The rice brown planthopper, Nilaparvata lugens (Stal), a major pest of rice in most of Asia, underwent optimum development at 25 and 29°C, but 33°C was detrimental to all life stages. However, this effect was moderated considerably by rearing the insects at 12-hour alternations of 25° and 33 °C or 29° and 33 °C. While high planthopper populations caused "hopper burn," lower infestations reduced the number of tillers, number of panicles, and total grain weight of the plants. Unfilled grains resulted from infestation during the reproductive growth stage of plants but not from infestation during the vegetative phase. There were distinct differences in the susceptibility of 20 selected varieties to this species. While some of these varieties were less preferred by the insect and showed some antibiosis effects, tolerance to hopper burn appeared to be the major factor in the differences of susceptibility. There were no apparent correlations between the resistance of these varieties to the brown planthopper and their resistance to the rice green leafhopper. The brown planthopper, Nilapan'ata lugens (Stal), I From a thesis submitted by the senior author in partial fulfillment of the requirements of the degree of Master of Science in Entomology, College of Agriculture, University of the Philippines.

Field experiments during 2 consecutive rice crops showed the relative abundance of common rice leafhopper and planthopper species as Nephotettix spp. > Sogatella furcifera (Horvath) > Nilaparvata lugens (Stil) > lnawl11a dorsalis (Motschulsky). The Nephotettix spp.