Abstract
Aim of the present study was to evaluate powders and aqueous extracts of <em>Melia azedarach</em>, <em>Mentha piperita</em>, <em>Phytolacca dodecandra</em>, <em>Schinus molle</em> and <em>Xanthium strumarium</em> leaves against maize weevil Sitophilus zeamais. Repellent activity of plant powders were evaluated by mixing 0.625, 1.25, 2.5, 5 and 10 g of powder per 100 g of clean uninfested maize seeds individually in separate plastic container. The numbers of insects moving outside the container were recorded at 24 h and 48 h post exposure period and percentage of repellent activity was calculated. The insect mortality was recorded at 5 days, 10 days and 15 days post exposure period and percentage of insect mortality was calculated. In addition, aqueous solutions were prepared by mixing 0.0625, 0.125, 0.25, 0.5 and 1 g of plant powder with 10 mL of water and tested for their insecticidal activity by topical application method. Total numbers of dead insects were counted for every 24 h up to 96 h post exposure period and percentage of insect mortality was calculated. Plant powders admixed with maize seed failed to show satisfactory level of repellent activity. Maize seed admixed with 10 g of <em>Mentha</em> leaf powder showed 93.3% mortality followed by <em>Schinus</em> (90%) and <em>Phytolacca</em> (90%) 5 days of post exposure period. After 15 days, 100% mortality recorded in <em>Mentha</em>, <em>Melia</em> and <em>Schinus</em> leaf powder mixed with 10/100 g of maize seeds followed by <en>Phytolacca</em> (90%) and <em>Xanthium</em> (86.6%). The topical application of aqueous extracts did not show insecticidal activity at satisfactory level. In general, application of <em>Melia</em>, <em>Mentha</em> and <em>Schinus</em> leaf powders proved to be effective against <em>Sitophilus zeamais</em>.
Highlights
One of the challenging tasks for developing countries is to prevent insect infestation in the storage to reduce grain damage in order to feed on growing population
The experiment was conducted at the biology laboratory, College of Natural and Computational Sciences, University of Gondar, Gondar, Ethiopia from February 2013 to May 2013: Insect culture establishment: Adult Sitophilus zeamais were collected from infested maize seeds at Arada market storage site, Gondar, Ethiopia
Plant materials collection and processing: The fresh leaves of Melia azedarach, Phytolacca dodecandra and Xanthium strumarium was collected from Tewodros campus and Schinus molle was collected from Maraki Campus, University of Gondar and Mentha piperita was collected from GTZ area, Samunaber, Gondar
Summary
One of the challenging tasks for developing countries is to prevent insect infestation in the storage to reduce grain damage in order to feed on growing population. The loss and quality deterioration caused by this pest is a major obstacle to achieve food security in developing countries (Rouanet, 1992). The indiscriminate use of chemicals pave the way for developing resistant strains, toxic residue getting enter in to food of animal and man, workers safety and high cost of procurement (Sighamony et al, 1990). In this scenario, it is necessary to find out eco-friendly, economically viable alternative pest control methods which are affordable by resource poor farming communities. One of the alternative methods tried world wide is by using plant powders and their extracts (Cobbinah and AppiahKwarteng, 1989; Niber, 1994; Jembere et al, 1995; Lajide et al, 1998; Asawalam and Adesiyan, 2001). Talukder (2007) listed 43 plant species as insect repellents, 21 plants as insect feeding deterrents, 47 plants as insect toxicants, 37 plants as grain protectants, 27 plants as insect reproduction inhibitors and 7 plants as insect growth and development inhibitors
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