Part I.] Beeson : Life-History of Diapus furtivus, Sampson. 27 
beetle causes the tree to die oh in a rapid and striking manner. The 
first onslaught is made high up on the bole, just below the crown 
branches, and usually is not extended downwards to within less than 
15 feet of the ground until the tree is dead. The actual death of the 
tree is due to the mechanical girdling action of the crowded galleries, 
combined with the extraction of cell-sap by the mycelium of the am¬ 
brosia fungus. The water-current, already weakened by the diminution 
of the effective root area, is cut off from the crown, and the leaves 
rapidly wither, turn brown, and, in the course of a few weeks, fall. 
The economic importance of the beetle in this connection is affected 
by the length of time required by the root-fungus alone to kill off the 
tree, and varies directly with the number of years. If a tree, with one- 
half to two-thirds of its roots out of action, is destined to die within one 
year, the acceleration of its death, by shot-hole borer within that period, 
can be neglected. If, on the other hand, the diseased tree normally 
lingers for a period of five, or ten, or more years in the absence of insect 
attack, the economic status of the latter must be considered. 
It is worthy of note that about twenty-five per cent, of the insect- 
infested Sal trees in the Duars forests contained Diapus furtivus. 
Economic Importance as a Secondary Pest. 
The technical damage due to this species takes the form of shot- 
holes and lines and stained wood defects in the sap-wood and outer 
heart-wood of timber. In badly attacked trees the outer two inches 
of heart-wood is perforated to such an extent as to render it useless. 
In Assam and Bengal, the attack of shot-hole borers is more serious 
than in the United Provinces and the Central Provinces, and, according 
to the reports of divisional officers, the sale price of the timber is appre¬ 
ciably affected. 
Control Measures. 
The following preventative measures should be introduced and 
kept in force annually as a permanent protective operation. The 
measures have the advantage of protecting timber against the attacks, 
not only of Diapus furtivus but of all shot-hole and pin-hole borers, 
of bark beetles, and of the large longicorn borer, Hoplocerambyx spini - 
cornis. 
1. Fellings .—Trees, in annual coupes felled, should be barked at once, 
unless converted and removed from the forest within one month. 
[ 27 ] 
D 
