496 TILMUS CAMPESTRIS. 
after doing this, she dies, without making her way out again, as she may often 
be found dead at the end of the channel. About September, the larvse are 
hatched, which commence feeding upon the matter of the inner bark, at the 
edge of the channel ; and, in a very slight degree, on that of the soft wood oppo- 
site, advancing, as they feed, in a course at about right angles from the primary 
channel, on each side of it. The true food of the insect is the inner bark ; and 
the erosion of the soft wood is so slight, as to be, perhaps, nearly accidental. 
The course of each individual larva, on each side of the primary channel, is 
about parallel to that of the larva next to it ; and each forms a channel by its 
feeding that is enlarged as the larva increases in size. When each larva has, 
finished its course of feeding, it stops in its progress, turns to a pupa, and then 
to a beetle; and, in the latter state, gnaws a straight hole through the bark. 
These beetles begin to come out in about the end of May, or the beginning of 
June, of the year following that in which the eggs were deposited. The sexes 
afterwards pair, and the females, bearing eggs, pierce through the bark, as above 
detailed ; and so on, from generation to generation, and year to year. The 
result of the erosions of the female parent, and of the larvse, in the inner bark and 
soft wood, is that of cutting off the vital connection between these two parts ; 
and, when the erosions effected in a tree have become numerous, of occasioning 
its death, by preventing the ascent and descent of the sap. It has been asserted 
that the female scolytus never attacks a tree in a perfectly healthy state, for the 
purpose of depositing her eggs; and, also, that trees suffering under carcinoma 
are particularly liable to her ravages. It has also been remarked that these 
insects seldom destroy the trees they attack the first year ; and that they prefer 
a tree that they have already begun to devour, to one that is young and vigor- 
ous ; but they never attack a tree that is entirely dead. Yet it is true that both 
the males and females pierce young and healthy trees for the purpose of eating 
the inner bark, which constitutes their principal food; and that the numerous 
holes which they thus cause, partly from the loss of sap which exudes from them, 
and partly from the effect of the rain that lodges in them, in a few years bring 
the trees, in which they occur, into an incipient state of decay. These trees are 
indiscriminately selected by the female insects for the deposition of their eggs, just 
as in trees beginning to decay naturally; and thus healthy trees are effectually 
destroyed by the combined operations, first and last, of the scolyti of both sexes, 
though not in consequence of the sole deposition of the eggs of the female. The 
most effectual mode recommended to prevent the future depredations of these 
insects, is, first, to pare away, with a spoke-shave, or other tool, the rough exte- 
rior bark of the trees bearing the marks of their ravages ; and if there be no trace 
in the inner bark, either of small holes in old trees, or of those superficial furrows 
which the scolyti of both sexes make for food in young trees, they may be pro- 
nounced as being in a sound and healthy state. But if the inner bark exhibits 
small holes which communicate with channels as described above, the next 
thing to be done is to determine whether the female has already deposited her 
eggs within it, or whether it contains the young scolyti either in a larva or 
chrysalis state. In order to know this, it will be necessary to cut away, here and 
there, portions of the bark, quite into the wood ; and if the existence of either 
the eggs or of the insects be proved, the trees should be cut down, and the bark be 
taken off and burnt. Those trees pierced with exterior superficial holes or fur- 
rows, which have no larvae in them, are such as have been attacked for food 
only; and, if they be carefully brushed over with coal-tar, the fumes of which is 
highly offensive to the perfect scolyti, there is every probability that they will be 
secure from the future attacks of the females; and that the repetition of the same 
process in the spring, for one or two years, would enable them to resume then 
vigour, and become healthy trees.* 
* See Loudon's Arboretum Britannicum, iii.. p. 1387, et seq. 
