Genetic structure, dispersal pathways, and northern expansion predictions of Solenopsis invicta: A two-decade journey through China's diverse landscapes.

The red imported fire ant, Solenopsis invicta, has invaded China for over two decades, advancing northwest from Guangdong to the Yangtze River coast at 30.8° N latitude. A decade since the last genetic analysis, this study revisits the species' genetic structure and invasion trajectory amidst intensifying selective pressures. Through mitochondrial DNA resequencing of 96 samples across 6 Chinese provinces, we identified 2 haplotypes (H5 and H22), with H22 predominating in Zhejiang, the northern limit of our study. Phylogenetic analysis suggests a likely invasion source from Guangdong and Fujian, with long-distance dispersal facilitated by the horticultural trade, particularly Cycas revoluta. Local dispersal rates varied significantly, with 40 m/year in northern Zhejiang and 118-186 m/year in Guangdong. A regression model (y = -303.2523 + 10 855.1813/x) forecasts a northern expansion threshold near southern Shandong. However, considering the bridgehead effect, repeated invasions, and climate change, the species' invasive range may extend further north.