Blocking effects of landscape factors against dispersal of the red imported fire ant, Solenopsis invicta

Most alate adults of the red imported fire ant, Solenopsis invicta Buren, fly for only a limited distance and altitude, so their flights may be easily blocked by certain landscape factors, which as a result may hinder the dispersal of this ant. However, the related researches have not been reported yet. Here, we selected 23 invaded sites in Zhejiang Province and modeled the relationship between the proportion of S. invicta nest density decline and the length, width and height of the barriers existing in local landscape (e.g., rivers, woodlands, hills, buildings, etc.). Our results showed that the extent of nest-density decreases (blocking efficiency) due to landscape-factor blocking had a significant S-curve relationship with the ratio of length of barriers to length of the source areas, and had a significant logarithmic-curve relationship with the width of barriers. However, we did not find significant relationship with the height of barriers. When the ratio of barrier length to S. invicta source-area length reached 0.8, the blocking efficiency was evidently elevated, particularly as the ratio reached 2.0. If the width of barriers was less than 50 meters, the blocking efficiency varied from 25% to 100%, but the blocking effect was obvious when the barrier width was over 100 m. Our results will hopefully enrich the knowledge on S. invicta dispersal features, and can be taken into consideration when we monitor and control this fire ant.