gall aphids of the elm. 213 



Discussion. 



The introduction of the gall form of this species is of peculiar 

 interest. Perhaps no aphid gall is more generally familiar than 

 the cockscomb gall of the elm. This gall has always been 

 associated in our literature only with ulmicola. It was, there- 

 fore, with considerable surprise that I found that the species 

 emerging from the cockscomb gall in Maine in 1909 was not 

 a Colopha but a true Tetraneura by virtue of its venation — M 

 being constantly unbranched. After examining 2,000 wings 

 (1,997 of which had M simple) to be sure of a safe basis, I 

 found I was confronted with the dilemma, either two species 

 of aphid occur in similar cockscomb galls on the elm or Colopha 

 ulmicola is dimorphic. As there are no well established spe- 

 cific characters sufficient to separate ulmicola and colophoidea 

 except the venation, there is as yet no positive proof as to which 

 is the case. But as both ulmicola and colophoidea show con- 

 stant venation in certain large collections, the former with M 

 branched and the latter with M simple, it is certainly desirable 

 to treat them as distinct for the present. Especially is this true 

 because Tetraneura graminis is shown* to be the grass form of 

 Tetraneura colophoidea and a sweeping amalgamation of four 

 species is not desirable without very definite biological proof. 



Tetraneura colophoidea has a manuscript history of no slight 

 interest as is indicated in the following extracts from Mr. 

 Monell's recent letters : 



"Tetraneura coloplioidea inhabits a cockscomb gall agreeing exactly 

 A'ith my recollection of Colopha iihiiicola. * * * About 1886 at 

 Washington, Pergande first discovered the Tetraneura and a few years 

 ago I discovered it here (at St. Louis, July 7, 1906). * * * 7^_ 

 :oloplioidca is a mss. name that got into print, f I do not know just 

 how. Pergande says I used it years ago but I have no recollection of 

 it. * * * A good many years ago I had some correspondence with 

 Pergande regarding the Tetraneura that makes galls similar to Colopha 

 ulmicola (= comprcssa Koch ? ? ?) and suppose this term colopJioidea 

 may have been used in correspondence then. Certainly nothing was 

 ever published by me. * * * So I have no objection if you describe it 

 as coloplioidea Monell mss. I also sec no objection to ignoring the 

 colophoidea and giving the i^pecies any name you desire. * * * jt 

 has been my opinion that Colopha eragrostidis is one of the stages of 

 C. ulmicola (or C. comprcssa Koch as Lichtenstein would call it") and 



*Sce page 212. 



tEnt. News, October, 1908, p. 365. 



