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2002 Kluwer Academic Publishers. Printed in the Netherlands. Research note. Indigenous fish species for the control of Aedes aegypti in water storage tanks in ...
BioControl 47: 481–486, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Research note

Indigenous fish species for the control of Aedes aegypti in water storage tanks in Southern México J.A. MARTÍNEZ-IBARRA∗, Y. Grant GUILLÉN, J.I. ARREDONDO-JIMÉNEZ and M.H. RODRÍGUEZ-LÓPEZ Centro de Investigación de Paludismo, Instituto Nacional de Salud Pública. Cuarta Norte y 14 Calle Poniente, 30700 Tapachula, Chiapas, México ∗ Author for correspondence, Área de Entomología Médica, Centro Universitario del Sur, Universidad de Guadalajara, Km 1 Carretera Ciudad Guzmán-Guadalajara, 49000 Ciudad Guzmán, Jalisco, México; e-mail: [email protected] Received 18 December 2000; accepted in revised form 20 June 2001

Abstract. Because of inadequate supply of water, inhabitants of five villages close to Tapachula, Chiapas, México, store water in cement tanks that support large populations of Aedes aegypti. Biological control using indigenous fish species were studied to control A. aegypti larvae in those containers, since other organisms used as biological control agents are expensive and unfamiliar to inhabitants of those towns. Other measures (chemical or physical control) are expensive and time consuming. Five indigenous fish species, Lepisosteus tropicus (Gill) (Lepisosteiformes: Lepisosteidae), Astyanax fasciatus (Cuvier) (Cypriniformes: Characinidae), Brycon guatemalensis (Regan) (Cypriniformes: Characinidae), Ictalurus meridionalis (Günther) (Cypriniformes: Ictaluridae) and Poecilia sphenops Valenciennes (Cyprinodontiformes: Poeciliidae), currently used as mosquito control agents in the area were tested. Container indexes (a measure of disease transmission potential) in the tested area were always zero during the year of the study, independent of towns and fish species; this was significantly (P < 0.05) different from container indexes prior to the test as well as from controls without fish. No significant (P > 0.05) differences were recorded in the efficiency of the tested fish species feeding on A. aegypti larvae. Our results show that all tested fish species can be considered as good biological agents for controlling A. aegypti larvae in Southern Mexico. Key words: Aedes aegypti, indigenous fish species, water storage tanks

Introduction Some mosquito species are considered important threats to public health; among them Aedes aegypti L (Diptera: Culicidae) is outstanding because of its behavior of breeding and feeding, and its capacity for transmission of dengue viruses to human populations. In Mexico, from 1980 to 1990

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more than 226474 dengue cases (12 of hemorrhagic dengue) were detected (OPS, 1997). A similar number of cases was recorded from 1991 to 2000, with an annual mean of 18031 (J. Méndez-Galván, personal communication). Control of A. aegypti larvae has been developed using many different measures (chemical, physical, community, or biological control); however, chemical control pollutes water sources, it is expensive, and many trained people are necessary for constant surveillance of mosquito breeding places. Physical control is also expensive and time consuming. Community programs seem to be one of the best methods of mosquito control in small rural communities. However, occasionally it is difficult to get community cooperation to implement theses projects, and the measure under study is eliminated by the community. Some biological control programs have been successful in controlling A. aegypti populations (Wu et al., 1987; Wang et al., 1990, 2000; Marten et al., 1994; Batra et al., 2000), but in other programs, introduced animals have represented potential sources of pathogen microorganisms (e.g. turtles: Borjas et al., 1993). Other times, the communities from the study areas have rejected the use of some organisms because these organisms are unfamiliar [e.g., insects such as some Hemiptera or Odonata species, or copepods (Copepoda: Ciclopoidea)]. Native larvivorous fish species are acceptable mosquito control agents to most communities and should be evaluated as potential control agents (OPS, 1997). Some indigenous larvivorous fish species have been successfully used for controlling mosquito species other than A. aegypti (Gerberich and Laird, 1968; Alio et al., 1985; Nelson and Keenan, 1992; Taylor et al., 1992; Koldenkova et al., 1993; Torrente et al., 1993; Boklund, 1997; Lee 2000). However, only a few papers (Wu et al., 1987; Wang et al., 1990, 2000) report successful A. aegypti control by larvivorous fish because this mosquito uses domestic water storage containers as breeding places, and these habitats do not support many larvivorous fish species. In Mexico, no reports have been published on mosquito control by larvivorous fish, even when some empirical controls have been recorded in Southern Mexico. In the Tapachula, Chiapas area, the inhabitants of some towns use certain indigenous fish species, Lepisosteus tropicus (Gill) (Lepisosteiformes: Lepisosteidae) “armado”, Astyanax fasciatus (Cuvier) (Cypriniformes: Characinidae) “sardina dorada”, Brycon guatemalensis (Regan) (Cypriniforme: Characinidae) “macabil”, Ictalurus meridionalis (Günther) (Cypriniformes: Ictaluridae) “bagre” and Poecilia sphenops Valenciennes (Cyprinodontiformes: Poeciliidae) “pupos o popoyotes” for A. aegypti control into cement water storage tanks. These fish are easily obtained by town residents from mangroves or a river running close to towns. A research program was developed to study the ability of the above indi-

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genous larvivorous fish species for controlling A. aegypti larvae in cement tanks in a highly infested area of Southern Mexico.

Materials and methods The study area was represented by five small localities close to Tapachula, Chiapas, (15◦ 8 N, 92◦ 27 W) in Southern Mexico. These towns were selected because their inhabitants rarely used any form of control, the lack of use of chlorinated water in tanks (since wells are primary sources for drinking water), similarity of town size (65 ± 5 houses), homogeneity of the size of cement tanks (1 m × 2 m × 1 m = 2 m3 ) and complete community support for the project. A preliminary sample was done to calculate the container index (number of containers infested by A. aegypti larvae/total number of tested containers) × 100 (WHO, 1972; OPS, 1997) in the area. Container indexes varied from 83.3 to 91.7 (high level of risk of transmission of dengue, OPS, 1997) among towns before intervention, since inhabitants rarely use control measures. Sixty cement tanks were selected in each town and grouped into six equal groups, for testing one fish species in each group (L. tropicus, A. fasciatus, B. guatemalensis, I. meridionalis or P. sphenops) and a control without fish. Fish were collected from mangroves or a river close to towns. The Ávarez del Villar (1970) keys were followed to identify al species. The number of released fish varied according to the species; one L. tropicus per tank (since this is a very aggressive species and feed on other fish), 10 A. fasciatus, 10 B. guatemalensis or 10 P. sphenops (small size species), or 2 I. meridionalis (medium size species). Data for larval density were collected every week for a year, according to the established WHO (1972) method and expressed as container index (Table 1). This index was used to evaluate the efficacy of control measures as well as to make further improvements in the control strategy. Comparisons among container indexes “prior” to treatments, as well as treatments and controls were tested by Kruskal-Wallis analysis. Comparisons of mortalities among species were tested by ANOVA tests. Most of released specimens survived during the year of the study, but when they did not, they were replaced with other specimens from the mentioned sources.

Results Fish eliminated A. aegypti larvae from each tank during the year of the study. Container indexes for containers containing fish were always zero during the

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Table 1. Mean annual container indexes on each group of cements tanks under Aedes aegypti control by larvivorous fish species, in Southern Mexico Groups of cement tanks

Container indexes before intervention (Mean ± SD)

Container indexes during intervention (Mean ± SD)

A. Lepisosteus tropicus B. Astyanax fasciatus C. Brycon guatemalensis D. Ictalurus meridionalis E. Poecilia sphenops F. Control

83.3 ± 5.7 84.5 ± 4.9 91.7 ± 5.8 90.1 ± 4.6 88.7 ± 8.9 84.5 ± 6.8

0 0 0 0 0 85.9 ± 9.6

year of the study, independent of towns and fish species tested. Container indexes for controls were over 80.0 (Table 1), did not differ significantly from index values before intervention, and differed significantly from container indexes for containers supporting fish. No significant (P > 0.05) differences were recorded on efficiency among fish species feeding on A. aegypti larvae. This pattern was observed in all towns. Mortality was not significantly (P > 0.05) different among fish species, since only one specimen of A. fasciatus and one of B. guatemalensis died during the study, and no L. tropicus, P. sphenops and I. meridionalis died. None of the species could reproduce under cement tanks conditions. As a result, no significant (P > 0.05) differences were recorded among densities fish species.

Discussion In this area of Southern Mexico, the five studied fish species (L. tropicus, A. fasciatus, B. guatemalensis, I. meridionalis and P. sphenops) were very efficient and no significant (P > 0.05) differences in controlling A. aegypti larvae in domiciliary cement tanks were recorded. No significant (P > 0.05) differences were recorded for mortality of any species. Most released specimens survived the study period, since environmental conditions on cement tanks were favorable to fish; the water lacked chlorine and was constantly renovated (keeping high level of oxygen), the food (mosquito larvae) was constantly supplied, and fish counted on support by inhabitants (since many children “adopted” fish as pets).

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As a result of the positive reaction of inhabitants to the presence of some familiar fish species with some species even used as food, a high efficiency of those five species and simplicity on getting free fish from close sources, the fish species tested can be considered as good biological control agents for A. aegypti larvae in Southern Mexico.

Acknowledgements We thank the invaluable support by inhabitants for this study, since they fed fish specimens (with bread or crushed corn) when A. aegypti larvae were too low for supporting them.

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