Life History of Tetropium gabrielt. 199 
Normally, the imago takes about 10 days to mature in the pupa- 
cell after transforming. It then bites away the stopping of wood- 
fibre before it, scrapes it behind it with its fore and intermediate tarsi 
and treads it firmly into the bottom of the pupa-cavity with its hind 
tarsi. This obstacle removed, the beetle advances along the burrow 
to the opening, eats through the thin layer of outer bark and makes 
its escape. 
In the event of it choosing the bark to pupate in, it makes its way 
from the wet bast to the dead and drier outer bark, excavates a 
pupa-cell upwards and slightly outwards, reverses its position, fills in 
the hole beneath, reverses its position again, and, standing on its tail, 
transforms thus. 
As to the selection of wood or bark in which to pupate, Ratzeburg 
(Die Forst Insekt., vol. i, p. 237) says of the kindred species Ceram- 
byx lwridus, Fabr. (= T. luridwm, L.), that it pupates either in the 
bark in summer, or burrows (if compelled to hibernate) in the wood 
(“Und verpuppen sich entweder (in Sommer) auch in derselben, 
oder graben sich (wenn sie uberwintern miissen in das Holz”). It is 
probable that he was mistaken here, for in 7’. gabrieli the pupating 
larva is not influenced in its choice of wood or bark by the season. 
In the case of a brood reared from eggs laid in May, pupating in 
July and emerging in August, some of the larvee chose the wood and 
others the bark in which to pupate. Here the question of hiberna- 
tion was not involved, the weather being hot throughout from the 
time of oviposition to the time of emergence of the perfect insect. 
Moreover a large proportion of the larve may always be found 
established in their pupa-cells close to the surface of the outer bark 
during the winter, and others, not full fed, resting in the position in 
which the winter overtook them while feeding in the bast. 
Whether in wood or bark the larva excavates the pupa-cell in such 
a way as to admit of its always pupating standing erect on the ex- 
tremity of the abdomen, or, in a few cases, nearly so. In this position, 
after it has stiffened for pupation and also after it has transformed 
to a pupa, it is given to spinning round and round in the cell. 
Neither pupa nor imago has room to reverse its position in the 
pupa-cell, nor has the imago sufficient endurance to excavate more 
than a very little hard wood, so the beetle depends on the instinct of 
the larva to provide for its safe exit by facing in the right direction 
before transforming. I have not known this instinct fail in the 
standing tree in hundreds of burrows I have examined. 
The larve mutilate each other when they are very 
numerous in the bark. I have frequently found dead ones 
where the burrows cross each other much, On one occasion 
TRANS. ENT. SOC. LOND. 1907.—PARTII. (SEPT.) 14 
