Interference competition between two invasive fire ants
Author of the article:LEI Yan-Yuan1** Lü Li-Hua1*** HE Yu-Rong2 Li Shi-Mao1, 2 SHI Qing-Xing1, 2
Author's Workplace：1. Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Institute of Plant Protection, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; 2. College of Agriculture, South China Agriculture University, Guangzhou 510642, China
Key Words： Solenopsis invicta, Solenopsis geminata, interference competition, competition mode, conspecific interactions
Abstract： [Objectives] To explore the mechanism of interference competition between two successful invasive fire ant species, Solenopsis invicta (Buren) and Solenopsis geminata (Fabricius). [Methods] A series of individual and group behavioral assays were conducted to examine the aggressive responses of these two species. [Results] In individual aggression assays, aggression was mostly at level 3; workers or soldiers of both species tended to adopt threat postures rather than actually fighting. The greatest proportion of level 4 aggressive behavior was displayed by major workers of S.invicta and workers/soldiers of S. geminate (33.04% and 37.92%, respectively). Soldiers of S. geminate, and all castes of S. invicta, did not differ significantly in aggressive responses. Minor S. invicta workers andS. geminata workers had a significantly higher aggression index (3.49) than those of medium and major S.invicta workers and S. geminata workers (3.32 and 2.97, respectively), suggesting that aggression between minor S. invicta workers and S. geminata workers was more intense. Level 3 aggressive behavior, which was comprised of either physical attack, chemical attack, or both, was variable in either species. Physical attack was the first aggressive response by all S. invicta workers, whereas S. geminata employed any of the three aggressive modes at random. Either of the two species tended to avoid physical combat when they were defenders rather than aggressors. At level 4, both physical and chemical attacks were the major mode of aggression, or defense, by either species. In interspecific group aggression tests, both aggressive intensity and conspecific interactions were stronger in S. invicta than in S. geminata, and the aggressive ability of S. geminata against S. invicta increased with cumulative individual biomass, suggesting that S. invicta was competitively superior to S. geminata. [Conclusion] This work lays a theoretical foundation for further study of the mechanism of interference competition and competitive displacement between these two invasive fire ant species.