ON METHODS OF PRE\i:XTIN(i INSECT ATTACK 



39 



and two bark-boring beetles. 

 In fact, the formation of pure 

 woods in the Western Hima- 

 laya is, from the point of 

 view of the great danger to 

 which they are liable from 

 insect attacks, to be depre- 

 cated. Again, the pure casu- 

 arina plantations of the east 

 coast of Madras have suffered 

 to some extent from the at- 

 tacks of several insect pests, 

 amongst the worst being 

 those of the larva of the 

 moth Arhela tctraonis. 



(2) Mixed Woods. — It is 

 perhaps too early yet to dis- 

 cuss the question of the 

 formation of mixed woods 

 in India. Natural mixtures 

 predominate throughout the 

 country, and our knowledge 

 of the insect pests of the 

 trees is as yet too imperfect 

 to enable definite statements 

 to be made save in one or 

 two cases. For instance, 

 there is a scolytid beetle 

 (Polygraphiis) which attacks 

 young blue pine. When the 

 trees are too few in number 

 to provide sufficient food for 

 it, it will attack the deodar. 

 Thus a mixture of a few blue 

 pine amongst deodar is bad, 

 since it exposes the deodar 

 to attack from an insect 

 which does not ordinarily in- 

 fest it. I have seen two 

 instances of this nature. The 

 bark-beetle attack in the Sim- 

 la Catchment Area of igo8 

 was aided in this manner. 

 The area contains few blue 



Frr,. 23. — I'oition of a young Finns longifolia pole, 

 showing the larval galleries of Cryptorhynchus 

 brandid, Steb., in the bast layer and outer sap- 

 wood. Near the top a larva is shown in situ in a 

 gallery ; an exit-hole of a weevil is seen in the bark 

 at the bottom. Kumaun, N.W. Himalaya. 



