THE AMERICAN ENTOMOLOGIST. 



Generic Classification of the .loint-worm Fly, 

 It will be withia the knowledge of most 

 American entomologists, that the Joint-worm 

 Fly has always been referred by all writers, 

 from Harris and Fitch down to the times of 

 (Hover and Packard, to a genus of C7irtfct« Flies 

 [Etu-i/toma) known to be generally parasitic 

 in its habits. But — as has been shown above from 

 the examination of its larval history in Its earlier 

 and immature stage as well as in its mature 

 stage, and as was long ago asserted, both by Dr. 

 Fitch and by Dr. Harris, from the examination 

 of its larval history, solely in its mature stage 

 —the Joint-worm Fly is a true gall-maker and 

 therefore a true vegetable feeder. Here, then, 

 ;is it seems at tirst sight, we have at once a 

 glaring exception to the law of the Uxrrv op 

 Haiuts, which has been laid down above as 

 universally prevalent in the Animal Kingdom ; 

 for we have one species, the Joint-worm Fly, of 

 a particular genus {Eurytoma) , which is a 

 vegetable feeder, and a great number of other 

 species of the very same genus which arc para- 

 sitic upon other insects. Indeed it was prin- 

 cipally from his unwillingness to believe in the 

 violation of the above great Law, that the 

 Senior Editor of this journal formerly dis- 

 credited the theory, that the so-called Joint- 

 worm Fly was a gall-maker and a vegetable 

 feeder, and strongly inclined to suspect that 

 these galls were in reality made by some 

 unknown species, probably a Gall-gnat, upon 

 which the so-called Joint-worm Fly was 

 parasitic. 



In reality, however, there is here no real vio- 

 lation of the law of the Unitv of Haiuts; for 

 —as we shall now proceed to show— the Joint- 

 worm Fly does not belong by any manner of 

 means to the parasitic genus (Eurylomi), to 

 which all preceding authors have been in the 

 habit of referring it; but to an entirely distinct 

 genus {Isosoma), none of the species belonging 

 to which have ever, so far as we arc aware, been 

 shown to be parasitic in their habits. 



Below will be found magnilied iigures (Fig. 

 115, a?, 6 J) of both sexes of the true genus 

 -Euri/toma, all the species of which are closely 

 alike iu shape and structure, though they dift'er 

 very greatly in size, and occasionally iu colora- 

 tion, and at least five species of which are 

 personally known to us to be one or more of 

 them parasitic on the insects of twenty-four 

 different kirtfls of galls, growing respectively 

 on Oak, Blackberry, Rose, ^Villow. Hickory, 

 (loklearod, and Ironweed. Of these twenty- 

 four galls, ten are made by Gall-flies (C^Hi>«) 

 upon Oak, one by a Gall-fly upon Blackberrv. 



C.ilor— Black. 



one by a Gall-fly upon Rose, three by Gall-gnats 

 (Cecidomi/ia) upon Willow, five by Saw-flies 

 (Tenihredo) upon Willow, one by a Gall-gnat 

 upon Goldenrod and Ironweed indiscriminately, 

 one by a Plant-louse {Aphis) upon Hickory, 

 one by a Bark-louse (Coccus) upon Hickory, 

 and one by a small Moth (Tinea) upon Golden- 

 rod; and in addition, a few specimens of the 

 very same parasitic genus have been bred by 

 us from certain large black woody funguses, 

 growing respectively upon Oak and Hickory and 

 inhabited by other insects. The whole number 

 of specimens of this parasitic genus (Eury- 

 <omrt)> bred from the above galls and funguses 

 and now contained in the colleotion of the 

 Senior Editor, is 279. 



There is another closely allied parasitic genus 



(Decatoma), the sexes of which are represented 



in the annexed drawings (Fig. IIG, a '^ , b ^), 



and of which four different species, all closely 



[v\e 116 ] 



alike except in size and color, arc personally 

 known to us to be parasitic on the insects of 

 eleven different galls. Of these eleven galls, 

 no less than ten are made by Gall-flies on Oak, 

 and but a single one is made by a Gall-gnat on 

 AVillow. The whole number of specimens of 



