THE chinch-bug: a dimorphic form. 



155 



A Dimorphic Form of the Chinch-Bug. 



In addition to the ordinary form described and figured on page 150, 

 there is also to be met with in limited numbers in some localities, a 

 "dimorphic" form which has been characterized by Dr. Fitch as one 

 of nine varieties observed by him, under the name of var. cqiterus. It is 

 shown in figure 39. Prof. Riley has remarked of this and allied forms: 

 " There are, as is well known to entomologists, many 

 genera of the half-winged bugs, which in Europe 

 occur in two distinct or ' dimorphous ' forms, with 

 no intermediate grades between the two, viz., a short- 

 winged or sometimes a completely wingless type 

 and a long-winged type. Frequently the two occur 

 promiscuously together, and are found promiscu- 

 ously copulating, so that they cannot possibly be 

 distinct species. Sometimes the long-winged type 

 n' occurs in particular seasons, and especially in very 



^FiG.39-The Short-winged hot scasons. More rarely the short-winged type 

 Chinch-bug. occurs in a different locality from the long-winged 



type, and usually in that case in a more northerly locality. We have a 

 good illustration of this latter peculiarity in the case of the chinch-bug^ 

 for a dimorphous short-winged form occurs in Canada, and Dr. Fitch 

 describes it from specimens received from the States as a variety under 

 xhensimt oi apteriis [Second Report on tlie Insects of Missouri, 1870, p. 22, 

 f. 2; also, Seventh Report on the Insects of Missouri, 1875, p. 20, f. 4). 



Of a number of specimens sent to Mr. B. D. Walsh for identification, 

 from Canada, in 1866, which had been taken from under the bark of an 

 old log, all (eleven) were of this form, and were regarded by him as a 

 " geographical variety " {Practical Entomologist, ii, p. 21) 



Fig. JO — Wing-covers and wings of the chinch-bup;, and its short-winged form, showing their nervula- 

 tion : 1, wing-cover of normal form; 2, wing of the same; 3, wing-cover of short-winged form; J, wing 

 of the same. Enlarged to 18 diameters. 



The same form was remarkably abundant among the specimens sent 

 to me from Jefferson county, by Mr. Smith, and in those that were 



