Repellency and Toxicity of Commiphora Africana Resin Extract and It’s Constituents against Cimex Lectularius and Characterization of its Active Constituents
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Date
2022
Authors
Wairagu, Norman Wachira
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Bedbugs (Cimex lectularius Linnaeus) pose a great menace in many homes, hotels,
public transport and institutions where they obtain blood meal from humans, chicken
and domesticated animals. They cause physical and mental problems to the affected
humans, on heavy and frequent feeding on the host leading to anemia. Bedbug control
has not been successful due to their resistance to conventional insecticides,
environmental pollution of the insecticides and the high costs involved. There is need
to explore natural herbal-based insect control phytochemicals in control methods due
to their environmental friendliness as compared to synthetic pesticides. Commiphora
africana (A. Rich.) Engl. resin has been used traditionally to control blood-feeding
insects and other arthropods such as lice, bedbugs, fleas, honey beetles and ticks. This
research sought to extract bioactive compound(s) from C. africana resin, evaluate the
repellency and toxicity of the extracts/compounds/selected blends against bedbugs.
The isolated compounds were characterized using conventional spectroscopic
techniques. The resin was tapped from the stem of mature C. africana trees in their
natural habitat. The plant resin was extracted with H2O and in a separate set up
sequentially extracted with CH3(CH2)4CH3, CH2Cl2, EtOAc and MeOH. The extracts
were evaluated for insecticidal activity against C. lectularius. The CH2Cl2 crude
extract proved to be the most effective against bedbugs with mean repellency of
98.5% and LC50 of 4.96 mg/L after 24- and 72- hrs exposure respectively. The extract
was subjected to chromatographic separation and purification where the eluents
(fractions) were evaluated at different doses for repellency and toxicity against
bedbugs. The most active chromatographic fraction against bedbugs was analyzed by
Gas Chromatography Mass Spectrometry (GC-MS) and identified 20 compounds in
the class of esters, carboxylic acids, alkanes, alkenes, heterocyclics, aromatics,
alcohols, amine and alkyne. Among the identified compounds, cedrol and citronellyl
formate had significantly (p < 0.05) higher mean repellency (80.5% and 77.0%
respectively after six hours of exposure) and toxicity (27.43 and 37.01 mg/L
respectively after 24 hours exposure) against bedbugs than the rest. Selected blends of
these compounds showed synergistic repellency and toxicity effects as compared to
individual compounds. A six-constituent blend comprising of 9-octadecenoic acid,
ethyl ester + octadecadien-1-ol + citronellyl formate + cedrol + hexadecanoic acid +
1,2-dihydro-6-methoxy-Naphthalene had the highest mean repellency (93.4 ± 6.61 %
after 12 hours exposure) and toxicity (8.83 mg/L after 72 hours exposure) against
bedbugs. The isolation of compounds from the CH2Cl2 resin crude extract gave five
triterpenoid compounds (taraxasterol, pseudo-taraxasterol, beta-sitosterol, fungisterol
and guggulsterol) which were characterized by conventional spectroscopic techniques
and evaluated for repellency and toxicity against bedbugs. Fungisterol showed highest
mean repellency (100%) and toxicity (14.40 mg/L) after 12 and 72 hours of exposure
respectively. This study proves that the resin of C. africana contains compounds that
can be used as an insecticide in bedbug control.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Analytical Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, December, 2021
Keywords
Repellency and Toxicity, Commiphora Africana Resin, Extract, Constituents, Cimex Lectularius, Characterization, Active Constituents