Capsicum chinensis (Hot Pepper) Powder Larvicidal Activity Against Mosquitoes Larvae in Lafia Local Government Area, Nasarawa State, Nigeria Activity Against Larvae in

Mosquitoes spread more diseases than other known arthropod and have shown resistance to conventional insecticides despite several control efforts, prompting the need to explore alternative control measures such as the use of bio-larvicides which are environmentally friendly. To this end, a study on larvicidal activity of the powder of Capsicum chinensis against mosquitoes larvae in Lafia Local Government Area, Nasarawa State, Nigeria was carried out through collection of wild field mosquitoes larvae from April to July 2018. Fresh Capsicum chinensis fruits were collected from farmlands and dried under room temperature and further processed to fine powder from which varying concentrations were used against the larvae. The larvae were exposed at 24, 48 and 72 hours, respectively. Anopheles gambiae larvae were susceptible (100% mortality) to the various concentrations of the powder at the end of the 72 hours exposure period while Culex quinquefasciatus were resistant (0% mortality). There was a very high significant difference (P < 0.0001) in mortality rate of An. gambiae larvae in relation to concentrations while there was no significant difference (P = 1) in mortality rate of Cx. quinquefasciatus across concentrations. LD 50 and LD 90 values for An. gambiae at 24 hours were 21.88mg/ mL and 52.48mg/mL respectively; 16.98mg/mL and 38.90mg/mL respectively at 48 hours and 13.80mg/mL and 30.19mg/mL respectively ay 72 hours. This study shows that Capsicum chinensis is a promising bio-larvicide for controlling An. gambiae. Also, Cx. quinquefasciatus may possibly require higher multiple doses of Capsicum chinensis to influence mortality.


Introduction
Mosquitoes are considered insects of public health importance due to their ability to transmit a variety of diseases including West Nile, dengue, yellow fever, lymphatic filariasis (elephantiasis) and malaria which is the leading cause of morbidity and mortality in DOI: 10.26717/BJSTR.2020. 31.005162 Nigeria [1]. Malaria, which causes about 1.2 million deaths (majorly among pregnant women and children under five years old) is caused by Anopheles gambiae s. l. [2]. Despite several efforts in controlling this vector, the medical and economic burdens caused by it continue to grow [3]. Currently, mosquito control strategies are fixated on the use of synthetic insecticides as constituents for Long Lasting Insecticide Treated Bed Nets (LLINs) and Indoor Residual Sprays (IRS) as methods recommended by the World Health Organization (WHO) [4]. Unfortunately, the success recorded by this strategy in terms of reduction of morbidity and mortality [5] is short-lived as mosquito resistance to insecticide has increased through time [6][7][8][9][10][11]. The failure in current control measures and the growing insecticide resistance is necessitating the search for newer and more effective control strategies [12]. The use of botanicals (plant-based products) is one of the best alternatives to synthetic insecticides [13,14]. This is because they offer a more environmentally friendly method of mosquito control [15] in that they have very weak adverse effect on non-target subjects [16] and are easily biodegradable [17]. Consequently, several plant species have been employed, worldwide, to control mosquito populations.
Capsicum chinensis (hot pepper) has both medicinal and insecticidal value and is used traditionally as medicine for treatment of various illnesses [18] including asthma, pneumonia, diarrhea, cramps, indigestion and toothache and it has been reported to possess repellent activity against insect pests of stored grains [19]. Extracts of Capsicum species have been proven as repellants to some species of some stored product beetles such as Sitophilus zeamais Motschulsky (Coleopteran: Curculinidae) and Tribolium castaneum (Herbst) (Coleopteran: Tenebrionidae) [20]. There are reports of using Capsicum as biopesticides against Alfalfa weevil larvae Hyper brunneipennis [21]. The toxicity of Capsicum species against insects is thought to be the effects of secondary metabolites such as alkaloids, saponins and flavonoid compounds [22]. Against this backdrop, this study was carried out to determine the larvicidal efficacy of the powder of Capsicum chinensis on mosquitoes' larvae in Lafia Local Government Area, Nasarawa State, Nigeria.

Study Area
The study was carried out in Lafia Metropolis with the following coordinate's 8°29′30″N 8°31′0″E/8°49′16″N 8°51′66″E. It is the capital and the largest town in Nasarawa State. The dried plant was ground into fine powder in an electric grinder [23] then weighed on a weighing balance to get 20mg, 40mg, 60mg, 80mg and 100mg doses, respectively.

Mosquitoes Larvae Collection
First and second in star larvae of Anopheles and Culex mosquitoes were collected between April and July, 2018 from different breeding sites in Lafia using standard dippers and identified using identification keys by Gillies and de Mellion [24] and Burges and Cowan [25]. The larvae were kept in containers and allowed to acclimatize for 24 hours at room temperature before carrying out the test.

Preparation of Bioassay
The bioassay was prepared according to the recommended protocol of World Health Organization [26] for susceptibility.
The larvae of Anopheles gambiae and Culex quiquefasciatus were exposed to varying doses (20mg, 40mg, 60mg, 80mg, and 100mg) of the powder of Capsicum chinensis. Each treatment (concentration) had four replicates and a control of two replicates. In each of the replicates, 25 first and second in star larvae were released into disposable 250 ml bowls containing 100 ml of distilled water and thereafter treatment was added. Control (0mg) was prepared as 100 ml distilled water only. The knockdown rate of larvae was recorded after 5mins, 15mins, 20mins, 30mins and 60mins, respectively. Larval mortality was recorded in 24, 48 and 72 hours exposure period. Mortality was confirmed by gentle prick on the abdomen of the larvae with a needle [26,27].

Test Analysis
The interpretation of the mortality rate of Anopheles gambiae and Culex quinquefasciatus larvae is as described by WHO [26] where: a) Mortality rate between 98 -100% within the diagnostic time indicates susceptible. b) Mortality rate between 80 -97% suggest possible resistance.

Percentage Mortality
Unmoved and moribund larvae were recorded as dead.

Determination of LD 50 and LD 90
The mortality data were further subjected to probit analysis for estimating lethal dose values (LD 50 and LD 90 ) using Finney method [28]. The 24, 48 and 72 hours LD 50 and LD 90 were determined through Microsoft excel regression analysis using the regression

Data Analysis
Data obtained was analyzed using R Console version 3.2.2.
Pearson's Chi Square test was used to compare mortality rate of mosquitoes' larvae in relation to concentrations of C. chinensis powder. Level of significance was set at P < 0.05.   The lethal dose of C. chinensis that will exhibit larvicidal activity against 50% and 90% respectively of An. gambiae larvae at 24 hours exposure period is 21.88mg/ml and 52.48mg/ml ( Table 2).

Discussion
The present investigation revealed that the powder of C.
chinensis showed promising larvicidal efficacy against An. gambiae but may not be against Cx. quinquefasciatus. This agrees with the studies by Abok et al. [14] and Dalis [29] who recorded that the leaf extracts of H. suaveolens were potent against the larvae of An. gambiae. However, this result did not conform to that of Madhumathy et al. [30] in which the ethanol extract of C. annum proved to be more effective on Cx. quinquefasciatus than An.
stephensi in India. This could be due to the difference in species  it difficult for the mosquito species to survive [14] and also from the activity of capsaicin in the plant powder, which has significant lethal and anti-feedant effect on mosquito larvae [30]. Generally, An. gambiae larvae were completely susceptible to all doses while absolute resistance was observed in Cx. quinquefasciatus larvae. Consequently, the finding by Meenakshi and Jayaprakash [34] showed that Anopheles larvae were more susceptible to the leaf extract of Rhizophora mucronata than Aedes larvae. Also, Kemabonta et al. [35] reported mortality of An. gambiae in relation to the insecticidal activity of essential oils for both P. nigrum (black pepper) and C. longa (turmeric) to be a 100.0%. Furthermore, the habitat of Culex larvae suggests a possible reason for their resistance as they thrive in dirty, toxic and polluted water unlike Anopheles mosquitoes that prefer clean and clear water [25].

Conclusion
The result of this study clearly shows that Capsicum chinensis possesses larvicidal properties against larvae of An. gambiae while very high concentration of the powder of C. chinensis would be required to kill Cx. quinquefasciatus. Hence, mosquitoes breeding success can be interrupted by pouring multiple doses of the powder of C. chinensis in stagnant water bodies as a direct control measure on vector populations. Also, it will be good to assess the impact of C.
chinensis powder on non-target organisms.