides withoutthe flanges, were covered by wrapping glass mi-crofiber paper around each plate and by tapingit down on the other side. The plates containingthe exit holes were covered although the holeswere not. The plates were treated as shown inTable l, using the same procedure as outlinedpreviously. Prior to their assembly into boxes,the plates were dried for 4 h. Each treatment wasreplicated 3 times.

After assembly, a truncated paper cone (height10 cm) with a 2-cm-diam hole at the apex wasfitted exactly over the hole in each box and at-tached with tape. The inner surface ofeach conehad previously been coated with 'Fluon' (poly-tetrafluoroethylene) to provide a surface unat-tractive for mosquito settling. All boxes were or-ientated such that the exit holes and cones wereon the front vertical faces. A glass cylinder (4.5cm diam x 12.5 cm length) was then tightly fittedover the apex of each cone. Nylon netting wasused to seal the cylinders at the ends farthestfrom the cones. The cylinders were held in placeby means of clamps attached to retort stands.

Approximately 18 h later, 40-50 mosquitoeswere introduced into each test box, Mosquitoesthat found conditions in the test boxes unfavor-able were able to escape by exiting into the Conesand then passing into the glass cylinders. Onceinside the cylinders, mosquitoes could be seenand removed using an aspirator pushed througha hole in the netting. Between collections, these

C-oncentration ofactive

ingedient (Al) informulationt

(o/o w/w)Dose

(mg Al m-'�)Insecticide

Bendiocarb

Lambda-cyhalothrin

DDT

400.0"133.3b40.0"30.0"10.0b3.0.

2,000.0"666.7b200.0.

I All formulations were water-dispersible powders. All spraysolutions were made up in distilled water. ": srandard fieldrate, b: Vr field rate, " = 7o field rate. Doses less than thestandard field rates were evaluated to estimate the iritancy ofaged deposits, originally treated at field rate.

light source (40-W clear light bulb) resulting ina light intensity of 86 lx inside each tube. Theadaptation period lasted 30-40 min for eachmosquito and served to mimic the main exper-imental conditions under which observationswere made (i.e., a contact surface ofglass micro-fiber paper and a transmitted light intensity of86 lx).

Adaptation tubes were individually taken fromthe rack as required. With minimal disturbance,the stopper was removed while holding the endof the tube over the exit hole of a WHO conicalexposure chamber held in a ceramic box. Withgentle tapping of the tube, the mosquito was in-duced to fly into the chamber and the exit holethen sealed with a cotton wool plug. The boxcontained 3 grooves into which fitted a sheet oftranslucent glass (10 cm2 x 2 mm thick), a sheetof glass covered with treated glass microfiber pa-per and the exposure chamber. The exposurechamber frt tightly onto the paper surface. Bymeans of a circular hole (9 cm diam) in the backofthe box, transmitted light entered the exposurechamber via the translucent tile. The box waspositioned at a distance (ca. 25 cm) from the lightsource sufficient to produce a light intensity inthe chambers equal to that in the adaptation tubes.

After an adaptation period of I min, the be-havior of each mosquito was monitored for 7min following placement in the exposure cham-ber. During observations, the following param-eters were recorded: I ) length of time to first takeofffrom the paper (once having landed for thefirst time on the paper during the observationperiod), 2) number of takeoffs from the paper,

80

l 0

75

JounN,c,L or rnr AugtrcAN Moseurro Col"rnol AssocrlrroN Vor. 9, No. 3

^ 5 m

fr.

o. ' - 4m

- )

F 300v)&f&

9 r *F

q

F l m

z

V)I & 6

1 4 5va' 4

d 1tdgl

zZ rI t l

F loo

r l

t r oz3 ' oFJ< 4 0F

F.2 2 0

t20

ffiHconrRor-ITITM LANTBDA-CYHALoTHRIN

ffi seNproceRBffiffi oor

Fig.2. Observations of the behavior of mosquitoes placed in WHO conical exposure chambers. Bars sharingthe same letter at each dose rate in each histogram are not significantly different (P > 0.05).

SEsrnrvrsEn 1993 INsEcrrcrDE lrnruNcv ro ANoPHELES oAMBIAE 289

greater numbers of takeoffs (P < 0.05) and longertotal flight durations (P < 0.05). Irritancy wasleast pronounced at t/ro field rate with only timeto first takeoff and total flight duration signifi-cantly different from the control (P < 0.001).Lambda-cyhalothrin was more irritant than ben-diocarb at all rates evaluated. The greatest dif-ference occurred at Y: fleld rate, where for allbehavioral measures, lambda-cyhalothrin hadsignificantly greater irritancy (P < 0.001). At fieldand r/rs field rate, lambda-cyhalothrin was sig-nificantly more irritant than bendiocarb for onemeasure of behavior only (P < 0.05).

For all measures of behavior, DDT was sig-nificantly more irritant than the control and ben-diocarb at all 3 dose rates (P < 0.05). In com-parison with lambda-cyhalothrin, DDT resultedin significantly more takeoffs and a longer totalflight duration at field rate, and significantly moretakeoffs at 'lo field rate (P < 0.05). Lambda-cyhalothrin resulted in a significantly longer totalflight duration than DDT at Vr field rate (P <0.05) .

ER test boxes: Exiting data exhibited a veryclear response to treatment (Fig. 3). Mosquitoesplaced into the control boxes consistently showeda very low level of exiting with <8% leaving theboxes during the 2-h observation period. Thelevel of exiting induced by bendiocarb was sim-ilarly very low (< l2o/o) at all 3 dose rates' Lamb-da-cyhalothrin and DDT induced far greater lev-els ofexiting, with both insecticides causing > 50o/oexit rates at all dose rates. Mosquitoes generallyexited the boxes during the first 15 min of theobservation period, but, particularly at t/to fieldrate, exiting was spread more evenly with severalmosquitoes exiting after 30 min.

The proportion of mosquitoes that had exitedthe boxes at the end of the observation periodwas calculated for each treatment and a one-wayanalysis of variance performed (Table 2). Priorto analysis, data were arcsine transformed to sta-bilize the error variability and validate the as-sumption of normality. At no dose rate was thelevel of exiting associated with bendiocarb sig-nificantly different from the control treatment (P> 0.05). Both lambda-cyhalothrin and DDTcaused significantly greater exiting than either thecontrol or bendiocarb at all dose rates (P < 0.0 I ).DDT consistently resulted in greater exiting thanlambda-cyhalothrin, although significantlygreater exiting occurred only at field rate (P <0 .01 ) .

The proportion of mosquitoes that had exitedthe boxes after 2 h and were alive in 24-h mor-tality counts (i.e., exiting-survivors) was calcu-lated for each treatment, and after arcsine trans-formation, one-way analysis of variance wasperformed (Table 3). Treatment effects were

closely correlated with those apparent for theproportion exiting data. Bendiocarb did not causesignificantly greater numbers of mosquitoes toexit and survive than the control at any dose rate.The number of exiting-survivors associated withlambda-cyhalothrin and DDT was significantlyg,reater than for either the control or bendiocarbat all dose rates (P < 0.01). In comparison withlambda-cyhalothrin, DDT resulted in signifi-cantly gleater exiting-survival at field rate (P <0.01), with no sigrrificant diference between the2 al lhe lower rates (P > 0.05).

Knockdown speed data as assessed using theexposure chambers showed bendiocarb to havethe most rapid action, followed by lambda-cy-halothrin and then DDT. In no insecticide treat-ment at any dose rate did the time for l00o/o ofthe mosquitoes to be knocked down exceed 90min. These data confirmed the validity of adopt-ing a 2-}a cut-offpoint with the ER boxes.

DISCUSSION

Anopheles gambiae exposed to the water-treat-ed control paper showed a strong adaptation toconditions in both the exposure chambers andER boxes, although considerable variations inbehavioral response occurred over the course ofthe 3 insecticide dose rate evaluations. Thesewere probably due to different generations ofmosquitoes being used in each case. Mosquitoesshowed a clear behavioral response to each ofthe insecticides evaluated. Exposure to bendio-carb resulted in a low stimulation to take offandfly and low exiting behavior, with less than 2o/oof the mosquitoes introduced into the ER boxesexiting and surviving. I-ambda-cyhalothrin andDDT had far higher irritancy inducing a strongerstimulation to take off and fly and also a higherlevel of exiting behavior. Of those mosquitoesexiting the lambda-cyhalothrin- and DDT-treat-ed boxes, a high proportion had not picked up alethal dose and were alive 24 h later. Levels ofexiting-survival associated with lambda-cyhal-othrin and DDT were consistently at least l5ol0,and reached as high as 51olo for lambda-cyhal-othrin at tlo field rate. Of these 2 insecticides,the irritancy associated with DDT was slightlythe greater.

These findings are in agreement with the wide-ly reported low irritancy ofbendiocarb and highirritancy of DDT to mosquitoes. Irritancy oflambda-cyhalothrin has not yet been widely re-searched, although Pell et al. (1989) did report alaboratory evaluation ofthe irritancy ofthis in-sccticide to An. gambiae using conical exposurechambers. Lambda-cyhalothrin could not be dis-tinguished from DDT in terms of time to ftrstflight, althoueh for both flight frequency and the

290 JourNer or rHn ArvrsnrceN Moseurro CoNrnor AssocIATIoN Vol. 9, No. 3

FIELD RATE

FIELD RATE

ONE-TENTH FIELD RATE

ITITBOACYHALOTHRIN DDTlflTmII| ffi

Fig. 3. Numbers of mosquitoes exiting the excito-repellency test boxes over the 2-h exiting period. A. Fieldratei B. One-third field rate; C. One-tenth field rate.

100

80

sllJo-

OU'uJuJ

l-Jf=fo

0

100

CONTROL[ffi

BENOIOCARBFir#r

.^^oNE-THIRD

TIME nFrER INTRODUCTION TO BOX (MlN)

Serrensen 1993 lNsecrrcrop IulnlreNcv ro A*opxntns GAMBIAE

Table 2. Mean t SE arcsine-transformed proportion mosquitoes exiting ER boxes. Valuessharing the same letter at each dose rate are not significantly different (P > 0.01).

291

Treatment Field rateOne-thirdfield rate

One-tenthfield rate

Distilled watercontrol

Bendiocarb

Lambda-cyhalothrin

DDT

12.27 ! 4.15a

9.73 + 2.77a

45.16 + 7,45b

63.32 + 3.76c

2.34 ! 4.O6a

6.56 + 5.93a

56.35 + 4.07b

63.93 + 7.67b

16.48 + 5.12a

13.71 + l2.l6a

51.38 + 3.24b

64.tt + 12.78b

relative amount oftime spent on a treated surfaceor in flight, lambda-cyhalothrin induced a sig-nificantly different response from that of DDT'In comparison with deltamethrin and cyfluthrin,lambda-cyhalothrin was the least irritant pyre-throid for all aspects of behavior examined. Theirritancy ofbendiocarb was also assessed and wasfound to be low. Artem'ev et al. ( I 99 I ) comparedthe irritancy of lambda-cyhalothrin and bendio-carb and concluded that because neither insec-ticide led to any redistribution of mosquitoesbetween sprayed and unsprayed buildings, bothinsecticides were nonirritant. Artem'ev et al.(1991), however, did not monitor the numbersof mosquitoes exiting the sprayed buildings andhence their data do not strictly represent the ir-ritant effect of either insecticide, as mosquitoesmay have migrated to the external environment.

In the present study, the evaluation of doserates lower than the standard field rates was notcompletely realistic of the field situation. As de-posits age in the field, breakdown products mayresult that themselves have behavioral effects anda changing ratio ofactive ingredient to the inert

components of the insecticide formulation mayoccur. The marked peak ofirritant behavior seenatthrate for lambda-cyhalothrin suggests that inthe field, irritancy to this insecticide may notreach a maximum until considerably after ap-plication. Irritancy to lambda-cyhalothrin andDDT may also remain high for a considerabletime thereafter, as both induced marked irritantresponses at the t/rs field rate dose. Coosemansand Sales (1977) reported a constant irritant ef-fect of permethrin and deltamethrin as the in-secticide deposits became older. Ree and Loong(1989) observed An. maculatar Theobald to showa graded response of irritable behavior to in-creasing doses of permethrin, although this didnot occur with An. farauti Laveran or Culexquinquefascialus Say. Mosquito species may alsotherefore be a factor governing the importanceof irritancy of ageing insecticide deposits.

The escape behavior of mosquitoes exposedto an insecticide consists of independent com-ponents with generally increased activity notnecessarily leading to specific passage through anexit hole (Gerold and l-aarman 1967). Sole re-

Table 3. Mean + SE arcsine-transformed proportion exiting-survivors of ER boxes. Valuessharing the same letter at each dose rate are not significantly different (P > 0.01). (No. of

mosquitoes Placed into box.:s).

Treatment Field rateOne-thirdfield rate

One-tenthfield rate

Distilled watercontrol

Bendiocarb

Lambda-cyhalothrin

DDT

9.27 + 1.97a( l 36)

0 + 0 b( l 4 l )

22.64 + 3.65c( l 34)

35.04 + 5.26d(143)

0 + 0 a(r42>

0 t 0 a(140)

44.68 + 4.30b( l 38)

42.12 + 6.O6b(l 34)

5.42 + 4.69a( l 3e)

3.32 + 5.76a(135 )

45.82 + 8.03b(r44)37.88 + 7.53b( l 33)

292 Joumtlr or ure AunnrceN Mosqurro Corvrnol Assocrerrox Vor-.9, No. 3

liance on conducting observations of mosquitoesin conical exposure chambers should thereforebe avoided as this methodology does not givedata on the exiting process and may not providea realistic indication oflikely house-leaving be-havior in the field. In addition to excito-repel-lency test boxes, other methods for measuringthe exiting response of mosquitoes exposed toinsecticides have been proposed. Gerold (1970,1977) developed methodologies for measuringflight activity and escape reaction involvingmodifications to the standard WHO bioassay testkits and use of a twin-funnel apparatus. Geor-ghiou et al- (1972) reported an apparatus thatcould be used to assess simultaneously the be-havior of mosquitoes in both the presence andabsence of insecticide, a situation more analo-gous to that occurring in the field. In conductinglaboratory evaluations of insecticide irritancy,choice of methodology and bloodfeeding statusof the mosquitoes should be carefully considered.IJnfed mosquitoes may show more pronouncedirritant behavior (Qutubuddin 1967) and maytherefore require extra experimenters to recordthe data.

Although laboratory studies of irritancy tomosquitoes may provide useful data on the be-havioral effects ofinsecticides, data from the fieldare necessary to determine whether these effectsare important under operational conditions. Anumber of studies have assessed insecticide ir-ritancy in the field. Bown et al. (1987) observedAn. albimanus Wiedemann to have greater con-tact with the insecticide in bendiocarb-treatedhouses, resulting in higher mortality than oc-curred in deltamethrin-treated houses. Similarly,Mpofu et al. (1991) reported very few An. arabi-er?sri Patton to escape from bendiocarb-treatedhuts and concluded that the lethal effect ofben-diocarb was more pronounced than any irritanteffect. Insecticide irritancy may also be observedas a reduced entrance of treated houses. In thestudy of Bown et al. (1987), mosquitoes attempt-ed to enter houses treated with bendiocarb inhigher densities than those treated with delta-methrin. Reduced entrance of houses treated withDDT has been reported by Rozendaal et al. ( I 989)and Suwonkerd et al. (1990). Mosquitoes mayalso show significantly reduced entrance ofhous-es containing permethrin-impregnated nets(Darriet et al. 1984).

Insecticide irritancy has on occasion been im-plicated as a factor resulting in the failure tocontrol mosquito populations in the field. Theirritancy of both permethrin and deltamethrinwas seen as a primary factor leading to the escapeand survival of many An. gambiae and An. fu-nestus Glles from treated huts, and an unsatis-factory impact on population levels was recorded

(Rishikesh et al. 1978). Similarly, Bondareva etal. (1986) and Sharp et al. (1990) recommendedthe cessation of use of DDT due to its high ir-ritancy in Soviet Central Asia and South Africa,respectively. However, other researchers haveviewed insecticide irritancy as a favorable meansof providing protection against indoor man-vec-tor contact. Roberts and Alecrim (1991) believedthe strongly reduced entrance ofhouses by An.darlingi Root following spraying of DDT in Bra-zil would provide considerable protection frommalaria transmission.

There is as yet no widespread agreement aboutthe importance of insecticide irritancy for thecontrol of malaria, although there is a consensusthat insecticide nonirritancy is desirable for re-ducing mosquito numbers. The key to the pre-vention of malaria transmission. however. relieson reducing the level of man-vector contact,which may not be directly related to mosquitopopulation size. Until more field studies are per-formed that directly compare the impact of ir-ritant and nonirritant insecticides on malariatransmission, this subject is likely to remain openand controversial.

ACKNOWLEDGMENTS

My primary debts are to C. Boase and J. Goosefor advice during the planning and implemen-tation of the work and to D. Valenta, A. Sunleyand C. Bradford for assistance in the preparationof equipment and collection of data. I also thankB. Sawyer ofthe London School ofHygiene andTropical Medicine for providing the mosquitoes.Comments on the manuscript by R. lrmon weremuch appreciated. The lambda-cyhalothrin wasprovidedby ICI Agrochemicals Limited, UnitedIGngdom and the DDT by Rhdne-Poulenc Lim-ited, Indonesia.

REFERENCES CITED

Artem'ev, M. M., N. N. Sorokin, A. I. Aliev, A. N.Stepanova, E. V. Dem'yanova, R. A. Bakiev, A. A.Chabanenko and V. V. Labzir;'. 1991. Trials withthe insecticides Icon and Ficam against mosquitoesin the southern USSR. Medit. Parazitol. Parazit. Bo-lezni 1:13-16. [ In Russian.]

Barlow, F. and A. B. Hadaway. 1968. Interactionbetween insecticides and cellulose substrates. Soc.Chem. Ind. Monogr.293.

Bondareva, N. I., M. M. Artem'evandG. V. Gracheva.1986. Susceptibility to and irritability caused byinsecticides to malaria mosquitoes in the USSR. Partl, Anopheles pulcherrinus Theobald. Medit. Para-zitol. Parazit. Bolezni 6:52-55. [In Russian.]

Bown, D. N., E. C. Frederickson, G. del Angel CabanasandJ. F. Mendez. 1987. An evaluation ofbendio-carb and deltamethrin applications in the same Mex-

293SnmBLaseR 1993 INsEcrrcIDE IRRrrANcy ro ANornotgs GALTBTAE

ican village and their impact on populations ofAnopheles albimanus. PAHO Bull. 2l:l2l-135.

Charlwood, J. D. and N. D. Paraluppi. 1978. Ousode caixas excito-repelentes corn Anopheles darlingiRoot, l. nuneztovari Gabaldon e Culex pipiens quin-quefasciatus Say obtidos em areas perto de Manaus,Amazonas. Acta Amazonica 8:605-6 I 1.

Coosemans, M. H. and S. Sales. 1977. Stage IV eval-uation of five insecticides-OMS-43, OMS-1810,OMS-1821, OMS-1825 and OMS-1998 aga ins tanopheline mosquitoes at the Soumousso Experi-mental Station, Bobo Dioulasso, Upper Volta. WHO/vBC/77.663.

Darriet, F., V. Robert, N. ThoVien and P. Carnevale.1984. Evaluation of the efficacy of permethrin im-pregnated intact and perforated mosquito nets againstvectors of malaria. WHO/VBC/84.899.

Gerold, J.L. 1970. Selection and analysis of the dis-turbed behaviour after contact with DDT of Anoph-eles atroparvus. Acta kiden. 37:l-94.

Gerold, J. L. 1977. Behavioural differences in fieldpopulations of Anopheles sacharovi in Turkey andin selected strainsof Anopheles atropanus. Acta Lei-den. 45:67-77.

Gerold, J. L. and J. J. Laarman. 1967. Behaviouralresponses to contact with DDT in Anopheles atro'p4rvrs. Nature 21 5:5 I 8-520.

Gheorghiu, T., E. M. Ungureanu and C. Garrett-Jones.1972. An apparatus for the study ofthe behaviourpatterns ofmosquitoes under the influence ofinsec-ticides. Bull. W.H.O. 46:122-126.

Kennedy, J. S. 1947. The excitant and repellant ef-fects on mosquitoes of sublethal contacts with DDT-Bull. Entomol. Res. 37:593-607.

Metcalf. R. L.. A. D. Hess, C. E. Smith, G. M. Jeffreyand G. L. Ludwig. 1945. Observations on the useof DDT for the control of Anopheles qua'drimacu-latus. r?rrblic Health Rep. 6O:753-774.

Mpofu, S. M., K. H. Kanyimo and H. Masendu. 199 I .Potential use of bendiocarb (Ficam VC) for malariacontrol in an area of Zimbabwe. J. Am. Mosq. Con-trol Assoc. 7:536-542.

Pell, J. K., M. A. Spinney and K. J. Ward. 1989'Observations on the behaviour of adult Anophelesgambiae encountering residual deposits of lambda-cyhalothrin compared with the other major classesof commercially available insecticides, p. 18. Proc.4th Annu. Conf. Soc. Vector Ecol. Eur. Region.

Quinones, M. L. and M. F. Suarez. 1989. Irritabilityto DDT of natural populations of the primary ma-laria vectors in Colombia. J. Am. Mosq. ControlAssoc. 5:56-59.

Qutubuddin, M. 1967. Irritability of Anopheles pha-roensisTheobald to different insecticides as observedin laboratory experiments. Sudan Med. J. 5:18-28.

Rachou. R. G., L. A. Schinazi and M. M. Lima. 1973.An intensive study ofthe causes for failure ofresidualDDT spraying to interrupt the transmission of ma-laria in Atalaya and Fall, two villages on the coastalplain of El Salvador, Central America. Rev. Bras.Malariol. Doencas Trop. 25;5-293.

Ree, H. I. and K. P. Loong. 1989. Irritability ofAnopheles farauti, An. maculatus and Culex quin-quefasciatus to permethrin. Jpn. J. Sanit. Zool.4O:47-5r .

Rishikesh, N., J. L. Clarke, H. L. Mathis, J. S. Kingand J. Pearson. 1978. Evaluation ofdecamethrinand permethrin against Anopheles gambiae andAnophelesfunestas in a village trial in Nigeria. WHO/vBC/78.689.

Roberts, D. R. and W. D. Alecrim. 1991. Behavioralresponse of Anopheles darlingi to DDT-sprayed housewalls in Amazonia. PAHO Bull. 25:2lO-217.

Roberts. D. R., W. D. Alecrim, A. M. Tavares and K.M. McNeill. 1984. Influence of physiological con'dition on the behavioral response of Anopheles dar'lingi to DDT. Mosq. News 44:357-362.

Rowland, M. 1991. Behaviourand fitness of'v HCH/dieldrin resistant and susceptible female Anophelesgambiae and Att. stephensi mosquitoes in the ab-sence of insecticide. Med. Vet. Entomol. 5:193-206.

Rozendaal. J. A.. J. P. M. van Hoof, J. Voorham andB. F. J. Oostburg. 1989. Behavioral responses ofAnopheles darlingi in Suriname to DDT residues onhouse walls. J. Am. Mosq. Control Assoc. 5:339-350.

Sharp, B. L., D. le Sueur and P. Bekker. 1 990. Effectof DDT on survival and blood feeding success ofAnopheles arabiensis in Northern Kwazulu, Repub-lic of South Africa. J. Am. Mosq. Control Assoc.6:197-202.

Suwonkerd, W., B. Amg-Ung, K. Rimwangtrakul, S-Wongkattiyakul, B. Kattiyamongftool, V. Chitpra-rop and M. Takagi. 1990. A field study on theresponse oflz opheles dirus to DDT and fenitrothionsprayed to huts in Phetchabun province, Thailand.Trop. Med. (Nagasaki) 32:l-5.

Trapido, H. 1952. Modified response of Anophelesalbimanus to DDT residual house spraying in Pan-ama. Am. J. Trop. Med. HYg. l:853.

WHO. 1970. Instructions for determining the irri-tability of adult mosquitoes to insecticides. Techn.Rep. Ser. Annex 17:158-164.