Abstract
The insecticides fipronil and imidacloprid are effectively used against sucking insect pests of rice. Since these agents are absorbed by rice seedlings and stored in their tissues, they are usually applied to nursery boxes before planting. The effects of imidacroprid and fipronil on the life history of Sympetrum frequens larvae and adults were monitored using an experimental micro-paddy lysimeter(350mm× 500mm× 300mm (H)) for the duration of the cultivation period. Three lysimeters were treated with imidacroprid, three with fiproni, and the remaining three were left untreated and were used as controls. Three hundred eggs were laid on the soil surface of each of the nine lysimeters and the larval populations, larval development, and emergence patterns of Sympetrum frequens were observed in each lysimeter. The absence of Sympetrum frequens larvae from fipronil-treated-lysimeters was most remarkable and exuviae were not observed. Imidacroprid-treated-lysimeters had approximately 60% of the larvae observed in control lysimeters. In addition, larvae in the imidacloprid lysimeter had lower mean specific growth rates and the length of adult wings was decreased relative to those observed in the control lysimeter. Emergence in imidacloprid lysimeters was also significantly lower than it was in the control. The application of fipronil and imidacroprid to seedling in the nursery box, and the subsequent transplanting of these into an experimental lysimeter, was associated with a decrease in the abundance of Sympetrum frequens larvae and adults.
