Phytochemical Profiles and Bioefficacy of Selected Organic Leaf Extracts of Tithonia Diversifolia and Vernonia Lasiopus against Sitophilus Zeamais

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dc.contributor.advisorMathew Piero Ngugien_US
dc.contributor.advisorDavid Mburuen_US
dc.contributor.advisorAlex Machochoen_US
dc.contributor.authorGitahi, Stephen Maina
dc.date.accessioned2022-03-31T09:45:52Z
dc.date.available2022-03-31T09:45:52Z
dc.date.issued2021
dc.descriptionA Thesis Submitted in Fulfillment of the Requirements for Award of the Degree of Doctor of Philosophy (Biotechnology) of the School of Pure and Applied Sciences of Kenyatta University, November, 2021en_US
dc.description.abstractMaize is among the worlds most important crops. Uses of maize include human consumption, livestock feed as well as raw material for industrial processing. There are a number of pest that attack maize and contribute to grain loss in the tropics. Weevils infestation has been recognized as an increasingly constraint to maize production causing an estimated annual loss of 30 - 50% of stored maize grains in tropical Africa. The damage caused by S. zeamais can therefore, lead to food insecurity. Conventional use of synthetic insecticides is the most common and effective method insect pest control around the world. However, these chemicals are expensive and are arguably associated with deleterious side effects on environment. They kill even the non-targeted organisms and pose severe hazards to human health that were not anticipated at the time of their introduction. Therefore, to achieve sound management of stored cereals, there is an increasing interest in medicinal plants as complementary and alternative pesticides owing to their afford-ability, assumed safety and eco-friendly status due to their highly reduced negative effects on environment. This study therefore, evaluated the efficacy of selected organic leaf extracts of Tithonia diversifolia and Vernonia lasiopus against S. zeamais on maize grains. The phyto-chemical profile of T. diversifolia and V. lasiopus was determined using Gas Chroma-tography Mass Spectrophotometer (GC-MS). The extracts were assayed for their insecticidal abilities through fumigant and direct-contact toxicity-induced mortalities of S. zeamais exposed to treated grains for the period of 96 hour. The repellency effects of these extracts on weevils were experi-menttally determined using area preference method. The effects of T. diversifolia and V. lasiopus on weevils‟ reproduction and development were tested through determination of their rate of oviposition and the first filial (F1) progeny emergence in the treated grains. The extracts‟ antifeedant potential parameters determined included the reduction in insects‟ damage and grain weight loss on treated grains. Crude acetlycholinesterase (AChE) was extracted from adult weevils and the effects of the extracts on enzyme activity determined using Ellman method. The results indicated that T. diversifolia and V. lasiopus leaf extracts exhibited potent pesticidal effects against S. zeamais. They significantly exhibited insecticidal abilities that ranged between 1.67 to 99.98% and 32.45 and 98.7% through fumigant and contact toxicity-induced mortalities respectively. The extracts also manifested repellency effects of between 26-96% on weevils. Moreover, they showed oviposition deterrence (12.18-100%) and F1 progeny emergence inhibition of weevils (38.38-100%). Further, it was evident that the extracts have antifeedant potentials as indicated by reduction in damage by insects (weevil perforation indices (WPI) below 50) and reduction in grain weight loss (2.7-15.4%) of treated maize grains. The studied organic leaf extracts of T. diversifolia and V. lasiopus showed potent AChE inhibitory effects (10.75-89.25%) in Vitro. The GC-MS analysis revealed the presence of bioactive compound in T. diversifolia and V. lasiopus which are associated with the pesticidal and the antiacetyl-cholinesterase activities observed. This study, therefore, scientifically confirms the traditional use of the T. diversifolia and V. lasiopus. It provides important data and a platform for further study on T. diversifolia and V. lasiopus as bio-resource of pesticides that could serve as novel postharvest protectant of maize grains against S. zeamais. However, there is need for bioassay-guided fractionation and purification of specific phytochemicals in T. diversifolia and V. lasiopus associated with specific insecticidal effects witnessed. Besides, further investigations are recommended to establish whether there are non-target effects on other insects, especially the weevil predators.en_US
dc.description.sponsorshipKenyatta Universityen_US
dc.identifier.urihttp://ir-library.ku.ac.ke/handle/123456789/23454
dc.language.isoenen_US
dc.publisherKenyatta Universityen_US
dc.subjectPhytochemical Profilesen_US
dc.subjectBioefficacyen_US
dc.subjectSelected Organic Leaf Extractsen_US
dc.subjectTithonia Diversifoliaen_US
dc.subjectVernonia Lasiopusen_US
dc.subjectSitophilus Zeamaisen_US
dc.titlePhytochemical Profiles and Bioefficacy of Selected Organic Leaf Extracts of Tithonia Diversifolia and Vernonia Lasiopus against Sitophilus Zeamaisen_US
dc.typeThesisen_US
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