294 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 1 



accurately the cause of these "light" cocoons and, in this day of dis- 

 cussion of parasites, to determine if possible the relative effectiveness 

 of parasites and other causes in checking the development and increase 

 of certain species. 



I therefore asked Mr. H. H. Brehme of Newark and Mr. J. Doll of 

 Brooklyn to gather and send me a lot of these ' ' light ' ' cocoons so that 

 I might at least approximately determine the cause of death of the 

 larvffi that spun them. 



Mr. Brehme brought in a lot of 302 cocoons, of which nine turned 

 out to be sound ; eighteen were old specimens from which the adults 

 had emerged ; forty-two were parasitized and 233 had died in the lar- 

 val stage, of disease. Of the forty-two that were parasitized only a 

 few were infested by Opliion, while the remainder appeared to be 

 infested by some species that makes its cocoons in a mass. 



The dead larvae Avere in most cases mere shells and were filled 

 with a powdery mass. There was some difference, however, and I 

 judged that at least two kinds of disease organisms had been respon- 

 sible for death. The interesting feature in the matter is that less 

 than 15 per cent of the deaths had been caused by parasites and over 

 65 per cent by disease. 



It was quite possible to separate out two series of cocoons contain- 

 ing diseased larv«. In 59 of the 233, the cocoon was incomplete or 

 imperfect ; i. e., the inner cocoon was very thin or practically wanting, 

 or the outer cocoon was reduced to a mere covering of loose silk. In 

 other words, the vitality of the larva had not been sufficient to enable 

 the caterpillar to do its spinning work propei-ly. although death did 

 not ensue until after it was completed. 



Two lots of cocoons were sent in by INIr. Doll, one consisting of 

 430 and the other of 330 specimens. Both lots were collected between 

 Maspeth and Laurel Hill, Long Island, one lot, the 430, during the 

 fall of 1907, the second lot, 330, during March, 1908. In the first 

 lot the object had been to collect good cocoons and the obviously light 

 ones were rejected in the field ; in the second lot all light cocoons were 

 taken. The first lot was part of a much larger number — over 2,000 — 

 collected as prol)ably sound, and the material sent me was that which 

 was sorted out as probably- bad when they were again tested at home. 

 In neither case does the material afford any clue as to the actual per- 

 centage of infestation ; it simply indicates the percentage of the dif- 

 ferent causes of death. 



In the lot collected in 1907, sixteen cocoons were found to contain 

 sound pup£fi. and from fifteen adults had issued, leaving 399 that 

 had dead lai'va- oi- pnpa\ Thirty-four eatcrpillais liad icachcd the 



