Life table parameters and survivorship of Spodoptera exigua (Lepidoptera: Noctuidae) at constant temperatures.

Age-specific life table parameters, survivorship, and extra molting of the beet armyworm, Spodoptera exigua (Hübner), were determined at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34, and 36°C with a variation of 0.5°C on sugar beet leaves. No development was observed at 12 and 36°C. The survivorship of overall immature stages was higher at 25°C than the other temperatures. The highest (0.276 d(-1)) and lowest (0.149 d(-1)) value of the intrinsic rate of increase (r) was observed at 30 and 20°C, respectively. Although the highest value of the net reproductive rate was at 25°C (377.7 female offspring at 25°C and 127.4 female offspring at 30°C), the highest value of r was at 30°C, which indicated the importance of shorter development time (16.9 d at 30°C and 27.2 d at 25°C) in enhancing r. The relationship between temperature and r was modeled using the Lactin-2 model. The lower temperature threshold, the upper temperature threshold, and optimal temperature for the r were estimated at 13.1, 32.2, and 34.1°C, respectively. The mean generation time decreased significantly with increasing temperature, with the longest (35.9 d) and shortest (15.1 d) mean generation time was calculated at 20 and 33°C, respectively.