102 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
sumption of the entire supply of available food before growth was 
completed. Under such circumstances the disease has been of posi- 
tive benefit to the gipsy moth, rather than the reverse. 
STUDIES IN THE PARASITISM OF NATIVE INSECTS. 
Among a considerable number and variety of native insects studied 
at the laboratory which resemble the gipsy moth in habit, or which 
are more or less closely allied to it in their natural affinities, no two 
have been found in the economy of which parasitism has played an 
exactly similar role. There is this to be said, however, that only one 
amongst them, and this the tent caterpillar, appears to be ineffectually 
controlled by parasitism, except under unusual circumstances. 
Several very beautiful examples of control by parasites have been 
encountered in the course of these investigations, and, comparatively 
speaking, the exceptional instances in which parasites lose control 
through one reason or another are exceedingly rare. Such instances 
are usually, if not inevitably, accompanied by a conspicuous outbreak 
of the insect in question. 
The destructiveness of the white-marked tussock moth in cities is 
apparently due to the fact that it is peculiarly adapted to life under 
an urban environment. It is an arboreal insect, and one which is pre- 
vented through the winglessness of its females from dispersing over 
the country as the brown-tail moth, for example, would do under simi- 
lar circumstances. Its parasites, on the other hand, are not always 
fitted for a peculiarly arboreal existence. Many of them are partially 
terrestrial, and in addition they are strong upon the wing. 
Most of the introduced parasites of the gipsy moth and brown-tail 
moth which are known to have established themselves in America are 
known to be dispersing at a rapid rate. Several of them have been 
reared as parasites of the white-marked tussock moth from cater- 
pillars or pupae collected under urban surroundings, and since we 
have positive proof of their wandering habits there is every reason to 
behove that the native parasites of the tussock moth possess similar 
characteristics. That is to say, instead of staying within the limited 
area in which their host abounds, they are likely to scatter throughout 
the country immediately following the completion of their transforma- 
tions. They are neither fitted for continued existence in the city to 
the degree which is characteristic of their host, nor are they compelled, 
like it, to accept it when they find themselves city-born through 
chance ancestral wanderings. 
Every season's observations (and for four consecutive years the 
tussock moth has received more than a modicum of attention) has 
added arguments to support the contention that the white-marked 
tussock moth is controlled in the country through parasitism and not 
by birds or other predators. In any event it is controlled to such an 
