December, '09] journal OF economic entomology 455 



when the cocoons were injured or used for experimental purposes. 

 Secondary parasitism was of fairly frequent occurrence, but probably 

 amounted to less than 5 per cent. 



The new light which was thrown upon that most remarkable 

 parasite, Thergnia fulvescens as a result of these investigations was 

 in itself almost sufficient to justify the undertaking. The species has 

 variously been recorded as primary and secondary in its relations 

 with different hosts, and the apparently incontrovertible evidence 

 w^hich has been adduced in support of both contentions has been, to 

 say the least, very perplexing. It is of particular interest, since it is 

 the most common parasite of the gypsy moth native to America, and 

 in nearly every instance it appears to be primary in its relations to 

 this host. Theronia atalantce, in Europe, and other closely allied 

 and possibly identical species in Japan are indistinguishable in their 

 early stages, and while they are relatively insignificant parasites of 

 the gypsy moth in their respective countries, they are about as com- 

 mon as T. fulvescens in that connection. 



So far as known the adults always hibernate, and in consequence 

 no living larv£e or pupae were found in any of the cocoons which were 

 opened. There were twenty cocoons which contained dead adults or 

 pupa3, or from which the adults had escaped leaving their character- 

 istic, rudimentary cocoons of dark brown silk as certain indication of 

 their former presence. Twelve contained dead, fully formed adults, 

 which had been unable to escape through the dense silken walls. Two 

 contained dead pupae, and from six only had the adults emerged suc- 

 cessfully. It is obvious that the host is not particularly well adapted 

 to the parasite when above 50 per cent are unable to effect their 

 escape after completing all of their transformations, but the phenom- 

 enon presented is not out of keeping with other, somewhat similar 

 observations which have been made, and which go to show that the 

 discretionary powers possessed by the parent females of parasites 

 generally are decidedly limited. 



In four out of the twenty instances, Theronia was apparently 

 primary, and there seems not to be the slightest doubt that it was so 

 in one instance in which the dissection of the host remains, for the 

 purpose of discovering traces of any other parasite which might have 

 been present, was so thorough as to result in finding all three larval 

 moult skins as well as the pupal exuvium. In three out of the four 

 it was internal in the promethea pupa, in the other it appeared to 

 have fed externally upon the caterpillar prior to pupation. 



In a single instance a dead Theronia, in the form of a fully colored 



