Abstract: In order to explore the mechanism of interference competition of the red imported fire ant, Solenopsis invicta Buren, against native ants and the success of invasive species, important invasive species S. invicta and two native ants Tapinoma melanocephalum (Fabricius) and Pheidole fervida Smith were used as test insects in this study. Interference competition between S. invicta and two native ants at one-on-one and community levels was studied in the laboratory. The aggressiveness test at the one-on-one level between S. invicta and T. melanocephalum revealed that the mutual aggressiveness was weak because workers of both species did not perform stronger tussle, but only displayed threatening posture although S. invicta had more competitive advantage. The aggressive level was concentrated on level Ⅲ. The aggressive indices between one of minor, medium workers of S. invicta and soldiers of P. fervida were significantly higher than those between major workers of S. invicta and soldiers of P. fervida, suggesting that the aggression between those two ants are more intensive. In tests at the community level, no dead S. invicta ants were found in competitive combination of S. invicta against T. melanocephalum with the average mortality of 31.80% for T. melanocephalum ants, although the mortality for S. invicta was 0.20%-12.00% in competitive combination of S. invicta against P. fervida with the average mortality  of 49.91% for P. fervida ants. The results indicated that the aggressive intensity of S. invicta was stronger than the two native ants, and the aggressiveness between S. invicta and P. fervida was stronger than that between S. invicta and T. melanocephalum. The lower mortality of T. melanocephalum may owe to its chemical defensive ability. This work laid a theoretical foundation for further study on protection and utilization of the dominant native species T. melanocephalum against S. invicta.

Key words: Red imported fire ant (Solenopsis invicta), Tapinoma melanocephalum, Pheidole fervida, interference competition, aggressiveness test