The Potato Beetle in a Desebt 



371 



ACTIVITIES DURING HIBERNATION. 



It was observed that hibernating beetles were inactive when first dug from the 

 soil, and if the insects were moved to a warm room they soon began to crawl ; 

 then entrance into hibernation occurred if they were brought into contact with 

 moist earth. At Chicago, during the winter of 1911-12, it was observed that 

 beetles which had hibernated out-of-doors migrated more deeply than usual 

 during the cold winter. From the following test it appeared that beetles would 

 move to moist regions in the earth during hibernation, for late in April 1913, 

 at Tucson Station A, several hundred individuals were found to be hibernating 

 in the open air cage. Accordingly a corner of this cage was watered and the 

 soil was sifted ; thus, all the beetles were removed in that locality, but the newly 

 dug soil was kept moist, and each week it was examined for adults ; during each 

 observation a large number was always discovered. 



WATER RELATION OF SOILS AND HIBERNATING BEETLES. 



The beetles hibernate in small cavities or cells, which contain air of a relative 

 humidity, that is in proportion to the water-content of the surrounding earth. 

 During heavy rains the soil becomes flooded with water, so that some air is 

 driven from the cavities, but if the rain continues for too long a period the 

 beetles may die. On the other hand, if the soil is too dry, desiccation of the 

 insects takes place and death may result ; therefore, the part soil-moisture plays 

 in mortality during hibernation is of great significance. Tower (1906), in 

 discussing results with soils, states: 



" The water-content of soil is controlled, not by an abundant rainfall, nor by 

 telluric water, but almost wholly by adhesion and capillarity in the soil — that 

 is, physical conditions alone, such as permeability, capillarity, and the power to 

 absorb and to retain water are the factors which influence the moisture content 

 of soil .... In all soils the pores which do not contain water are filled with air 

 in which the percentage of relative humidity is controlled by the amount of 

 water in neighboring pores. Likewise, the cells in which these beetles pupate 

 are filled with air ; the relative humidity is controlled by water in the pores of 

 the surrounding earth." 



Thus the physical composition of the soil is important in preserving insect 

 life, and the adobe soil of the Tucson Desert, although it contains but little 

 moisture, does possess other physical potentialities which act in retaining 

 moisture, for through drying it becomes impervious to water and hibernating 

 animals are sealed up in their cells and thus preserved from desiccation. To 

 determine how dry the adobe soil was when containing living beetles, samples 

 of it were taken from the walls of the cells (Table 11) and those of June 30 



Table 11. 



