Abstract: This paper deals with the habitat niche of planthoppers and their predators on rice plant and studied the relationship between the habitat niche and the predation effect in the coexistence system containing two insect pests and five species of predators. The results showed that in the system investigated the magnitude of positive main effect of predation on brown planthop pers (Nilaparvata lugens) varied with species in a diminishing order as follows. Clubiona japonlcole, Paederus fuscipes, Tetragnalha praedon ia, and Ummeliata insecticeps; while Pirata subpira ticus exhibited the highest negative effect. The sequence of intensity of positive main effect on rice leaf rollers (Cnaphalocrocis medinali;) was C.japonicola, T. praedonia and P. fuscipes.H had been found that P. subpiraticus, U. insecticeps and Bianor hotingchiehi mainly preyed on planthoppers, T. praedonia on rice leaf rollers and C.japonicola was important for thecontrcl of the both pests. These were consistent with their habitat niche (niche width). Under a certain prey density, the predation effect of the predators reached a maximum when there was a good biological order (I.e. optimal proportion of various species). The results from experiments using addition and exclusion methods in&cared that increase in predator density could not increase the number of prey taken in a coexistence system with a defined density in each species. It is believed to be due to the interactions between inter-species and intra species.

Key words: habitat niche——predation effect——predator——paddy field