GENERAL PRA CTICE. ENEMIES. 



263 



causing them to wither. Others bore into young branches, and by their galleries cut 

 off the supplies of sap, whole branches occasionally collapsing when laden with 

 fruit. Not a few infest the stems and limbs, tunnelling those through to the " heart," 

 often hollowing out the centre, or causing it to decay by admitting fungi ; but a majority 

 of boring beetles use only the alburnous parts, which, being full of sap, afford the best 

 nourishment for their brood. The channels become coated with a glutinous substance, 

 which forms a nidus for fungus, and food for the boring-beetle grubs. Caterpillars the 

 Iarva3 of a moth subsist upon the substance, and their castings are ejected through the 



Fig. 77. XYLEBORUS DISPAB, INFESTING YOUNG PLUM TREE. 



References: I , female, magnified; 2, female, enlarged, showing " shot-like" head, natural size at side; 3, male; 

 C, young plum-tree stem attacked by " borer," showing " pin-holes," all natural size ; D, old plum-tree butt, reduced ; 

 4, stubs of shortened limbs, usual breeding-places of Xyleborus dispar ; E, section of tree (C), showing tunnelling of 

 beetles. 



mouth of the burrow. The different borers will be treated under the respective fruits, but 

 an example will be elucidatory of the damage inflicted on fruit trees by borers generally. 

 The Common Borer (Xyleborus dispar) affects chiefly apples, pears, and plums, but 

 it attacks apricots, cherries, nectarines, and peaches against walls and under glass, also 

 vines and fig-trees. A nearly allied species (Scolytus pruni) occasionally proves hurt- 



