Life History of Tetropium gabrielt. 207 
that, in the single instance before them, there does not appear to be 
any fungal parasite. They incline to the opinion that the affection is 
due to malnutrition and subsequent ulceration, or to bacterial action. 
The affection has been most prevalent under the abnormal and 
unhealthy conditions of forcing over gas in a warm damp atmosphere. 
I have also observed it in larve taken from under bark of trees 
where the burrows were mildewed and several larvae had died. I 
have observed what is apparently the same disease in larve of 
Siricidx affecting larch and willow. 
PROPAGATION.—In timber-yards the species is propagated to a large 
extent, the beetles emerging and laying on adjacent timber felled in 
the current year. Much of this is cut up before the following 
summer, and a great many of the larve and pupe perish in passing 
through the saw-mills. But a large number remain in the slabs and 
posts, ete., after the logs are cut up. 
In cutting up timber of any considerable size, slabs are removed 
first from the logs, either one or more according to what the timber 
is required for. These slabs consist of bark and sapwood, and are 
sufficiently thick to take in many of the burrows containing pupating 
larvae (November—April). 
In these slabs and in smaller timber sawn in two or quartered for 
posts, the insect is transported in all directions to emerge in new 
districts and establish itself in the nearest plantation containing this 
conifer, 
This doubtless has been a potent factor in the spread of the beetle 
throughout the country ; but it is probable that it has been spread 
in a still greater degree in incoming timber, infected in the plantations 
and brought from long distances to the saw-mills. 
I have seen such logs brought in containing hundreds 
of larvee, and, where there is sickly Zarix in the neigh- 
bourhood of these saw-mills, little of it escapes oviposition 
and the species becomes abundant there. 
A large percentage of larvae remain in the timber-yard 
in uncut logs till the summer, when the perfect insects 
emerge and lay their eggs on incoming timber freely. To 
raise the bark of logs in timber-yards between September 
and the following summer is to find a large proportion of 
it affected. 
The LARCH CANKER, the LARCH APHIS (Chermes laricis, 
Hartig.), and unsuitable environment multiplying the 
number of sickly and dying trees * lend themselves to the 
* Tam indebted to Mr. G. Massee of the Royal Gardens, Kew, for 
this information. 
