Received Date: 25/11/2015 Accepted Date: 09/11/2015 Published Date: 11/12/2015
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The aim of the present study was to evaluate the larvicidal activity of plant powders of Bauhinia variegata and Croton sparsiflorus against the fourth instar larvae of Aedes aegypti. The macerated leaf powders of B. variegata and C. sparsiflorus were tested against the larvae of A. aegypti upto 24 hr exposure period with the concentrations of 100, 120, 140, 160, 180, and 200 mg/100 ml of tap water. The leaf powder of C. sparsiflorus had LC50 value of 122.73 mg/100 ml and LC90 value of 180.04 mg/100 ml followed by B. variegata with LC50 value of 142.47 mg/100 ml and LC90 value of 210.16 mg/100 ml respectively. The present investigation clearly demonstrates that C. sparsiflorus showed cent percent mortality followed by B. variegata against the larvae of A. aegypti. With further isolation and identification of bioactive molecules from B. variegata and C. sparsiflorus can be evaluated and developed novel biopesticide against mosquitoes as well as other insect pests.
Croton sparsiflorus, Bauhinia variegata, Aedes aegypti, Larvicidal activity.
Mosquitoes are haematophagous insects and serve as vectors for spreading dreadful human diseases. Dengue fever is considered as a serious public health problem in the world. Dengue is endemic in all continents except Europe, and epidemic Dengue viruses, causative agents of dengue fever and more severe dengue haemorrhagic fever/dengue shock syndrome, infect over 100 million people every year. Dengue is the most common and widespread arboviral infection in the world today . The excessive usage of synthetic organic pesticides during the last decade has resulted in environmental hazards and development of physiological resistance in vector mosquito species. Insecticides residual problem together with the insect resistance pose us in the environment to seek attention towards alternative methods . This has necessitated the need of research and development on environmental safe, bio-degradable and indigenous method for vector control. Many herbal products have been evaluated and used as natural insecticides early before the use of synthetic insecticides . The plant B. variegata is widely used in folklore medicine. Its bark, root, leaves, seeds and flowers are used for their medicinal properties. It has been used in dyspepsia, bronchitis, leprosy, ulcer, to prevent obesity, as an astringent, tonic and anthelmintic . The phytochemical screening revealed that B. variegata contained terpenoids, flavonoids, tannins, saponins, reducing sugars, steroids and cardiac glycosides. Pharmacological studies showed that B. variegata exerted anticancer, antioxidant, hypolipidemic, antimicrobial, anti-inflammatory, nephroprotective, hepatoprotective, antiulcer, immunomodulating, molluscicidal, wound healing effects  and insecticidal activities [6-7]. Croton sparsiflorus leaves were used to treat antidiarrhoeal, insecticidal  and other ailments [9-10]; glycoside, saponins tannins, flavonides, terpenoids and alkaloids also reported [11-12]. The objective of this study was to investigate the larvicidal effect of leaf powders of Croton sparsiflorus and Bauhinia variegata against the larvae of Aedes aegypti.
Fresh and matured leaves of Bauhinia variegate L. (Figure1) and Croton sparsiflorus L. (Figure 2) were used for the research work. They were collected from Periyar university campus, Salem, Tamil Nadu, India based on their abundance, availability, medicinal and insecticidal properties. The leaves were shade dried and macerated with electric blender and stored at the temperature of 4°C. The LC50 and LC90 values were calculated using EPA Probit analysis software.
Aedes aegypti L. larvae were collected from stagnant water bodies in and around Periyar university campus, Salem, Tamil Nadu, India. They were colonized and maintained continuously for generations in the laboratory free of exposure to pathogens, insecticides or repellents. They were maintained at 27 ± 2°C, 75-85% RH under a photoperiod of 14:10 hr (light/dark) in the insectary. Larvae were fed on finely ground dog biscuit and yeast extract in the ratio of 3:1. Water was changed every day to avoid scum formation which might create toxicity. Pupae were transferred from the trays to a cup containing tap water and placed in screened cages (30 × 30 × 30 cm dimension) where the adults emerged. The adult mosquitoes were reared in the glass cages of 30 × 30 × 30 cm dimension. The adult colony was provided with 10% sucrose solution and was periodically blood-fed on restrained rats. After three days, ovitrap was kept in the cages and the eggs were collected and transferred to the enamel trays. Two developmental stages, larvae and adult, were continuously available for the experiments and were maintained at the same condition as mentioned above.
Larvicidal activity was evaluated by using Patil et al. method . Twenty five late third or early fourth instar larvae of A. aegypti were released in a 250 ml glass beaker containing 100 ml of dechlorinated tap water mixed with and desired plant powder concentration (mg). Five replicates of each concentration were run at a time. The experimental concentrations were 100, 120, 140, 160, 180 and 200 mg, respectively. The LC50 and LC90 values were calculated by EPA Probit analysis software.
The LC50 and LC90 value of C. sparsiflorus leaf extracts exhibited 122.73 and 180.04 mg/100 ml against A. aegypti. The B. variegata leaf powder exhibited the LC50 and LC90 value of 142.47 and 210.16 mg/100 ml against A. aegypti. Among the two plant powders C. sparsiflorus exhibited highest larvicidal activity against A. aegypti (Table 1). In the present investigation C. sparsiflorus showed cent percent mortality followed by B. variegata against the immatures of A. aegypti. Our results were coincides with earlier findings of Santos et al. fresh and stored oil from C. rhamnifolioides exhibited substantial larvicidal activities with LC50 values of 122.35 and 89.03 ppm, against A. aegypti. Croton zambesicus exhibited moderate larvicidal activity with LC50 value of 155.19 and LC90 value of 580.16 ppm against Anopheles stephensi . The LC50 and LC90 values of C. macrostachyus exhibited 89.25 and 224.98 ppm, against A. arabiensis . However, the ethylacetate extract of B. racemose showed lowest toxic effect against An. stephensi . Kaushik and Saini  reported that Bauhinia variegata leaf extract showed moderated larvicidal activity with the LC50 value of 204.2 ppm against A. aegypti. Our result clearly demonstrates that the leaves of C. sparsiflorus were highly effective against A. aegypti followed by B. variegata. Powdered leaves of C. sparsiflorus and B. variegata may be a good source to control vector mosquitoes. With further isolation, purification and identification of active compound from B. variegata and C. sparsiflorus can be evaluated and developed novel biopesticide against mosquitoes.
|Replication||Control||Concentration(mg/100ml)||LC50||95% Confidence limit||LC90||95% Confidence limit|
|200 mg||180 mg||160 mg||140 mg||120 mg||100 mg|
|% of mortality||0||89.6||74.4||59.2||44.8||36||24|
|% of mortality||0||100||90.4||72.8||60||46.4||38.4|
Table 1. Larvicidal activity of Bauhinia variegata L. and Croton sparsiflorus L. against the larvae of Aedes aegypti L.
The authors are grateful to the management of Periyar University, Salem, Tamil Nadu, India for supporting this work.