87 
Part V.] Sweet: On Air Seasoning of Indian Timbers. 
(in) The liability of timbers to insect attack. 
The liability of a given species of tree to attack by borers is influ- 
enced by several factors, of which the following are the more import- 
ant: — 
(a) Locality. 
(b) Date of felling and girdling. 
(c) Treatment of logs after felling. 
(a) Locality. 
(1) The factors which determine the natural distribution of a 
species of forest tree, e.g., climate, altitude, soil, associates, etc., do 
not necessarily influence in the same way the distribution of the boring 
insects that attack it. The borer-fauna of a tree is composed of several 
species of insects, some of which may occur throughout the habitat of 
the tree, but most of which are restricted only to parts of its habitat. 
Thus, living teak is attacked by a bee-hole borer only in Burma and 
by a, canker grub {Haplohammus cervinus) in Bunna and Assam, and 
not in the peninsula of India. Sal in Bengal and Assam is attacked 
by a whole series of shot-hole borers, that do not occur in the United 
Provinces, Central Provinces or in Orissa. The large longicorn borer 
{Hoplocerambyx spinicornis) is found throughout the habitat of sal 
except in the isolated forests of the Gangetic plains and the dry parts 
of Orissa and the Central Provinces. Leguminous trees with well- 
marked heartwood are generally more liable to attack by powder-post 
beetles (Bostrychidae) in dryer than in moister regions. 
(2) A species of borer may occur in the same locality as a parti- 
cular tree species, but its relative abundance is frequently determined 
by the occurrence of alternate host-trees. A widely distributed shot- 
hole borer {Platypus solidus) is likely to do more damage in a depot 
containing several rather than one species of trees in which it breeds 
by preference. On the other hand the species, although polyphagous, 
may locally be composed of strains having marked preference for 
one kind of tree to the exclusion of its other normal food-plants. 
{b) Date of felling or girdling. 
The life-cycles of borers vary very much in different groups, from 
a period of two months or less, in the case of those species with five 
broods in a year, to 12 months in the case of those with annual 
life-cycles. The borers with short life-cycles are therefore on the wing 
at 4 or 5 almost continuous periods of the year, while those with an 
annual cycle are able to attack the host tree at only one period in 
the year. The danger-period for liability to attack is further affected 
by local climates, e.g., in cold or mountainous regions there is a 
long dead winter season, while in moist or warm regions there is no 
dead season in winter, but often a period of diminished activity in the 
hot weather. Variations from the normal annual climate of a place 
affect the duration or frequency of danger-periods. 
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