DISEASE IN CONTROL OF MOTHS. 97 
DISEASE AS A FACTOR IN THE NATURAL CONTROL OF THE GIPSY 
MOTH AND THE BROWN-TAIL MOTH. 
In continuing this work consideration must be given to the proba- 
ble effect which the prevalence of disease would possibly have in the 
reduction of the gipsy moth and the brown-tail moth to the ranks 
of ordinary rather than of extraordinary pests. In America, as is 
generally well known, the brown-tail moth is annually destroyed to 
an extraordinary extent as the result of an epidemic and _ specific 
fungous disease, while the gipsy moth is frequently subjected to very 
material diminution of numbers through a much less well known 
affection popularly known as ‘‘the wilt,” apparently similar to the 
silkworm disease “flacherie.”’ 
In more respects than one the prevalence of these diseases has 
been inimical to the prosecution of the parasite work. In the be- 
ginning, when it was expected that the parasites would remain in 
the immediate vicinity of the localities where they were first given 
their freedom, great pains were taken to provide colony sites in 
situations where the caterpillars were not only common but where 
there was reason to believe that they would remain healthy for at 
least one or two years. This was an exceedingly difficult matter, 
and one which was the cause of more troubles, doubts, and fears 
during 1907 and 1908 than almost any other phase of the parasite 
work. 
With the final recognition of the great superiority of the large col- 
ony, which came about through a better knowledge of the powers of 
rapid dispersion possessed by the parasites, this seeming obstacle to 
success wholly disappeared, except in the case of such parasites as 
Anastatus, which actually did remain in the spot where they were 
placed, and which could not travel beyond a certain limited radius, 
no matter how great the necessity. 
At the present time the association with the parasite problem of 
the otherwise wholly separate question of disease as a factor in 
the control of the gipsy moth and the brown-tail moth is entirely 
confined to speculations as to the probable future of these pests, pro- 
vided their control is left to disease alone. If, as is conceivable, 
effective control is exerted through disease, further importation of 
parasites is rendered not only needless but wholly undesirable. If, 
on the contrary, such control is likely to be inefficient, from an eco- 
nomic standpoint, every effort should be exerted to make the parasite 
work a success. In other words, the decision as to the adoption of a 
policy for the future conduct of the activities of the laboratory 
depended very largely upon whether or not disease seemed likely to 
become effective in the case of the more important of the two pests. 
The fact that the present plans provide for the continuation of the 
95677 °—Bull. 91—11——7 
