F. M. CAMPBELL-THE HESSIAN FLY. 
183 
Description. 
The Hessian fly was first scientifically described by Say in 1817,*' 
who gave it the name of Cecidomyia destructor. The genus Cecido- 
myia belongs to the family Cecidomyidse, which is a large Dipterous 
group. The eggs of most of the species are laid in the stems, 
leaves, buds, etc., of plants, and the irritation thus caused produces 
galls. In the case of the Hessian fly the eggs are laid on the leaf, 
and do not give rise to galls. 
The egg f “is about -roth of an inch long, cylindrical, pointed at 
each end, the shell shining and transparent, the egg being of a pale 
red colour when the embryo is nearly developed.” 
The larva. —“The body is soft, smooth, shining, oval-cylindrical, 
beneath a little flattened, and consists of twelve segments besides 
the head, the latter soft, fleshy, and but slightly separated from 
the body, with very rudimentary mouth-parts (jaws, etc.). The 
rings or segments are moderately convex and tolerably distinct 
from each other; the sutures between the segments in the living- 
larva being indicated by faint transverse lines of a greenish- 
brown hue, according to Pitch, who also states that the mature 
larva, freshly taken from the roots of the wheat, measures about 
0 15 of an inch in length by 0*06 of an inch in width.” 
According to Lindeman,j the larva on leaving the egg has on 
the first segment two symmetrical colourless hooks (Haaken), which 
point outwards, and between them in the middle of the head is a semi¬ 
circular chitinous plate, while the last segment bears two bristles. 
Unfortunately I have not met with this first stage. The plate, 
hooks, and bristles are removed and shed with the skin, after which 
the larva has the appearance just described. 
In common with other larvae of the Cecidomyidse there is an 
“anchor-process” or “breastbone” upon the under surface of the 
second segment, the use of which may be to bruise the stem of the 
plant on which it is feeding. This process varies in different species 
as shown in the Fig. 2, but I am not aware that it occurs in the 
first larval stage of C. destructor. 
Fig. 2 . (1) Process of C. destructor. (2) Process of C. tritici. 
The puparium is somewhat larger than the larva, of a rude 
spindle-shaped form, and of a bright chestnut colour. When the 
* ‘ Journal of the Philadelphian Academy of Sciences,’ vol. i, p. 45. 
f The passages within marks of quotation in the descriptions of egg, larva, 
male, and female, are from Packard’s ‘ Third Report of the U. S. Entomological 
Commission,’ p. 207, and infra. 
f “Die Hessenfliege in Russland,” ‘ Bull. Soc. Imp-, de Moscou,’ 1887, p. 402. 
