8 BULLETIN 170, U. S. DEPARTMENT OF AGRICULTURE. 



damage to pine forests and more often to pine nurseries. They are 

 the more capable of injury because there are two generations an- 

 nually and they thus have two chances each year to accomplish their 

 damaging work. Xone of these native species can, however, even 

 with this advantage, be compared in destructiveness to the European 

 species just introduced. This is partly due to the larger size of the 

 introduced species and to the greater voracity of the larva, but is 

 mainly due to the difference in the attack, which causes a different 

 reaction of the tree. 



The larva of the native species of the genus confines itself to a 

 single twig and finds its food within this or within a single bud. or at 

 most a few buds. This bud or twig dies, but the tree responds with 

 the natural growth of the next set of buds and very often recovers 

 from the injury without permanent disfigurement. The resulting 

 injury to the trees is serious only when these native species are present 

 in unusually large numbers- Moreover, each of the native American 

 species is more or less confined to a single or a few species of Pinus, 

 but the European pine-moth thrives indiscriminately on all species 

 of Pinus and has consequently a greater chance to become excessively 

 abundant. While several of the native species are continually of 

 some economic importance and periodically become a serious menace 

 even to larger trees, it is mainly when they occur in large numbers in 

 nurseries that they become really troublesome. Large trees become 

 checked in their growth by the loss of terminal twigs, but are not 

 necessarily seriously deformed in their future growth, although an 

 undesirable forking of the tree top is a quite common result. 



On the other hand, the larva of the European pine-shoot moth is 

 very voracious and not only destroys a number of buds and young 

 sprouting shoots by eating their interior, but it invariably damages 

 the remaining shoots in the cluster by nibbling their bases on the 

 inner side. The subsequent growth of these injured shoots, in the 

 effort to supplant the destroyed leader, causes greater permanent 

 injury to the value of the tree than if they were entirely removed. 



NATURAL ENEMIES. 



Evetria huolianu in Europe is, to some extent, kept in check by a 

 large number of parasitic enemies. As early as 1838 Hartig 1 

 recorded 11 ichneumonid wasps and 1 tachinid fly 2 which he had 

 reared from pupa? of the pine-shoot moth. It has since been ascer- 

 tained that there are several other parasites; among the ichneumonids 

 Eatzeburg considered the following three, which he himself had 

 reared, as the more important : Pristomerus vulnerator Panz., Cre- 

 mastus interruptor Grav., and OrgiTus obscurator Hald. 



1 See " Literature," p. 10. '-Actio pinipennis Fallen. 



