5-Hydroxy-1,4-naphthoquinone and its derivatives were evaluated for insecticidal effect against Sitophilus oryzae and S. zaemais adults. This study was examined using fumigant method. Mortality was determined after 72 h of treatment. 5-Hydroxy-1,4-naphthoquinone showed strong (+++) activity at 5 mg and the 1,4-naphthoquinone showed strong (+++) and moderate (++) activity at 5 mg, against S. oryzae and S. zaemais, respectively. However, 5-hydroxy-2-methyl-1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, and 2-methoxy-1,4-naphthoquinone had non-activity (-) at 5 mg. Based on the LD50 values, the compound most highly effect to S. oryzae was 1,4-naphthoquinone (0.012 mg/cm2), followed by 5-hydroxy-1,4-naphthoquinone (0.013 mg/cm2). However, against S. zeamais, 5-hydroxy-1,4-naphthoquinone (0.044 mg/cm2) was the most toxic compound, followed by 1,4-naphthoquinone (0.155 mg/cm2). These results suggest that the introduction of various functional group (hydroxy, methyl and methoxy) into the 1,4-naphthoquinone skeleton contributes to insecticidal activity. Accordingly, 5-hydroxy-1,4-naphthoquinone and 1,4-naphthoquinone could be used highly effective rice weevil control agents.

The rice weevil, Sitophilus oryzae, is the most serious storage pests worldwide of grocery shops, flour mills, and warehouses. The phototactic response of the rice weevil, S. oryzae, to light emitting diodes (LEDs) at five different wavelengths and various light intensities was tested within an LED-equipped Y-maze chamber, and compared with its response to a luring lamp, which is used in commercial traps. Various wavelengths in this study were UV (365 nm), blue (450 nm), green (520 nm), red (660 nm), and infrared (IR) (730 nm). Based on attraction rate (%), blue (84.3%) was the most attractive to S. oryzae, followed by green (74.3%), red (64.3%), UV (63.3%), and IR (48.7%). Moreover, blue and green wavelengths were 1.5 and 1.3 times more attractive than luring lamp (56.7%), whereas the UV wavelength was slightly less attractive to the weevils than luring lamp. These results suggested that blue and green wavelengths could be more useful than those currently used for monitoring and mass trapping of S. oryzae.