ABSTRACT
Mosquitoes constitute a serious Public menace, resulting in millions of death worldwide each year. Emergence of insecticide resistant strains of the mosquitoes poses a serious and hence calls for alternative control .
This study assessed the larvicidal efficacy of the methanolic and aqueous of different parts of Picralima nitida against the 4th instar of the malaria vector Anopheles gambiae.
Larvicidal activities of the leaf, seed and pulp of the plant were therefore studied on laboratory reared larvae of A. gambiae at concentration ranges of 0.5 mg/ml to 5.0 mg/ml. The LC50 and LC95 values were obtained from probit analysis using SPSS version 16.0, at 95% confidence limit (CL).
The Median Relative Potency of the extracts was also obtained using probit analysis at (P ≤0.05). Results of the study indicated that the LC50 and LC95 values of the aqueous leaf extracts were 3.14 mg/ml and 42.15 mg/ml at 24 h, 0.35 mg/ml and 4.73 mg/ml at 48 h and 0.16 mg/ml and 2.20 mg/ml at 72 h.
A lower larvicidal activity was however observed with the methanolic leaf extract: LC50 value of 48.38 mg/ml, 15.82 mg/ml and 0.33 mg/ml at 24 h, 48 h and 72 h respectively.
Methanolic seed extract on the other hand, exhibited a higher degree of potency compared with the aqueous seed extract with a low LC50 value of 0.87 mg/ml, 0.21 mg/ml and 0.15 mg/ml at 24, 48 and 72 h respectively; and an LC95 values of 0.74 mg/ml, 0.18 mg/ml and 0.12 mg/ml at same time interval.
A higher efficacy of activity was exhibited by the aqueous pulp extract than the methanolic pulp extract; with lowest LC50 of 2.79 mg/ml at 72 h, and LC95 value of 10.40 mg/ml.
The relative potency estimate of the aqueous extract at 24 h gave the following result: aqueous leaf extract was 5.48 times more potent than the aqueous seed; the aqueous pulp 2.20 times greater than the aqueous seed whereas the aqueous leaf was 2.50 times more potent than the aqueous pulp.
Similar trend was also observed at 48 and 72 h. Comparatively, at 24 h the methanolic seed extract was 269.76 times more potent than the methanolic leaf extracts; the methanolic pulp extract 2.40 times more potent than the methanolic leaf while the methanolic seed gave a potency of 112.49 times more than the methanolic pulp.
However at 48 and 72 h, there was a reversal in trend with the methanolic leaf extract showing a relative potency of 2.73 and 11.51 times that of the methanolic pulp.
The LT50 (Median Lethal Time) of the extracts, evaluated at concentration of 1.0mg/ml with P = 0.05, was the following LT50; 28h, 3.6 h and 57 h for aqueous leaf extract, methanolic seed extract and methanolic leaf extract respectively.
Similarly, comparative evaluation of the overall efficacy of the various extracts showed that the methanolic seed extract exhibited the highest degree of activity (P<0.05), followed by the aqueous leaf extract and methanolic leaf extract.
Conclusively, aqueous seed, methanolic pulp and aqueous pulp extract showed a relatively lower activity and an LT50 value of 300 hrs and above at a concentration of 1.0 mg/ml.
The results of this research therefore underscores the efficacy of the plant and further suggest the use of methanolic seed, aqueous leaf and methanolic leaf extracts of P. nitida as an eco-friendly alternative in malaria vector larviciding.
TABLE OF CONTENTS
Title page i
Certification iii
Dedication iv
Acknowledgement v
Table of Content vi
List of Figugutres ix
List of Tables x
List of Acronyms xi
List of Appendices xiii
Abstract xiv
CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW
- Introduction 1
- Literature Review 3
- Botanical description of the plant Picralima nitida 3
- Classification 3
- Uses of the Plant “Picralima nitida” 4
- Biology of mosquito 5
- Ecology of Mosquitoes 6
- Habitat productivity 7
- Spatial and temporal distribution 8
1.5.2 Gonotrophic cycle 9
- Malaria Prevention and Control 9
- Drug treatment 10
- Indoor residual spraying (IRS) 10
- Mosquito nets 11
- Larval control 12
- Chemical larvicides 13
- Microbial insecticides 13
- Phytochemicals as Larvicidal Agents 14
- Major Phytochemicals from Plants 15
- Extraction Procedures 20
1.9.10 Mode of action of phytochemicals in target insect body 22
- Review of Synthetic Insecticides 23
- Insecticide resistance 24
- Classes of Insecticides 24
- Mechanism of Resistance 26
- Insecticide Resistance Detection Techniques 27
CHAPTER TWO: METHODOLOGY
- Collection of Plant Materials 30
- Sample Preparation and Extraction 30
- Phytochemical Screening 31
- Test for alkaloids 31
- Test for saponins 32
- Test for phenols/tannins 32
- Test for anthraquinones 32
- Test for glycosides 32
- Test for flavonoids 33
- Test for steroids and terpenoids 33
- Raising of Anopheles gambiae larvae 33
- Larvicidal Bioassay 34
- Determination of LC50 and LC95 35
CHAPTER THREE: RESULTS
- Larvicidal Effect of Plant Extracts on Anopheline Larva 36
- Relative Median Potency 49
- Median Lethal Concentration 58
- Median Lethal Time 67
- Percentage yield 69
- Phytochemical Characteristics 71
CHAPTER FOUR: DISCUSSION AND CONCLUSION
REFERENCES 78
APPENDICES
INTRODUCTION
Mosquitoes are vectors of disease causing agents found within almost all tropical and subtropical countries.
They are responsible for the transmission of pathogens causing some of the life threatening and debilitating diseases of man, such as; malaria, yellow fever, dengue fever, chikungunya, filariasis, encephalitis, etc (Chandra et al., 2008; ICMR, 2003).
Beatty et al., 2007, reported that fifty-five percent (55%) of the world’s population are at risk of mosquito borne diseases in 124 countries.
According to WHO/UNICEF (2005) first comprehensive report on the Roll Back Malaria partnership, malaria is endemic in 117 countries with some 3.2 billion people living in risk areas all over the world.
It further states that each year, there are about 350- 500 million clinical cases of malaria worldwide with over 1 million death. About 59% of all clinical cases occur in Africa, 38% in Asia, and 3% in the Americas.
Malaria mortality is also highest in Africa with 89% of all deaths whereas 10% occurs in Asia and less than 1% in the Americas. Of all malaria cases caused by Plasmodium falciparum, the most deadly human malaria species, 74% are in Africa, 25% in Asia and 1% in the Americas.
Anopheline mosquitoes are the vectors responsible for the transmission of deadly malaria etiological agent “plasmodium” (Wendy et al., 2012).
Despite several efforts in the field of vector control, the medical and economic burden caused by vector-borne diseases continues to grow as current control measures fail to cope (Radhika et al., 2011).
There is therefore an urgent need to identify new control strategies that will remain effective, even in the face of growing insecticide and drug resistance (Achs and Malaney, 2002).
REFERENCES
Abbott, W.S. (1925). A method of computing the effectiveness of an insecticide. Journal of Econometric Entomology; 18: 265-267
Abdullahi, K., Abubakar, M.G., Umar, R.A., Gwarzo, M. S., Muhammad, M. and Ibrahim,H.
(2011). Studies on the larvicidal efficacy of aqueous extracts of Striga hermonthica (Delile) Benth and Mitracarpus scaber (Zucc) on Culex quinquefasciatus (culicidae) mosquito larvae. Journal of Medicinal Plants Research, 5(21): 5321-5323.
Achs, J. and Malaney, P. (2002). The economic and social burden of malaria. Nature, 15: 680- 685.
Ademola, O. and Eloff, J.N. (2011). Anthelmintic efficacy of cashew (Anarcadium occidentale L.) on in vitro susceptibility of the ova and larvae of Haemonchus contortus. African Journal of Biotechnology, 10(47): 9700-9705.
Afrane, Y.A., Lawson, B.W., Githeko, A.K., Yan, G. (2005). Effects of microclimatic changes caused by land use and land cover on duration of gonotrophic cycles of Anopheles gambiae (Diptera: Culicidae) in western Kenya highlands. Journal of Medical Entomology, 42: 974-980.
Ameneshewa, B., Service, M.W. (1996). The relationship between female body size and survival rate of the malaria vector Anopheles arabiensis in Ethiopia. Medical and Veterinary Entomology, 10: 170-172.
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