LETTER OF TRANSMITTAL. 
I 
United States Department of Agriculture, 
Division of Entomology, 
Washington, I). C., June 2, 1897. 
Sir : I have the lioiior to suomit for publication the seventh of the 
technical series of bulletins of this Division. It has been prepared by 
Mr. D. W. Coquillett, of the office force, and consists of a revision of 
the species of the parasitic flies belonging to the family Tachinidse, 
which occur in the United States and Canada. The desirability of 
such a revision of these economically important flies has been apparent 
to all workers in economic as well' as systematic entomology for many 
years. They are among the most important enemies of many of our 
most injurious insects, and their characters are so obscure that workers 
have had the greatest difficulty in separating one species from another, 
and the result is that the literature of economic entomology in par- 
ticular contains many wrong determinations and absolute misstate- 
ments based upon such erroneous names. During the last eighteen 
years many species of Tachinidse have been reared at this oflice from 
injurious insects which were being studied. It has been heretofore 
impossible to record the results of these roarings, on account of the 
confusion which existed in this family, and in its original conception 
this study of the group was undertaken in order to enable us to record 
the results of this biologic work. The records are now given in the 
shape of two tables — one of parasites and hosts and the other of hosts 
and parasites — and a glance at these tables will be instantly convin- 
cing as to the important and beneficial role which these insects play. 
With the clear and systematic diagnoses of the genera and species 
which Mr. Coquillett has prepared, any economic entomologist should 
be able to determine just what species of Tachina flies are assisting 
him in his work against injurious insects. 
Kespectfully, L. O. Howard, 
Entomologist. 
Hon James Wilson, 
Secretary of Agriculture. 
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