EVALUATION OF GARLIC OIL EXTRACT AS POTENTIAL PYRETHRUM SYNERGIST AGAINST SIGNIFICANT POST HARVEST PESTS

Abstract

Post-harvest grain loss remains a major challenge facing farmers especially in developing countries. Pyrethrin is natural plant oil that forms the active ingredients of conventional insecticides combined with piperonyl butoxide as synergist. Garlic bulb is a plant that has been studied for various pharmacological properties. A study was done to evaluate the ability of natural Allium oil as a potential pyrethrin synergist against Sitophilus zeamias and Prostephanus truncatus significant post-harvest maize pests. The treatment solutions for bioassay tests was mixture of garlic oil extracted using hexane solvent and pyrethrin oil. The experimental design used for bioassay test was completely randomized design and was done in triplicate. The analysis of garlic oil extract using Fourier transform infrared spectroscopy confirmed the presence of amide, lipids and aromatic compounds linked with insecticidal activity The treatments used for bioassay were solutions containing pyrethrin with garlic oil in a ratio of 1:10 selected after preliminary tests. The highest concentration ratio of pyrethrin to garlic oil was 20 mg/ml: 200 mg/ml while the lowest was 14 mg/ml: 140 mg/ml. The insect’s mortality rates were determined after 24, 48 and 72 hours intervals. There was significant change in percentage mortality rates of the insects with increase in concentration of test solutions and exposure time after the treatments. The treatments were found to be more potent on Prostephanus truncates compared to Sitophilus zeamais. The result showed piperonyl butoxide as the most effective pyrethrin synergist with mean mortality of 90% compared to garlic oil of equivalent concentration which caused 50% mortality. The standard convectional insecticide used 20 mg/ml actellic super dust recorded the highest mean mortality for both insects’ species of 100% and 93%.The non-synergized pyrethrum containing 20 mg/ml pyrethrin only had a mean mortality of 29% which was lower compared to some treatments with less concentration of pyrethrin but synergized with garlic oil. The results were analysed using R CRAN software and value p ≤ 0.050 was considered to be statistically significant at 95% confidence limit. The parameters used to evaluate efficacy were mortality rates relative to concentrations of the test solution and insect’s exposure time. The study revealed that garlic oil can enhance the efficacy of pyrethrin against significant post-harvest pests. This can provide a benign solution to challenges associated with the current convectional pesticides. Garlic oil as a natural synergist may open prospect for farmers to start cultivating the plant as an insecticide cash crop.