Life-History Responses of the Fall Webworm Hyphantria cunea to Temperature Change: Not Following the Temperature–Size Rule

Temperature serves as a critical environmental factor for ectotherms and significantly impacts numerous life history traits. This study examined the influence of temperature on life-history traits of the fall webworm Hyphantria cunea at 20°C, 22°C, 24°C, 26°C, and 28°C. There were no significant differences in larval survival rates across the temperatures tested. However, pupal survival at 28°C was significantly lower compared to other temperatures. Sex ratios remained consistent at 20°C–26°C but skewed toward males at 28°C. The developmental time from egg to adult decreased as the temperature rose, with males emerging earlier than females (protandry), primarily due to shorter larval stages. Pupal weight exhibited temperature- and sex-dependent trends: female pupae peaked at 22°C (184.6 mg) and there was a 9.2% increase at 28°C as compared with 20°C, demonstrating a reverse temperature-size rule. In contrast, male pupal weight decreased by 8.2% at 28°C, indicating greater thermal sensitivity. Growth rates increased with temperature, showing sex-specific variations at lower temperatures. Adult weight mirrored pupal trends, with females consistently larger than males. Metamorphic weight loss increased with temperature in both sexes, but males experienced more pronounced losses. Female-biased sexual size dimorphism (SSD) is inclined to increase along with weight gain and temperature, not conforming to the Rensch's rule. Furthermore, positive relationships were discovered between pupal weight and larval development time, and between adult weight and fecundity. These findings emphasize temperature-driven plasticity in development, SSD, and thermal tolerance, highlighting the species' adaptability to warming climates and its implications for pest management strategies.