25O HABITS AND INSTINCTS IN LEPTINOTARSA. 



wise, in the higher forms, as in insects, increased capacity to resist extremes is 

 due to the lowering of the water content in the protoplasm. 



In the more arid portions of the American continent which are inhabited by 

 these beetles, as, for example, on the Pacific coast of Mexico or the northern 

 portion of the same country, the dry season is frequently prolonged for weeks 

 or even, in extreme cases, for a year or more. In many such places these 

 beetles live and are not exterminated by this excessive variation in their 

 environment, or, more correctly, there is no evidence that they are, and it is 

 of interest to know how they are able to withstand this extreme condition. I 

 have not had an opportunity to study this phenomenon in nature, but I have 

 reproduced in experiment such conditions with success and with suggestive 

 and conclusive results. 



In September, 1902, I placed a lot of 300 decemlineata in a cage which was 

 prepared for maintaining constantly a high temperature and a low percentage 

 of humidity. These beetles, which were of the second generation of 1902, 

 had been reared under normal conditions and would have hibernated in a 

 few days, and yet hibernation was postponed for weeks, although by about 

 December 1 all that were alive had entered the ground. The beetles in this 

 experiment were kept constantly dry and warm, although the diurnal range 

 in temperature was considerable, and a small amount of moisture was added 

 from time to time to compensate for that which would be supplied in nature 

 by dew and by the soil lower down. The beetles continued their hibernation 

 through the remainder of the year 1902, all the year 1903, and the winter 

 of 1903-1904, and only finally emerged when, in May, 1904, I gradually 

 increased the amount of moisture in the tank until the conditions found in 

 nature at that time were reproduced. Near the end of the month 76 beetles 

 emerged and began feeding, and during the summer of 1904 two normal gen- 

 erations were produced, the second of which hibernated in due course of time. 

 As far as I was able to see this prolonged aestivation did the beetles no harm 

 whatsoever ; and it is quite possible that if I had been able to restrain my 

 curiosity as to whether they were alive or not, they might still be contentedly 

 hibernating in their tank, to emerge at some future time. This experiment 

 shows how these beetles may be enabled to pass successfully over unfavorable 

 conditions of long duration, and I have not the slightest doubt that this is the 

 way in which the beetles of Chihuahua, San Luis Potosi, and other States in 

 northern Mexico manage to survive where there occur from time to time 

 seasons or a succession of seasons in which there is not enough rainfall to 

 start vegetation and animal life into activity. At any rate, the beetles are 

 found in these regions now, and if they have been exterminated in the past, 

 they have been able to reoccupy the region by immigration from the sur- 

 rounding territory with a swiftness which is astonishing and improbable, 

 owing to the slowness of the dispersal of these beetles in arid regions. More 

 crobable, especially in the light of this experiment, is the hypothesis that they 



