Abstract: Different combinations of temperature and relative humidity(RH) significantly affected the development and the fecundity of beet armyworm (Spodoptera exigua). The combination of 26℃ and RH 80% or 94% was optimal for the development of beet armyworm. Under this combination, the hatchability of egg, the survival rate of 1～5 instar larvae, the rates of emergence, female, and female ovipositing, and the mean quantity of oviposition were 82.63～83.70%, 81.90 ～82.47%,88.00～88.03%, 90.40～91.00%, 93.36～94.17%, 95.97～96.26%, 92.77～94.16%, 0.42 ～0.43, 0.98 and 605～606 eggs/female respectively, which were all significantly higher than those of other combinations. Under combination of 32℃ and RH94%, the population's innate capacity of increase was the highest (0.225).

Key words: Spodoptera exigua, Temperature, Humidity, Fecundity