The Progress of the Hessian Fly. 
445 
Nature has provided the most effectual means of preventing 
the Hessian Flv in the shape of other insects parasitic upon 
and destructive to it at certain stages of its life. 
Many other insects injurious to agricultural crops are pro- 
videntially held in check by other insects which prey upon 
them, either as parasites like the Platijfjaster tipulae and Macro- 
'■^■nes penetrans, — tiny flies which inlest the dangerous Wheat 
-Midge, Cecidonn/ia trifici — and Pachi/merus calcitrator, so 
I'Ctive in lessening the numbers of the Corn Saw-Flv, Cephns 
mans, that has been verv prevalent in wheat-plants and barley- 
aits in this last summer. The dreaded Hop Aphis, and 
.er Aphides peculiar to crops, are devoured wholesale by the 
aillar " Ladvbird," Coccinella punctata, and its larva, termed 
.igger" in the hop country because of its colour and ugli- 
ss. Butterflies, and moths of all kinds, are particularlv liable 
to the attacks of their peculiar parasites. And the parasite 
(il the Hessian Fly, a tinv fly itself, has accompanied it, 
and has emerged from its pupa-case, after having spoiled the 
1. j:vptian. 
Ox this there is no doubt, though as to the species of this 
pirasite there is some doubt. It has not yet been clearly 
liefined whether it belongs to the special parasites of the Hessian 
Fly in the United States, or to those in Russia. It has been 
declared by some to be Semiotellus destructor ; but Professor 
Riley, to whom a specimen was submitted, believed it to be 
I'isiis infermcdius, Lindeman, rather than Semiotellus destructor, 
V. Another specimen, said to be Sei7iiotelliis destructor, was 
I 'nsidered to be a new species of Thomson's Isc>ci/rtus. Professor 
Piiley was of opinion that none of the specimens were from 
America. 
This is a very strong argument in favour of the idea that the 
Hessian Fly was introduced into England from Russia, rather 
in Irom America. But it requires a specialist to determine the 
\ ^ct species of these tinv parasites ; the examination of Professor 
liiley was necessarily cursory, and made with a pocket lens, so 
\t it may turn out that the parasites are American after all.* 
, ecimens, however, have been sent to Mr. Howard, of the 
L nited States Department of Agriculture, whose determination 
is awaited with great interest. Dr. Lindeman concludes an 
interesting paper upon the parasites of the Hessian Flv, by 
remarking that the general result of his work will show that 
the larvae of the Cecidonnjia destructor are liable to be attacked 
by the same genus of Pteromali in America and in Russia, 
" Since this was \5Titteii, Professor Eiley, in conrersation ■with the writer, haa 
;.x^ res>icJ hid strong belief that the pnrasitt^ are Ba;ssian. 
