Chemical Variability and Fumigant Toxicity of Essential Oils from Peels of Citrus reticulata L. Native to Nigeria

Cowpeas infested with Callosobruchus maculatus have lower protein quality compared to the uninfected cowpeas. The affected cowpeas are usually treated with synthetic insecticides that are expensive and hazardous to man. Essential oils were established to possess insecticidal properties without detrimental effects on the users. The properties are influenced by environmental conditions that changes with time in a day and as well determine the type of chemical compounds present in the oils. In this study, we investigated the chemical composition and fumigant toxicity of essential oils from rinds of Citrus reticulata collected at 7.00am and 2.00pm against C. maculatus. Hydrodistillation of the pulverized (500 g each) rinds from morning and afternoon harvests afforded 0.56±0.06 % and 0.38±0.03 %(w/w) of volatile oils. GC-MS was employed to analyze the oils and the results showed abundance of D-Limonene (55.7% and 61.1%), linalool (12.5% and 16.9%), terpinen-4-ol (7.7% and 5.4%), nerol (1.1% and 4.0%) and α-terpineol (3.3% and 4.5%). The insecticidal property of the oils was examined against bean weevils using fumigant toxicity bioassay. The activity of the oils differs significantly with LT50 of 1.967 hours and 1.297 hours for the oils from the rinds of fruits harvested at 7.00am and 2.00pm respectively. The oil from the 2.00pm harvest is therefore more potent and thereby recommended as a safer insecticide against stored product insect pest, C. maculatus.