Control of Aedes aegypti with temephos in a Buenos Aires cemetery , Argentina

Financial support by Consejo Nacional de Investigaciones Científicas y Técnicas and Dirección General de Política y Control Ambiental (Secretaría de Planeamiento Urbano y Medio Ambiente del Gobierno de la Ciudad de Buenos Aires). Received on 5/1/2004. Approved on 17/5/2004. Correspondence to: Darío Vezzani Departamento de Ecología, Genética y Evolución Universidad de Buenos Aires, Ciudad Universitaria Pabellón 2, 4° piso (C1428EHA) Buenos Aires, Argentina E-mail: vzztato@fibertel.com.ar


INTRODUCTION
The cemeteries of Buenos Aires, Argentina, as in other Latin American countries, provide a high density of potential breeding sites of Aedes aegypti. 1,5In these environments, traditional mourning habits are hard to change. 1 Slow-release larvicides as temephos can reduce the frequency and cost of insecticide application to control mosquito populations. 2The present study evaluated the efficacy of temephos for controlling Ae. aegypti in an environment with the highest urban container density.

METHODS
The study area was Británico cemetery in Buenos Aires.This is a 5-hectare private cemetery with high vegetation cover (82%) and high availability of containers (1499/ ha) that showed to have one of the highest Ae.aegypti infestation rates in the city (container index = 25%).The larvicide used for controlling Ae. aegypti population was 1% temephos (Abate ® ).No control measure was put in place during the first study period.In the second period temephos was applied to all containers available in mid-September, before the beginning of the mosquito reproductive season, and in mid-February.In the third period the larvicide was applied in mid-September, at the end of December, at the beginning of February and March, and in mid-April.
Ae. aegypti breeding sites and positive ovitraps proportions were compared between consecutive periods using the z-test for two independent proportions.
The Figure shows monthly breeding sites and positive ovitraps proportions in the three study periods.Ae. aegypti was not seen in November and December in both periods in which temephos was applied during early spring (September).The highest monthly breeding site infestation rate decreased from 43.7% in the first study period to 0.4% in the third one.The highest monthly positive ovitraps decreased from 41.8% in the first study period to 0.4% in the third one.

DISCUSSION
The use of temephos in an environment with high availability of potential breeding sites was effective in reducing Ae. aegypti populations.With only two larvicide applications, one before and the other during the reproductive season, there was a eight-time decrease in breeding site infestation and three-time decrease in oviposition activity.Subsequently, in the third study period when there were five temephos applications, Ae. aegypti immature population was almost completely eliminated (remained only 1 breeding site).However, a 3% ovitraps with eggs were detected throughout this period, reaching a maximum of 11.4% in February.These eggs may come from oviposition of isolated females from the cemetery surroundings.
Considering that at the time of the study there were no records of periodical use of temephos in Buenos Aires, it is unlikely that mosquito populations had develop resistance against this insecticide.High and moderate resistance to temephos has been described in the Caribbean region 4 and Brazil 3 respectively.In Buenos Aires, where no local transmission of dengue virus has been demonstrated, it is recommended to save insecticides as an efficient tool for preventing potential epidemics only rather than for routine control.

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www.fsp.usp.br/rspControl of Ae. aegypti with temephos Vezzani D et al During three consecutive study periods (November 1998 to May 1999, Nov 1999 to May 2000, and Nov 2000 to May 2001), between 400 and 1400 containers were examined monthly for immature stages of Ae. aegypti, and 11 ovitraps were examined weekly to monitor oviposition activity.

Figure
Figure -Monthly percentages of breeding sites of Ae. aegypti and monthly percentages of positive ovitraps in the cemetery Británico (Buenos Aires City, Argentina), from November 1998 to May 2001.