Abstract

Objective: To evaluate the toxicity potential of lemon grass [Cymbopogon citratus (C. citratus)] products against adult rice weevil, Sitophilus oryzae. Methods: Lemon grass (C. citratus) leaves were sundried for 7 days, pulverized and sieved using 0.5 mm mesh size to obtain fine powders. About 500 g of the powder were dissolved in 1 000 mL of 90% methanol to produce the extract. The powder and extract were used for the bioassay. The powder was tested at 1.0, 1.5, 2.0 and 2.5 g/10 g rice grains, respectively. The toxic potential of the extract of concentration of 1.0, 1.5, 2.0, and 2.5 mg/mL were evaluated using the filter paper method. The experiment was setup on a completely randomized design using three replicates per treatment. Results: The results indicated significant difference (F = 7.450; df = 3.15; P < 0.05) in mean percentage mortality after 24, 48, 72, and 96 h exposure with the powder compared with the control. Significantly (F = 5.519; df = 3.15; P < 0.05) higher percentage adult mortality was also observed in the extract after 24, 48, 72, and 96 h exposure compared with the control. The LC 50 value of the powder was 4.91 g/10 g of rice while the LT50 was 160.51 h. The LC50 value of the extract was 2.16 mg/20 mL of methanol with an LT50 of 75.10 h. The methanol extract of C. citratus showed the highest mortality compared to the powder which was less toxic. Conclusions: The study showed that C. citratus products are promising insecticides and can be used effectively in the management of Sitophilus oryzae in storage.

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