38 IMPORTED PARASITES. 



has been reared in the laboratory from a considerable variety 

 of native caterpillars, including such common species as the 

 fall web worm and the Datana caterpillars, which are frequently 

 so abundant upon various trees and shrubs in the fall. 



Tachina larvarum and Tricholyga grandis. 



These two species of Tachinid parasites are exceedingly sim- 

 ilar in many respects and are so difficult to separate in their vari- 

 ous stages as to have been confused under the name of Tachina 

 larvarum during the first three years of the work. On this ac- 

 count, considerable confusion exists concerning the early history 

 of both in America. 



Tachina (Fig. 13), like Oompsilura, is a parasite of both the 

 brown-tail and the gypsy caterpillars, while Tricholyga is prin- 

 cipally confined to the last-mentioned in its host relations. Both 

 deposit large flattened eggs upon the body of the larger cater- 

 pillars, and the minute maggots hatching from these eggs bur- 

 row into the body of their host, where they grow rapidly. The 

 larva of Tachina usually leaves its host and completes its trans- 

 formations upon or just beneath the surface of the earth. That 

 of Tricholyga may do this, or it may remain attached to the host 

 and never drop to the ground at all. Both species usually kill 

 the host caterpillars before pupation, but not always. 



Several thousands of one or both specjes were liberated in vari- 

 ous localities in 1906 and 1907. Both were colonized in small 

 numbers in 1908, and in very large numbers in 1909. It was 

 not known that either species had established itself until late in 

 the summer of 1909, when Tricholyga was recovered from the 

 field as a parasite of the gypsy moth from the near vicinity of a 

 very small and unsatisfactory colony of the year before. There 

 seems to be every reason to believe that it has succeeded thor- 

 oughly in establishing itself, and that it is a mere matter of 

 time until it shall become so common as to be of active assist- 

 ance in the control of the gypsy moth. 



The Tachina, strangely enough, is scarcely distinguishable as 

 an adult, or in any other way than by its behavior as a gypsy 

 moth parasite, from a native American species which has upon 

 rare occasions been reared as a parasite of the gypsy moth. The 

 native species is probably the one which deposits its conspicuous 



