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 I2°C, 2~C, and 32°C were significantly different, although biologically the differences were negligible. The LDSO values were between 40.8°C and 44.0°C and the LD95 values between 4!U °C and 47.3°C. MATERIALS AND METHODs.-Four species of fire ants were collected in Texas: Solenopsis aurea Wheeler and S. xyloni McCook from Garza Co., S. geminata (Fabricius) from Kimble and Val Verde Cos., and S. invicta Buren from Bandera Co. Colonies of ants were collected, separated from the soil, and housed following the methods of Banks et aL (1981). All colonies were maintained with similar regimens of food, water, and light. Ants were fed cockroaches, Nauphoeta cinerea (Saussure), and mea1worms, Tenebrio sp. Free water and a 1:1 solution of honey and water were
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