This study was conducted to evaluate the insecticidal effects of ethyl formate (EF), methyl bromide (MB), and phosphine (PH3) fumigants against PH3-susceptible and -resistant strains of the rice weevil (Sitophilus oryzae), a major rice pest. The highest lethal concentration time 50 (LCt50) values of the PH3-susceptible strains were 255.797, 21.104, and 6.171 mg h L-1 for EF, MB, and PH3, respectively, at pupal stage. The highest LCt50 values of the PH3-resistant strains were 149.028 and 48.170 mg h L-1 for EF and PH3, respectively, at late larval stage, and 43.520 mg h L-1 for MB at pupal stage. In comparison to the susceptible strains, the PH3-resistant strain collected in South Korea had a resistance level 4 to 56 times higher. Use of the major quarantine fumigants EF, MB, and PH3 indicated the existence of PH3-resistant rice weevils in South Korea for the first time.
Keywords: Sitophilus oryzae; ethyl formate; methyl bromide; phosphine; resistance.