Population model of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae)

Abstract

The population model of the beet armyworm, Spodoptera exigua (Hübner), was constructed to understand its population dynamics in the fields. Major components of the population model of S. exigua are temperature-dependent development models of each stage and an adult oviposition model. To develop the temperature-dependent development model, development time and survival of each life stage were investigated at ten constant temperatures (12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, and 35℃) under a photoperiod of 14:10 (L:D) h. To develop the oviposition model, longevity, fecundity, and survival of adult were investigated at nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, and 35℃) under a photoperiod of 14:10 (L:D) h. Relationship between the development rate for each life stage and temperature was fitted by a linear and six nonlinear models, and was fitted best by the Lactin 2 model (r2=0.95-0.99). The lower developmental thresholds were 12.18, 13.67, 14.19, and 13.12℃ for egg, early (1-3rd instar) larva, late (4th-last instar) larva, and pupa, respectively. Thermal constants for each stage were 42.92, 85.47, 76.92, and 98.04 DD, respectively. The developmental variations of each stage were described against the physiological age by the three-parameter Weibull function. Relationship between female adult developmental rate (1/mean longevity) and temperature was fitted by the Lactin 2 model (r2=0.95). Fecundity of adult was highest at 30℃ and lowest at 15℃. Cumulative oviposition rate and survivorship were well described by the three-parameter Weibull function, and the sigmoid function, respectively. The simulation model was evaluated by comparing model outputs with adult occurrence data from the welsh onion fields in 2010 and 2011. The population model of S. exigua will be useful to predict its seasonal population dynamics in the fields.