DIMORPHISM IN BL1SSUS LEUCOPTERUS. 335 



be added that the developmental stages occur at a season of 

 great drought. Taken all together we have a picture par ex- 

 cellence of a xerophilous insect which is only another way of 

 designating a species capable of withstanding hard or unfavorable 

 conditions of living. Among the hard conditions which are 

 responsible for dwarfed wings as well as more or less dwarfed 

 bodies of chinch bugs, I should place first drought and poor food 

 supply. Latitude and climate do not influence them, but edaphic 

 conditions that may extend over large areas are the potent factors. 



The only recorded observation that seems to oppose this view 

 is that of Mr. E. P. Van Duzee. 1 He states that in portions of 

 Ontario and New York where the short-winged form usually pre- 

 dominates, in dry, hot summers they mostly acquire fully de- 

 veloped wings. It seems possible, however, that a dry hot 

 summer added to an ordinarily unfavorable habitat may have 

 destroyed the short-winged form to an extent, only those in the 

 most favored places being allowed to develop. 



That the short-winged form should extend at times beyond 

 the borders of the particular habitat which served to develop the 

 dimorphic tendency (as occurs for example in northern Ohio) 

 may be regarded only as the persistence for a time of a charac- 

 ter acquired by the race even when the insect is in different sur- 

 roundings. The mixed forms, however, always cling to old 

 food habits as far as possible, taking by preference to grass 

 meadows instead of attacking grain fields as do the long-winged 

 insects of the interior. 



1 Van Duzee, E. P., Canadian Entomologist, Vol. XVII., pp. 209-210, 1886. 



UNIVERSITY OF CHICAGO, 

 June, 1903. 



