The Potato Beetle in a Desert 381 



SUMMARY AND CONCLUSION. 



In general the results indicate for the potato-beetle that : 



(1) The optimum breeding activity of this insect coincides with the highest 

 water-content of the atmosphere, since periods of oviposition are exactly con- 

 current with those of rain and low rates of evaporation. 



(2) Differences in soil-moisture produce alterations in the water-content 

 of these animals which modify their behavior, since beetles will lay their eggs 

 sooner if they emerge from a soil of high moisture- content than if they issue 

 from a dry soil. 



(3) Egg-production is also modified by differences in the evaporating power 

 of the air which surrounds these insects, since a low rate of evaporation en- 

 courages oviposition. 



(4) The beetle dies if buried when all its activities are normal, but either 

 the summer or winter generation may be buried without injury if previously 

 desiccated. 



(5) The adobe soil of the arid region retains a relatively high percentage of 

 water and is thus an excellent medium for the sustentation of the life of this 

 beetle, as in other desert animals. 



(6) These insects exhibit a physiological behavior not unlike that of trans- 

 piration in plants; but further, their tropisms are modified by loss of water, 

 which is governed by the evaporating power of the air. 



(7) The evaporating power of the air surrounding these insects determines 

 their behavior through transpiration ; even their responses to light and gravity 

 are controlled by evaporation. 



(8) Entrance into hibernation in a desert region may be produced at any 

 time through desiccation, except at low temperatures, when little desiccation 

 takes place. 



(9) The hibernating period in an arid region is controlled by the duration of 

 the dry season, but is dependent upon the length of the winter in a temperate 

 region. 



(10) The water-relation is the controlling factor in the emergence of this 

 insect from hibernation if the temperature is above 15° C. 



(11) When surrounded by a moist medium (above 15° C.) , either atmosphere 

 or soil, these beetles are positive to light and negative to gravity, but desiccation 

 reverses this behavior. 



(12) This insect absorbs very little water below 12° C. ; its death-point under 

 a high water-content was found to be 58° to 60° C, but when desiccated it can 

 withstand from 1° to 5° C. more of heat. 



(13) Alterations in the behavior of the potato-beetle may be due to differ- 

 ences in metabolic activity as influenced through the water-relation. 



(14) This animal also imbibed water directly, but no studies were made upon 

 metabolic water. 



We may conclude that Leptinotarsa decemlineata, when introduced from its 

 grassland habitat into an arid region, is equilibrated immediately with respect 

 to its surroundings, especially in regard to its water and temperature medium ; 

 that its behavior is changed to resemble those responses still present in an 

 organism long accustomed to a desert complex, and that, since water is the 



