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

## TL;DR

This study shows how temperature fluctuations during aphid nymph stages affect adult insecticide sensitivity, with implications for pesticide risk assessment under climate change.

## Contribution

The study introduces the role of diurnal temperature fluctuations and insecticide temperature coefficients in altering adult aphid toxicity and reproduction.

## Key findings

- Wide temperature amplitudes reduced fecundity but increased early reproduction in adult aphids.
- Insecticides mitigated or reversed the harmful effects of temperature fluctuations on aphid survival and longevity.
- Insecticide temperature coefficients significantly influenced adult phenotypes under different temperature amplitudes.

## Abstract

As environmental stressors, climate change and insecticides interact in intricate ways that can adversely affect the growth and reproductive success of living organisms. This study explores how temperature amplitudes experienced during the nymphal stage affect the insecticide sensitivity of the adult Sitobion avenae (Fabricius) (Hemiptera: Aphididae). Using two insecticides with opposing temperature coefficients of imidacloprid (positive) and beta-cypermethrin (negative), we found that temperature amplitude significantly altered the survival, longevity, and reproduction of the adult. Notably, both insecticides mitigated or even reversed the negative effects of wide temperature amplitudes. These findings highlight the importance of considering diurnal temperature fluctuations and insecticide temperature coefficients when assessing pesticide risks under climate change.

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 S. avenae. 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.