TEMPERATURE PREFERENCES OF FOUR SPECIES OF 
FIRE ANTS (HYMENOPTERA: FORMICIDAE: 
SOLENOPSIS )* * 
By James C. Cokendolpher 1 and Oscar F. Francke 2 
Introduction 
Temperature preferences are predicted to occur in insects due to 
homeostatic considerations. Enzymes should be adapted to function 
optimally within the narrow range of temperatures encountered by 
an organism during its peak activity periods (Heinrich, 1981). In 
ectotherms adapted to function optimally at low temperatures (e.g., 
living at higher latitudes or higher elevations), their biochemical 
machinery becomes inactivated or denatured at high temperatures. 
Conversely, those adapted to function optimally at high tempera- 
tures (e.g., living in the tropics or at lower elevations), experience 
reduced rates of biochemical activity at lower temperatures. Opti- 
mality theory predicts that ectotherms which habitually encounter 
temperature gradients should have the physiological and behavioral 
adaptations necessary to detect and respond to those gradients. 
A temperature gradient which fluctuates with daily and seasonal 
changes in solar radiation exists in the soil. This gradient is used by 
ground-nesting organisms to achieve some thermoregulatory homeo- 
stasis: they can move up and down their burrows to avoid tempera- 
ture extremes, especially those occurring near the soil surface. 
Superimposed on this temperature gradient is a moisture gradient, 
because the higher temperatures reached at the soil surface during 
the day promote evaporation. Ants which nest in the soil are known 
to respond to the temperature/ humidity gradients in the soil, and 
this response is particularly noticeable by the movement of brood 
among the various nest chambers (Ceusters, 1977; Seeley and 
Heinrich, 1981). Our research has focused on the responses of four 
species of fire ants to these soil gradients: elsewhere we (Potts et al . , 
'Department of Entomology and 2 Departirient of Biological Sciences, Texas Tech 
University, Lubbock, Texas 79409. 
* Manuscript received b v the editor December 27, 1984. 
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