8 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
Two beetles, a male and female, make a gallery in spring, and in 
it they deposit from 80 to 120 eggs; let us take the average and 
say 100. In ten weeks or so, these, having passed through the 
stages of larva and pupa, become beetles, of which 50 will be males 
and 50 females. In the same year, towards the end of July, these 
50 couples proceed with the work of reproduction, each pair pro- 
ducing 100 young, so that by the end of the first year the numbers 
have increased from 2 to 5000. These beetles hibernate in the 
manner already described, and proceed to breed the following 
spring, when the 2500 couples will give birth to 250,000 indivi- 
duals, and these, reproducing themselves in the same year, will, 
before the autumn is past, have multiplied to no less than 12,500,000 
head. In these calculations no allowance has been made for those 
which would be destroyed in various ways, but if we even deduct 
20 per cent. from each of the broods, we are still left at the end 
of the second year with over five millions of pine beetles as the 
result of our having neglected to destroy the original pair. 
Some idea of the rate of increase may be gained in another way. 
Where pine beetles are abundant, the bark of suitable trees is 
undermined to such an extent that, on a large pine, scarcely a 
square inch will be found that is not occupied by the galleries of 
the parent beetles or their larve. From observations and measure- 
ments, I have calculated (allowing 40 square inches of bark to each 
family) that a large pine can produce quite 100,000 beetles, so that 
the leaving of ten large Scots pines, or of twenty average sized 
ones, lying on the ground, or standing dead in the wood, till the 
middle or end of July, is sufficient to ensure the birth of 1,000,000 
pine beetles. Now, although comparatively little damage is done 
to timber during the breeding season, so long as the insect is 
represented by but small numbers, the case is entirely altered 
when a large increase has taken place, such as happened in Scot- 
land a few years ago. In the insect world the principle of ‘first 
come first served” receives striking illustration. Those beetles 
which first awake from their winter’s sleep exercise their usual 
discrimination, and oviposit only on thoroughly suitable material. 
It happens, however, when the insects are very abundant, that 
every particle of suitable Scots pine is occupied, with the result that 
late comers have to take what they can get, and are forced to 
oviposit on other conifers, such as the spruce, and, as I have found, 
on the larch as well.?| Under such circumstances, comparatively 
1 Proc. Roy. Soc. Edin., vol. xvii. p. 255, 
