ATTACKING THE TRUNK. 21 



with a glutinous substance, usually under the loose scales or 

 within the cracks and crevices of the bark; sometimes singly, 

 at other times several in a group. The young larva soon 

 hatches, and, having eaten its way through the outer bark, 

 feeds on the sap-wood within, where, boring broad and flattish 

 channels, a single specimen will sometimes girdle a small tree. 

 As the larva approaches maturity, it usually .bores into the 

 more solid wood, working upwaFd, and, when about to change 

 to a chrysalis, cuts a passage back again to the outside, eating 

 nearly but not quite through the bark. Within its retreat it 

 changes to a chrysalis (Fig. 4, 6), which is at first white, but 

 gradually approaches in color to that of the future beetle, 

 and in about three weeks the perfect insect emerges, and, 

 having eaten through the thin covering of bark, escapes and 

 roams at large to continue the work of destruction. 



The mature larva (Fig. 4, a) is a pale-yellow footless 

 grub, with its anterior end enormously enlarged, round, and 

 flattened. At c in the figure the under side of the anterior 

 swollen portion of the body is shown. Whether this larv^a 

 requires one or two seasons to reach maturity has not yet 

 been determined with certainty, but the opinion prevails that 

 its transformations are completed in a single year. 



Remedies. — One might reasonably suppose that this larva 

 in its snug retreat would be safe from the attack of outside 

 foes ; but it is hunted and devoured by woodpeckers, and also 

 destroyed by insect parasites. A very small fly, a species of 

 Chalcid, destroys many of the larvse; besides which two larger 

 parasites have been bred from them by Prof. C. V. Riley, 

 one of which, Bracon charus Riley, is represented magnified 

 in Fig. 5, the hair-lines at the side showing its natural size. 

 The other species, Oryptus graUator Say, is somewhat larger : 

 they both belong to that very useful group of four-WMUged 

 flies known as Ichneumons. 



Although healthy, well-established trees are not exempt 

 from the attacks of this enemy, it is found that sickly trees 

 or trees newly transplanted are more liable to suffer, es- 



