The Potato Beetle in a Desert 367 



ground during one month of the rainy season. At Chicago, however, no induced 

 entrance was discovered, since the conditions were more favorable there for 

 normal activities, as the daily environmental readings indicate. From these 

 observations it is evident that a type of hibernation occurred during periods 

 of low water-content in the surrounding medium ; this produced a lowering of 

 the beetles' content and induced a set of reactions so that a type of behavior, 

 potentially hibernation, resulted ; to determine exactly the role of water-loss in 

 the observed reactions other experimental tests were performed. 



For the purposes of this particular problem, the first test consisted of inducing 

 aestivation by desiccating adults of the summer generation, which do not 

 normally hibernate. The beetles for this experiment consisted of 259 adults 

 (Tucson A, g. Ill) which had been placed in a culture cage filled with potato 

 plants. They were allowed to feed until July 15, when a few bunches of eggs 

 were deposited, and at 4 p. m. 200 of these beetles were collected and divided 

 into two groups of 100 each, regardless of sex. The beetles were weighed, 

 group A weighing 12.16 grams and group B 11.52 grams, respectively. Group 

 A was now placed under a bell-jar with calcium chloride and group B under a 

 similar jar filled with wet filter-paper. The jars with the beetles were placed 

 side by side in an adobe building under identical conditions, except for differ- 

 ences in the desiccating capacity of the medium within the bell-jars. Through- 

 out the experiment the temperatures ranged from 26° to 38° C. At 8 p. m. 

 July 24 these insects were removed from the soil in the bell- jar and re weighed. 

 Group A from the desiccator weighed 8.53 grams, showing a loss of 3.63 grams, 

 and group B from the humidor weighed 10.92 grams. Previously a box of soil 

 (90 by 60 by 15 cm.) had been filled with a mixture of equal parts of sand and 

 adobe, which also had been already saturated with water and was kept slightly 

 moist throughout the experiment. Two bell-jars (a humidor and a desiccator) 

 were placed side by side over the slightly moist soil in the above box ; insects of 

 group A were placed in the latter, and those of group B in the former; after 

 28 hours group A was in hibernation, but group B did not hibernate, although 

 the beetles remained active upon the filter-paper. The calcium chloride was 

 now removed from the bell-jar over the hibernated group A, and the soil was 

 kept saturated ; at the end of 3 days 12 beetles emerged and after 6 days 57 more 

 beetles were discovered, but at the end of 2 days no others had emerged; the 

 soil was then sifted and 31 dead beetles were found. The individuals of group 

 B still remained active, but none, however, had hibernated. These results 

 show clearly that in the summer generation " induced " hibernation with a high 

 death-rate may be produced through desiccation and, furthermore, that when 

 water-balances were restored, all the living individuals emerged again and 

 resumed the activities normal to their generation and season. 



To further substantiate the above conclusions other tests follow. In the 

 fall generation, which hibernates normally, 1,000 newly emerged adults (Tucson 

 A, g. IV) were collected on August 14, and divided equally, regardless of sex, 

 into the following four groups: Each group was placed immediately in a 

 separate wire-netting tube in the screened vivarium at Station A, and the tubes 

 were made of wire-netting (95 cm. deep and 35 cm. in diameter), with a similar 

 material covering the top. These were sunk 55 cm. into adobe soil composing 

 the bottom of the vivarium, and each tube was filled to a depth of 53 cm. with a 

 mixture of equal parts of sand and adobe. 



