We tested the hypothesis that early-planted seedbeds of rice are more heavily infested with brown planthopper (BPH) than later seedbeds, and that transplanted plants with BPH are a source of subsequent population increase and possible outbreaks. The experiments were conducted at CARDI and Takeo province in wet season 2000 and early wet season 2001. BPH at 0, 25, 50, 100, 200 /$ extrm{m}^2$ were infested onto plants with low and high fertilizer treatments. Rice seeds of varieties moderately and highly susceptible to BPH were sown 3 weeks early, 2 weeks early, at the normal time, and later than normal (5 weeks) and treated with low and high fertilizer rates. At Takeo, the 3 weeks early seedbeds were infested by BPH migration, and both varieties with high fertilizer caught more immigrant insects and subsequently had damaging outbreaks of BPH in the third generation. At CARDI, no seedbeds were infested with immigrant BPH. Seedbeds in areas with continuous cropping of rice have a high risk of BPH attack. Seedlings infested wish 200, 100, and 50 BPH/$ extrm{m}^2$ resulted in death of the plant. Plants with 100 and 200 BPH/$ extrm{m}^2$ were killed sooner. With 25 BPH/$ extrm{m}^2$ plants were not killed, but subsequent population increase caused yield reduction. Yield loss was high in high fertilizer treated plants.