INTRODUCTION OF PARASITES AND NATURAL ENEMIES. 71 



semiliquid and putrid. When tlio cholera is prevalent, the trunks 

 of trees below tanglefoot or burlap bands, where the caterpillars con- 

 gregate, are sometimes completely covered with dead or dying larvae. 

 Isolated cases of caterpillars that had died from this disease were 

 observed previous to the year 1900, but at that time the insects 

 killed by it were relatively few. This trouble, which is supposed 

 to be a disease known as '^flacherie," was recognized as fatal to 

 the silkworm many years ago. 



Both of the diseases above mentioned are being carefully inves- 

 tigated by specialists of Harvard University in cooperation with the 

 office of the Massachusetts state forester. 



THE INTRODUCTION OF PARASITES AND NATURAL ENEMIES OF 

 THE GIPSY AND BROWN-TAIL MOTHS. 



Although the work of introducing parasites and natural enemies 

 of the gipsy and brown-tail moths is entirely separate from the field 

 work which is being carried on for the control of the insects mentioned, 

 a brief statement is made concerning it, as it has an enormous prac- 

 tical bearing on the problem at hand. 



It is evident that if the natural enemies of these insects can be 

 introduced into the infested district in large numbers and be able 

 to survive our climatic conditions and reproduce in the same ratio 

 that they do in their native homes, it should be possible by this means 

 to largely curtail the destruction that is now prevalent in New Eng- 

 land. An effort in this direction has been carried on for the past 

 four years by the Bureau of Entomology in cooperation with the State 

 of Massachusetts, and Dr. L. O. Howard, Chief of the Bureau, has 

 had the matter in charge. 



A considerable number of parasites and natural enemies have been 

 received and liberated, and conditions at the present time seem to 

 warrant the hope that eventually much good will result from this 

 work. It should be borne in mind, however, by some of those who 

 are overenthusiastic as to the possibilities of controlling the insect 

 pests by means of their parasites or natural enemies, that few cases 

 are on record where work of this sort has been entirely effectual. 

 Furthermore, it should be pointed out that the gipsy moth was lib- 

 erated in this country nearly twenty years before it became such 

 a serious pest as to cause widespread notice and the adoption of 

 active measures for its suppression. This being the case, it will 

 undoubtedly be several years before it will be possible to notice 

 definite results from the reproduction of parasites in the field, and 

 until it has been demonstrated that natural enemies can control the 

 situation it is folly to curtail the amount of hand work which is being 

 employed for the destruction of these pests. 



