38 INDIAN FOREST INSECTS 



attack under which many trees would have been lost and the water supply 

 have been to some extent endangered. 



In the Bre forests in Chamba State numbers of trees were killed 

 out on an important Catchment x\rea between igo6 and igo8, without the 

 true source of danger being understood. I inspected many of these trees 

 in 1909, and they had all been killed by bark-borers. 



Deodar sowings in the nursery and out in the forest have suc- 

 cumbed to attacks of insects on a larger scale than has been recognised 

 in the past, owing chiefly to the life histories of the insects concerned not 

 having been known or understood. And the same applies to the loss 

 of young Pinus longifolia plants in plantations in the Naini Tal Division and 

 in the district forests under the attacks of the cryptorhynchid weevil 

 (p. 428). 



Heavy crops of seed of both coniferous and broad-leaved trees are 

 almost entirely lost under the attacks of grubs of weevils, Scolytidae, 

 and the caterpillars of small moths, thus seriously interfering with the 

 regeneration of the forests. 



Other instances might be quoted, but enough has been said to endorse 

 the contention that the Indian forests are as liable to serious infestation 

 from insects as are those of other countries, where an efficient Forest 

 Department is engaged in improving the forest areas entrusted to its 

 charge. 



2. Aids to Insect Increase and Depredation. 



There are various ways in which unpremeditated assistance is given to 

 an insect, enabling it to increase in a forest in such numbers as finally to 

 become a danger to the very existence of the trees themselves. 



(i) Pure Woods. — The first of such causes is to be looked for in the 

 creation of pure forests as against mixed ones. The bulk of the natural 

 forests in the country are mixed ones in which one or more predominant 

 species occur in company with a variety of, at present, less abundant or less 

 important ones. The danger from insect invasion in this class of forests is 

 much less than in the case of pure forests — i.e., forests consisting of one 

 species of tree only. In these latter the insect, finding dense contiguous 

 masses of its food plant available, may, given favourable climatic conditions, 

 increase in such numbers as seriously to threaten the life of the forest as a 

 whole. As an instance, a note of warning has been already struck in the 

 case of forests of pure deodar in the Himalaya. The tree suffers from the 

 attacks of several dangerous scolytid pests {Scolytus), as also from a buprestid 

 and a longicorn {Sphcnoptcra and Tvinophyllum). Already on several occasions 

 trees have been found killed by these pests at a centre or at more than one 

 centre in the deodar areas. Instances are not wanting to show that Finns 

 longifolia in dense pure forests is likely to suffer seriously from the attacks of 

 the weevil Cryptorhynchus (fig. 23), from those of the longicorn NotJwrrhina, 



