Temperature: Metabolic Aspects and Perception 357 



wings of the cabbage butterfly, Pieris, reflect more of the infrared and reflect 

 least at 3 fiJ^^ A light snout beetle (Compsus niveus) absorbs 26 per cent and 

 a dark carrion beetle (Silpha ohscura) absorbs 95 per cent of the infrared 

 impinging on it. A dark brown grasshopper on sunny desert sand remained 

 4-5° warmer than a light buff^ grasshopper. ■'■' Desert locusts ( Schist ocerca) are 

 very inactive below 17°, begin to move at 17 to 20°, and at this temperature in 

 the morning take a position on an eastern slope with their bodies oriented 

 perpendicularly to the sun's rays, thus receiving maximal radiation.""' "' At 

 28° they start to migrate, or at higher temperatures (above 40°) they rest on 

 a bush parallel to the sun's rays, thus receiving minimum radiation. In the 

 evening when the temperature falls the locusts again aggregate in a position 

 perpendicular to the sun's rays, this time on a western slope. 



Teviperatiire "Sense" in Insects. Another factor in maintenance of some 

 constancy of temperature in terrestrial poikilotherms, particularly insects, is 

 selection of a "preferred" temperature when subjected to a gradient.^^^ The 

 selected temperature is not necessarily "optimal," and often varies greatly 

 with the temperature to which the insects have prexiously been adapted. The 

 eff^ect of acclimatizing temperature on the selected temperature is shown by 

 the following data: 



ticks' 



In some other insects the temperature prior to a gradient test makes little 

 difference. 



The type of insect and also the stage in life cycle are important. For example, 

 some dung maggots while actively feeding select a tenrperature of 30° to 37°, 

 which is within the usual temperature range of their medium and near the 

 temperature of maximum growth (34""); when they become ready to leave the 

 dung to enter the ground for pupation the temperature selected falls to 15°.^*^^ 

 In general, diurnal beetles select higher temperatures than do nocturnal 

 species, and temperature preferences vary with geographic races of the same 

 species.^"'* 



Often the selected temperature is higher for insects with a high lethal 

 temperature than for those with a low lethal temperature, as shown by the 

 following data^^*' on flies: 



At low temperatures activity of insects ceases and the temperature at which 

 movement resumes diff^ers with the species. This is particularly evident when 

 one watches the "awakening " of diff^erent species in the morning after a cool 

 night. 



