The high surface area to volume ratio of terrestrial insects makes them highly susceptible to desiccation mainly through the cuticle. Cuticular permeability (CP) is usually the most important factor limiting water loss in terrestrial insects. Water loss rate, percentage of total body water (%TBW) content, CP, and desiccation tolerance were investigated in workers of four Solenopsis species in the southeastern USA. We hypothesized that tropical/subtropical ants (S. invicta and S. geminata) will have lower CP values and tolerate higher levels of desiccation than temperate ants (S. richteri and S. invicta × S. richteri). The %TBW content was similar among species. Solenopsis invicta had a 1.3-fold and 1.1-fold lower CP value than S. invicta × S. richteri and S. richteri, respectively. Solenopsis geminata had a 1.3-fold lower CP value than S. invicta × S. richteri, and a 1.2-fold lower CP value than S. richteri. The LT50 values (lethal time to kill 50% of the population) ranged from 1.5 h (small S. geminata) to 8.5 h (large S. invicta). Desiccation tolerance ranged between 36 and 50 %TBW lost at death and was not related to a species' location of origin. This study is the first report of water relations of S. invicta × S. richteri. It demonstrates that desiccation stress differentially can affect the survival of different Solenopsis species and implies that environmental stress can affect the distribution of these species in the southeastern USA.
Keywords: Solenopsis geminata; Solenopsis invicta; Solenopsis invicta × S. richteri; Solenopsis richteri; cuticular permeability; desiccation resistance; distribution.