Predicting the spread speed of red imported fire ants under different temperature conditions in China

Red imported fire ants (RIFA, Solenopsis invicta Buren), are invasive species that have strong negative impacts on ecosystems and human society. Since the invasion of Chinese Mainland in 2004, the average annual spread rate of RIFA in southern China has exceeded 26.5 km, showing a rapid expansion trend. Given that this species has two spread pathways - natural expansion (nuptial flight and nest migration) and human-mediated transmission (horticultural plant transfers, etc.), we hypothesized that natural mechanisms alone cannot account for the observed spread rate, and human activity induced transmission should be the dominant factor in its high spread rate. To test this hypothesis, we developed a mathematical model based on nuptial flight to simulate the natural spread process. We inputted historical temperature data from seven representative Chinese cities into this model. Simulations revealed a natural spread rate of merely 1.4-7.0 km/year, lower than the observed actual speed (26.5-48.1 km/year). This simulation result indicates that human-mediated transmission may be the main reason for the rapid spread in southern China.