57-' FAMILY SCOLYTIDAE 



insect, such as a long drought and warm winter followed by an early spring, 

 the latter will increase in such numbers that the ordinary supply of trees 

 suitable for egg-laying becomes insufficient : the beetle will then attack green 

 standing healthy trees. When this happens it is usually found that the 

 insect chooses those which are growing on exposed aspects, especially dry 

 southern aspects where the soil is poor, and those growing in open forest. 

 Once, however, a centre of attack has started, the insect, by means of suc- 

 cessive generations, spreads outwards from the centre in more or less 

 concentric rings, each generation attacking the trees nearest to those in 

 which it was reared. The attack on the deodar in Bashahr by this beetle, 

 reported by Mr. B. Ribbentrop, C.I.E., Inspector-General of Forests, and 

 Mr. Minniken, spread in this manner. In this way in serious attacks 

 of the insect whole areas of forest may be killed off in a few months 

 owing to the incredible swiftness with which the beetles multiply. That 

 this latter is very rapid will be understood when it is stated that a tree 

 of 3 ft. diameter at base and 100 ft. bole produced, as a result of a single 

 generation reared in it, 56,300 beetles, allowing for 50 per cent, casualties. 

 Observations have shown that in a dry year the casualties are from 15 to 

 20 per cent. only. Fig. 26, p. 49, shows the effects of the insect's 

 attacks on young deodar in the Simla Catchment Area in 1908. The 

 trees shown were killed by the beetle. 



Once the life history of this beetle is well understood the introduction 

 of certain measures to check its further increase on a 

 lar e scale becom es possible. It is obvious that any 

 measures which will result in the killing off of the grubs 

 before they change to pupae and beetles will result in the disappearance 

 of the insect from the area as a pest, since there will be no further egg- 

 laying on a large scale. Our present knowledge of the life history enables 

 us to cope with the pest in this manner. I have shown already that 

 three full generations and a partial fourth may be expected in an ordinary 

 year. 



I have also given the approximate periods at which the larvae of each 

 generation will become full-grown. In order to deal with an attack which 

 threatens to assume serious proportions it will be necessary therefore to take 

 steps to destroy the larvae of each generation as it appears. 



The beetles may be attacking trees in any one or all of the following 

 conditions : 



Newly felled or fallen green trees (wind- or snow-breaks). 

 (b) Standing sickly trees. 



green trees in the neighbourhood of a "centre" of 

 infection. 



step to be taken, then, is to seek out and mark all infested 



and fallen, and standing sickly or attacked healthy 

 trees. 



