Uneven farm practices between farmers cause the patchy pest distribution, especially in the brown planthopper (BPH: Nilaparvatalugens(St${aa}$l)) in Cambodia. Sine 1994 BPH have attacked Cambodian rice fields in patchy form. Moe BPH attacked in field where farmers have more opportunity to use fertilizer and insecticides. Rice production in Cambodia will probably face more problems with BPH outbreaks as rice production intensifies. The birth and/or survival rate of BPH that leads to population outbreaks are related to fertilizer, plant variety and insecticide treatments. The experiments were conducted in the field and laboratory in Cambodia in 1999 to test the hypothesis above. A traditional variety (Eath Chhmoush), low and high fertilizer rates, and an organic phosphate insecticide (Diazinon)ere used in the field experiment and two varieties(susceptible and tolerant to BPH) and three rates of NPK fertilizer were used in the laboratory study. BPH population and others arthropods wre collected weekly from the field experiment a D-vac machine. Two kinds of net cages (temporary and permanent) were covered the rice plants to determine the birth and survival rate of BPH population with and without natural enemies. Number of O cytes was counted from BPH females, which reared in plant-cages. Birth and survival rates of BPH were higher in susceptible plant with high fertilizer rate used. The experiment indicated that natural enemies have played the important role to control the BPH population. The realized fecundity and survival of BPH was higher in susceptible host plant variety with high rate of NPK feritlizer used. The immediate response of fertilizer application to the BPH offspring production was not shown and will be tested in wet season 2000.