African Journal of Biomedical Research Ibadan Biomedical Communications Group ISSN: 1119-5096 Vol. 8, Num. 1, 2005, pp. 31-33

African Journal of Biomedical Research, Vol. 8, No. 1, 2005, pp.31-33

Full Length Research Article  

Larvicidal and Adult Emergence Inhibition Effect of Centella asiatica Brahmi (Umbelliferae) against Mosquito Culex quinquefasciatus Say (Diptera : Culicidae) 

Rajkumar, S and *Jebanesan, A

Division of Vector Biology, Department of Zoology, AnnamalaiUniversity, Annamalainagar – 608 002, Tamil Nadu, India.
*Author for correspondence: Dr. A. Jebanesan, Division of Vector Biology, Department of Zoology, Annamalai University, Annamalainagar – 608 002, Tamil Nadu, India. Tel.: 91-4144-239050; E-mail: drjeban@rediffmail.com

 Code Number: md05005

Abstract

Ethanolic extract of Centella asiatica leaves were evaluated for the larvicidal and adult emergence inhibition activity against mosquito Culex quinquefasciatus under five constant temperatures 19, 22, 25, 28 and 31°C in the laboratory. Toxicity of this extract increased with temperature. The 50% medium lethal concentrations ranged between 6.84 ppm at 19°C and 1.12 ppm at 31°C. A similar trend was observed for the 90% lethal concentrations which varied from 9.12 to 3.63 ppm at the two temperatures, respectively. The adult emergence inhibition activity of this extract at LC₅₀s of different temperatures was generally more pronounced in increased temperatures. These results suggest that the leaf extract of C. asiatica is promising as larvicide and adult emergence inhibitor against Culex quinquefasciatus and might be used directly in small volume aquatic habitats or breeding sites of limited size around human dwellings.

Keywords: Centella asiatica, Culex quinquefasciatus, Larvicidal activity, Adult emergence inhibition activity. 

INTRODUCTION

Mosquitoes not only cause nuisance by their bites but also transmit deadly diseases like malaria, filariasis, yellow fever, dengue and Japanese encephalitis, contribute significantly to poverty and social debility in tropical countries (Jang et al., 2002). The mosquito Culex quinquefasciatus acts as a vector for Wuchereria bancrofti responsible for filariasis in India. However, control of such diseases are becoming increasingly difficult because the over production of detoxifying mechanisms of chemical insecticides has been reported for Culex species (Severini et al., 1993). On the other hand, some mosquito species have developed high levels of resistance to microbial control agents (Rao et al., 1995). One alternative approach is the use of natural products from plant origin (Consoli and Oliveira, 1994). The botanical insecticides are generally pest specific and are relatively harmless to non-target organisms including man. They are also biodegradable and harmless to the environment. One plant species may possess substances with a wide range of activities, for example extracts from the neem tree Azadirachta indica showed antifeedant, antioviposition, repellent and growth–regulating activity (Schmutterrer, 1995).

The species Centella asiatica Brahmi (umbelliferae) grows as a climber in most part of the Asia. The leaves of this plant used for skin diseases like chronic ulceration, psoriasis and leprosy (Vishnurao, 1996). The objectives of this study were to determine the efficacy of Centella asiatica against the larvae of Culex quinquefasciatus under constant temperatures ranging between 19 and 31°C.

MATERIALS AND METHODS

Preparation of phyto-chemical extract

Fully developed leaves of C. asiatica were collected from the medicinal plant garden of our university campus. The dried and powdered leaves (1.0 kg) of C. asiatica were extracted with ethanol (3 l) at soxhlet apparatus for 8 hrs. The extract was concentrated in a rotary vacuum evaporator to yield a dark greenish, gummy extract (143.31 g). The residue was then made into 1.0% stock solution with acetone.

The test organism namely Culex quinquefasciatus was reared in the laboratory. The larvae were fed on dog biscuits and yeast powder in the 3:1 ratio. Adults were provided with 10% sucrose solution and 1-week – old chick for blood feeding. Mosquitoes were held at 28 ± 2°C, 70± 5% RH, and a photoregime of 16:8 (L:D) h.

The larvicidal activity of the extract against Culex quinquefasciatus at constant temperatures of 19, 22, 25, 28 and 31°C was evaluated as per the standard procedure (WHO, 1996). The stock solution of the extract was volumetrically diluted to 250 ml filtered tap water to obtain the test solutions of 1.0, 2.0, 4.0, 6.0, 8.0 and 10.0 ppm. The acetone was served as a control. Early third instar larvae (25) were introduced to each of the test solutions as well as control. For each dose five replicates were run at a time. The larval mortality was recorded after 24 h post treatment. Probit analysis (Finney 1971) was used to determine the median lethal concentration (LC₅₀) and lethal concentration (LC₉₀) at all the tested temperatures.

The effect of leaf extract on the inhibition of adult emergence was determined by the use of the LC₅₀ at each of the tested temperatures. Twenty five larvae were placed in capped one litre glass jar containing 250 ml of water in which the LC₅₀ of the extract for each temperature was mixed. Control groups were set up for each temperature in a similar fashion. The number of emerged adults was recorded until adult emergence was completed in the control jars.

C. asiatica leaf extract caused mortality against larvae of Culex quinquefasciatus at all the tested temperatures. However, the sensitivity of the insects was positively correlated to temperatures. Thus, the 24 h LC₅₀ was 1.12 ppm at 31°C and increased the LC₅₀ value with the decrease in temperature to reach 6.84 ppm at 19°C (Table 1).

The larvae susceptible in 31°C was 6.10, 5.03, 3.5 and 2.49 times more effect than 19, 22, 25 and 28°C, respectively. The results showed that this extract can be used to control larvae of Culex quinquefasciatus over wide range of temperature.

The adult emergence inhibition of Culex quinquefasciatus by C. asiatica leaf extract presented in Table II. The emergence inhibition of adult from the treatment of survivors with LC₅₀s of different temperature generally increased with temperature. Therefore, the data suggest that the leaf extract of C. asiatica also act as a adult emergence inhibition against mosquito Culex quinquefasciatus.

Today, the environmental safety of an insecticide is considered to be of paramount importance. An insecticide does not have to cause high mortality on target organisms in order to be acceptable (Kabaru and Gichia, 2001). Phytochemicals may serve as suitable alternatives to synthetic insecticides in future as they are relatively safe, inexpensive, and are readily available in many areas of the world. According to Bowers et al. (1995) the screening of locally available medicinal plants for mosquito control would generate local employment, reduce dependence on expensive imported products and stimulate local efforts to enhance public health.

The crude extracts of the leaves of C. asiatica has been found to possess larvicidal and adult emergence inhibition activity against the mosquito Culex quinquefasciatus. The biological activity of the plant extract might be due to the various compound, including phenolics, terpenoids, and alkaloids, exist in plants, these compounds may jointly or independently contribute to produce larvicidal and adult emergence inhibition activity against Culex quinquefasciatus.

The larvicidal efficacy of C. asiatica is comparable to well established insecticidal plant species. Pizzarro et al (1999) studied the activity of the saponine fraction of Agave sisalana and estimated the LC₅₀ and LC₉₀ against 3^rd instar larvae of Culex quinquefasciatus, that were 183 and 408 ppm, respectively. These concentrations were much higher than those reported in this study, but these authors suggested its use for control of this mosquito. The leaf extract of C. asiatica is superior to various neem extracts, which are reported to be effective with LC₅₀ values ranging from 55-65 ppm against mosquito larvae (Ascher and Meisner 1989). The median lethal concentrations (LC₅₀) of various parts of Melia azederach ranging from 30-40 ppm against larva of Culex pipiens (Al-Sharook et al., 1991). The effect of the various neem extracts and various parts of Melia azederach was slightly lower than that reported for the C. asiatica leaf extract. The adult emergence inhibition activity of C. asiatica is also comparable to different species of plant extract in different families (Muthukrishnan et al., 1999; Pushpalatha and Muthukrishnan, 1999).

The findings of the present investigation revealed that the leaf extract of C. asiatica possess remarkable larvicidal and adult emergence inhibition activity against mosquito Culex quinquefasciatus. Further investigations are needed to elucidate this activity against a wide range of mosquito species and also the active ingredient(s) of the extract responsible for larvicidal and adult emergence inhibition activity in Culex quinquefasciatus should be identified and utilized, if possible, in preparing a commercial product / formulation to be used as a mosquitocidal.

The authors are grateful to the Professor and Head, Department of Zoology, Annamalai University for the facilities provided.

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