GYPSY AND BROWN-TAIL MOTHS. 47 



in excess of those which have become temporarily or permanently 

 abundant enough to attract attention. 



It has never been expected that all of the parasites and 

 ■ predatory enemies of the gypsy and brown-tail moths which have 

 been introduced into Massachusetts would continue to exist here. 

 It has always been expected that certain of them would do so, 

 and the only cause for uneasiness as to the ultimate success of 

 the work has been the fear that not enough different kinds of 

 parasites could be secured for colonization, or, if colonized, that 

 not enough to form a natural and effective parasitic sequence 

 would be able to continue to exist. At the present time there is 

 no parasite of the gypsy moth, and only one or more of the 

 brown-tail, of which it can be said that the progress is unsatis- 

 factory. Just what the progress is, or whether there is any 

 actual progress, is not known in every case; but, as will be 

 shown, it may be very satisfactory, and at the same time in- 

 conspicuous. 



In the beginning it was expected that increase, if it followed 

 colonization, would be rapid ; but it was not thought that many 

 of the several species would be likely to fly very far from the 

 point of liberation until they had increased for several genera- 

 tions. Had these expectations been fulfilled, practical results 

 would have been apparent, locally, within three or four years. 



So far as it is possible now to state, the rate of multiplication 

 has generally been gratifyingly rapid; but it has been accom- 

 panied by a rate of dispersion so much greater than was ex- 

 pected as to materially change the aspect of the situation. It 

 is now evident that, if success follows the work of parasite in- 

 troduction, the parasites will become practically effective over 

 a considerable portion of the infested area, and possibly through- 

 out its whole extent, at about the same time. 



In order better to illustrate this point, a theoretical example 

 may be taken of an insect introduced into a new country, where 

 it increases at the rate of twenty-five-fold annually, and spreads 

 from the point of liberation at the rate of about 10 miles an- 

 nually. It is supposed that 1,000 individuals are liberated in 

 a territory where they can be spread in every direction, and 

 where their increase will be unhampered for a period of six 

 years. 



