Egg-Stage Daily Temperature Amplitude Constrains Adult Fitness and Population Growth in Tuta absoluta (Meyrick)

Daily temperature variation associated with climate change can strongly affect the survival, development, and population growth of insect species. However, whether the amplitude of daily temperature fluctuation experienced during the early development of insects leads to carry-over effects across the later life stages remains insufficiently understood. Using the invasive pest Tuta absoluta, we exposed the eggs to different thermal regimes under two mean-temperature backgrounds (22 and 25 °C) and measured the immediate egg-stage responses and the subsequent carry-over effects. The immediate responses depended on mean temperature, consistent with the nonlinear shape of thermal performance curves. At 22 °C, the wide amplitude accelerated egg development and increased variation in developmental duration without significantly affecting egg survival. At 25 °C, the moderate amplitude accelerated development, whereas the wide amplitude partially reversed this acceleration and produced a steeper age-dependent increase in mortality. Temperature conditions experienced during the egg stage also generated pronounced carry-over effects: wide amplitudes reduced larval survival, shortened female adult longevity, and decreased fecundity, whereas male longevity remained comparatively stable—a pattern consistent with sex-specific sensitivity of adult fitness to early thermal history. The wide amplitude during the egg stage also reduced the intrinsic rate of increase and net reproductive rate. Thus, the thermal regime during the egg stage can suppress population growth through cross-stage effects and sex-dependent fitness responses. Models based only on mean temperature may overestimate population growth potential and mischaracterize phenology. Incorporating egg-stage thermal history and daily temperature fluctuation into phenological and demographic models could improve pest forecasting and integrated pest management decisions under climate change.