Toxic and repellent effect of Zanthoxylum armatum (Sapindales:Rutacae) essential oil to Sitophilus zeamais (Coleoptera:Curculionidae)

Abstract The essential oil from Zanthoxylum armatum (Prickly ash) fruit was evaluated for its insecticidal properties against the Sitophilus zeamais (maize weevil) with different concentrations (10, 5, 2.5, 1.25, 0.62, 0.31, and 0.15%) in both a glass vial bioassay and in oil-treated maize grain. The repellency effect of the oil was tested through a filter paper test. The results revealed that the lethal concentration (LC 50 ) for the oil at 96 and 144 h was estimated as 11.6% (y = 0.97x-1.03) and 4.5% (y = 1.10x-0.721.03) percent concentration of oil. The lethal time (LT 50 ) at the highest oil concentration (10%) was calculated as 13.84 h, whereas, it took approximately 197 h to achieve 50% mortality at the lowest concentration in the glass vial bioassay. In essential oil treated maize bioassay experiment, a concentration of 0.01% of the oil (y = 0.56x + 0.41) was sufficient to kill 50% of the tested maize weevils within 10 days. Repellency tests exhibit strong deterrent effect of 97.5% repellency with 10% concentration after 24 h, while the lowest concentration (0.15%) repelled around 55% of the weevils. The results suggest that Zanthoxylum armatum essential oil could be an effective natural compound for managing maize weevil in grain storage, which can be an environmentally friendly alternative to conventional chemical pesticides.