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University of Khartoum (2004)

Studies on the Insecticidal Properties of Extracts from Roots of Mucuna Pruriens (Fabaceae) Against Migratory Locust, Locusta Migratoria and Desert Locust, Schistocerca Gregaria

Abdalla, Abdalla Mohamed

Titre : Studies on the Insecticidal Properties of Extracts from Roots of Mucuna Pruriens (Fabaceae) Against Migratory Locust, Locusta Migratoria and Desert Locust, Schistocerca Gregaria

Auteur : Abdalla, Abdalla Mohamed

Université de soutenance : University of Khartoum

Grade : Doctor of Philosophy (2004)

Résumé
Locusts and their control have attracted a plethora of attention especially in the context of eco-toxicological studies and development of environmentally friendly control alternatives. Plant products have proved to be suitable candidates that fit reasonably well in locust management programs. This manuscript, contains results of laboratory trials undertaken, in CIRAD- Prifas in Montpellier, France, during the period extending from 2000 to 2003 mainly to evaluate some botanical extracts against the Migratory locust, Locusta migratoria (Linné 1758) (Orthoptera : Acrididae) and to further investigate the bio-activity of Mucuna pruriens (Fabaceae) as locusticide against the foregoing species and the Desert locust, Schistocerca gregaria (Forskهl 1775) (Orthoptera : Acrididae). A field survey was conducted in Western Sudan where 104 respondents were interviewed for their experience with Mucuna as pest control agent and about their indigenous knowledge in the field. In this thesis, the importance of these locusts, their control and the role of plant materials as locusticides are reviewed. The varying views on locust control strategies are also discussed. Materials from some plant species namely : Mucuna pruriens, Adenium obesum, Azadirachta indica and Calotropis procera were collected from four different sites in the Sudan and processed to perform extraction and laboratory tests in France. Plant extracts were prepared using water or water/ethanol as solvents. These plant extracts were screened for their locusticidal properties and mode of action (contact and stomach) against the Migratory locust. The knockdown effect, mortality and time to death were recorded to evaluate the efficacy. Root extracts from Mucuna pruriens (Fabaceae) were used against the Migratory and the Desert locusts to determine the contact and stomach modes of action. Extracts of neem seed kernels were used as standard botanical insecticide and Deltametherin as standard synthetic locusticide. Mucuna mixed with reduced concentrations of Deltametherin was evaluated for compatibility, additive effect and/ or the possible synergism. Knockdown effect on locust was recorded one hour after treatment while mortality was recorded on 24h. basis. Mucuna extracts were evaluated through a series of bioassay tests by applying concentrations of the extracts (by direct spraying, topical application and dipping of the locust in the tested plant materials) to investigate their efficacy as contact locusticides. As stomach poison the effect of the extracts was manifested through provision of treated wheat seedlings, cabbage leaf-discs and impregnated filter paper offered to the locusts. Mortality and faecal output was recorded in each test. Data were statistically analyzed using M-statc software statistical package, representative data for each test are presented, the most significant results are discussed and some recommendations are given. The bio-tests have shown that Mucuna extracts act both as contact and stomach poisons. As contact locusticide mortality of up to 98% and 99% was achieved by direct spaying of water and water/ethanol extracts of Mucuna at 50g/l on the Migratory locust respectively. In topical application tests high concentration of Mucuna at 200g/l is required to cause mortality of 90% and relatively low knockdown effect was detected but it was statistically higher than that of the control treatment. Dipping of the insects in Mucuna extracts caused knockdown effect and mortality which were significantly higher than those obtained in untreated locust under untreated control. Mortality of up to 99% were obtained when locusts was fed on wheat seedlings treated with Mucuna at 50g/l (water/ethanol extract) indicating high stomach action. Mucuna extracts also appeared to act faster on locust than neem extracts. The effect given by Mucuna extracts was statistically similar to that of the standard botanical insecticide "neem" and the standard chemical insecticide Deltametherin "Decis". The toxic effect of low doses of Decis was enhanced when the insecticide was applied in combination with Mucuna root extracts. The Mucuna plant materials could be stored for a period of up to three years without serious losses in efficacy. The study concluded that : Mucuna being a cheep natural product that can easily be obtained and processed in a simple way, may be of practical importance in future crop protection activities. For the upcoming studies further laboratory investigations on the biochemical properties and eco-toxicological aspects of the active molecules are recommended. Moreover, semi-field and field studies should be undertaken before recommending the root extracts for use as a pest control product.

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