POPLAR BORERS. 441 
its teeth on the segments and the spinose process on the front, by which it forces 
itself, by stretching and contracting the abdomen, through the wood scrapings which 
close the cell, until it comes to the end. We have noticed a fine thread of silk pro- 
ceeding from the spinneret of the larva, although in the cocoon we have found no 
silk whatever. The cocoon or pupa-cell seems to have been formed by wedging first 
coarser and then finer strips of the wood together, and seems to be merely a more 
carefully and smoothly finished enlargement of the original burrow. 
The pupa. — A specimen of the pupa which I have examined is about 30 mm in length, 
narrow, brownish black, shining rugose. The clypeus presents a strong, broad, 
spinous process, supported at base by lateral projections. On the under side it descends 
into a wide sulcat ion terminating in a broad projection. The capital appendages 
are visible, aud here and there arise isolated hairs as in the previous stage. The 
abdominal segments are provided with teeth over the dorsum, decreasing in size to- 
the stigmatal line. The anal segment is provided with two unequal-sized terminal 
teeth on each side of the vent. (Plate I, Figs. 8 and 9.) 
The chrysalides vary much in size, and some of them are infested with an ichneu- 
mon fly, which preys on the caterpillar. A pupa was observed endeavoring to make 
its way to the surface of the bark, but seemingly unable to extricate itself, when 
assistance was rendered by enlarging the orifice. It was laid in a paper box for 
hatching. A few days afterwards many minute ichneumons were observed resting 
upon the wall near the box. On examination they were found to be escaping through 
minute holes in the pupa, which would barely admit a No. 3, entomological pin. Fif- 
teen of these perforations were counted in this pupa. I presume that the larva of the 
Cossus is pursued in its burrows by the parent parasite. If so it is curious that 
the Cossus pupa is not killed by the parasites until it has worked itself up to the 
mouth of the tunnel, thus allowing the ichneumon flies to escape outside. 
When ready to emerge, the pupa, by means of stout cusps on its abdominal 
segments, works itself to the end of the opening, and with its pointed head-case the 
thin portion of the bark which has been left by the caterpillar's instinct is severed 
and removed. It pushes itself through the opening as far as the base of the abdo- 
men, by a sort of rotary motion, which acts in its mode of cutting like a carpenter's 
center-bit. The thoracic end of the pupa, after exposure a short time to the air, 
becomes dry and splits, and the moth escapes, climbing up the bark of the tree, 
shaking out its wings until developed. After the moth has escaped the empty pupa- 
case may still be seen protruding from the entrance of the tunnel. It is not true 
that Cossus centerensis prefers dead wood to burrow in. It is a fact that it is most 
frequently found in partially decayed trees, for after the larva obtains a lodgment, 
by its perforations in diverse directions through the heart and alburnum, admitting 
air and water, it causes irreparable decay. There are three species of poplar found 
in the vicinity of Centre,* viz, grandidentata, dilatola, and tremuloides, but as yet 
C. centerensis has only been found in Populus tremuloides. 
It is stated by Harris that C. ligniperda deposits her eggs on the bark near the 
root of the tree, which I believe is the habit of most of the borers. It would seem 
from the following that it is not the invariable mode : In splitting open a tree trunk 
on June 12 a Cossus was observed to fly from the cleft, which, on being captured, 
proved to be a female. It was supposed she had taken possession of a tunnel for the 
purpose of deposting her eggs. The loose de'bris from the excavations was gathered 
together, an examination of which revealed Cossus eggs. (Plate I, Figs. 1 and 2.) 
The female was confined in a box ; the next morning she had deposited fifty-two 
eggs ; some of them were attached to the sides and others on the bottom of the box. 
Some of the eggs were deposited singly and some in confused heaps, and were 
attached to each other and to the box with a viscid substance. 
Another female was captured June 20, and in forty-eight hours after being pinned 
she had deposited sixty eggs, which varied somewhat in color from the former. 
*Now called Karner. 
