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Title: Efficacy of Ethanolic Extract of Thevetia Peruviana (Pers.) K. Schum. (Milk Bush) Root in the Control of Major Insect Pests of Cowpea
Authors: Amoh-Amoah, Barbara
Issue Date: 10-Jun-2010
Abstract: Insect pests are a serious constraint to cowpea production in sub-Saharan Africa. Every phenological stage in the life cycle of the crop has at least one major insect pest. Aphids, Aphis craccivora Koch (Hemiptera: Aphididae) attack cowpea especially at the seedling stage, flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae) at flowering, the pod borer, Maruca vitrata Fabricius (Lepidoptera: Pyralidae) at flowering and pod formation stages, and, a complex of pod sucking bugs at pod formation stage. The cowpea bruchid, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) is the major storage pest. The attack of one or more of these pests may result in total crop loss. Their successful management is therefore critical to ensuring food security. Reports show that these pests are developing resistance to some of the synthetic pesticides commonly used for their control. This and many other reasons have led to the quest for extracts from pesticidal plants to control these pests. The efficacy of ethanolic extract of the roots of milk bush, Thevetia peruviana (Pers.) K. Schum, was therefore assessed for the control of the major field insect pests of cowpea in the 2008 minor season and 2009 major season. The extract was prepared from the dry coarse powder using 77% v/v ethanol in a soxhlet apparatus for four hours. The concentrations of the extract used were 0.1%, 0.5% and 1% in the first experiment but changed to 5%, 10% and 15% in the second experiment. These concentrations were compared with the recommended insecticide, cymethoate 25 EC (cypermethrin + dimethoate). The root extract at 15% was superior in reducing insect populations and compared favourably with the synthetic insecticide for many of the parameters measured. Pod density was also enhanced on cowpea plants treated with 10% and 15% of the extract compared with the control plots (P≤0.05). M. vitrata was the most susceptible to the extract whilst M. sjostedtii was not much affected. Cymethoate was consistently superior to all the root extract treatments in substantially reducing the population densities of all the insect pests. But the results of this study indicate that, root extract of T. peruviana has the potential to replace synthetic products for the control of the major insect pests of cowpea.
Description: A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science in Crop Protection (Entomology), December-2010
URI: http://hdl.handle.net/123456789/4681
Appears in Collections:College of Agric and Natural Resources

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