Insecticidal Activity of Chrysanthemum Cinerariifolium & Allium Sativa Natural Oils against Prostephanus truncatus

Abstract

The larger grain borer (Prostephanus truncatus) is one of the most destructive post-harvest pest that affects maize and other crops like cassava. Synergists are substances added to pyrethrin increase efficacy and also to reduce the quantity of insecticides in formulation. The application of chemicals in pest control has been limited by toxicity, insect resistance and environmental degradation. A research was conducted to determine the ability of natural garlic oil to enhance the efficacy of pyrethrin against Prostephanus truncatus. The treatment solutions used were mixtures containing garlic bulb extract and pyrethrin oil. The experimental design used for bioassay was completely randomized design while the tests were done in triplicate. The test solutions used for bioassay tests were prepared by combining pyrethrin with garlic oils in ratio of 1:10. The concentrations ratio of pyrethrin to garlic oil used were between 20 mg/ml: 200 mg/ml to 14 mg/ml: 140 mg/ml while mortality rates were assessed after 24, 48 and 72 hours. Analysis of garlic oil extract using Fourier transform infrared spectroscopy showed the presence of several functional groups linked with insecticidal activity. There was significant variation in percentage mortality rates of P truncatus with change in concentration of treatment solutions and exposure time. The pyrethrin synergized with garlic oil recorded over 50% mortality rate during the test period. The non-synergized pyrethrin containing 20 mg/ml pyrethrin oil alone had a mean mortality rate of 29%. This was same as 14 mg/ml pyrethrin with 140 mg/ml garlic oil but less than 16 mg/ml pyrethrin with 160 mg/ml garlic oil that had 46%. The parameters used to estimate the efficacy during bioassay test were mortality rates which were compared with the concentrations and insect’s exposure time. The findings from this study revealed that garlic oil can augment the efficacy of pyrethrin against P truncatus.