26 THE HESSIAN FLY IN THE UNITED STATES. 
other evidence now available, would seem to favor the conclusion that 
wheat, rye, and barley are the normal and only food plants of the 
species. 
With regard to the identity of the specimens obtained from Elymus 
in California, Dr. Howard considered there was some doubt, and sub- 
mitted the material to Mr. Theo. Pergande for critical comparison, the 
result of which is presented in the following record: 
4855. Cecidomyid on Elymus americanus, not the Hessian fly. — Examined and com- 
pared larvae and imagos of the Cecidomyid from Koebele (4855) with those of Ceei- 
domyia destructor with the following results : 
The differences in the imagos of both are very small, though I find in the male of 
the Hessian fly that the inner pair of claspers are provided, near or close to the apex 
of the posterior edge, with four or five stout and blunt teeth, and that the large 
basal piece of the external claspers bears, near the lower external edge, a number 
of stout, conical, black tubercles. 
In 4855 the teeth of the inner claspers are wanting, while the whole posterior edge 
is strongly serrate. The tubercles of the external claspers are rather small, color- 
less, and difficult to be seen. 
The hairs of the genital organs and the tubercles from which they arise are also 
more prominent in the Hessian fly than in 4855. 
Of the larvse of the Hessian fly we have only such as were taken from {he pupa- 
riurn. Whether or not these materially differ from those before pupation I am 
unable to say, though the figure in Packard's Bulletin No. 4 indicates that there are 
two tubercles at the end of the body, whereas in 4855 this segment bears four large 
and acutely pointed processes, entirely unlike those of the Hessian fly. These dif- 
ferences in adult and larvae seem to be of enough importance to consider 4855 to be 
a different species.* 
Professor Lindemann, in 1887, believed he had sufficient ground to 
declare that the Hessian fly develops only in wheat, rye, or barley, 
never in other grasses, this conclusion being based on extended and 
careful observations in fields where a variety of grasses occurred. 
Later (in 188S) he seems to have felt it necessary to revise this opin- 
ion, and records having larvae sent to him that were found upon tim- 
othy (Phleum pratense) and Triticam repens, and also on account of the 
record by Mr. C. H. Whitehead of the occurrence of the puparium on 
Rolcus lanatus. 
Marchal, in reviewing this question, suggests that Lindemann has 
given unnecessary weight to these observations, and that even if com- 
parisons with larvae or adults showed close similarity, it would still be 
necessary to prove their identity from biologic criteria. Uis own 
results convinced him of the close limitation of C. destructor to wheat, 
rye, and barley, and he separates the species avenae finally on careful 
experimentation, that proved the inability of destructor to survive on 
oats or of avenae to live on wheat. 
There seems strong reason, in view of the evidence produced by Mar- 
chal and the differences indicated by Pergande, to adopt as final the 
position taken by Marchal. While precise experimental evidence in 
* Department record made by Theo. Pergande. 
