i68 



COLORATION IN LF.PTINOTARSA. 



THE EXPERIMENTAL MODIFICATION OF COLOR AND COLOR 



PATTERNS. 



Animal colors are to a considerable extent direct!}* modified by the action of 

 external agents, such as temperature, moisture, food, altitude, and light. In 

 the genus Leptinotarsa variations in color corresponding to different localities 

 or seasonal changes are common, and these have been considered under the 

 topics of place and geographical variation. The methods of biometry are 

 not, however, adequate for the analysis or interpretation of these color 

 changes ; as from this source we gain knowledge only of the existence of the 

 phenomena, of their extent, and of the laws governing the observed changes. 

 We shall now inquire into the causes of color changes their nature and 

 extent. 



MODIFICATION OF COLOR IN L. DF.CF.MLINEATA. 



My experiments in the modification of both larval and adult color in decem- 

 lincata cover a period of ten years, and comprise work with temperature, 

 moisture, food, light, soil, composition of the atmosphere, and atmospheric 

 pressure. 



TEMPERATURE EXPERIMENTS. 



Temperature experiments were begun in 1894, and have been continued 

 each year since then. The results are given in condensed form, the data of 

 many experiments of the same kind being combined into one comprehensive 

 statement. 



Experiment i. To determine the effect of a slightly increased temperature upon the 

 color and color pattern of L. decemlineata. 



Conditions. Temperature on the average 5.78 C. above that in nature. 

 Other conditions normal. 



Apparatus. Glass cages and glass breeding tanks, warmed by the sun and 

 protected from radiation at night. 



In these experiments, which were conducted during the years 1894 to 1901, 

 5,500 larvae of this beetle taken at random from potato fields were used. 

 They were placed in the conditions of the experiment in late larval life, and 

 remained there until the full imaginal colors had been developed. The tem- 

 perature records for the series are given in the following table : 



Table 44. Temperature conditions. 



