Evaluation of potential use of nootkatone against maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [S. oryzae (L.)](Coleoptera: Curculionidae)

Nootkatone is a natural sesquiterpene ketone that shows insecticidal activity against insects and ticks. Its contact toxicity and repellency against two major stored-product insect pests, maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [Sitophilus oryzae (L.)], were investigated in the current study. Contact toxicity was evaluated using a no-choice test with treated filter paper, while repellency was evaluated using a choice test with treated corn (for maize weevils) or wheat (for rice weevils). Nootkatone showed low contact toxicity (ranging from 0 to 51%) against the two weevil species at the tested concentrations (ranging from 11.58 μg/cm2 to 1158.08 μg/cm2) on filter papers. In choice tests, corn treated with 0.10% or higher and wheat treated with 0.5% nootkatone or higher had significantly fewer maize or rice weevils compared with the solvent only treated control, indicating a repellent effect. The repellency percentage ranged between 46.3 and 93.1% against maize weevils and 39.2–67.2% for rice weevils.