The Potato Beetle in a Desert 351 



relation due to a reduction of normal physiological activities through desicca- 

 tion? If so, what relation exists between such organisms and changes in the 

 physical composition and especially the moisture-content of the medium sur- 

 rounding them ? For these tests, animals of different physiological activities, 

 induced by differences in humidity, were buried for certain periods of time in 

 soils of varying degrees of moisture and texture. The criteria used in deter- 

 mining the power of resistance were the number of individuals surviving in 

 the test at the end of a given period of time, and the differences in activities of 

 the insects produced through desiccation, as compared to a similar set in which 

 the behavior was normal. The capacity of these animals to resist was tested, 

 and beetles were placed in wire-netting tubes (50 cm. long by 10 cm. in diam- 

 eter) which permitted a free circulation of air and moisture. The tubes con- 

 taining the insects were buried upright, so that the base of each was 60 cm. deep 

 in the soil. The plots were 10 meters apart, in the open, at Tucson Station A. 

 Earth was removed from each plot so as to leave two holes 6 meters square by 

 1 meter deep, and each cavity was further divided into equal parts by a partition 

 of red- wood boards 1 inch thick ; one side was filled in with sand, the other with 

 adobe. One of these plots was exposed under natural conditions in the open, 

 while the other was covered with a roof, which extended on each side 1 meter 

 beyond the limits of the plot. This roof was raised 1.5 meters above the ground 

 in order to give a free circulation of air and to keep the soil dry underneath. 

 Water from rains was collected in ditches which conveyed it beyond the plot. 

 The plot in the open was designated Plot A, and that under roof as Plot B. 

 The soils in both plots were kept moist by adding water by means of a garden 

 hose until October 20, but after this date they were exposed to the conditions 

 of the winter of 1911-12 at Tucson. 



The first set of experiments concerned only beetles of the summer generation 

 that were emerging from the pupa state. Such insects do not normally hiber- 

 nate, but may be caused to do so through adverse conditions such as those which 

 cause desiccation. It should be noticed that in one instance the animals were 

 buried with all activities normal; in the other, they were first induced to 

 hibernate in cages in the vivarium, and they were sifted out in the soil; in 

 either case they were finally buried under the conditions described above. 



In the former test in which the beetles were buried with all their activities 

 normal, 400 emerging individuals (Tucson A, g. I) were collected on August 

 12 ; 50 of these were then placed into each of the 8 wire-netting tubes ; 4 of these 

 tubes were filled with sand and 4 with adobe soil; the insects were placed at 

 corresponding levels in each of the 8 tubes ; 2 of these containing sand were 

 buried in the open plot and 2 under the shelter, while the 4 tubes with adobe soil 

 were sunk in the adobe sections of the plots, 2 in each. These were left unmo- 

 lested until May 1, when one tube under each set of conditions was examined 

 but no living beetles were found. On October 1, the remaining 4 tubes were 

 inspected with the same results ; there were no living organisms found. These 

 results showed that no beetles of the summer generation with their activities 

 normal hibernated successfully when buried under the conditions of this experi- 

 ment. These observations are tabulated in Table 4. 



