Abstract
This study assessed the larvicidal efficacy of the methanolic extract of Cymbopogon citratus, Ocimum gratissimum and Vernonia amygdalina against the third instar larvae of Culex quinquefasciatus. Qualitative analysis of the plants revealed that alkaloids, flavonoids, saponins, steroids, tannins, terpenoids and glycosides were present in all three plant extracts. Phlobatannins was present in trace amounts in O. gratissimum and absent in C. citratus and V. amygdalina. Larvicidal activities of the leaf extracts were studied on laboratory reared larvae of Cx. quinquefasciatus at a concentration range of 250 ppm to 1000 ppm. The percentage mortality was calculated and LC50, LC90 values were obtained from probit analysis using SPSS version 16.0 at 95% confidence limit (CL). Result of this study indicated that the percentage mortality of O. gratissimum extract was dose dependent with 250 and 1000 ppm having the percentage mortality of 18.33 and 43.3% respectively after 72 hrs. The percentage mortality in C. citratus extract after 72 hrs was 66.67% at 1000ppm concentration whereas at 750 ppm mortality was 8.33%. The percentage mortality for V. amygdalina increased from 250 to 750 ppm but decreased at 1000ppm with 750 ppm having a mortality of 63.33% and 1000ppm having a percentage mortality of 56.6% after 72 hrs. The LC50 and LC90 values of the methanolic leaf extract obtained after 72 hrs was 1008.19 and 1930.992 ppm for C. citratus, 1148.47 and 2210.727 ppm for O. gratissimum and 754.712 and 1548.499 ppm for V. amygdalina respectively. The methanolic extract of V. amygdalina exhibited a higher degree of potency when compared with the methanolic extract of C. citratus and O. gratissimum with a low LC50 value of 758.403ppm, 758.03 ppm and 754. 712 ppm at 24, 48 and 72 hrs respectively. In summary, this study reports the larvicidal effects of C. citratus, O. gratissimum and V. amygdalina against Cx. quinquefasciatus larvae which can serve as an lternative to synthetic pesticides in Nigeria.Keywords: Leaf extracts, Culex quinquefasciatus, larvae, toxicity, mortality
Highlights
Culex quinquefasciatus Say 1823 is known globally as a nuisance and a vector of many diseases of humans
This study investigated the phytochemical contents and larval efficacy of O. gratissimum, C. citratus and V. amygdalina against larvae of Cx. quinquefasciatus
Unachukwu et al (2015) reported the absence of glycoside in the methanolic extract of O. gratissimum, while Talabi et al (2017) reported the absence of flavonoids whereas flavonoids and glycosides were detected in O. gratissimum in this report which may be due to the method of extraction used or plausibly differences in localities of the plant itself
Summary
Culex quinquefasciatus Say 1823 is known globally as a nuisance and a vector of many diseases of humans. The use of conventional chemicals such as pyrethroids against mosquitoes showed promising results in reducing the spread of these vectors, there are undesirable side effects which occurred as a result of indiscriminate use This resulted in loss of the environmental integrity, increased cases of secondary pest resurgence and non-target effects on native flora, fauna and humans (Koul et al, 2008), it has become necessary to seek alternative control strategies. The insecticidal properties of plants have been the subject of intense research with an explosion of research over the past decade One of such plants is Cymbopogon citratus (Poaceae) widely distributed in the tropical and subtropical regions of Africa, Asia and America. The presence of colour ranging from crimson to magenta indicated that flavonoids are present
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