184 Journal of Agricultural Research voi. in, No. 2 



HABITS OF OTHER MEMBERS OF THE GENUS AGRILUS 



The apple root borer, Agrilus vittaticollis , belongs to a group that is 

 represented by several well-known enemies of cultivated and forest 

 plants and trees. The raspberry gouty-gall beetle {Agrilus ruficollis 

 Fab.), the two-lined chestnut borer {A. bilineatus Weber), the bronzed 

 birch borer {A. anxius Gory), and the sinuate pear borer (^4. sinuatus 

 Oliv.) are destructive pests whose food plants are indicated by their 

 common names. The damage done by the different members of the 

 genus is usually due to the larvae working in or about the cambium, quite 

 often of small branches or twigs. The root-feeding habit is not known 

 to be common, although there are at least two or three other species in 

 the Eastern States whose habits have not been fully described, the 

 larvae of which live in the roots of forest trees and shrubs. 



NATURAL ENEMIES 



So far as could be observed, the natural enemies of the apple root 

 borer are confined to one species of hymenopterous parasite which 

 attacks and destroys the larva and pupa (PI. XXX, fig. 4). The adult 

 of this parasite was first reared in April, 191 2, and was described by Mr. 

 H. L. Viereck' of the Bureau of Entomology, as representing a new genus, 

 under the name Xylophruridea agrili (Pis. XXX, fig. 2, and XXXI, 

 fig. 6). Two generations of this parasite occur annually, one brood of 

 the adult appearing early in the spring and another late in the fall. 

 Oviposition was not observed, but it is presumed that the female uses 

 her strong external ovipositor to pierce the bark and wood, in order to 

 get at her host. The spring brood of adult parasites oviposits on the 

 root-borer pupae or on the larvae just before pupation, and the fall brood 

 oviposits on the larvse at about the time the pupal cell is being formed. 

 The parasitic larvae attack their host externally, those from the spring 

 eggs developing rapidly, and, when full grown, constructing cocoons 

 which occupy the host cell. This generation passes the greater part of 

 the warm season of the year as larvae in the cocoon. The larvae from the 

 fall brood of eggs develop less rapidly, some of them reaching full growth 

 and constructing cocoons in the fall and early winter and others not 

 entering the cocoon until very early in the spring. 



The adult parasites have difficulty in escaping from their transforming 

 quarters, and many of them die in their effort to gnaw their way out 

 through the bark. Parasitization is much more frequent with the borers 

 that are in very small trees. This is doubtless due to the fact that the 

 borers in such trees are forced to work nearer the bark, where they are 

 more constantly within reach of the ovipositor of the parasite. On the 

 whole, from 25 to 40 per cent of the root borers are destroyed by this 

 parasite. 



REMEDIAL AND PREVENTIVE MEASURES 



On account of the larva's concealed method of feeding, the diggmg-out 

 process, which is used effectively against several species of fruit-tree 

 borers, is not practicable or possible in this case. Control measures must 

 be directed toward the protection of the. trunk of the tree against the 



1 Viereck, H. L. Contributions to our knowledge of bees and ichneumon flies. includiuR the descriptions 

 of 21 new genera and 57 new species of ichneumon flics. Proc. U. S. Nat. Mus.. v. 42, p. 646. 1912. 



