Abstract: Using fluorescent element Eu⁺³ tracing method, the food chain of late-season rice-Nilaparvata lugens Stål-Pirata subpiraticus (Bosenberg et Strand) was studied quantitatively. Three concentrations of Eu₂O₃, 20 mg/L, 50 mg/L and 100 mg/L, with no obvious negative effect on growth of rice plant, were applied in substrate of potted rice, respectively. During rice booting, tasseling, milking and maturing stages, the content of u⁺³ in rice, N. lugens and P. subpiraticus markedly increased with the rise of concentrations of Eu₂O₃ applied. Ingestion of rice by N. lugens during the tasseling stage was the highest (17.5910 g/g biomass day), while the lowest (8.7070 g/g biomass day) occurred during the maturing stage. Between them, ingestion of rice by the planthopper was higher during the booting stage (17.4510 g/g biomass day) than during the milking stage (13.8290 g/g biomass day). Predation of N. lugens by P. subpiraticus was almost the same, about 3.6380 g/g biomass per day during the milking stage, higher than during the booting stage (3.0830 g/g biomass day) and the tasseling stage (3.0770 g/g biomass day) while the smallest predation (28000 g/g biomass day) occurred during the maturing stage. Based on the investigation in rice fields, the number of N. lugens consumed by P. subpiraticus during these four growth stages of the rice plant was estimated to be 11, 11, 13 and 10 respectively.

Key words: Rice plant, Nilaparvata lugens, Pirata subpiraticus; food chain, fluorescent substance, quantitative determination