Interference competition and mechanisms between Solenopsis invicta Buren and Crematogaster rogenhoferi Mayr

Crematogaster rogenhoferi is a native ant in south China that coexists with the invasive red imported fire ant, Solenopsis invicta. To explore the mechanism of interspecific competition between C. rogenhoferi and S. invicta, the competitiveness of C. rogenhoferi against S. invicta at one-on-one and group levels was tested. The contact toxicity and repellency of crude extract of C. rogenhoferi venom on S. invicta were evaluated as well. At the one-on-one level, the aggression indexes of large workers, medium workers of S. invicta against C. rogenhoferi workers were 2.03 and 1.97, respectively. S. invicta contributed 85% of active attacks in which aggression indexes were over 3, and their attacks were mainly physical, while C. rogenhoferi workers primarily relied on chemical defenses. At all group levels, the mortality of S. invicta was higher than that of C. rogenhoferi. In the 10:10 combination, the mortality of S. invicta reached 60%, and the mortality rate of C. rogenhoferi was only 7%, indicating that the latter had significantly stronger competitiveness at the group level. After sting was sealed by nail polish, the mortality of C. rogenhoferi increased to 75.00% in the 10:10 combination, suggesting that its venom played a crucial role in competition against S. Invicta. The contact bioassays showed that the mortality of S. invicta increased with longer treatment times using different dilutions of C. rogenhoferi venom. After 48 hours of treatment with an 8% crude extract, the mortality of S. invicta exceeded 85%. The repellent rate of 10% crude extract of C. rogenhoferi venom was 81.67% against S. invicta, slightly lower than the 91.67% repellent rate of 10% DEET. Other concentrations of the venom extract showed significantly lower repellency compared to DEET at the same concentration. In conclusion, the chemical defenses of C. rogenhoferi provided a competitive advantage with S. invicta, and its chemical defense compounds exhibited high biological activity against S. invicta.