Laboratory Evaluation of the Irritancy of Bendiocarb

Home , Cyhalothrin

Journal of the American Mosquito Control Association,9(3\:285-293, 1993 Copyright @ 1993 by the American Mosquito Control Association, Inc. LABORATORY EVALUATION OF THE IRRITANCY OF BENDIOCARB. 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 to Anophelesgambiaewas evahratedat field, Yrfield and Nofield ratesusing WHO conical exposurechambers and excito-repellencyt€st boxes.Bendiocarb was the least irritant insecticideat all rates, inducing levels of takeofr flight and exiting behavior similar to those of a distilled water control treatment. Of those mosquitoes introduced to the bendiocarb-treated boxes, not more than l% exited and survived at any dose rate. Lambda-cyhalothrin and DDT were highly irrit^ntto An. gambiae, indrcrnga strong stimulation to take offand fly and alsoa high level ofexiting. Exiting-survival ratesassociated with lambda-cyhalothrin and DDT werebetween I 5 and 5 l0l0.The relevanceof thesefindings to the control of mosquito populations and the prevention of malaria transmission is discussed.

INTRODUCTION This study reports a laboratory investigation of the irritancy of 3 insecticidescurrently spec- adults of mosquito Irritancy of insecticidesto ified by the WHO for mosquito control: bendio- long recognized(Metcalf vector specieshas been carb (a carbamate), lambda-cyhalothrin (a py- Insecticideirritancy etal. 1945,Kennedy 1947). rethroid) and DDT. Irritancy was assessedusing it is a factor governing the is important because both conical exposurechambers and ER test box- number and duration of contacts between the es. mosquito and the insecticidedeposit, and hence is a critical determinant of the probability of mosquitoesacquiring lethal doses(Trapid o 1952). MATERIALS AND METHODS Most data so far have been generatedfor irritancy to DDT, often to the neglectof studies on Mosquitoes: The mosquitoesused in the study other insecticides.No method of studying irri- were 4-5-day-old, freshly bloodfed, An. gambiae tancy is yet widely accepted,thus preventing the sensu stricto (G, strain). This strain was colo- generation of strictly comparable data (Roberts nized from The Gambia and had been held in et al. 1984). laboratory culture, with no insecticidal pressure, In 1970, the World Health Organization since1975. (WHO) proposed their latest methodology for WHO conical exposurechambers: Sheetsof assessinginsecticide irritancy to mosquitoes in glass(10 crn2 x 2 mm thick) were covered with an attempt to standardizetechniques. This con- glass microfiber paper (Whatman GF/A) and sistsof observationsof mosquitoesplaced inside treated with bendiocarb, lambda-cyhalothrin or transparentconical exposurechambers held over DDT. A distilled water control treatment was impregnated papers. With modifications, this also included. The insecticide formulations anq method has been used to show a high irritancy dosesapplied are shown in Table l. Glass mi- of DDT to severallnopheles spp. (Bondarevaet crofiber paper was chosen becauseofits lack of al. 1986,Quinones and Suarez1989), a high ir- interaction with insecticides (Barlow and Had- ritancy of permethrin to 2 anophelinesand one away 1968). The treatment procedure involved culicine (Ree and Loong 1989) and a high irri- use of an automated spraying device fitted with tancy of cyfluthrin, deltamethrin and lambda- a Tee-jet 8004-E nozzle,which moved at a speed cyhalothrin to Anophelesgambiae Giles (Pell et of I m sec-r and a height of 29.5 cm above the al. 1989).More realisticand lesstime-consuming targets.This produced an application rate of40 data on the behavioral effectsofinsecticides on ml m-2. mosquitoes may be obtained from the use of the Approximately 18 h later, mosquitoes were excito-repellency (ER) test box (Rachou et al. placed individually in adaptation tubes (trans- 1973).In this apparatus,mosquitoes are able to parent plastic cylinders 2 cm diam x 7.5 cm escapecompletely from perceived unfavorable height), and a stopper fitted to each tube. The conditions by movement from a treatedbox into baseof each tube contained a 2-cm-wide disc of an untreated location, usually a smaller exit box. glass microfiber paper that had been soaked in Marked escaperesponses ofanophelines to DDT distilled water 24 h earlier. Tubes were placed have been reported using this technique (Charl- in an aluminium rack and held horizontally. The wood and Paraluppi 1978, Rozendaalet al. 1989). basesof all tubes were illuminated by a uniform 285 286 JounN,c,Lor rHs ANrEnrceNMosquno CoNtnol AssocnrroN Vol. 9, No. 3

Table l. Insecticide formulations and doses and 3) total time in flight. If a mosquito landed evaluated. on the paper prior to the 7-min observation period, but did not take offfrom the paper during C-oncentration of the course ofthis period, a score of 42Osec was active given for time to first take ofl, Similarly, if a ingedient (Al) in mosquito landed on the paper during the obser- formulationt Dose vation period and had not taken offby the end Insecticide (o/ow/w) (mg Al m-') of this period, a scoreequal to the length of time Bendiocarb 80 400.0" spent on the paper was given. Mosquitoes main- 133.3b taining contact with either the exposurechamber 40.0" or the cotton wool plug for a period > 30 secwere Lambda- l0 30.0" induced to move by gentle tapping of the apparatus. cyhalothrin 10.0b Any immediate flight induced was not 3.0. recorded in (3). Each treatment was replicated 20 times and the order in which treatments were DDT 75 2,000.0" observed was randomized to control for effects 666.7b of circadian rhythm on mosquito behavior, ex- 200.0. perimenter fatigue, etc. All observations took I All formulations were water-dispersible powders. All spray placebetween 0830 and 1900h at 23-25t and solutions were made up in distilled water. ": srandard field b: " = 55-650/oRH. rate, Vr field rate, 7o field rate. Doses less than the ER standard field rates were evaluated to estimate the iritancy of test boxes: Light-proof test boxes, each ageddeposits, originally treated at field rate. consistingof 6 platesof aluminium (30 cmr) that could easily be assembledand dismantled, were constructed (Fie. l). Adjacent plates could be light source (40-W clear light bulb) resulting in attached by means of 2 screwspositioned through a light intensity of 86 lx inside each tube. The flangesrunning along the edgesof the plates.One adaptation period lasted 30-40 min for each plate ofeach box had a circular exit hole (10 cm mosquito and served to mimic the main exper- diam) cut into it. The plates,on the sideswithout imental conditions under which observations the flanges,were covered by wrapping glassmi- were made (i.e., a contact surfaceofglass micro- crofiber paper around each plate and by taping fiber paper and a transmitted light intensity of it down on the other side. The plates containing 86 lx). the exit holes were covered although the holes Adaptation tubes were individually taken from were not. The plates were treated as shown in the rack as required. With minimal disturbance, Table l, using the same procedure as outlined the stopper was removed while holding the end previously. Prior to their assembly into boxes, of the tube over the exit hole of a WHO conical the plateswere dried for 4 h. Each treatment was exposure chamber held in a ceramic box. With replicated 3 times. gentle tapping of the tube, the mosquito was in- After assembly,a truncated paper cone (height duced to fly into the chamber and the exit hole 10 cm) with a 2-cm-diam hole at the apex was then sealed with a cotton wool plug. The box fitted exactly over the hole in each box and at- contained 3 grooves into which fitted a sheet of tached with tape. The inner surfaceofeach cone translucentglass (10 cm2 x 2 mm thick), a sheet had previously been coated with 'Fluon' (poly- of glasscovered with treated glassmicrofiber pa- tetrafluoroethylene) to provide a surface unat- per and the exposure chamber. The exposure tractive for mosquito settling. All boxeswere or- chamber frt tightly onto the paper surface. By ientated such that the exit holes and coneswere meansof a circular hole (9 cm diam) in the back on the front vertical faces.A glasscylinder (4.5 ofthe box, transmitted light enteredthe exposure cm diam x 12.5cm length)was then tightly fitted chamber via the translucent tile. The box was over the apex of each cone. Nylon netting was positioned at a distance(ca. 25 cm) from the light used to seal the cylinders at the ends farthest source sufficient to produce a light intensity in from the cones.The cylinders were held in place the chambers equal to that in the adaptation tubes. by means of clamps attached to retort stands. After an adaptation period of I min, the be- Approximately 18 h later, 40-50 mosquitoes havior of each mosquito was monitored for 7 were introduced into each test box, Mosquitoes min following placement in the exposurecham- that found conditions in the test boxes unfavor- ber. During observations,the following param- able were able to escapeby exiting into the Cones eterswere recorded: I ) length of time to first take and then passing into the glass cylinders. Once offfrom the paper (once having landed for the inside the cylinders, mosquitoes could be seen first time on the paper during the observation and removed using an aspirator pushed through period), 2) number of takeoffs from the paper, a hole in the netting. Between collections, these

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ffiHconrRor- ffi seNproceRB ITITMLANTBDA-CYHALoTHRIN ffiffi oor Fig.2. Observationsof the behavior of mosquitoesplaced in WHO conical exposurechambers. Bars sharing the same letter at each dose rate in each histogram are not significantly different (P > 0.05). SEsrnrvrsEn1993 INsEcrrcrDE lrnruNcv ro ANoPHELES oAMBIAE 289 greaternumbers of takeoffs(P < 0.05) and longer closely correlated with those apparent for the total flight durations (P < 0.05). Irritancy was proportion exiting data. Bendiocarbdid not cause least pronounced at t/rofield rate with only time significantly greater numbers of mosquitoes to to first takeoff and total flight duration signifi- exit and survive than the control at any dose rate. cantly different from the control (P < 0.001). The number of exiting-survivors associatedwith Lambda-cyhalothrin was more irritant than ben- lambda-cyhalothrin and DDT was significantly diocarb at all rates evaluated. The greatestdif- g,reaterthan for either the control or bendiocarb ference occurred at Y: fleld rate, where for all at all dose rates (P < 0.01). In comparison with behavioral measures, lambda-cyhalothrin had lambda-cyhalothrin, DDT resulted in signifi- significantlygreater irritancy (P < 0.001).At field cantly gleater exiting-survival at field rate (P < and r/rsfield rate, lambda-cyhalothrin was sig- 0.01), with no sigrrificantdiference between the nificantly more irritant than bendiocarb for one 2 al lhe lower rates (P > 0.05). measureof behavior only (P < 0.05). Knockdown speeddata as assessedusing the For all measuresof behavior, DDT was sig- exposurechambers showed bendiocarb to have nificantly more irritant than the control and ben- the most rapid action, followed by lambda-cy- diocarb at all 3 dose rates (P < 0.05). In com- halothrin and then DDT. In no insecticidetreat- parison with lambda-cyhalothrin, DDT resulted ment at any dose rate did the time for l00o/oof in significantly more takeoffs and a longer total the mosquitoes to be knocked down exceed 90 flight duration at field rate, and significantly more min. Thesedata confirmed the validity of adopt- takeoffs at 'lo field rate (P < 0.05). Lambda- ing a 2-}acut-offpoint with the ER boxes. cyhalothrin resultedin a significantly longertotal (P < flight duration than DDT at Vr field rate DISCUSSION 0.05). ER test boxes: Exiting data exhibited a very Anophelesgambiae exposedto the water-treat- clear responseto treatment (Fig. 3). Mosquitoes ed control paper showed a strong adaptation to placed into the control boxes consistently showed conditions in both the exposure chambers and a very low level of exiting with <8% leaving the ER boxes, although considerable variations in boxes during the 2-h observation period. The behavioral responseoccurred over the course of level of exiting induced by bendiocarb was sim- the 3 insecticide dose rate evaluations. These ilarly very low (< l2o/o)at all 3 doserates' Lamb- were probably due to different generations of da-cyhalothrin and DDT induced far greaterlev- mosquitoesbeing used in eachcase. Mosquitoes elsofexiting, with both insecticidescausing > 50o/o showed a clear behavioral responseto each of exit rates at all dose rates. Mosquitoes generally the insecticidesevaluated. Exposure to bendio- exited the boxes during the first 15 min of the carb resultedin a low stimulation to take offand observation period, but, particularly at t/tofield fly and low exiting behavior, with less than 2o/o rate, exiting was spreadmore evenly with several of the mosquitoes introduced into the ER boxes mosquitoes exiting after 30 min. exiting and surviving. I-ambda-cyhalothrin and The proportion of mosquitoesthat had exited DDT had far higher irritancy inducing a stronger the boxes at the end of the observation period stimulation to take off and fly and also a higher was calculatedfor eachtreatment and a one-way level of exiting behavior. Of those mosquitoes analysis of variance performed (Table 2). Prior exiting the lambda-cyhalothrin- and DDT-treat- to analysis,data were arcsinetransformed to sta- ed boxes,a high proportion had not picked up a bilize the error variability and validate the as- lethal dose and were alive 24 h later. Levels of sumption of normality. At no dose rate was the exiting-survival associatedwith lambda-cyhal- level of exiting associatedwith bendiocarb sig- othrin and DDT were consistently at least l5ol0, nificantly different from the control treatment (P and reached as high as 51olofor lambda-cyhal- > 0.05). Both lambda-cyhalothrin and DDT othrin at tlo field rate. Of these 2 insecticides, causedsignificantly greater exiting than either the the irritancy associatedwith DDT was slightly control or bendiocarbat all doserates (P < 0.0 I ). the greater. DDT consistentlyresulted in greaterexiting than Thesefindings are in agreementwith the wide- lambda-cyhalothrin, although significantly ly reported low irritancy ofbendiocarb and high greater exiting occurred only at field rate (P < irritancy of DDT to mosquitoes. Irritancy of 0.01). lambda-cyhalothrin has not yet been widely re- The proportion of mosquitoes that had exited searched,although Pell et al. (1989) did report a the boxes after 2 h and were alive in 24-h mor- laboratory evaluation ofthe irritancy ofthis in- tality counts (i.e., exiting-survivors) was calcu- sccticide to An. gambiae using conical exposure lated for each treatment, and after arcsinetrans- chambers.Lambda-cyhalothrin could not be dis- formation, one-way analysis of variance was tinguished from DDT in terms of time to ftrst performed (Table 3). Treatment effects were flight, althoueh for both flight frequency and the 290 JourNer or rHn ArvrsnrceNMoseurro CoNrnor AssocIATIoN Vol. 9, No. 3

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

One-third One-tenth Treatment Field rate field rate field rate Distilled water control 12.27! 4.15a 2.34 ! 4.O6a 16.48+ 5.12a Bendiocarb 9.73+ 2.77a 6.56+ 5.93a 13.71+ l2.l6a Lambda- cyhalothrin 45.16+ 7,45b 56.35+ 4.07b 51.38+ 3.24b DDT 63.32+ 3.76c 63.93+ 7.67b 64.tt + 12.78b relative amount oftime spenton a treatedsurface components of the insecticide formulation may or in flight, lambda-cyhalothrin induced a sig- occur. The marked peak ofirritant behavior seen nificantly different responsefrom that of DDT' atthrate for lambda-cyhalothrin suggeststhat in In comparison with deltamethrin and cyfluthrin, the field, irritancy to this insecticide may not lambda-cyhalothrin was the least irritant pyre- reach a maximum until considerably after ap- throid for all aspectsof behavior examined. The plication. Irritancy to lambda-cyhalothrin and irritancy ofbendiocarb was alsoassessed and was DDT may also remain high for a considerable found to be low. Artem'ev et al. ( I 99 I ) compared time thereafter, as both induced marked irritant t/rs the irritancy of lambda-cyhalothrin and bendio- responsesat the field rate dose. Coosemans carb and concluded that becauseneither insec- and Sales(1977) reported a constant irritant ef- ticide led to any redistribution of mosquitoes fect of permethrin and deltamethrin as the in- between sprayedand unsprayedbuildings, both secticidedeposits becameolder. Ree and Loong insecticides were nonirritant. Artem'ev et al. (1989)observed An. maculatar Theobald to show (1991),however, did not monitor the numbers a graded response of irritable behavior to in- of mosquitoesexiting the sprayedbuildings and creasingdoses of permethrin, although this did hence their data do not strictly representthe ir- not occur with An. farauti Laveran or Culex ritant effect of either insecticide, as mosquitoes quinquefascialusSay. Mosquito speciesmay also may have migrated to the external environment. therefore be a factor governing the importance In the present study, the evaluation of dose of irritancy of ageinginsecticide deposits. rates lower than the standard field rates was not The escapebehavior of mosquitoes exposed completely realistic of the field situation. As de- to an insecticide consists of independent com- posits age in the field, breakdown products may ponents with generally increased activity not result that themselves have behavioral effectsand necessarilyleading to specificpassage through an a changingratio ofactive ingredient to the inert exit hole (Gerold and l-aarman 1967). Sole re-

Table 3. Mean + SE arcsine-transformedproportion exiting-survivors of ER boxes. Values sharing the same letter at each dose rate are not significantly different (P > 0.01). (No. of mosquitoes Placedinto box.:s).

One-third One-tenth Treatment Field rate field rate field rate Distilled water 9.27+ 1.97a 0 +0a 5.42 + 4.69a control (l 36) (r42> (l 3e) Bendiocarb 0 +0b 0 t0a 3.32+ 5.76a (l4l) (140) (135) Lambda- 22.64+ 3.65c 44.68 + 4.30b 45.82+ 8.03b cyhalothrin (l 34) (l 38) (r44) DDT 35.04 + 5.26d 42.12+ 6.O6b 37.88+ 7.53b (143) (l 34) (l 33) 292 Joumtlr or ure AunnrceN Mosqurro Corvrnol Assocrerrox Vor-.9, No. 3 liance on conducting observations of mosquitoes (Rishikesh et al. 1978). Similarly, Bondareva et in conical exposure chambers should therefore al. (1986) and Sharp et al. (1990) recommended be avoided as this methodology does not give the cessation of use of DDT due to its high ir- data on the exiting process and may not provide ritancy in Soviet Central Asia and South Africa, a realistic indication oflikely house-leaving be- respectively. However, other researchers have havior in the field. In addition to excito-repel- viewed insecticide irritancy as a favorable means lency test boxes, other methods for measuring of providing protection against indoor man-vec- the exiting response of mosquitoes exposed to tor contact. Roberts and Alecrim (1991) believed insecticides have been proposed. Gerold (1970, the strongly reduced entrance ofhouses by An. 1977) developed methodologies for measuring darlingi Root following spraying of DDT in Bra- flight activity and escape reaction involving zil would provide considerable protection from modifications to the standard WHO bioassay test malaria transmission. kits and use of a twin-funnel apparatus. Geor- There is as yet no widespread agreement about ghiou et al- (1972) reported an apparatus that the importance of insecticide irritancy for the could be used to assess simultaneously the be- control of malaria, although there is a consensus havior of mosquitoes in both the presence and that insecticide nonirritancy is desirable for re- absence of insecticide, a situation more analo- ducing mosquito numbers. The key to the pre- gous to that occurring in the field. In conducting vention of malaria transmission. however. relies laboratory evaluations of insecticide irritancy, on reducing the level of man-vector contact, choice of methodology and bloodfeeding status which may not be directly related to mosquito of the mosquitoes should be carefully considered. population size. Until more field studies are per- IJnfed mosquitoes may show more pronounced formed that directly compare the impact of ir- irritant behavior (Qutubuddin 1967) and may ritant and nonirritant insecticides on malaria therefore require extra experimenters to record transmission, this subject is likely to remain open the data. and controversial. Although laboratory studies of irritancy to mosquitoes may provide useful data on the be- ACKNOWLEDGMENTS havioral effects ofinsecticides, data from the field are necessary to determine whether these effects My primary debts are to C. Boase and J. Goose are important under operational conditions. A for advice during the planning and implemen- number of studies have assessed insecticide ir- tation of the work and to D. Valenta, A. Sunley ritancy in the field. Bown et al. (1987) observed and C. Bradford for assistance in the preparation An. albimanus Wiedemann to have greater con- of equipment and collection of data. I also thank tact with the insecticide in bendiocarb-treated B. Sawyer ofthe London School ofHygiene and houses, resulting in higher mortality than oc- Tropical Medicine for providing the mosquitoes. curred in deltamethrin-treated houses. Similarly, Comments on the manuscript by R. lrmon were Mpofu et al. (1991) reported very few An. arabi- much appreciated. The lambda-cyhalothrin was er?sri Patton to escape from bendiocarb-treated providedby ICI Agrochemicals Limited, United huts and concluded that the lethal effect ofben- IGngdom and the DDT by Rhdne-Poulenc Lim- diocarb was more pronounced than any irritant ited, Indonesia. effect. Insecticide irritancy may also be observed as a reduced entrance of treated houses. In the study of Bown et al. (1987), mosquitoes attempt- REFERENCES CITED ed to enter houses treated with bendiocarb in Artem'ev, M. M., N. N. Sorokin, A. I. Aliev, A. N. higher densities than those treated with delta- Stepanova,E. V. Dem'yanova, R. A. Bakiev, A. 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