Insecticidal Potential of Some Plant Extracts and Synthetic Dusts for Control of Sitophilus zeamais (Motscholsky) Infesting Maize Seeds
The use of inorganic chemicals has proven to eradicate pests with an efficiency record of up to 100% mortality to target pest, hence, the need to adopt integrated pest management system (IPM). Sequel, to this, bio-insecticidal potentials of some plant extracts and synthetic dust on control of Sitophilus zeamais in maize seeds was investigated. Two botanicals: Eugenia aromatica and Piper guineense, were used in combination with synthetic dust at different treatment combinations for the control of S. zeamais. The S. zeamais used were derived from a culture maintained in Kilner jars under ambient laboratory conditions of 28± 2°C, and relative humidity of 70 ± 2% and maintained on DMR-S-W maize variety. The maize variety seeds were obtained from IAR&T, Ibadan, Nigeria. The botanical plant extracts were obtained from a herbal store in Owerri. They were oven- dried at 60°c for 48hrs and grounded to a powder form in an electric mill. Both the synthetic dust and the plant extracts were used singly and in combination. Exactly 20g of maize grain in a plastic plate (8.5cm diameter) was treated with the plant powders alone and in combination with pirimiphose-methyl or permethrin dust in 20 adults of S. zeamais (less than 1 week old and unsexed) were introduced. The mortality of S. zeamais was monitored within the time intervals of 12, 24, 48 and 72hrs. The result showed that at 72hrs post-treatment, 100% mortality of S.zeamais was recorded in three (3) treatments. Treatment involving Eugenia powder (0.1g) mixed with pirimiphos-methyl (0.1g) was significantly the highest but was not different from mortality in treatments involving Eugenia powder (0.08g) mixed with pirimiphos-methyl (0.1g) and Eugenia powder (0.1g) mixed with permethrin (0.1g). Eighteen treatments, including the control, recorded zero mortality even at 72hrs post infestation. The study revealed that there is great potential in reducing the rate of application of synthetic organic insecticides by mixing with a sub-lethal. The result showed that a sub-lethal dose of Eugenia powder (0.08g) mixed with pirimiphos-methyl (0.1g)/20grams of DMR-S-W maize variety seeds produced 100% adult mortality of S.zeamais at 72hrs post-infestation thus recommended at a dose of insecticidal materials.
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