[Objectives]  To clarify the influence of larval rearing density and temperature on immature developmental stages (eggs, larvae, pre-pupae and pupae) of Hypera sp. [Methods]  The survival, growth and development of the above immature developmental stages were measured and compared under different larval densities and temperatures. [Results]  Larval density had a significant effect on survival and growth; survival was significantly higher, and the developmental duration significantly shorter, at a density of 50 larvae per box than that at other densities. The pupal weight of females raised at any of the larval densities tested was significantly greater than that of males. Sex ratio (♀/♂) was not affected by larval density but temperature had a significant effect on survival and growth. The survival rates of larvae and pupae were significantly higher at 27 °C than at other temperatures. The survival rate of 1st instar larvae was highest at 30 °C, whereas that of 3rd instar larvae was highest at 27 °C. Temperature had no significant effect on the survival rate of 2nd instar larvae. The developmental duration of different developmental stages and instars was significantly shorter at higher temperatures. [Conclusion]  Larval density and temperature significantly affect the population demographics of Hypera sp., a finding that contributes to better forecasting, prevention and control of this pest.