The Potato Beetle in a Deseet 373 



none died. We may therefore conclude that death in the first experiment was 

 due to heat. 



Many tests of various kinds have been given elsewhere and with the same 

 result — ^that when hibernating beetles were caused to emerge by applying water, 

 they reacted positively to light and negatively to jgravity. The next experiment 

 consisted in testing the reactions of hibernating beetles, in which emergence 

 was attained by digging and no water was added to the cage. 



For this test 47 hibernating beetles (Tucson A, g. II) were removed by 

 digging at 8 p. m. on June 12. They were negative to a 33 c. p. lamp, but 33 of 

 these insects were positive to candle-light of a weak intensity. These were 

 immediately placed under a bell- jar containing moist filter paper, and when 

 tested on June 13 they were found to be positive to light but negative to gravity. 

 This behavior was repeated in the following case. 



Twelve hibernating beetles (Tucson A, g. II), when removed by digging at 

 7 p. m. on Jime 30, were found to weigh 1.3573 grams, but they gave no response 

 to light or gravity. (A soil-sample taken from the earth surrounding the beetles 

 showed that it contained water to the extent of 13.7 per cent of dry weight.) 

 When the animals were placed in a humidor at 10 a. m. on June 33, they 

 weighed 1.3057 grams, having absorbed 0,1484 gram of water from the moist 

 chamber; 10 of these beetles, when tested, were positive to light, but 3, which 

 were inactive, died in a very short time after the experiment. The 10 adults 

 were also negative to gravity, for when placed in the constant-temperature dark- 

 room, all crawled to the top of the cylindrical wire-netting tube. These experi- 

 ments showed that positive phototropic and negative geotropic reactions were 

 induced in hibernating beetles by increasing the water-content of the surround- 

 ing mediiun, because the beetles under the moist bell-jar increased in weight and 

 imbibed water directly from the moist air. It was also true that they absorbed 

 water from the air in the soil. This relation was further shown in the following 

 observations, which were made upon the emergence response. 



The time of emergence is controlled by the environmental complex, for if 

 water were added to the medium surrounding hibernating beetles, when the soil 

 temperatures were above 14° to 16° C, emergence resulted. This was evident 

 at Tucson, for no emergence was discovered at either station until the rainy 

 season in July, and furthermore, the winter rainy season caused no emergence 

 because of low temperatures. At Chicago, emergence occurred whenever the 

 soil-temperatures reached 14° to 16° C, for enough precipitation always took 

 place during the winter and spring months so that emergence occurred as soon 

 as the proper temperature relations existed, which was from May 20 to June 25. 



SUMMARY AND DISCUSSION UPON THE RELATION OF WATER 

 TO HIBERNATION. 



The conclusions arrived at from these previous results indicated that a type 

 of hibernation might be produced at any time through desiccation, except with 

 low temperatures, when little desiccation took place. This condition produced 

 a loss of water from the beetles in such a way that they responded negatively to 

 light and positively to gravity, so that they burrowed into the soil and remained 

 there until the moisture-content of the soil was sufficiently high. They then 

 absorbed hydroscopic water, which raised their water-content and reversed their 

 reactions, so that they became positive to light and negative to gravity, hence 



