Heat tolerances of four species of fire ants (Hymenoptera: Formicidae: Solenopsis)

Minor workers of the four fire ants species found in Texas, Solenopsis aurea Wheeler, S. geminata (Fabricius), S. invicta Buren, and S. xyloni McCook were exposed for one hour to upper critical temperatures. Solenopsis aurea and S. xyloni are typically desert adapted ants whereas S. geminata and S. invicta are found in mesic regions. We predicted that those species from hot desert regions would have higher temperature tolerances than their more mesic congeners. Mortality rates were not siginificantly affected by relative humidity conditions (0% or 100%), indicating that the ants did not die from dehydration. The responses of ants acclimated at 12°C, 22°C, and 32°C were significantly different, although biologically the differences were negligible. The LD50 values were between 40.8°C and 44.0°C and the LD95 values between 43.1°C and 47.3°C.