Assessment of the Larvicidal Efficacy of the Hexane-Leaf-Extracts of Selected Tropical Plant Species

The proliferation of mosquito vector in tropical countries has increased the prevalence of malaria with high morbidity and mortality burden. This research is concerned with the biolarvicidal efficacies of Cassia alata, Microdesmis puberula ̧ and Spilanthes filicaulis extracted with hexane solvent, and screened against mosquito larva. Results on the negative control had no mortality on the larvae compared to the positive control, which had total mortality (p<0.05). The C. alata plant extracts was the most active with LC50 value of 25.26 ppm, followed by; M. puberula (32.83 ppm), and S. filicaulis (36.46 ppm). Based on the outcome of the larvicidal bioassay, Hexane-leaf-extracts of all plants can be recommended for the formulation of biolarvicide due to their efficacies.


I. Introduction
Malaria diseases are a major problem ravaging the tropical county. Statistically, malaria was reported to affect over 3.5 billion persons annually (Ohimain et al., 2014). It was also reported in literature that there are over 100 countries, with about 700 million incidence of malaria, especially tropical Region (Okumu et al., 2007). Malaria disease has been reported in the many developing countries in especially in Africa.
There are diverse species of mosquitoes that exist in nature, but around 30 -40 species were reported to be carriers of the plasmodium parasite (Ghosh et al., 2007). In Africa, the most endemic transmitter of malaria is the female species of Anopheles gambiae and An. Arabiensis (Okumu, et al., 2007;Angaye, et al., 2014a;2014b;Hamza et al., 2014;Owoeye et al., 2016).
According to Angaye (2015), the therapeutic efficacy of plant is not farfetched because plant produce elaborate metabolites as their genetic makeup, defence mechanisms and otherwise. As reported by Devappa, et al., (2010), tannins produced by some plants have ability to retard the palatability, nutrient absorption and growth rate of predators. These metabolites found in plant, these includes about 10,000 and 25,000 alkaloids and terpenes respectively (Cheeke, 1998).
There are several compounding factors responsible for plant efficacies as antioxidant; this include age of the plant, location, season and even ability of the plant to withstand harsh environment (Devappa et al., 2010;Angaye, 2015), or even the part of the plant (root, stem, fruits, leaves, and seeds) and/or applied solvent used for the bioassay (Angaye, 2015). Therefore, this investigation on the larvicidal efficacies of the hexane extracts of C. alata, M. puberula¸ and S. filicaulis.

Collection and Preparation of Plant Samples
The fresh leaves of C. alata, M. puberula and S. filicaulis were collected from vegetation around Wilberforce Island in Southern Ijaw Local Government Area of Bayelsa State, Nigeria. The plants were identified, washed and shade-dried for 7 days. The shade-dried plants were Budapest International Research in Exact Sciences (BirEx) Journal Volume 2, No 2, April 2020, Page: 136-140 e-ISSN: 2655-7827 (Online), p-ISSN: 2655 www. placed in oven at 50°C for 30 minutes (Angaye et al., 2017a;Angaye et al., 2017b), and powdered with electric blender.

Extraction Process
Three hundred grams (300 g) of the powdered leaves of each plants were weighed using Satoric AG Gottingen Electronic weighing balance. The weighed powdered leaves were respectively macerated in 500 ml of the Hexane solvent for 72 hours and filtered into conical flask using whatman No.1 filter paper (Azoro, 2000). The filtrates distinctly extracted using a rotary evaporator at 60°C.

Mosquito Larva Collection
Mosquito Larvae used for this bioassay were cultured in the wild using methods as described by some authors (Rai et al., 2004;Okumu et al., 2007;Ohimain et al., 2014), with slight modification. Plastic containers and automobile tyres half-filled with stagnant water, and sand were kept in vegetation of conspicuous breeding sites. Prior to the laboratory bioassay, the larvae were placed on enamel tray and acclimatized to laboratory condition.

Experimental Setup
A minimum of 10 larvae, were distinctly placed in a 500 ml solution of the methanolicextract at varying concentrations, in a 24-hour static non-renewal test. The bioassay was performed with the standard of the World Health Organization guidelines (Dibua et al., 2013). Mortality rates (%), of larvae were recorded after the period of exposure (24 hours). A concentration of 1 ppm of Dipex pesticide was used as the positive control, while 500 ml of distilled water was used as the negative control. The larvicidal screening protocols were twophased, involving the rapid and final Screening (Agboola et al., 2011).

Statistical Analysis
The data for mortality rates were expressed as mean± standard deviation using version 20 of SPSS statistical package. A one-way analysis of variance was used to carry out the statistical analysis, while Duncan multiple range test was used to determine the source of observed difference using SPSS Version 20.

III. Result and Discussion
Results of mortality rates for leaf Hexane extracts of the three plants is presented in table 2. For the Cassia alata extract, the mortality rates ranges from 26.66 -100.00% significantly (p<0.05), with minimal and total mortalities at concentrations of 10 and 70 ppm respectively. In addition, the positive control had total mortality at concentration of 10 ppm, compared to the negative control that showed no mortality rate (Table 1). Furthermore, results of the larvicidal efficacy of the C. alata hexane extract were demonstrated with LC50 value of 25.26 ppm (Figure 1).  2, No 2, April 2020, Page: 136-140 e-ISSN: 2655-7827 (Online), p-ISSN: 2655 www. bircu-journal.com/index.php/birex emails: birex.journal@gmail.com  Results of the M. puberula bioassay showed that mortality rates ranges from 13.33 -100.00%, with significant difference (p<0.05). While mortality rates increased as concentration increases (Table 1). The minimal mortality rate was reported at concentration of 10 ppm, while the total mortality was at 70 ppm. In addition, the activity of M. puberula hexane extract was demonstrated with LC50 value of 32.83 ppm (Figure 8). The S. filicaulis biolarvicidal bioassay showed that mortality rate ranges from 10.00 -100%, with significant increase in mortality rate and concentration increases (Table 4.2). The minimal mortality rate was reported at concentration of 10 ppm, while the total mortality rate was displayed at 80 ppm. In addition, the no adverse effect level was at 0.00 ppm (Table 4.2). The biolarvicidal activity of hexane extract of S. filicaulis was demonstrated with LC50 value of 36.46 ppm (Figure 1).
Results reported for hexane extracts of the current study are comparable to results by other authors. Comparatively, the larvicidal activities of the hexane extracts of the bark (11.02 ppm) and root (28.08 ppm) Azadirachta indica were (Angaye et al., 2014a), induced higher activities than hexane extracts of the 3 plants in the current. The larvicidal efficacies of the hexane leaves of Niger Delta mangrove plants against Anopheles gambiae was reported with activities for Rhizophora mangle (275.63 ppm), R. racemosa (225.00 ppm), A. germinans (250.50 ppm), and L. racemosa with value of 308.50 ppm (Angaye et al., 2014b); these values were higher than values reported in the current study for all three plants.