THE BLACK LOCUST TREE 213 



would be of very great industrial value if it were not for the ravages 

 of those insects. Other insects, the imported gypsy moth for example, 

 commit their terrible ravages upon the foliage of different kinds of 

 trees indiscriminately, but the insect pests of the black locust and the 

 mezquite are indigenous, and each species attacks only its own destinate 

 tree. The chief injury to each of these trees is done by the larva? which 

 burrow in its living wood. 



There are at least three species of insects which injure the black 

 locust tree. The small larvae of one of them tunnel the parenchyma of 

 the leaflets, and another species produces a gall-like enlargement of the 

 tips of tender twigs as a result of depositing and hatching its eggs 

 there. But worst of all, the large, vigorous and abundant larvae of 

 one of the longicorn beetles, Cyllene robinice, burrow throughout the 

 wood of the entire trunk and larger branches, rendering it unfit for 

 economic uses. All these insect species are known to be dependent for 

 their own existence upon the black locust tree because all three of them 

 deposit their eggs nowhere else than in its tender tissues ; all three of 

 them pass their entire larval stage, the only stage in which the insect 

 really increases in growth, in its living substance, and all three of them 

 derive their only incremental nourishment from that tree. If, there- 

 fore, the black locust tree were exterminated, all those insects would 

 necessarily perish; and if all those insects were first exterminated we 

 should have restored to us one of the most valuable of our forest trees. 

 But none of those contingencies is likely to occur. 



Great damage is sometimes done to the black locust tree by the two 

 insect species first mentioned, but usually their depredations are so 

 much less disastrous than are those of the tree borer that, for only the 

 present occasion the two former species may be regarded as negligible 

 and only the latter need be specially noticed. Because this article is 

 written with reference to a matter of public interest it is thought de- 

 sirable to give a brief popular account of the characteristics and habits 

 of that destructive insect. The beetle, which dies naturally soon after 

 the function of reproduction is completed, is nearly an inch long, some- 

 what slender, and has a pair of slender curved antennae as long as the 

 body ; and the larva is a vigorous grub nearly or quite as long as is the 

 beetle. The metamorphosis from the larva to the pupa stage and from 

 that of the pupa to the imago or beetle stage occurs as the insect is 

 about to emerge from its burrow in the tree; the final change and 

 emergence beginning to occur in late summer and continuing through 

 autumn. The beetles soon mate and hover about the Solidagoes and 

 other late flowers, feeding scantily and harmlessly upon the pollen. 

 The females immediately seek the black locust trees by flight, pierce the 

 bark and deposit their eggs in the soft cambium layer beneath it. The 

 resulting larvae burrow at once into the tree, traversing the wood of the 

 trunk and larger branches in all directions. The insect there completes 



