28 THE HESSIAN FLY IN THE UNITED STATES. 
the fact that Say, in his original description of the Cecidomyia, pre- 
sented a description of one of the most abundant of the parasites which 
was already at that time recognized as an efficient agent in the destruc- 
tion of the pest. 
It is also shown by the estimate commonly made by the writers who 
have dealt with the subject that fully nine tenths of the Hessian flies 
are destroyed by parasites, a circumstance which accounts for the fact 
that the Hessian fly is seldom abundant or excessively destructive for 
more than one year at a time in any particular locality. In the speci- 
mens which were received from different points in Iowa in 1896 I was 
unable, because of the parasites, to secure a single perfect fly, and I am 
informed by Dr. Lugger, the State entomologist of Minnesota, that his 
experience for 1897 was the same as reported in his annual report for 
1896. 
This being the case, there is abundant reason for a careful consider- 
ation of the various species known to attack it, and the presentation 
of descriptions whereby they may be recognized should be one of the 
most serviceable parts of a discussion of the insect. 
An interesting comparison of the parasites of the insect in Europe 
and America ha? been made, whereby it has been brought out that 
there are similar parasites in the two regions, and, furthermore, that in 
some cases where the species do not appear to be identical the same 
genera are represented, and that a list of species presenting counter- 
parts may be arranged for the different regions where the insect occurs. 
A comparative list adapted from Marchai will be useful to show this 
point. 
PRIMARY PARASITES. 
For America the following species have been recorded : 
C'HALCTDID.E. 
Merisus destructor Say. 
Bcvotomus subapterus Riley. 
Pteromalus pallipes Forbes. 
Eupelmus allynii French. 
Entedon epigonus Walk. (Artificially introduced.) 
Pkoctotrypid.e. 
Polygnotns hiemalis Forbes. 
Platygaster herrickii Packard. 
As secondary parasites we may record Tetrastich us product it* Riley and Tetraslichvs 
carinatus Forbes. 
In Kussia, Lindemann records the following: 
Chalcidid^e. 
Merisus intermedins Lindra. 
Entedon epigonus Walk. (Seiniotellus nigripes Lindm.). 
Eupelmus karschii Lindni. 
Euryscapus saltator Lind. (Reared also from g;ills of Tsosoma hordei.) 
Tetrastiches rileyi Lindm. (Secondary parasite of Merisus.) 
PROCTOTRYPID.E . 
Polygnotus minutus Lindin. 
