Abstract
This study was undertaken to examine the insecticidal properties of Neem plant. Powder and aqueous extracts of Neem, Azadirachata indica leaves were evaluated as grain protectants against the bambara nut weevil (Callosobruchusmaculatus) and bean seed weevil (Acanthoscelidesobtectus), in the laboratory at 1.5, 2.0, and 2.5 (%v/w) concentrations per 20g of bambara nut and bean seeds respectively. Aqueous and powder extracts of Azadirachataindica leaves were applied to the bambara nut and beans seed using the contact method of application in the laboratory. Results revealed that 2.0%v/w (p=0.014) and 2.5% v/w (p=0.008) had significant increase in adult mortality of C. maculatus and A. obtectus in aqueous treatment of A. indica on beans and bambara nut after 72h at p<0.05. Similar results were obtained for beans and bambara nuts using powdered A. indica treatment. Percentage grain weight damage in bambara nut powder treatment of A. indica decreased significantly (p=0.002) at (P<0.05) in a proportionate, dose dependent manner and there was no adult emergence for either of bambara nut weevil or bean weevil. The 1.5 (%v/w) concentration was the least effective when compared with other concentrations. There was significant difference between A. indica treated grains and the control. There was no observed discoloration of the treated seeds. A. indica (aqueous and powder) extracts effectively reduced the weight loss of the treated bambara nut and seeds with 2.5% concentration being the most effective after 168hours. Phytochemical analyses of the extracts revealed presence of alkaloids, tannins, phenols, terpenes, saponins, cardiac glycosides, steroids while reducing sugars, carbohydrates and anthraquinones were absent. This study shows the insecticidal effects of A. indica against crop pests and at such there is need to further exploit Neem in order to maximize the potential. Farmers in developing countries can use A. indica as an alternative to chemical pesticide in rural grain storage.
Highlights
Pests are a major constraint which reduces yield and quality of harvested products both on the field and in storage [15]
Callosobruchusmaculatus heavily infest cowpea in storage [14]
Synthetic pesticides are of increasing concern as they accumulate in the
Summary
Pests are a major constraint which reduces yield and quality of harvested products both on the field and in storage [15]. The nutritional advantages associated with cowpea over other arable crops render all parts of the plants susceptible to insect pests. Neem plant has been known for three decades for its potential against insect pests [2]. The principle component that has insecticidal activity in neem extracts is a limonoid, azadirachtin. It has been evaluated as the most promising insecticide of botanical origin, used against more than 400 species of insects [16]. Certain activites of genes and proteins are altered byazadirachtin [3] Another neem derived compound is the saponin which is known to have insecticidal activity [17]. Neem plant is a potential source of biopesticides that has been appraised against many important insect species.
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