Laboratory evaluation of Mesocyclops aspericornis as a biocontrol agent of Aedes aegypti R. Ramanibai#, Kanniga S. Unit of Biomonitoring, Department of Zoology, University of Madras, Guindy Campus, Chennai–600 025, India
Abstract Mesocyclops aspericornis abounds in village ponds. Hence, the predatory capacity of M. aspericornis was considered for use as a biological control agent for Aedes aegypti mosquitoes. In laboratory experiments, M. aspericornis consumed 33–50 mosquitoe larvae within 24-hours time period. M. aspericornis preyed upon only the first instar larvae of Ae. aegypti within a few seconds after their introduction. It started feeding on the tail portion first and ended with the head capsule. The mean value (triplicate) showed that the predatory capacity was 45.76 against the control 1.2. M. aspericornis prefers only the first instar mosquitoe larvae and feeds on them voraciously. When the Aedes larvae attained the second instar stage, M. aspericornis attacked and killed them. Keywords: Biological control; Aedes aegypti; Mesocyclops apericornis; Predatory capacity.
Introduction In India, particularly in the state of Tamil Nadu, dengue and chikungunya have been reported from many places. The National Vector-Borne Disease Control Programme (NVBDCP) recommended the Integrated Vector Management (IVM) approach. This includes biocontrol agents. It has been proved that larvicidal measures sustain mosquito population for a short period and require repeated applications of chemicals and eventually develop resistance against that chemical[1]). Therefore, search for an effective biocontrol E-mail: rramani8@hotmail.com
agent to control mosquito population has become top priority among researchers. Predatory fishes and zooplankton have been widely used as a biocontrol method to control vector population[2,3,4]. Integration of these methods can be a low-cost and environmentally-friendly approach in controlling mosquito vectors[5,6]. Cyclopoid copepods (planktonic microcrustaceans) have been extensively used as biocontrol agents in the South-East Asian countries for containerbreeding mosquito species like Ae. aegypti[7]. The copepod, Mesocyclops aspericornis, is an effective predator of Ae. aegypti. It is known
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for its wide distribution and predatory efficiency against several species of mosquito larvae. The present study was conducted as a brief laboratory experiment designed to understand the mode of destruction of mosquito larvae by M. aspericornis.
Results M. aspericornis preyed upon the first instar of Ae. aegypti larvae within 24 hours, which was recorded. In general, they attacked the tail region of the mosquito larvae and consumed them. On a few occasions they left out the head capsule of the mosquito larvae, and, at times they killed the mosquito larvae without consuming them. Ten experiments were conducted for 10 days in the laboratory on relay basis. M. aspericornis consumed about 33 to 50 first instar larvae of Ae. aegypti within 24 hours time period. The number of mosquito larvae left inside the experimental beakers ranged from nil to 17 nos. On the whole, the mean predatory capacity of a single M. aspericornis was calculated at 45.75 (see Table).
Methodology Out of a few preliminary surveys carried out in the nearby environs of Chennai, Capital of Tamil Nadu, two ponds were identified for the collection of cyclopoid copepods. The plankton mesh size used for the collection was 100 µm. Mesocyclops were isolated from the sample and identified up to species level with the help of standard keys[8,9]. M. aspericornis, once its species identity was confirmed, was selected for experimental studies and reared in the laboratory. Females with egg sacs collected from the stock were placed on a petridish and were examined under the dissection microscope. These were transferred into 600 ml beaker where 50 newly-hatched Ae. aegypti larvae were introduced. We sacrificed the secondgeneration Mesocyclops collected from our stock for experimental purposes. Fully-fed Ae. aegypti females were collected from the house and kept in a small cloth cage for egg-laying. The mosquitoes were provided a small dish, half filled with water, and a paper strip for egglaying. The eggs were hatched in a Petri dish and used for experiment. Fifty newly-hatched first instar larvae were introduced into a 600 ml beaker containing 500 ml dechlorinated water where a single M. aspericornis was introduced. The experiment lasted for 24 hours. The number of larvae that survived at the end of 24 hours was recorded. Triplicates were maintained simultaneously at 26±1 °C under photoperiod 12L:12D along with the control without the introduction of M. aspericornis.
Discussion and conclusions According to Nam et al. [10] , the daily consumption/killing average of a single M. aspericornis ranged between 16 to 41 larvae. Through continuous observations, M. aspericornis attacked the first instar larvae within a few seconds. They mainly consumed the central portion, leaving the head capsule. Occasionally, they just killed the larvae without consuming it. Using their strong mandible they pierced and crammed the larvae into pieces. According to Lardeux et al.[11], M. aspericornis served as a good biocontrol agent against Ae. aegypti within a three-weeks time period. In the present study, 10 experiments were conducted simultaneously to know the predatory capacity of M. aspericornis under laboratory conditions. The maximum predatory capacity of M. apericornis was found to be 49.3 (mean value) and the minimum 39.3 (Table). Our results demonstrate that M. aspericornis is an efficient predator of Ae. aegypti under laboratory conditions.
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Table: The mean value of Ae. aegypti larvae consumed by M. aspericornis S. no. Experiment no. No. of Ae. aegypti larvae consumed by M. aspericornis Triplicates A 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 42 33 50 50 46 47 46 50 45 44 B 42 40 50 44 50 47 46 48 47 44 C 45 45 48 46 46 48 48 48 45 44 43 39.3 49.3 46.6 47.3 47.3 46.6 48.6 45.6 44 Total mean: 45.75 Mean value
Acknowledgements We thank the University Grants Commision (UGC) for financial support (grant no F,no.33-
362/2007(SR) and the anonymous reviewers for their critical comments that helped in improving the manuscript.
References [1] Gratz NG. Emerging and resurging vectorborne diseases. Annual Review of Entomology. 1999; 44: 51-75. [2] Russell BM, Wang J, Williams Y, Hearnden MN, Kay BH. Laboratory evaluation of two native fishes from tropical North Queensland as biological control agents subterranean Aedes aegypti. Journal of American Mosquito Control Association. 2001; 17: 124-6. [3] Kay BH, Nam VS, Tien TV, Yen NT, Phong TV, Diep VTB, Ninb TV, Bektas A, Aaskov JG. Control of Aedes vectors of dengue in three provinces of Vietnam by use of Mesocyclops (copepoda) and community-based methods validated by entomologic, clinical and serological surveillance. American Journal of Tropical Medicine and Hygiene. 2002; 6: 40-8. [4] Micieli MV, Garcia JJ, Andreadis TG. Epizootiological studies of Amblyospora albifasciati (Microsporidiida: Amblyosporidae) in natural populations of Aedes albifasciatus (Diptera: Culicidae) and Mesocyclops annulatus (Copepoda: Cyclopidae) in a transient floodwater habitat. Journal of Invertebrate Pathology. 2001 Jan; 77(1): 68-74. [5] Tietze NS, Hester PG, Snaffer KR, Prescott ST, Schreiber ET. Integrated management of waste tire mosquito utilizing Mesocyclops longisetus (Copepoda: Cyclopidae), Bacillus thuringiensis var, Israelenisis, Bacillus sphaericus and methoprene. Journal of the American Mosquito Control Association. 1994; 10: 363-73.
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[6] Wang CH, Chang NT, Wu HH, Ho CM. Integrated control of the dengue vector Aedes aegypti in Liu-Chiu village, Ping-Tung County, Taiwan. Journal of the American Mosquito Control Association. 2000 Jun; 16(2): 93-9. [7] Marco F, Marten G, Clark G. A simple method for cultivating freshwater copepods used in biological control of Aedes aegypti. Journal of the American Mosquito Control Association. 1992; 8: 4. [8] Battish SK. Freshwater zooplankton of India. New Delhi : Oxford and IBH Publishing Co. Pvt. Ltd., 1992. [9] Edmondson WT. Freshwater Biology. 2nd edn. New York : John Wiley and Sons Inc., 1959. pp 420-94.
[10] Larduex F, Loncke S, Sechan Y, Kay BH, Riviere F. Potentialities of Mesocyclops aspericornis (Copepoda) for broad scale control of Aedes polynesiensis and Aedes aegypti in French Polynesia. Arbovirus Research in Australia. 1992; 5:154-9. [11] Nam VS, Yen NT, Holynska M, Reid JW, Kay BH. National progress in dengue vector control in Vietnam: survey for Mesocyclops (Copepoda), Micronecta (Corixidae), and fish as biological control agents. American Journal of Tropical Medicine and Hygiene. 2000 Jan; 62(1): 5-10.
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