Queen weights of polygyne Solenopsis invicta and S. xyloni suggest reduced competitive ability
Solenopsis invicta Buren populations were confirmed in southern New Mexico, resulting in a quarantine of Doña Ana County in 1998; however, Solenopsis xyloni McCook remains the dominant fire ant. This study compared the queen weights and egg production of polygyne colonies of both species. There was no difference in live weights of the major worker caste; however, queens were very different in weight. In this study, S. invicta queens weighed almost twice as much as S. xyloni (S. invicta = 11.32 ± 0.25mg vs. S. xyloni = 6.40 ± 0.30mg) and produced over 50% as many eggs as S. xyloni. [S. invicta = 8.4 ± 0.55 vs. S. xyloni = 5.4 ± 0.53 log(eggs produced in 72 hrs)] Although, this would suggest that S. xyloni are probably less fecund and would support the increased displacement rates of native fire ants in general, S. invicta is not increasing its range and may actually be displaced by S. xyloni in Doña Ana County.
Ramirez, R.A. and D.C. Thompson. 2006. Queen weights of polygyne Solenopsis invicta and S. xyloni suggest reduced competitive ability. Southwestern Entomologist 31: 49-54