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 \vinglessness 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 

 believe 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 thenjselves 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 



