INSECTS INJURIOUS TO AGRICULTURE 413 



to-day eclipsed by its congener, and it is only in these later years that 

 it has taken an importance of the first order, tending even in certain 

 districts to take the first rank over the gipsy moth. 



The caterpillars of these two species are extremely common in 

 Europe, their original home. They are injurious and from time to 

 time appear in great number. It is to be remarked that in a year 

 following their large multiplication, the caterpillars of these insects 

 become quite rare, and that they remain so for a long time. They 

 are, then, very far from being responsible for damage similar to that 

 which they cause every year on the other side of the Atlantic. With 

 us their presence is tolerable, and they do not cause notice since they 

 do not threaten the vitality of the trees. In Massachusetts, on the 

 contrary, they constitute a permanent plague which has commenced to 

 invade neighboring states. 



The difference in these conditions appears to be that in Europe the 

 insects are held in check by parasites, which are much more numerous 

 than in the United States. 



Some American parasites have adapted themselves to destroying the 

 gipsy moth. There are 5 hymenopterous and 6 dipterous parasites, 

 without counting several predaceous species which attack it. But this 

 is small in comparison with the 27 hymenopterous and 25 dipterous 

 parasites of the gipsy moth in Europe. While the parasites of the 

 brown-tail moth are less known, it is perfectly sure that in Europe 

 this insect is kept in check much more efficaciously by its natural 

 enemies than is the case in America. On account of these considera- 

 tions it was only natural to seek to introduce into Massachusetts the 

 original parasites of these two insects. For a long time it was not 

 judged wise to undertake the enterprise. A law obliging the sys- 

 tematic destruction of the gipsy moth and the use of insecticidal mix- 

 tures seemed to render it inadvisable. Moreover, there was confidence 

 in the fact that the native parasites would increase. Now the condi- 

 tions have changed. In 1900, the appropriations were stopped, at a 

 time when the insect was well in hand. In five years, however, it has 

 spread over a territory four times as great as that which it occupied in 

 1900 and has commenced to spread into the neighboring States of New 

 Hampshire and Ehode Island. 



On the other hand, in the 36 years that the insect had infested the 

 country about Boston, American parasites, if efficacious, would have 

 manifested it in an appreciable way. The same considerations ap- 

 plied to the brown-tail moth. 



Americans resolved, then, to attempt a last and great effort to master 

 the plague against which a long struggle had given insufficient results. 

 In the appropriation bill of the Federal Congress, in 1906, $2,500 were 

 appropriated to begin the importation of parasites of these two insects 



