The Use of the Copepod Mesocyclops Longisezus As a Biological Control

Journal of the American Mosquito Contol Association, 2O(4):4O1-404,2OO4 Copyright A 2OO4 by the American Mosquito Control Association, Inc. THE USE OF THE COPEPOD MESOCYCLOPSLONGISEZUS AS A BIOLOGICAL CONTROL AGENT FOR AEDES AEGYPTI IN CALI, COLOMBIA MARCELA SUAREZ-RUBIOI,z EIIU MARCO E SUAREZ3 ABSTRACT. We present data on the efficacy of Mesocyclops longisetus as a biocontrol agent in controlling Aedes aegypti larvae in catch basins in Cali, Colombia. Additionally, we determined some of the features that facilitated the establishment ofthe copepods in catch basins. Between June 1999 and February 200O,201 catch basins were treated with an average of 500 adult copepods. The copepods had established in 49.2Vo of all the basins and they maintained Ae. aegypti larvae at low densities until the end of the 8-month study. The corrected efficacy percent was 9O.44o. The copepods established in basins located in a flat area as opposed to those in steep areas, exposed to sunlight and with 0-7ovo of floating organic matter. when the catch basins were con- taminated with synthetic washing agents, like detergents, the copepods did not survive. The copepod M. longisetus cottld be incorporated as a biological control agent in an integrated Ae. aegypti control program. KEY WORDS Biological control, Aedes aegypti, copepods, Mesocyclops longisetus, Colombia INTRODUCTION vae (Su6rez et al. 1991) and can suppress larval populations to very low levels (Marten et al. 1994). Many strategies, such as vector eradication pro- Some cyclopoid copepods have been observed grams, chemical control measures, environmental to control Ae. aegypti larvae in domestic and peri- sanitation with community participation, and bio- domestic containers (Marten 1990, Marten logical control agents, have been used to prevent or et al. 1994, Schreiber et al. 1996). For control dengue outbreaks. An early approach to example, Macro- cyclops albidus (Cocal), Mesocyclops longisetus control yellow fever and dengue fever was to erad- (Thi6baund), and Mesocyclops (Da- icate the dengue vector, Aedes aegyprl (L.). The aspericornis day) are highly effective in controlling eradication programs failed due to financial, polit- Aedes al- bopictus (Skuse) (Marten l99O) and Ae. aegyptilar- ical, technical, and administrative problems. As a vae in abandoned tires (Su6rez 1991. consequence, dengue vector populations returned to et al. Marten et al. 1993, Marten et al. 1994) and in other previous or higher densities, and the mosquito dis- artifi- cial habitats (e.g., persed into new areas (Halstead 1984, Nelson 1986, barrels, water tanks). In other studies, M. aspericornis eliminated Clark 1995, Gratz and Knudsen 1995, PAHO 1995, 99Vo of the lst- stage larvae of Ae. aegypti and Aedes polynesiensis Gubler and Clark 1996). Chemical control was also (Marks) in artificial habitats (Riviere used to eliminate the vector, but the reduction of et al. 1987; Brown et al. l99ta,1991b). In addition, female mosquitoes was transitory (Leontsini et al. copepods may help in controlling mosquito 1993), and the mosquito developed resistance to larvae in natural habitats (e.g., (Lardeaux many insecticides (PAHO 1995). Environmental tree holes, crab holes) 1992). Mesocyclops sanitation with community participation involved aspericornis reduced larval populations of Ae. polynesiensis andAe. the elimination of all artificial breeding sites of the aegyptiby 9l-99%o (Riviere vector. Community-based approaches provide et al. 1987), demonstrating that the copepods have potential short-term success, but this control strategy has yet a value as a biological control agent (Kay to show a significant impact on vector populations et al. 1992). In Cali, Colombia, the principal in operational levels (Gubler and Clark 1996). Bi- breeding sites of Ae. aegypti (Fig. ological control is a safe strategy and does not have are catch basins 1), located along streets in residential some of the negative environmental drawbacks of areas. Catch basins have been primary insecticides (Howarth 1991). The main drawbacks described as a breeding site in Cali because Ae. aegypti larvae were present of biological control are that the predator has to in 57.2Vo of the city's basins (Gonz6lez colonize the habitats of its prey in urban environ- et al. 1993). Due to their design, the basins ments, there is a lag time for its establishment contain water throughout the year, thus providing appropriate (Rawlins et al. 1997), and repeated applications are conditions for the needed for effective control (Laird 1981). development of mosquito larvae. Additionally, Copepods attack and kill lst-stage mosquito lar- catch basins in Cali produce 27 times more pupae than all other breeding sites combined within a city block (GonzLlez and Sudrez, unpublished data), rUniversidad del Valle, Departamento de Biologfa, suggesting that catch basins are mosquito factories. Apartado 2536O, Cali, Colombia. The characteristics 2 Present address: Institute For Tropical Ecosvstem of catch basins make it dif- Studies, University of Puerto Rico, PO-Box 2334i, San ficult to incorporate traditional control strategies Juan, Puerto Rico 00931-3341. that are effective in other places. For example, 3 Secretaria de Salud Municipal, Calle 48 36-00, Cali, chemical control, especially liquid or granular for- Colombia. mulations, require continued applications to control 401 402 JounNar- oF THE AMERICANMoseulTo Cor.{TRoL AssocrATroN Vor-.20, No.4 determine the proportion of basins with and without Wets €ntEn6 copepods IJ and Ae. aegypti larvae. In each visit, 4 ::.:...f}---.., samples of water were taken from each basin using a2OO-cm3 ladle. The samples were taken from each corner of the basin at 5-min intervals to allow the larvae and the copepods to return to the organic matter, and each sample was considered individu- ally for further analysis. In addition, to identify the characteristics correlated with copepod establish- 2/ Exit tub€ ment in the basins, we evaluated 3 physical features of catch basins (i.e., percentage shade, percentage cover of floating organic mattel and the topography around the basin). The topography was Fig. 1. Schematicdrawing of catch basins.The basins measured constantly contain standing water, and they have various as a function of the inclination of the road where amounts of organic matter (OM). the basin was located. Finally, the presence of any synthetic washing agent, such as detergent, inside catch basins was recorded. mosquito populations because its effectiveness lasts for 8-15 days. Slow-release formulations are more Statistical analysis expensive and the government does not support Chi-square tests were performed to evaluate dif- them, and they may cause environmental damage ferences in presence of Ae. aegypti larvae and co- (Schreiber et al. 1996). Additionally, Ae. aegypti pepods in catch basins over time. The corrected ef- populations in Cali are resistant to temephos, one ficacy percent was calculated using the Henderson- of the most commonly used larvicide for their con- Tilton's formula (Henderson and Tilton 1955). A trol (Gonziilez et al. 1993). Thus, it became nec- principal component analysis (PCA) was performed essary to evaluate biological control as an alterna- to analyze the effect of the percent shade, percent tive to the chemical control of Ae. aegypti. cover of organic matter, and the topography on co- This article presents data on the efficacy of M. pepods establishment. Afterward, multiresponse longisetus as a biocontrol agent in controlling Ae. permutation procedures (MRPP) were used to de- aegypti larvae in catch basins and the appropriate termine if there were statistical differences between characteristics of catch basins for its establishment. the groups in the PCA. Moreover, an association We hypothesized that, after the introduction of M. test was used to determine differences in copepod longisetus, the proportion of catch basins with Ae. presence between catch basins with and without de- aegypti larvae would be reduced, whereas the pro- tergent. The level of significance for all tests was portion of catch basins with copepods would in- 0.05. crease. RESULTS MATERIALS AND METHODS The number of catch basins infested with Ae. ae- Study site gypti larvae significantly decreased after copepods We evaluated 2Ol catch basins along streets in were introduced (1' -- 36.48, df : 1, P < 0.000), residential areas in southern sectors of Cali but the number of catch basins with copepods did (3"27'N, 76"32'W), Colombia (elevation 995 m). not differ through time (1' : 0.3368, df = 1, P : The annual precipitation is 1,153 mm, with rainy 0.562). The number of catch basins with larvae de- peaks in April and October, and dry peaks in July creased significantly over time, but the basins and December, and the average temperature is 23"C where copepods established remained positive for (rGAC 1980). copepods (49.2Vo), and in these basins, the copepods were present for 8 months (Fig. 2). The corrected efficacy percent was 9O.47o and the mean of Field surveys larvae density per sample was 0.53. Between June 1999 and February 2OOO, 2Ol From the 201 catch basins, 68Vo were located in catch basins were evaluated on a monthly basis for places in which they were exposed to sunlight, 877o presence and absence of M. longisetus and Ae. ae- were located in roads with low slope, and 9l%o re- gypti larvae and 70 catch basins were used as con- ceived less than 5O7o of floating organic matter trols. In June, we sampled the Ae. aegypti larvae in (Fig. 3). The amount of shade and the nature of the catch basins to define the proportion of infested local topography were the most important features basins. In July, we introduced approximately 500 contributing to the establishment of copepod pop- adult copepods per basin. The copepods were taken ulations. In the PCA, axis I was correlated with from laboratory culture and counted using a plastic shade and topography, explaining 48.67o of thevar- dropper. In August, an 8-month survey began to iance with an eigenvalue of 1.458; while axis 2 was DECEMBER2004 Copepoos As A BIoLocIcAL CoNTRoL AGENT 403 s60 o =En o ?q o o^^ <ou o o o20 Shede Sbp€ Orgadc Maibr Phyliel fretss E!@ Fig.

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