Voltinism and life-history traits of the invasive fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) feeding on corn

Voltinism and life-history traits of the invasive fall armyworm (FAW) Spodoptera frugiperda were investigated under semi-natural conditions for a period of two years. The FAW invaded the corn field in the suburbs of Nanchang (28° 46′ N, 115° 50′ E) in early summer and produced six complete generations. The FAW had the characteristics of short developmental time, high survival rates and strong fecundity. The development time of female pupae was significantly faster than that of male pupae, resulting in the emergence of female pupae earlier than male pupae. Except for the sixth generation in 2021, there was no significant difference between female and male sex ratio, which was close to 1:1. The FAW showed male-bias sexual size dimorphism with male pupae being significantly larger than female pupae. Unlike pupal weight, in most generations, male adult weighed significantly less than females, because the weight loss of male pupae during metamorphosis was significantly greater than that of female pupae. The seasonal variation of pupal weight did not conform to the temperature–size rule. Compared with 22.8 °C, the 29.2 °C high temperature not only significantly reduced the development time of larvae but also significantly increased pupal weight. The adult fecundity feeding on fresh corn leaves was higher than that feeding on live corn plants in most generations. In most generations, pupal weight was positively correlated with larval development time and adult weight was positively correlated with fecundity. These results add to the understanding of the evolution of life-history traits in the FAW and may have important implications for predicting population dynamics of the FAW and optimizing control strategies.