LETTER OF TRANSMITTAL. 



United States Department of Agriculture, 



Division of Entomology, 

 WasMngton, I). C, June 2, 1897. 

 Sir : I have the houor to suomit for publication the seventh of the 

 technical series of bulletins of this Division. It has been iirepared by 

 Mr. D. W. Co(iuillett, of the oftice force, and consists of a revision of 

 the species of the parasitic flies belonging to the family Tachinid;c, 

 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 tlie most important enemies of many of our 

 most injurious insects, aud their characters are so obscure that workers 

 have had the greatest dilhculty 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 Tachinid;e have been reared at this ofiBce from 

 injurious insects which were being studied. It has been heretofore 

 impossible to record the results of these rearings, on account of the 

 confusion which existed in this family, and in its original conception 

 this study of tlie 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 siiould 

 be able to determine just what species of Tachina flies are assisting 

 him in liis work against injurious insects. 



Kespectfully, L. O. Howard, 



Entomologist. 

 Hon. James Wilson, 



Secretary of Agrirulfiuw 



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