1909.] PUBLIC DOCUMENT -No. 73. 61 



make their utility in this country very problematical, but there 

 are a few among them which are of greater promise than any 

 others among the numerous natural enemies which have been 

 studied at the laboratory. 



The work done by Mr. Townsend has demonstrated the ex- 

 istence of a very great diversity in the life of these insects 

 during their earliest stages ; and the results of this work have 

 served not only to indicate the best methods by which the para- 

 sites themselves may be imported and handled after receipt, 

 but have tended strongly to indicate the enormous possibilities 

 for good possessed by certain among them. 



Probably the most promising at the present time is one 

 technically known as Blepharipa scutellaia, a large and strong 

 insect, not unlike the common fly in general appearance. The 

 females of this species deposit several thousands of exceedingly 

 minute eggs upon the foliage of trees near where the caterpillars 

 of the preferred host are feeding. These eggs ai"e eaten by the 

 caterpillars, hatch in the alimentary canal, and the young mag- 

 gots resulting, establish themselves within the tissues of their 

 host. For a time they feed without causing it apparent in- 

 convenience, but when nearly full fed, which may not be until 

 after the caterpillar has changed to a pupa, they cause its 

 death, feed for a time upon the dead body, and then, dropping 

 to the earth, burrow into it and complete their transformations. 



The perfect flies do not emerge imtil the following spring, 

 and there appears to be but a single annual generation, in which 

 respect the parasite resembles the gypsy moth itself. An insect 

 depositing its eggs upon a leaf, in the chance that this leaf will 

 be eaten by an insect which is capable of nourishing its young, 

 is exposed to a very gi-eat liability of loss during its egg stage. 

 This is partially compensated for by the large number of eggs 

 deposited, amounting, as has been stated in this instance, to 

 several thousand, possibly 5,000 or more. It possesses at the 

 same time a potential fecundity far in excess of that of the gypsy 

 moth itself. When practical defoliation occurs, as it frequently 

 does where the caterpillars are numerous, the increase of the 

 parasites ought to be very rapid, and, other conditions being 

 equal, far to outstrip that of the gypsy moth itself. 



In spite of the relatively considerable abundance of this in- 



