RESUMO
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.
RESUMO
Twenty plant-derived oils were evaluated for their acaricidal and insecticidal activities against Sitotroga cerealella, Sitophilus oryzae, Sitophilus zeamais, and Tyrophagus putrescentiae adults, by using the fumigant and filter paper diffusion methods. Responses varied with bioassay systems, insect or mite species, plant oils, and exposure time. Based on the 50% lethal dose (LD50) values against S. oryzae and S. zeamais in the fumigant bioassay, Anethum graveolens oil (4.12 and 1.12 µg/cm(3), respectively) induced the highest mortality, followed by Achillea millefolium (21.92 and 14.91 µg/cm(3)) and Eucalyptus dives (28.02 and 24.02 µg/cm(3)) oils, respectively. The most toxic oil based on the 50% lethal concentration values against T. putrescentiae was E. dives (3.13 µg/cm(3)), followed by Melaleuca leucadendron (3.93 µg/cm(3)) and Leptospermum pertersonii (4.41 µg/cm(3)). Neroli birgard oil (1.70 µg/cm(3)) was the most toxic based on the LD50 values against S. cerealella, followed by Citrus aurantium (1.80 µg/cm(3)) and Artemisia vulgaris (1.81 µg/cm(3)). The insecticidal and acaricidal activities of the plant oils in the filter paper diffusion bioassay were similar to those in the fumigant bioassay. In comparison, A. millefolium, A. graveolens, and E. dives oils were more effective against S. oryzae and S. zeamais in the fumigant bioassay than in the contact bioassay. These results indicate that the insecticidal activity of the three plant oils against S. oryzae and S. zeamais may be due to their fumigant action. Acaricidal activities of the A. millefolium, A. graveolens, and E. dives oils against T. putrescentiae were 2.62, 1.11, and 122 times higher than that of benzyl benzoate in the contact bioassay. These results indicate that A. millefolium, A. graveolens, and E. dives oils have potential for development as agents to control stored-grain insects and mites.
