Aphid Nymphs Experiencing Diurnal Temperature Fluctuation Alter the Toxicity of Adults Depending on the Role of the Insecticide Temperature Coefficients

Climate change and insecticides negatively impact organism development and reproduction. Previous studies on climate change have focused on average temperature while ignoring diurnal temperature fluctuations. Therefore, this study investigates the interaction effects of the nymph experiencing temperature amplitudes (TAs) (+/-0, +/-6, +/-12 °C) at the same average temperature (22 °C) and two insecticides (beta-cypermethrin: negative temperature coefficient NT, imidacloprid: positive temperature coefficient PT) in the adult phenotypes and population parameter of <i>S. avenae</i>. The findings revealed that wide amplitude (+/-12 °C) significantly decreased fecundity, daily nymph reproduction, and the intrinsic rate of increase, while it significantly enhanced early fecundity. Medium amplitude (+/-6 °C) significantly lowered the intrinsic rate of increase. Notably, insecticides mitigated or even reversed the harmful impact of wide amplitude on adults. Under PT treatment, longevity was significantly higher than that under 22 °C. Under NT treatment, survival was noticeably greater than that under 22 °C. The interaction between insecticide and medium amplitude positively influenced adult phenotypes, with both PT and NT treatments resulting in higher survival, longevity, fecundity, and daily nymph production compared to 22 °C. These findings support the theory of climate-induced poison sensitivity and indicate that insecticide temperature coefficient is crucial in assessing insecticide safety risks under climate change scenarios.