HABITAT NICHE AND PREDATION EFFECT OF NATURAL ENEMIES OF INSECT PESTS IN PADDY FIELD
Wu JlN-CAI Lu ZI-QIANG (Department of Plant Protection, Jiangsit Agricultural College Yangzhou 225001)YANG JIN-SHENG SHU ZHAO-LIN(Zheng Jiang Institute of Agricultural Sciences for Jiangsu Hilly District, Jurong 212400)
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 coexisten-ce 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 japoni-cola, Paederus fuscipes, Tetragnatha praedonia, 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 medinalis) was C. japonicola, T. praedonia and P. fuscipes. It 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 the control of the both pests. These were consistent with their habitat nicie (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 specie.;). The results from experiments using addition and exclusion methods indicated 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.
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