The Potato Beetle in a Desert 



345 



At Tucson Station B the parent group of 104 adults for this culture was 

 received on July 15 and bred as a group-culture, producing 204 offspring in 

 25 days, thus giving generation I. As soon as the adults from the first genera- 

 tion appeared they were removed to another breeding-cage, but they immediately 

 burrowed into the ground within the experimental cages and hibernated there 

 until September, when they began breeding and in 21 days produced generation 

 II, of 293 progeny. A few days after emerging from pupation all of the beetles 

 went into hibernation without feeding, where they remained until the following 

 summer, when, on May 31, 7 males and 16 females emerged and bred immedi- 

 ately, giving generation III of 283 adults in 31 days. These were allowed to 

 reproduce as a group-culture, giving in 31 days generation IV of 127 offspring. 



Table 2. 



Early in September all were in hibernation and remained in the ground during 

 the winter. On the other hand, at the Chicago Station, the original wild parents 

 were allowed to breed as a group-culture, and gave generation I in 30 days. 

 These adults bred as a group-culture and produced generation II in 33 days, 

 which now hibernated during the winter from September until May, when they 

 reproduced and gave generation IV in 35 days : for the above data, see Table 2. 

 The animals for experiment were reared upon potato plants in cages of uni- 

 form size (6 by 6 by 6 feet), with sides of wire-netting, 16 meshes to the inch. 

 These cages were furnished with wooden bottoms (6 by 6 by 3 feet), which were 

 filled with a mixture of equal parts of adobe * and sand. This mixture proved to 



^ At Station A, where this soil was obtained, the adobe consisted of a clay loam, 

 which constituted the soil-mass of the river flood-plain. This soil was about 8 to 9 

 meters deep and rested on sand and gravel. Livingston (1910) found it to have a 

 water-holding power of about 18 per cent of its dry weight. The sand used in all 

 experiments was obtained from an arroyo near at hand and had a water-holding 

 power of about 39 per cent of its dry weight. 



