Dengue

Dengue Bulletin Volume 28 (2004)

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Philippine Species of Mesocyclops (Crustacea: Copepoda) as a Biological Control Agent of  Aedes aegypti (Linnaeus)

Cecilia Mejica Panogadia-Reyes*^#, Estrella Irlandez Cruz**  and Soledad Lopez Bautista***

*Department of Biology, EmilioAguinaldoCollege, Ermita, Manila, MM, Philippines
**Research Institute for Tropical Medicine, Alabang, Muntinlupa, MM, Philippines
***Department of Medical Technology, EmilioAguinaldoCollege, Ermita, Manila, MM, Philippines

Introduction

Copepods feed on paramecium (ciliates protozoans) while naupli feed on Chilomonas spp. The adult planktonic copepods utilize diatoms as the principal food, while predacious adult copepods feed on protozoa, rotifers and several
aquatic animals of their own size including small fishes and mosquito larvae. Some adults are able to tear pieces out of the body of their victims with their strong mandibles. In the Philippines, around 14 species of Cyclops have been recorded, of which Mesocyclops aspericornis and M. ogunnus are more common^[1,2].

In Brazil, a study^[3] reported that under laboratory conditions, four different strains of M. aspericornis showed the potential as biological control agents of Aedes aegypti larvae. In Viet Nam, under laboratory conditions, M. aspericornis consumed a mean 23.75 L1 and killed a mean 13.43 L1, or a total of 37.18 L1 within 24 hours. M. ogunnus, on the other hand, consumed a mean 8.48 L1 and killed a mean 7.54 L1 or a total of 16.02 L1 within 24 hours^[4]. In Australia, six species of Mesocyclops were evaluated as biological control agents of Aedes aegypti^[5]. Of these, M. aspericornis was found to be the most effective predator. This study attempted to evaluate, for the first time, the potential of the local population of two species of Mesocyclops as biological control agents of Aedes aegypti (L) under laboratory and field conditions in the Philippines.

Methodology

Mesocyclops culture

Mesocyclops aspericornis and M. ogunnus were raised in laboratory following the techniques adopted by Marten and Thomson^[6]. To ensure the establishment of a single species culture, a female with egg sacs was captured and placed in a petri dish for examination under a dissecting microscope before it was transferred to a wide-mouthed beaker containing 100 ml of mixed culture of Paramecium caudatum and Chilomonas sp. (food of Mesocyclops). Populations of Chilomonas sp. and P. caudatum in the culture bottle were maintained using sterile wheat seeds. Sample specimens from copepods culture were sent to Maria Holynska, Museum and Institute of Zoology, Warsaw, Poland, for identification. 

Laboratory trials

In a 600 ml beaker, 500 ml filtered tap water with pH 7 was poured. Then 50 Aedes aegypti L1 obtained from laboratory culture and a female M. aspericornis were added at the same time. The same procedure was done for M. ogunnus. The control group did not receive Mesocyclops. The experiment was replicated six times and was observed every day for five consecutive days, with daily replacements of new L1. The daily number of L1 destroyed or consumed by M. aspericornis and M. ogunnus and those that died in the control group were determined. Copepods’ feeding behaviour was observed.

Field trials

Permission to conduct the study in Estero de Tanque located at P Nieto Street, Barangay 674, Zone 73, Paco, Manila, was secured from the community health officials and Barangay chairperson. Members of the households were informed regarding the procedures to be undertaken and the possible benefit they could derive from it. Consent from the caretakers of the sample households was also secured.

A preliminary study was conducted for 15 days. Twenty houses were chosen as study sites. Two drums per household or a total of 40 drums were emptied and filled almost to the brim with tap water, pH 7.2. A litre of water as sample from each drum container was collected in sterile bottles and brought to the laboratory to exclude the presence of fungi, bacteria and indigenous copepods. Mosquito eggs that hatched into larvae in drums were monitored and collected daily for recording and identification. Water pH, water temperature and ambient temperature were taken daily. Drums were checked daily for the presence of mosquito eggs and larvae with the aid of a magnifying glass. Drums with mosquito larvae were marked and female copepods were introduced in experimental drums using the ratio one Mesocyclops aspericornis per 50 Aedes aegypti first instar larvae (L1). No copepods were introduced in the 20 control drums. Observation was made daily for 15 consecutive days. Surviving larvae were collected from all drums and brought to the laboratory for recording and species identification.

Results and discussion

Laboratory trials

The results of the predatory capacity of M. aspericornis and M. ogunnus as evaluated under laboratory conditions and analysis of variance are presented in Tables 1 and 2. The mean L1 consumed by M. aspericornis was 23.96 while that of M. ogunnus was 15.00. Control means were 0.63 L1 and 0.60 L1, respectively. The findings showed that there was a highly significant difference between the mean number of Ae. aegypti L1 consumed by M. aspericornis and that of M. ogunnus and the control group.

Table 1. Predatory capacity of female Mesocyclops aspericornis vs Aedes aegypti first instar larvae in 500 ml filtered water under laboratory conditions

Table 2. Predatory capacity of female Mesocyclops ogunnus vs Aedes aegypti first instar  larvae in 500 ml filtered water under laboratory conditions

To determine if there was a difference between the mean number of L1 consumed by M. aspericornis and M. ogunnus, the analysis of variance was carried out (Table 3). The findings showed that there was a highly significant difference between the mean number of L1 consumed by M. aspericornis and by M. ogunnus. The study showed that M. aspericornis was a more efficient predator of Aedes aegypti larvae.

Table 3. Comparison of the predatory capacity of M. aspericornis and M. ogunnus under laboratory conditions

Table 4. Predatory capacity of Mesocyclops aspericornis vs Aedes larvae in small-scale  field trials using drum containers

Field trials

The results of the field trials are presented in Table 4.

The mean L1 in experimental drums was 63.10 and 202.95 L1 in control drums. To determine the difference between the mean number of surviving larvae in the drums with M. aspericornis and in the drums without M. aspericornis, a Student t-test was used. The findings indicated that there was a significant difference between the mean number of surviving larvae in the drums with and without Mesocyclops. This significant difference suggests that M. aspericornis is a good biological control agent, for it consumed about two-thirds of the wild, dengue mosquito larvae population.

Conclusion

The results of the study showed that Mesocyclops aspericornis was an efficient predator of Aedes aegypti larvae both in laboratory and field conditions. These copepods could be effectively used for the control of Aedes breeding in non-removable containers, viz. drums and used tyres.

Acknowledgements

The World Health Organization and the Yaman Lahi Foundation, Inc. – Emilio Aguinaldo College provided financial support for this project. We acknowledge the kind assistance of Dr Kevin Palmer of the WHO Western Pacific Region; Dr Jose Paulo E. Campos of Yaman Lahi Foundation, Inc. – Emilio Aguinaldo College (YLFI-EAC), Philippines; Dr Remigio M. Olveda of the Department of Health – Research Institute for Tropical Medicine (DOH-RITM), Philippines; Dr Maria Holynska of Museum and Institute of Zoology – Polish Academy of Science (MIZ-PAS), Poland; Dr Vu Sinh Nam of the National Institute of Hygiene and Epidemiology (NIHE), Viet Nam; and Dr Brian H. Kay of the Queensland Institute of Medical Research (QIMR), Australia.

References

1.      Mamaril AC and Fernando CH. Freshwater zooplankton of the Philippines (Rotifera, Cladocera, and Copepoda). Natural and Applied Science Bulletin, 1978, 30(4): 109-221.

2.      Tuyor JB and Baay MO. Contribution to the knowledge of freshwater copepods of the Philippines. Asia Life Sciences, 2001, 10(1): 35-43.

3.      Kay BH, Cabral CP, Sleigh AC, Brown MD, Ribeiro ZM and Vasconcelos AW. Laboratory evaluation of Brazilian Mesocyclops (Copepoda: Cyclopidae) for mosquito control. J Med Entomol, 1992, 29(4): 599-602.

4.      Nam VS, Tien TV, Huan TQ, Yen NT, Kay B, Marchand R, Marten G, Holynska M and Reid J. Mesocyclops of Vietnam Part I - laboratory evaluation as biological agent for control of Aedes aegypti. Dengue Bulletin, 1999, 23: 89-93.

5.      Brown MD, Kay BH and Hendrikz JK. Evaluation of Australian Mesocyclops (Cyclopoida: Cyclopidae) for mosquito control. J Med Entomol, 1991, 28(5): 618-623.

6.      Marten G and Thompson G. Copepod production and application for control procedure for New Orleans Mosquito Board, City of New Orleans, USA, 1997.