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Butt Pan Am Health Orpn 15(4), 1981. FIELD TRIAL OF PERMETHRIN FOR THE CONTROL OF TRIA TOMA INFESTANSI R. Pinchin’, A. M. de Oliveira Filho”, and B. Gilbert* Field trials for control of the Chagas’ disease vector Triatoma infestans were conducted with the insecticide permethrin. The results indicate that permethrin gives more effective and longer-lasting control than the benzene hexachloride customarily usedfor this flnrpose. Introduction ticide to have at least a few months of residual activity-and longer residual activity if pro- Control of Chagas’ disease vectors in Cen- longed protection against reinfestation is re- tral and South America has relied principally quired. on repeated spraying of infested houses with The remarkably persistent synthetic pyre- benzene hexachloride (BHC) or dieldrin. throids (S), which are very toxic to insects but Nevertheless, the continued use of these chlo- may be considered safe for users and domestic rinated hydrocarbon insecticides is currently animals, appear ideal candidates to employ in under review. In Venezuela, strains of Rhod- this particular pest control situation. This arti- nius prolixus resistant to dieldrin and cross- cle describes the results of a preliminary field resistant to BHC have already emerged (1, Z), trial of one of these pyrethroids, permethrin and several organophosphorus and carbamate (NRDC 143,5 OMS 1821), for the control of insecticides are being evaluated as alternative Triatoma infestam, the primary vector species control agents (3, 4). In Argentina, ultra-low- in Brazil. volume application of malathion (5) has replaced BHC in a substantial part of the na- Materials and Methods tional campaign to control Chagas’ disease. It thus seems inevitable that BHC will eventual- The trial was conducted in a periurban ly be replaced as the preferred insecticide for district of Barreiras in Bahia State (12O 9’ S, triatomine control in Brazil as well. 44’ 51’ W) that had a history of heavy T. in- Prolonged residua1 activity is considered an festuns infestation (7). House walls in the area important feature of a triatomine control were made either of mud packed onto a wood agent. For one thing, the bugs can remain latticework (48 per cent), adobe or other brick hidden in deep wall-crevices many days before (23 per cent), or plaster (29 per cent). Tile emerging to feed. Also, egg-laying sites are roofing predominated, but 21 per cent of the often virtually invulnerable to direct insecti- houses involved did have palm-thatch roofs. cide spraying, and eggs can normally take up The insecticides used were permethrin to 20 days to hatch. Thus, to achieve effective (cis:truns, 1:3; 25 per cent wettable powder) population control it is desirable for the insec- obtained from the Wellcome Foundation, Ltd., and BHC wettable powder containing lWil1 also appear in the Boletin de la Oficino Sanitaria 30 per cent of the gamma isomer (supplied by Panamericana92(3), 1982. the Superintendency of Public Health Cam- khemist, Natural Products Research Group, Health paigns-SUCAM-of the Brazilian Ministry Sciences Center, Federal University of Rio de Janeiro, Rio de Ianeiro. Brazil. of Health). The insecticides were applied in a SBiol&ist, Natural Products Research Group. 4Principal Scientific Officer, Brazilian Navy Research ‘National Research Development Council, Great Bri- Institute, Rio de Janeiro, Brazil. tain. 370 Pinchin et al. l CONTROL OF T. ZNFESTANS WITH PERMETHRIN 371 water suspension at a rate of approximately 50 nal wall of length 1 and one of length w). The ml per square meter of sprayed surface. The values obtained for a ranged from 46 m2 to applications were made with Hudson X-pert 224 m2, the average being 123 m2. constant pressure pumps or Jacto PJH The charges of insecticide used to fill the manual pumps fitted with Teejet 8002 or ICI sprayers consisted of predetermined dosages polyjet nozzles. prepared for individual houses. Insecticide Synergized pyrethrins were used as flush- was then applied evenly to all internal wall ing-out agents to measure pre-treatment and surfaces and the underside of the roof. Any post-treatment infestations. The two formula- existing outbuildings or accumulations of tions used for this purpose were a 0.08 per material-such as chicken-houses or piles of cent solution of pyrethrins in kerosene (Aler- firewood-were also sprayed. Spraymen were ta, Raimundo da Fonte, S.A.) and a mixture instructed to apply all the insecticide allotted of tetramethrin and phenothrin (four parts for each house before moving on to the next. tetramethrin to one part phenothrin) such that Upon completion of spraying, the spray- the total concentration of pyrethroids (in kero- man gave each homeowner a plastic bag and sene) was 0.125 per cent (Neopynamin/Sumi- instructions to collect all the dead bugs that thrin, Sumitomo Chemical Co., Ltd.). appeared. These were received by an observer The houses in the study area, which had two days later. previously been numbered and mapped, were Whenever possible, an observer entered the divided as randomly as possible into different permethrin-treated homes within 10 minutes groups. Because the trial was designed to test after spraying was completed to count and the long-term effects of a single insecticide ap- record the number of bugs that had been plication, these groups were made as large as flushed out of their hiding places by the insec- possible. Nevertheless, a considerable portion ticide. Then, between one and three hours of these generally rustic and ramshackle dwell- later, the number of bugs “knocked down” in ings were eventually eliminated from the trial each house was counted and recorded. because they had been demolished, aban- Sometime during the month before treat- doned, or extensively rebuilt. ment, and later at 2, 7, 30, 90, 200, 300, and In general, only houses that had been found 520 days after treatment, each house was infested during pre-treatment examinations searched for 10 minutes by two experienced were included in the trial. However, many investigators equipped with flashlights and other houses, especially ones showing signs of forceps. Pyrethrum or tetramethrin-based triatomine infestation (feces or exuviae), were sprays were used to flush bugs out of deep also sprayed; and several such houses were in- cracks. The live bugs captured were separated cluded in the trial when the infestation was into their instars, counted, and recorded; and confirmed by collection of dead bugs two days the house was classified as infested or after treatment. A few infested houses were uninfested. left untreated because entry was denied, an The findings obtained after two days were occupant was in poor health and could not be modified in accord with the seven-day find- removed, or a newborn child was present. ings. That is, if a live nymph was found on The actual spraying was performed on day seven in a house previously classified as lo-13 September 1977. Before treatment, the “uninfested,” then that house was reclassified perimeter of each house was measured and the as having been infested on day two. Similarly, approximate internal wall and roof surface the presence of third, fourth, or fifth instars on area (a) was calculated according to the for- day 30 was accepted as grounds for revising mulaa=8(l+w)+l~w,wherelandware the day two and seven classifications of houses the length and width of the house (which is previously found uninfested; and the presence assumed to have walls 2 m high and one inter- of a fifth instar on day 90 was accepted as Some field trial activities and specimens: (1) Dr. Oliveira Filho searching for triatomid bugs in crevices of a home’s adobe brick wall in the area treated with permethrin. (2) A team member providing identification for a house in the suburbs of Barreiras, Bahia State, Brazil, that has been searched for Triutoma infcstans. (3) An adult male T. infestam, the main vector of Chagas’ disease in Brazil. (4) Nymph and adult specimens of T. infistans found behind a block of plaster from an adobe brick wall. Note the prominent fecal marks left by the bugs after feeding. Pinchin et al. l CONTROL OF T. ZNFESTANS WITH PERMETHRIN 373 grounds for correcting the day 30 classifi- product evaluation technique similar to that cation. used in the present work-showed evident After each examination, the percentage of reinfestation only live months after treatment houses found bug-free and the number of bugs with the most efficacious insecticide tested (3, collected per man-hour were calculated for 4). Although a direct comparison cannot be each group of houses-these figures being made, it is clear that the results obtained at based on the number of houses examined at 300 days after treatment with permethrin at 1 each reading. and 0.5 g per square meter-and at 520 days after application of 2 g per square meter-are quite remarkable. Results and Discussion The examination technique used was selected for its practical applicability to the The results of the trial are presented in number of houses involved in the trial. Unfor- Table 1. It is clear that the highest dosage of tunately, with this technique it was not possi- permethrin (2 g per square meter) provided ble to definitely classify a house as uninfested, excellent long-term control; reinfestation was even using a pyrethroid spray to flush out not observed in any of the treated houses bugs. So even though a series of consecutive during the 520 days of post-treatment obser- negative readings by experienced field workers vation. The next-highest dosage (1 g per does give considerable assurance that a house square meter) had a less enduring impact; that really is bug-free, the chance of error (espe- is, reinfestations were noted at 300 days post- cially when examining houses with small bug treatment, and at 520 days over half the populations such as might be found following houses were reinfested.