THE RELATION OF WATER TO THE BEHAVIOR OF 

 THE POTATO BEETLE IN A DESERT. 



INTRODUCTION. 



In a series of experiments maintained by Professor Tower to determine the 

 action of the Tucson Desert upon evolutionary processes in ehrysomelid beetles, 

 it was observed that soil-moisture, humidity, and the like played an important 

 role in modifying the activities of these organisms when introduced into the 

 arid region ; so, as a result of these observations, the author undertook a series 

 of investigations to discover any possible connection between this water-relation 

 and the reactions of the potato beetle, Leptinotarsa decemlineata (Say), when 

 transplanted into the desert from a temperate habitat. 



A large stock of this species was sent to Tucson from Chicago in June 1911, 

 so that comparative studies under different environmental complexes could be 

 made. Three cultures were established in several open-air breeding-cages at the 

 stations already equipped for Professor Tower at Tucson and Chicago. Two of 

 these stations, which were arid in character, are designated as Tucson Station A 

 and Tucson Station B, while the third one, known as the Chicago Station, was 

 temperate and located at the University of Chicago. The former of the two 

 desert stations was situated at the base of the northern slope of Tumamoc Hill, 

 just within the flood-plain of the Santa Cruz River, at an altitude of 2,370 feet, 

 while the latter was located on the shoulder of this hill, on which the Desert 

 Laboratory is situated, at an elevation of 3,705 feet. The biological significance 

 of the conditions at these stations, as indicated, is given elsewhere, and the 

 problems dealt with concern the relations which exist between the activities of 

 the beetles when allowed to reproduce at these localities and the changes pro- 

 duced in the water-content of the animals through the action of the various 

 environmental factors. 



INSTRUMENTATION AND CONDITIONS OF EXPERIMENT. 



At each station the evaporation rates were obtained by the Livingston at- 

 mometers, and Friez self-recording thermographs were employed to measure 

 the temperatures, air and soil, and the same maker's hygrographs were also 

 used for the relative humidities ; these instruments were calibrated and stand- 

 ardized fortnightly. The rainfall-readings were obtained from a standard 

 weather bureau rain-gage at the Laboratory site. It is interesting to notice that 

 the environmental data as recorded from these experiments showed for the arid 

 complex that the greatest daily fluctuations occurred at Station A and the 

 highest evaporation at Station B, while the lowest evaporation-rates and air- 

 temperatures were at Station C. The Tucson region as a whole, when contrasted 

 with the Chicago conditions, has a higher rate of evaporation, a lower relative 



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