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) <em>Spodoptera frugiperda</em> 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.本研究于半自然条件下，针对入侵性草地贪夜蛾（fall armyworm, FAW，学名*Spodoptera frugiperda*）的年发生代数及生活史特征开展了为期两年的调查研究。该虫于初夏侵入南昌市郊区（北纬28°46′，东经115°50′）的玉米田，在两年的调查周期内共完成6个完整世代。草地贪夜蛾具有发育周期短、存活率高、繁殖力强的特征。雌蛹的发育时长显著短于雄蛹，致使雌蛹羽化时间早于雄蛹。除2021年第6代外，各世代的雌雄性别比均无显著差异，且接近1:1。草地贪夜蛾表现出偏雄性的性大小二型性，雄蛹显著大于雌蛹。与蛹重情况不同，在多数世代中雄成虫体重显著低于雌成虫，这是由于雄蛹在变态过程中的体重损失量显著高于雌蛹。蛹重的季节变化并不符合温度-体型规则。相较于22.8℃，29.2℃的高温不仅显著缩短了幼虫的发育时长，同时显著提升了蛹重。在多数世代中，取食新鲜玉米叶片的成虫繁殖力高于取食活体玉米植株的成虫。多数世代中，蛹重与幼虫发育时长呈正相关关系，而成虫体重与繁殖力亦呈正相关关系。本研究结果深化了对草地贪夜蛾生活史特征演化的认知，可为该虫的种群动态预测及防控策略优化提供重要参考依据。