IIO VARIATION IN LEPTINOT ARSA. 



In decemlineata the range is from an albinic condition found in the Rio 

 Grande Valley and in the southern part of Arizona to the highly melanic con- 

 dition found on the Atlantic coast. From Colorado eastward into Illinois and 

 Ohio and on farther to the Atlantic coast there is apparent an increasing ten- 

 dency toward melanism, which culminates in New England and the maritime 

 provinces of Canada. Along the Great Lakes-St. Lawrence Valley this same 

 tendency is found, whereas toward the South an albinic tendency prevails 

 which is very distinct to the southwest and less so to the southeast. In this 

 respect the facts presented are in no wise different from those that have long 

 been known, that all animals in the United States are in general more melanic 

 to the north and east, less so to the south, southeast, and middle west, and 

 albinic in the extreme south and southwest. As long ago as 1877 Allen recog- 

 nized this tendency in birds and mammals, and Enteman finds the same to 

 be true in Polistes. L. decemlineata, however, is a form that has in recent 

 years invaded the area in which it is now found, and since becoming a mem- 

 ber of the fauna of a wider region, has responded to the conditions of the 

 new environment, and in adapting itself to new habitats has varied in the 

 same general directions as do the other animals with which it lives. It 

 is, therefore, to the environment and not to the animal itself that we must 

 look for the stimuli which are the cause of these modifications. The factor 

 assumed by all to be the most powerful in this general color variation is 

 moisture, and probably temperature is of equal importance. I have gathered 

 some interesting data on this subject concerning decemlineata. 



Live material was gathered from various parts of the United States and 

 Canada and was reared at Chicago under various conditions. The specimens 

 which will be considered particularly were from Massachusetts, Georgia, Ala- 

 bama, Kansas, northwestern Texas, Dakota, and Manitoba. Compared with 

 the material collected at Chicago the beetles from these various localities pre- 

 sented diverse appearances and conditions of coloration. At Chicago, during 

 the years 1902 to 1905, all were reared under uniform conditions, the result 

 in all cases being a complete and rapid change to the prevailing condition of 

 coloration at Chicago. In all but about 1 or 2 per cent of the specimens this 

 change was produced in one generation, and at most two were required ; nor 

 was there any tendency toward reversion in succeeding generations when 

 reared under the same conditions. 



At the same time beetles from Chicago were in experiment subjected to 

 the same conditions of temperature and moisture which obtain in different 

 sections of America, with the result that in one generation modification to the 

 conditions characteristic of the different regions was produced, and this per- 

 sisted as long as the conditions remained unchanged. In this way I have 

 experimentally modified the general color of these beetles in one direction or 

 another at will, producing by experiment the conditions found in nature in 



