Effects of nitrogen content in rice plants and densities on the survival, development and reproduction of brown planthopper, Nilaparvata lugens Stl

The brown planthopper (BPH), Nilaparvata lugens (St(a)。l), is an important insect pest of rice in Asia. Its importance has been attributed to the effects of “Green Revolution” which promoted intensive rice monocultures with high fertilizer and pesticide applications. Since BPH depends on rice for its existence, host plant chemistry plays a major role in the population biology of BPH. The combined effects of increased colonization and improved performance may result in rapid population growth and high densities in nitrogen enriched crops. To fully clarify the ecological mechanism of BPH outbreak on the rice plants with high nitrogen regimes, this study was emphasized on the response of BPH to high nymph density on rice plants with different nitrogen regimes and was conducted in International Rice Research Institute (IRRI), Philippines. The results indicated that the nymph survival rates were markedly decreased with the increase of nymph density and with the reduce of nitrogen content in rice plants, implying the negative feedback mechanisms restricting population growth by both high nymph density and low quality of host plants, while lower nymph survival rates were found in the populations of BPH fed on rice plants with low nitrogen regime. The ratio of nymphs to total number of BPH was negatively related to the content of nitrogen in host plants at high nymph densities of 80 and 160 per pot, indicating the shortened nymphal development on the rice plants with high nitrogen content under high nymph densities, meanwhile significant longer nymph durations of BPH were recorded in the populations continuously fed on rice plants with low nitrogen regime compared to those on rice plants with high nitrogen regime. The ratio of female to male adults was positively related to the nitrogen content in host plants at the nymph density of 40 per pot, however, it decreased with the increase of nymph density. Female adult weight was significantly reduced with increased nymph density on rice plants with low nitrogen fertilizer. Female adult longevities on high nitrogen host plants were 3-fold longer than those on low nitrogen plants at all three tested nymph densities. Increased nitrogen content in rice plants significantly increased BPH fecundity, and the great difference in fecundity among three tested nymph densities was recorded on rice plants with low nitrogen fertilizer. Those results should suggest the application of high nitrogen fertilizer increased the load capacity of rice plants for a high BPH density.