Abstract: To clarify the trophic level of each biological group and examine the food chain in Caohai, a National Nature Reserve, the characteristics stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope of aquatic organisms in Caohai were analyzed. The δ¹³C values in Caohai ecosystem ranged from -27.56‰ to -13.25‰ (Mean±SD: -21.52‰±3.61‰) and the δ¹⁵N varied from 0.32‰ to 15.14‰ (Mean±SD: 8.69‰±3.92‰). There was a significant negative correlation between δ¹³C and δ¹⁵N values (r=-0.423, P<0.01). The trophic levels in different biological groups ranged from 0.8 to3.7: fishes, 0.8-2.5; benthonic animals, 2.0-2.8; birds, 1.0-3.7. Moreover, the trophic levels in fishes and benthonic animals were different in different feeding habits, with an order of carnivorous>omnivorous>phytophagous. The food chain in Caohai had two transmitting carbon pathways: sediment/phytoplankton→zooplankton→ fish → birds, and hydrophyte→ fish → birds.

Key words: Liriomyza sativae, Secondary substance, Petroleum spray oil, Parasitoids, Population control