38 THE HESSIAN FLY IN THE UNITED STATES. 
least extremely probable, although there is yet too little evidence as 
to the issuing of parasites at times when the development of the host 
is retarded to warrant positive assertions. That the parasites do in 
some seasons issue with much less moisture than is necessary for the 
development of the host seems almost certain, and there is sufficient 
basis in this to delay the burning of stubble during dry summers until 
the parasites have had time to issue. 
There is another direction, however, in which the parasites may be 
employed, which is of interest more particularly to localities that have 
been recently invaded or where the parasites are not present. 
We have already seen that the regions where the Hessian fly is most 
widely distributed contain a goodly list of parasites, and such as would 
appear to occupy about the same position with reference to the host. 
We may easily conceive, however, of the introduction of the Hessian 
fly into a new territory, such as isolated wheat districts in Oregon or 
Washington, without the parasites accompanying them. 
In such cases there would be very evident advantage in the prompt 
introduction of parasitized pnparia and the setting free of the para- 
sites so they might establish themselves. Another direction for effort 
is the introduction of species not found in one country but which are 
common in another. Thus the introduction into this country of spe- 
cies common in Europe but not found here would add to the effective 
agents in control by whatever portion of the history of the species 
might be exposed to the attack of this species not open to the parasites 
already* present; and that the different parasites work at different 
times or in different ways is hardly to be doubted. 
Introduction of Entedon epigonus. 
One of the most promising efforts at introduction of the parasites 
occurring on the Hessian fly in the Old World was made in 1891, by Dr. 
0. V. Riley, who received pupae parasitized with Untedon epigonus 
(Semiotellus nigripes) of Russia from Mr. Fred Enock, of England. 
These were distributed to Trof. S. A. Forbes, in Illinois; Prof. A. J. 
Cook, in Michigan, and Prof. F. M. Webster, in Indiana. The report 
of results given by Professor Forbes is worthy of reproduction. I am 
not aware that any reports of the other introductions have been pub- 
lished. Professor Forbes's report, taken from Insect Life, Vol. IV (p. 
179), is as follows: 
According- to my promise I submit the following account of a recent experiment, 
begun at your instance and with material furnished by you, for the transfer of a 
European parasite of the Hessian fly to the United States. 
In accordance with arrangements made by telegraph, I received from you May 6 a 
package of Hessian fly puparia, said to have been parasitized by the European 
species Semiotellus nigripes, and with this package a letter from you asking me to take 
charge of and liberate the parasites in an inclosure of infested wheat, with an idea 
of introducing the species. A second package came two days later, accompanied by 
a letter of advice from your assistant, Mr. Howard. 
