DISEASE IN CONTROL OF MOTHS. 101 
It is very subject to a “wilt” disease, and no colony has been obsérved 
which has reached such proportions as to threaten the defoliation of 
street trees in which the disease has not appeared. In one instance 
the disease was so prevalent as to destroy practically all of the cater- 
pillars, and, as in the case of the gipsy moth, the scattering caterpillars 
which hatched from the eggs deposited by the few survivors were 
seriously affected the following year, notwithstanding the presence of 
an abundance of food. Furthermore, caterpillars hatching from 
eggs collected in this and similar colonies removed to the country 
where the few native caterpillars to be found have always been remark- 
ably healthy, perished through the “wilt” exactly as though they had 
hatched in the city. 
Nevertheless, the white-marked tussock moth has been for long, is 
now, and probably will remain the worst defoliating insect enemy of 
such trees as the horse chestnut, maple, sycamore, etc.,in strictly urban 
communities in the Eastern States generally. It does not appear un- 
reasonable to suppose that the gipsy moth may similarly continue to be 
a pest in spite of the disease. As a matter of fact, every observation 
which has been made upon either the fungous disease of the brown- 
tail moth caterpillars, the wilt disease of the gipsy-moth caterpillars, 
or diseases of other defoliating caterpillars, such as that of the white- 
marked tussock moth, the tent caterpillar, and the “ pine tussock moth,” 
has tended to confirm the conclusion that such insect epidemics rarely 
play more than the one réle in the economy of nature. They do not 
prevent an insect from increasing to an extent which renders it a pest, 
but they may, and frequently do, render very efficient service in effect- 
ing a wholesale reduction in the abundance of such insects when other 
agencies fail. When the insect in question is ordinarily controlled 
by parasites, as appears to be the case with the white-marked 
tussock moth, the “pine tussock moth,” etc., it is probable that a 
long time will elapse before it will again encounter the combination of 
favorable circumstances which make possible abnormal increase. 
When, as with the white-marked tussock moth in cities, the tent cat- 
erpillar in southeastern New England, or the brown-tail moth and gipsy 
moth in America, adequate control by parasites is lacking, reduction 
in numbers through disease is not likely to result in more than tem- 
porary relief. The more complete the destruction wrought by the 
insect the longer the period which must necessarily elapse before it 
again reaches the state of destructive abundance and, looking at it 
from this standpoint, it is not unlikely that the gipsy moth is much 
more abundant at the present time than it would have been had it 
not been for the prevalence of disease. There are, each year, an 
abundance of localities where the destruction of a great majority of 
the caterpillars by disease has been the only thing which has saved the 
whole race from complete extinction in that locality through con- 
