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

Control de Aedes aegypti con temefós en un cementerio de Buenos Aires, Argentina

Controle de Aedes aegypti com temefós em cemitério de Buenos Aires, Argentina

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

Controle de Aedes aegypti com temefós em cemitério de Buenos Aires, Argentina

Control de Aedes aegypti con temefós en un cementerio de Buenos Aires, Argentina

Darío Vezzani; Stella Maris Velázquez; Nicolás Schweigmann

Unidad de Ecología de Reservorios y Vectores de Parásitos. Departamento de Ecología, Genética y Evolución. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Buenos Aires, Argentina

^{Correspondence}

ABSTRACT

The efficacy of a larvicide, temephos, for controlling Ae. aegypti was evaluated in a cemetery in Buenos Aires, Argentina. Breeding sites decreased from 18.4% in the first study period (Nov 1998 to May 1999, without temephos) to 2.2% in the second period (Nov 1999 to May 2000, two applications), and to 0.05% in the third one (Nov 2000 to May 2001, five applications). Ovitraps with eggs decreased from 17% in the first period to 5.8% in the second period, and to 2.9% in the third one. Results suggest that, in Buenos Aires, Ae. aegypti populations are highly susceptible to temephos. It is recommended to limit the use of temephos to prevent potential epidemics rather than for routine control.

Keywords: Aedes. Temephos. Vector control. Mosquito control. Insect vectors. Insecticide resistance.

RESUMO

Avaliou-se a eficácia de um larvicida, temefós, para controlar Ae. aegypti em um cemitério de Buenos Aires, Argentina. Os criadouros reduziram de 18,4% no primeiro período de estudo (nov de 1998 a maio de 1999, sem temefós) para 2,2% no segundo (nov de 1999 a maio de 2000, duas aplicações), e para 0,05% no terceiro (nov de 2000 a maio de 2001, cinco aplicações). As. ovitrampas com ovos diminuíram de 17% no primeiro período para 5,8% no segundo e para 2,9% no terceiro. Os resultados sugerem que, em Buenos Aires, as populações de Ae. aegypti são altamente susceptíveis ao temefós. É recomendável seu uso para prevenir eventuais epidemias e não para o controle rotineiro.

Descritores: Aedes. Temefós, Controle de vetores. Controle de mosquitos. Insetos vetores. Resistência a inseticidas.

RESUMEN

Se evaluó la eficacia de un larvicida, temefós, para controlar Ae. aegypti en un cementerio de Buenos Aires, Argentina. Los criaderos descendieron de 18,4% en el primer periodo de estudio (Nov 1998 a May 1999, sin temefos) a 2,2% en el segundo (Nov 1999 a May 2000, dos aplicaciones), y a 0,05% en el tercero (Nov 2000 a May 2001, cinco aplicaciones). Las ovitrampas con huevos disminuyeron de 17% en el primer periodo a 5,8% en el segundo, y a 2,9% en el tercero. Los resultados sugieren que, en Buenos Aires, las poblaciones de Ae. aegypti son altamente susceptibles al temefós. Es recomendable limitar su uso para prevenir eventuales epidemias y no para el control rutinario.

Descriptores: Aedes. Temefós. Control de vectores. Control de mosquitos. Insectos vectores. Resistencia a insecticidas.

INTRODUCTION

The cemeteries of Buenos Aires, Argentina, as in other Latin American countries, provide a high density of potential breeding sites of Aedes aegypti.^1,5 In 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.² The 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%).⁵

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.

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.

RESULTS

The proportion of breeding sites seen in the first study period (929 breeding sites/5,044 water-filled containers: 18.4%) was significantly higher (z=22.06, p<0.001) than that found in the second period (70/3,240: 2.2%), and the latter was significantly higher (z=6.31, p<0.001) than that in the third period (1/1,969: 0.05%).

The proportion of positive ovitraps seen in the first study period (56/330: 17%) was significantly higher (z=4.29, p<0.001) than that found in the second period (18/308: 5.8%) but the latter and the proportion of positive ovitraps in the third period (9/308: 2.9%) did not differ significantly (z=1.57, p=0.12).

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 region⁴ and Brazil³ 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.

ACKNOWLEDGEMENTS

To the Dirección General de Política y Control Ambiental (Secretaría de Planeamiento Urbano y Medio Ambiente del Gobierno de la Ciudad de Buenos Aires) and to the Departamento de Zoonosis, Reservorios y Vectores (Ministerio de Salud Pública y Acción Social de La Nación) for their help in applying temephos. To the authorities of Británico cemetery for allowing our work at the site.

Received on 5/1/2004

Approved on 17/5/2004

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).

• 1. Barrera R, Machado-Allison CE, Bulla L. Mosquitoes and mourning in the Caracas cemetery. Antenna 1982;6:250-2.
• 2. Cilek JE, Knapp FW. Residual activity of three slow-release temephos formulations against Aedes aegypti larvae. J Am Mosq Control Assoc 1995;11:358-9.
• 3. Macoris MLG, Andrighetti MTM, Takaku L, Glasser CM, Garbeloto VC, Bracco JE. Resistance of Aedes aegypti from the State of São Paulo, Brazil, to organophosphates insecticides. Mem Inst Oswaldo Cruz 2003;98:703-8.
• 4. Rawlins SC. spatial distribution of resistance to insecticides in Caribbean populations of the dengue vector, Aedes aegypti and it's significance. In: Proceedings of the CAREC/PAHO, Port of Spain, Trinidad, June 1999; 1999. p. 11-17.
• 5. Vezzani D, Velázquez SM, Soto S, Schweigman N. Environmental characteristics of the cementeries of Buenos Aires City (Argentina) and infestation levels of Aedes aegypti (Diptera: Culicidae). Mem Inst Oswaldo Cruz 2001;96:467-71.

Publication Dates

• Publication in this collection
  18 Oct 2004
• Date of issue
  Oct 2004

History

• Received
  05 Jan 2004
• Accepted
  17 May 2004