ETHNOBOTANICAL SURVEY AND INSECTICIDAL POTENTIALS OF SELECTED PLANTS AGAINST Anopheles gambiae (DIPTERA: CULICIDAE) IN NORTH-CENTRAL, NIGERIA
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Date
2021-04
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UNIVERSITY OF ILORIN
Abstract
Widescale report of insecticide resistance in Anopheles mosquitoes is a major challenge confronting the usefulness of available interventions involving limited insecticides. Some plants have indigenously been used as insecticides without scientific validation. Therefore, this study was conducted to survey and evaluate the bio-efficacy of selected insecticidal-plants in North-central, Nigeria and to broaden the scope of available insecticides for management of Anophelesgambiae. The objectives were to determine the: species types and frequency; repellent activity; contact toxicity; vapour toxicity; and major potent chemical components of selected insecticidal-plants against A. gambiae.
Insecticidal-plant species types and frequency were determined from nine ethnic groups in North-Central, Nigeria using questionnaires. The common plants acclaimed to have insecticidal potency were collected, identified in the herbarium and thereafter screened for insecticidal activities against A. gambiae. Oils from selected plants were extracted using a Clevenger apparatus. The repellency, contact and vapour-toxicities of these oils were evaluated against the larva and adult stages of An. gambiae using modified World Health Organisation bioassay test-procedures. Standard insecticide (Deltamethrin) and repellent (N,N-Diethyl-meta-toluamide(DEET)) were used as controls. The major potent chemical components were determined using Gas-Chromatography-Mass-Spectrometry. Questionnaires, knock-down time (KdT50), mortality and repellency data were analysed using descriptive statistics, Chi-square, Analysis of Variance, Tukey post-hoc test, Preference Index and probit analysis (p<0.05).
The findings of this study were that: Hyptis suaveolens, Ocimum gratissimum, Citrus sinensis, Ageratum conyzoides, Cymbpogon citratus, Thymus vulgaries, Nicotiana tabacum, Capsicum annuum, Cassia mimosoides, Annona senegalensis, Eucalyptus globulus, Parkia biglobosa,
Hibiscus rosa sinensis, Allium cepa, Ertyphleum suaveolens, Latanna camara and Moringa oleifera were identified belonging to twelve families. The most represented families were: Lamiaceae (H. suaveolens, O. gratissimum and T. vulgaries) and Fabaceae (C. mimosoides and P. biglobosa); and species were: Hyptis suaveolens (19.6%), Ocimum gratissimum (18.7%), Citrus sinensis (10.8%), Ageratum conyzoides (6.2%), Thymus vulgaries (6.2%) and Nicotiana tabacum (5.6%). H. suaveolens and A.conyzoides leaves had the same preference index (-0.87) as DEET against A. gambiae. All plant-oils tested displayed better (p<0.05) repellent activities against A. gambiae at 3.0 and 5.0 mg/mlcompared to DEET in the presence of human-odour; H. suaveolens (3.0 mg/ml), C. sinensis (4.0 mg/ml),N. tabacum andA.conyzoides (5.0 mg/ml) recorded 100% mean larval mortality against An. gambiae24-hours post-exposure. Similarly, adult A. gambiaeexposure to 5.0 mg/ml N. tabacum resulted in 100% mortality which compared favourably (p>0.05) with Deltamethrin; knock-down activity of 5.0 mg/ml C. sinensis (80%) against adult A. gambiae was significantly higher (p<0.05) compared to DEET (70%) after 20 minutes of exposure. KdT50 was lowest in 5.0mg/ml O. gratissimum (31.32 minutes) and H. suaveolens (25.18 minutes) which was lower than DEET (36.10 minutes); and D-Limonene, was the most potent chemical component in C. sinensis;A.conyzoides and O. gratissimum.
This study concluded that H. suaveolens,A.conyzoides, C. sinensis,N. tabacum and O. gratissimum demonstrated excellent repellent, contact and vapour-toxic properties comparable to standard commercial insecticides against An. gambiae. These plants are therefore recommended as potential source of novel bio-insecticide for management of An. gambiae.
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ETHNOBOTANICAL SURVEY, INSECTICIDAL POTENTIALS, Anopheles gambiae, NORTH-CENTRAL, NIGERIA