1 Introduction
In tropical region, many vector borne diseases are easily seen because of abundance of various species of mosquitoes in high densities. Among several mosquito borne diseases, filariasis, malaria and dengue fever are most common. Filariasis is caused by Wuchereria species is mainly transmitted by Culex quinquefasciatus in tropical regions. Resent estimate states that about 120 million people in 83 countries of the world are infected with LF parasites. Approximately 21 million people with symptomatic filariasis and 27 million microfilaria carriers were estimated in India (Reddy et al., 2000). To reduce incidence of malaria, filariasis and other vector borne diseases, regulation of mosquito population is necessary. Mainly four classes of chemical insecticides namely Organochlorines, Pyrethroids, Carbamates and Organophosphates are used for mosquito control. Now a days, over exploitation of many of these insecticides resulted into accumulation of non-degradable toxic chemicals in ecosystem, biomagnifications through food chain, toxic effect on human health and other non-target organisms, and mosquito rapidly develops physiological resistance against them that leads to the recurrence of the mosquito borne diseases. The inevitability of insecticide resistance therefore necessitates the need for urgent development of additional pesticides, since current products are predicted to become ineffective in the near future (Maharaj., 2010). Now a day’s research on indigenous plants increases which contains an array of bioactive phytochemical compounds having larvicidal potentiality (Bhattacharya et al., 2013; Bhattacharya et al., 2014a; Bhattacharya et al., 2014b; Singh ray et al., 2014; Singh ray et al., 2015; Singh et al., 2015; Bhattacharya et al., 2015), antioxidant and antimicrobial properties (Mukherjee et al., 2015).
According to World Health Organization (WHO) the most effective strategy for the reduction of mosquito borne diseases is to destroy the vectors or intermediate hosts in the immature condition having minimum spatial dispersal. Mosquito in the larval stage is an easy target for control activity because their breeding ground is water and insecticides are easily applied in their natural habitats to control them. Halder et al., (2012) has described Typhonium trilobatum as a fast acting botanical having mosquito reducing potentiality control and this plant has no significant effect on non target organism. According to Hossain et al., (2011) Dregea volubilis and Bombax malabaricum leaf extracts show good efficacy against the filarial vector Culex quinquefasciatus. Singha et al., (2011) describes that crude and chloroform: methanol (1:1 v/v) extracts of common spices and vegetable wastes can be successfully used against Cx. quinquefasciatus. So under the alternative strategy of mosquito control, application of non toxic biodegradable natural herbal extracts is preferred now a day.
In view of the search of natural larvicidal product of herbal origin, present study was carried out to explore the floral diversity of Bankura, a District of the State of West Bengal of India in search of natural plant based phytochemicals having mosquito larvicidal properties. The crude plant extracts were also evaluated against some non target community to establish the eco friendly nature of the used extracts.
2 Materials and Methods
2.1 Mosquito larvae rearing
Present study was conducted at Bankura (23.14°N and 87.07°E), West Bengal, India during June to December 2014. Cx. quinquefasciatus larvae were collected with the help of standard scooping and dipping method (Robert et al., 2002) from stagnant water body and drains surrounding the Bankura Sammilani College campus and kept in enamel tray containing tap water. Larvae were fed with a mixture diet of Brewer yeast, dog biscuits and algae in a ratio of 3:1:1 respectively (Kamaraj et al., 2011). The last instar larvae on becoming pupae were manually collected, transferred to a beaker containing tap water and kept inside a mosquito cage for adult emergence. Adult mosquitoes were identified with the help of the key provided by Christophers (1933), Barraud (1934) and Chandra G (2000). Laboratory bred 1st generation larvae were used in bioassay experiments.
2.2 Preparation of crude plant extracts
Plant extracts were prepared either from the whole plant, and/or separate parts like fruits, flowers, leaves, stem, twigs, bark and root. The plant parts were randomly harvested from different localities of Bankura district, West Bengal, India. The harvested plants were identified properly. At first the plant parts were properly rinsed with tap water and distilled water and dried on paper towel. The crude phyto extracts were prepared by crushing the plant materials with the help of an electrical grinder individually and plant juices were filtered by Whatman No.1 filter paper and clear filtrates were stored at 4°C as stock solution for bioassay experiment. Crude plant extracts of 0.1, 0.5 and 1.0% concentrations were prepared by mixing 0.1 ml, 0.5 ml and 1 ml of each plant extracts with 99.9 ml, 99.5 ml and 99 ml of distilled water respectively to make 100 ml volume in each case.
2.3 Larvicidal bioassay
The larvicidal activity of the crude extract of each plant was examined separately against Cx. quinquefasciatus at room temperature under laboratory condition according to standard protocol of WHO (WHO, 2005) with necessary modifications. Required concentrations of crude extracts (0.1, 0.5 and 1 %) were prepared through the mixing up of stock plant extract with variable amount of distilled water to make it 100 ml. Twenty five third instar larvae were taken in each glass beaker (100 ml) containing different concentration of plant extracts. A control set up was established with distilled water only. Larval mortality was recorded after 24, 48 and 72 h of exposure and the data of mortality at 72 hours were expressed by addition of mortality of 24 and 48h, respectively. The experiments were replicated three times on three different days along with control set up.
2.4 Effect on non - target organisms
Effect of crude extracts on three non-target organism such as Tadpole larvae, larvae of Toxorhynchites sp. and Chironomus sp. were tested. Ten individuals of each non target species were exposed to 100 ml of water (control set) as well as to LC50 value at 72 h of exposure against non targets. The experiments were continued up to 72 h of exposure periods to observe any mortality or abnormalities, such as sluggishness and reduced swimming activity, if any in non target organisms.
2.5 Statistical analysis
The percentage mortality observed was corrected by Abbott’s formula (Abbott WS., 1925). Statistical analysis of the experimental data was performed using the computer software’s “STAT PLUS 2007 (Trial version)” and “MS EXCEL 2007” to find out the 50% (LC50) and 90% (LC90) lethal dose values of each of the crude plant extracts.
3 Results and Discussion
Present study revealed that members of family Solanaceae, Verbenaceae and Meliaceae were very effective against mosquito larvae. Results of Mosquito larvicidal activity of crude extracts of various plant parts and the respective Lethal Concentration values are presented in Table 1. From the results of laboratory bioassay, it was found that out of 32 plants, Cleome viscosa (Leaf), Clerodendrum viscosum (Leaf), Murraya koenigii (fruit), and Vitex negundo (leaf) showed 100% mortality against Culex quinquefasciatus larvae at 0.5% (v/v) concentration within 72 hours of exposure. Similarly, extracts of leavae of Azadirachta indica, pericarp of fruits of Alangium salvifolium, seeds of Polyalthia longifolia, fruits of Derris indica and Solanum sisymbrifolium also showed 100% mortality against 3rd instars larvae at 1% concentration of crude extract within 72 h of exposure (Table 1). When respective LC50 and LC90 values of different plant extracts were compared, lowest LC50 values were recorded in Solanum nigrum fruit and Alangium salvifolium Pericarp of fruit respectively. LC90 value of Solanum sisymbrifolium, Clerodendrum viscosum, Cleome viscosa, Murraya koenigii and
Vitex negundo were also satisfactory (Table 1).
Table 1 Mortality of Culex quinquefasciatus larvae using crude extract of various plant parts at 72 hours of exposure
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In an earlier study, Rawani et al., (2010) reported the larvicidal activity of crude leaf extract of S. nigrum, collected from Burdwan and they found the LC50 value to be 0.11%. In the present study the LC50 value of the same plant part was recorded as 0.17%. Similarly Rawani et al., (2009) reported that the LC50 and LC90 values of Murraya paniculata were 0.09 and 0.21 respectively but in the present study the LC50 value and LC90 of the same plant was 0.128 and 0.565 respectively. Present study was conducted in dry climatic condition with alluvial, loamy and red lateritic acidic soil. Similarly Rawani et al., (2010) studied in warm temperate rainy climates with mild winter environment. These variations in result may be attributed to the variations in soil quality of two different districts (Bankura & Burdwan) where from S. nigram plants were collected.
Over the past decade, many plant species have been reported for their mosquitocidal properties. Roark RC (1947) described approximately 1,200 plant species, whilst Sukumar et al., (1991) listed and discussed 344 plant species that exhibited mosquitocidal activity. Tennyson et al., (2015) and Kamaraj et al., (2010) described many plant derivatives having mosquito larvicidal property. Shaalan et al., (2005) reviewed the current state of botanical pesticides. Ghosh et al., (2012) reviewed the current state of knowledge on phytochemical sources and mosquitocidal activity, their mechanism of action on target population, variation of their larvicidal activity according to mosquito species, and promising advances made in biological control of mosquitoes by plant derived secondary metabolites. Rawani et al., (2009) descirbed larvicidal properties of crude extracts of three plants, viz. Carica papaya, Murraya paniculata and Cleistanthus collinus against Cx. quinquefasciatus. According to Arivoli and Tennyson et al., (2011) the aqueous extract of Murraya koenigii delayed 2-5 days in total developmental period of Aedes aegypti, An. stephensi and Cx. quinquefasciatus.
Singh et al., (2011) described the combined form of Croton caudatus fruits and Tiliacora acuminata flowers show good bioactive potentiality against Cx. quinquefasciatus larvae due to synergism of plant extracts. Halder et al., (2013) also synthesized new silver nanoparticles produced from D. roxburghii fruit extract which have some positive attributes in respect to mosquito biocontrol especially at larval stages.
In conclusion, the crude extracts of Solanum nigrum, Azadirachta indica, Alangium salvifolium, Polyalthia longifolia, Derris indica, Solanum sisymbrifolium, Cleome viscosa, Clerodendrum viscosum have the potentiality to kill mosquito larvae and tested non-target organisms were entirely safe. As all the plants are easily available in large quantity and our country has a rich diversity of plants so if we explore the floral diversity for mosquito control programs then it may reduce the dependence on expensive synthetic insecticides. However, further studies on the mode of action, their effects on other non-target organisms and formulations for improving their insecticidal potency are to be carried out for their standardization.
Acknowledgements
We want to acknowledge the help received from HOD, Department of Botany, Bankura Sammilani College, Bankura for the proper identification of plant species. We also want to acknowledge the financial support received from the Eastern Regional Office (ERO) of University Grants Commission (UGC), New Delhi through a Minor Research Project sanctioned to Mr. Rajendra Prasad Mondal to do this work [Grant No. F. PSW-004/13-14 (ERO) ID No. WB1-009; S. No. 219563].
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