412 POPULAR SCIENCE MONTHLY 



Moth and Brown-tail Moth. — If parasitic insects (hymenopteroiis and 

 dipterous) are at the present time behind the predatory ones, it does 

 not make their efficacy any the less that the work that they accomplish 

 is not so immediate and is less easily brought about. 



Everybody knows how some ladybirds will free a tree from plant 

 lice or scale insects, while there is some trouble in observing how a 

 parasitic insect lays its eggs in the interior of a caterpillar. Moreover, 

 while the victims of a predaceous insect are killed immediately, the 

 insects pierced by the hymenopteroiis insect continue in most cases to 

 feed and grow, and it is only in the following generation that the good 

 work can be seen. Finally, to appreciate the just value of parasites, it 

 should be remarked that several species, in certain cases more than 

 thirty, live at the expense of a single plant-feeding species and join 

 forces to hold it in check. To reestablish the equilibrium in a country 

 into which a plant-feeding species has been imported, not only one of 

 these parasitic species, but as many as possible, should be sought for and 

 should be naturalized. 



In a few years we will be much more certain concerning the ad- 

 vantages to be drawn from the utilization of these beneficial species. 



No experiment in any case can be better conceived to illustrate this 

 question than the gigantic undertaking now carried on by the govern- 

 ment of the United States which has for its object the importa- 

 tion of the European parasites of Bombycids, up to the present un- 

 masterable scourges, which ravage without interruption the trees of 

 Massachusetts. 



These two insects, Liparis dispar and L. chrysorrhoia, are European 

 insects which have been accidentally introduced into Massachusetts, the 

 first in 1868, and the second in 1890. It is difficult to imagine the 

 intensity of the ravages of these two insects. The damage occasioned 

 by the first of them, which is popularly known in America under the 

 name of the gipsy moth, is to-day celebrated in certain localities, notably 

 in the suburbs of Medford, which was the first point of infestation. 

 The caterpillars became so abundant that all the trees in the parks, 

 woods and public streets were entirely defoliated, and presented, in mid- 

 summer, a winter aspect. These trees, deprived of their vitality, were 

 killed by thousands. In certain suburban quarters, one could see the 

 walls of the houses carpeted with caterpillars, and the roads them- 

 selves so invaded that it was impossible to walk without crushing them 

 by hundreds. A special committee was started to organize the fight, 

 and from 1889 to 1895, $525,000 was spent in work against the destruc- 

 tion of this species. For the year 1897 alone, $150,000 was voted by 

 the legislature. 



As to chrysorrhaia, known to Americans under the name of the 

 brown-tail moth, although it has shown itself extremely injurious, it is 



