Bioefficacy Study Of Mosquito Repellent Produced From Ocimum Basilicum Using Aerosol Propellant As Carrier

Bioefficacy Study Of Mosquito Repellent Produced From Ocimum Basilicum Using Aerosol Propellant As Carrier

Abstract

Mosquito borne disease is a major public health problem globally, particularly the tropics being the major spot in the spread of malaria. The development of resistance to chemical insecticides has necessitated the research and development of natural mosquito repellent. The aim of this study is to extract, characterize and test the larvicidal activity of essential oil, produce mosquito repellent using the essential oil as its active ingredient and study the bioefficacy of the produced repellent on mosquito. 200g of Ocimum basilicum was extracted by soxhlet extraction method using n-hexane as solvent and percentage yield of the extract was calculated and found to be 12.85%.

The essential oil extracted was characterized using FTIR and GC-MS. Production of mosquito repellent, larvicidal activity of essential oil and bioefficacy study of mosquito repellent were conducted. The FTIR spectral indicated the presence of C=O, C=C, C-H and O-H functional groups. GC-MS study showed 12 prominent peaks with retention time of 5.756, 5.914, 10.486, 16.871,17.947, 19.883, 19.974, 20.807, 21.020, 21.231, 21.712 and 22.008 indicating the presence of twelve phyto-constituents namely: 2,4-pentadienoic acid, butanedioic acid hydroxyl-dimetyl ester, pentanedioic acid 3-oxo-dimethyl ester, palmitic acid methyl ester, stearic acid, 13-tetradece-11-yn-1-ol, 9-octadecenoic acid methyl ester, 9-octadecenoic acid (Z), hexadecanoic acid, 9,12-octadecadien-1-ol (Z,Z), 9,12-octadecadienoic acid methyl ester and E-9-tetradecenoic acid.

The essential oil showed larvicidal activity on Anopheles mosquito larva at concentration of 3ml/L, 4ml/L and 5ml/L. The mosquito repellent produced showed increasing repellent efficacy against adult Anopheles mosquitoes with increasing concentration of the essential oil. Hence it was concluded that Ocimum basilicum has a good efficacy as a repellent to Anopheles mosquitoes when used as active ingredient. The FTIR spectral reveal the presence of functional groups present in the essential oil which correlates with phyto-constituent identified by GC-MS characterization, with 9-octadecenoic (14.62%) having the highest % composition.

Chapter One

1.0 Introduction

Malaria is a mosquito-borne infection which is one of the most severe public health problems worldwide, most especially in the tropical and sub tropical countries where majority bears the burden. It is a leading cause of death and diseases in many developing countries, which affects both infants and adults, whereby children and pregnant women are the most affected. This disease is transmitted by an infected female anopheles mosquito by feeding on human blood. The mosquito bite introduces the parasites from the mosquito’s saliva into a person’s blood which can result in skin irritation to contracting malaria, dengue fever, filariasis e.t.c (Bernhard, et al., 2003). Mosquitoes are not just a nuisance but also potentially harmful. It is the primary host to the spread of malaria. It is a threatening disease as there is no proper vaccine yet found. As a result of little success in the development of effective vaccines against these diseases coupled up with the problem of drug and insecticide resistance, scientists have turned attention to mosquito control through prevention using different methods to combat both the parasites and diseases. Personal protection from mosquito bites has become a major approach to the control. Avoiding mosquito breeding by clearing stagnant water from drains, cutting of grasses and use of mosquito nets. These measures however, are often not enough and special products like mosquito repellent used to combat mosquitoes are required (Yang and Ma, 2005). Repellents are substances that act directly on the skin or in space away from the body, discouraging an insect from flying, landing on or biting human or animal skin. It can also refer to molecules that may alter the functioning of sensory motor systems and or have neurotoxic effects (Licciardi, et al., 2006). They act either through air borne molecules as vapour of volatile oilsor by non-volatile molecules with an antifeedant effect on the skin. By their action, they minimize contact between man and insect vectors to hinder the transmission of diseases (Stuart and Estanbole, 2003). Application ofrepellents to the skin is a common personal protection practice since it is a practical and an economical means of preventing transmission of these diseases to humans besides providing protection against a wide range of vectors (Pitasawat,et al.,2003). Synthetic repellent have been extensivelyused for mosquito control by either killing, preventing adult mosquito to bite human beings or by killing mosquito larvae at the breeding sites of the vectors. DEET (N, N-diethyl-3-methylbenzamide), formally known as diethyl-m-toluamide, is currently the most effective synthetic repellent available in various commercial formulations such as solutions, gels, creams, aerosols, sticks and impregnated towel etc (Frandin, 1998). However effective it is, toxic effects have been documented that include uncomfortable sticky skin, damage to plastics, synthetic clothes or rubber and the development of resistance by mosquitoes (Govere, et al., 2000). Moreover, continuous application can cause in folding of the skin epidermis with fewer hairs and thickened epidermis with more vascularity. This has highlighted the search of alternatives from plant origin that contains safe and biodegradable chemicals (Ansari, et al., 2005). Natural repellents are based on use of natural plants as repellent to insects and other pests. Plants that have been used as indigenous methods of insect control produces secondary plant compounds with insect feeding deterrent properties. The production of these compounds was due to co-evolution of the plants with insects. Essential oils from plants commonly used as fragrances, food flavorings agents and beverages contain bioactive phytochemicals, which have potential for use in insect control. Present in the essential oils, are monoterpenes, sesquiterpenes, diterpenes and triterpenes derivatives that possesses insect repellent activities (Isman, 1999).

However, repellent effects of plant products are commonly lower in both efficacy and duration than that of synthetic repellents, primarily DEET. This calls for the search of new bioactive compounds. Of particular interest, is the search of essential oil based compounds that are expected to supplement synthetic compound (Pitasawat, et al., 2006).

1.1 Aims and Objectives

To produce and study the bioefficacy of mosquito repellent produced from Ocimum basilicum using aerosol propellant as carrier.

Specific objectives include:

1. To extract the essential oil from the leaf of Ocimum basilicum.
2. To characterize the essential oil using FTIR and GC-Mass spectrophotometer.
3. To study the larvicidal activity of the essential oil.
4. To produce mosquito repellent using aerosol as carrier and basil as the active ingredient.
5. To test the bioefficacy and the time span of the produced repellent using adult mosquito species.

Chapter Five

5.0 Discussion Conclusion and Recommendation

5.1 Discussion

200g of grounded leaves of Ocimum basilicum was extracted by soxhlet extraction method and n-hexane as solvent. The percentage yield of the extract was found to be 12.85%, which correlates with findings of Lawal (2014). The characterization of the essential oil extracted was carried out using Fourier Transform Infrared Spectrophotometer (FTIR) and Gas Chromatography Mass Spectrophotometer (GC-MS). The FITR spectral shown in Table 4.2 revealed the presence of C=O (Stretch), C=C (Stretch), C=O (Stretch), C-H (Stretch) and O-H (Stretch). These indicate the presence of esters, aromatic compounds, carboxylic acids, alkanes and alcohols which correlate with the compounds reflected in GC-MS. This agrees with research of Lawal (2014) and Gabi et al., (2012). The GC-MS running time of the extract took 22 minutes, which reveal the presence of 12 phytoconstituents (Table 4.3), with 9-Octadecenoic acid (14.62%), Hexadecenoic acid (10.76) and Stearic acid (10.05) constituting the main part of the volatile oil. This correlates with research of Joey (2015). 9-Octadecenoic acid possess and contain repellent property, small amount is used as an excipient in pharmaceuticals. It is also used as an emollient, emulsifying or solubilizing agent in aerosol products (Carrasco et al., 2011). Hexadecanoic acid possess and also contain repellent property,anti-inflammatory, anti-androgenic, antioxidant, haemolytic hypercholesterol, nematode pesticide (Carrasco et al., 2011). Stearic acid is used as a chemical intermediate, emulsifier, gelling agent, releasing agent, anticaking agent, resin stabilizer, suspension agent and pigment depressant (Carrasco et al., 2011). Larvicidal activity of the oil shows that at high concentration the oil was more effective, the effect of the oil increases as the concentration increases with highest mortality rate in 5ml and was more effective at 24hrs. The efficacy of the mosquito repellent was tested by spraying 20 adult mosquitoes for each concentration in duplicate. The efficacy was recorded at concentration 100mg, 200mg, 300mg, 400mg and 500mg within time interval of 5, 10, 20 and 30 minutes, of which 500mg was more efficient. This is as a result of the presence and combination of active metabolites having the repellent activity (Trongtoki et al., 2005). Based on these, the efficacy of the repellent produced increases with increase in concentration.

5.2 Conclusion

This study has shown the repelling property of Ocimum basilicum when used in mosquito repellent production. It is concluded that Ocimumbasilicum has a good efficacy as a repellent to Anopheles mosquitoes whenused as active ingredient. The FTIR spectral reveal the presence of functional groups present in the essential oil which correlates with phyto-constituent identified by GC-MS characterization, with 9-octadecenoic (14.62%) having the highest % composition. Based on the result obtained, it is evident that there was a significant efficacy shown by Ocimum basilicum as a result of active compounds which were easily distinguishable fattyacids, esters and alcohols. The use of essential oil as active ingredient in controlling mosquito is expected to reduce the cost and environmental effect of mosquito repellents.

5.3 Recommendation

Ocimum basilicum is a natural repellent which has high efficacy to Anopheles mosquito. However, further investigation is required to test the toxicity and concentration that is efficient and harmless. Industries are adviced to incorporate essential oil of Ocimum basilicum as an active ingredient in the production of mosquito repellent. The need to conserve Ocimum basilicum is advised.

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