Does Temperature Tolerance Increase in Long-Term Domesticated Frankliniella occidentalis Under Constant Temperature?

The wide distribution of <i>Frankliniella occidentalis</i> is largely due to its extreme temperature adaptability. In current studies, most scholars consider environmental changes to be the main factor affecting insect temperature adaptation. However, our previous studies have shown that the adaptability of <i>F. occidentalis</i> to extreme temperature conditions can be strengthened through domestication. In this study, the population of <i>F. occidentalis</i> raised in the laboratory for a long time (2008-2022) under relatively constant temperature and humidity conditions was used as the experimental material. Over 14 years, changes in temperature tolerance after the same high- and low-temperature stress were evaluated by comparing the survival data of the 2010 population, 2016 population (more than 100 generations), and 2022 population (more than 200 generations). The survival data and LT₅₀ values demonstrated significant stage- and sex-specific differences in thermal tolerance: The cold tolerance of <i>F. occidentalis</i> improved significantly, with LT₅₀ decreasing from -12.5 °C (P2010) to -13.4 °C (P2022) for females and -11.5 °C to -13.0 °C for males. Notably, male adults showed higher survival rates than females at -14 °C and -15 °C. Meanwhile, heat tolerance increased most markedly in 2nd instar larvae (ΔLT50 = +4.1 °C). These findings indicate an environment-independent evolutionary pathway within the population, providing a new research direction for insect population evolution.