Insecticidal Effects of Fumigants (EF, MB, and PH(3)) towards Phosphine-Susceptible and -Resistant Sitophilus oryzae (Coleoptera: Curculionidae)

This study was conducted to evaluate the insecticidal effects of ethyl formate (EF), methyl bromide (MB), and phosphine (PH(3)) fumigants against PH(3)-susceptible and -resistant strains of the rice weevil (Sitophilus oryzae), a major rice pest. The highest lethal concentration time 50 (LCt(50)) values of the PH(3)-susceptible strains were 255.797, 21.104, and 6.171 mg h L(−1) for EF, MB, and PH(3), respectively, at pupal stage. The highest LCt(50) values of the PH(3)-resistant strains were 149.028 and 48.170 mg h L(−1) for EF and PH(3), respectively, at late larval stage, and 43.520 mg h L(−1) for MB at pupal stage. In comparison to the susceptible strains, the PH(3)-resistant strain collected in South Korea had a resistance level 4 to 56 times higher. Use of the major quarantine fumigants EF, MB, and PH(3) indicated the existence of PH(3)-resistant rice weevils in South Korea for the first time.