1908.] PUBLIC DOCUMENT- -No. 73. 221 



their effectiveness far exceeds that of any other natural agency. As I 

 am informed, the brown-tail moth was almost exterminated by disease 

 in a number of badly infested localities in 1906, and during the trip 

 just completed I noticed that a very large percentage of the caterpillars 

 seen more than 50 per cent. were obviously sick and dying. An 

 epidemic may not come more than once in five or ten years, naturally; 

 but each year there is some period during which weather conditions are 

 favorable to the spread of disease, and if the disease germs are present 

 in sufficient numbers everywhere, or can be placed promptly, good re- 

 sults may be secured which would not have come about naturally. One 

 feature of this work which is in itself sufficient to authorize it is the 

 following up the spread of the insects with the disease germs. Brown- 

 tail moths may fly or be carried for long distances. A female may be 

 earned and found a colony twenty miles or more away from the nearest 

 infested point, and in a place where the disease of the brown-tail larva 

 does not exist. It may be years before it gets there under natural 

 conditions, and not until the insect has done great injury and has be- 

 come plentiful. If in a case like this the disease can be artificially 

 introduced as soon as the colony is discovered, a great advantage will 

 be gained and an epidemic will await only proper climatic conditions. 



My experience has been that as against some injurious species disease 

 checks are far more important than any other; and, while I do not 

 mean to say that this will be so in this instance, nevertheless, I do 

 think there is sufficient probability of it to warrant a thorough study 

 of the subject. To illustrate my point, I would refer to the elm-leaf 

 beetle, an introduced species very abundant and in the past very 

 troublesome in New Jersey and indeed in the New England States as 

 well, which has been of late almost completely controlled in New Jersey 

 by disease alone. 



About six years ago the disease developed at New Brunswick, and in 

 two favorable seasons so completely destroyed the pupae that for two 

 years thereafter no spraying was necessary. In the summer of 1905 

 the disease was not active, and in early 1906 the beetle occurred again 

 in sufficient numbers to disfigure some foliage; but the late summer of 

 1906 again favored the disease, and this year (1907) thera is scarcely 

 a larva to be found. Not a tree has been sprayed, and even if every 

 existing larva comes safely to maturity, there cannot be increase enough 

 to make the insect troublesome in 1908. 



It is not improbable, after the experience of 1906, that similar condi- 

 tions may be brought into existence against the brown-tail moth, and not 

 impossible that some influence may be obtained even against the gypsy 

 moth. At all events, I consider the effort well worth while. 



In the direction of field work I have no recommendations to make. 

 The methods now in use seem to cover the ground as well as it can be 

 covered, and the scheme of work devised seems to leave no point un- 

 guarded and no opportunity for effective applications missed. It goes 



