INDIAN FOREST INSECTS 



the families or genera or individual species which are already, or are likely 

 to become in the future, of chief importance to the executive forest officer. 



When a distribution list of forest pests was first attempted it was con- 

 sidered possible that the forest tracts might be divided for this purpose 

 broadly into those of the hot dry region, those of the hot moist region, those 

 of the regions intermediate between these two, and those of the Western and 

 Eastern Himala}'a and contiguous mountain ranges. Or that, failing such 

 a classification, a distribution could be based on the classes of forest, i.e. 

 the areas occupied by the chief species of trees at present economically 

 useful to the forester. A distribution list based on either of these factors 



has been found to be impracticable. Whilst 

 some genera or species, it is true, seem to be 

 confined to the hot dry localities or the hot 

 moist ones, others appear to flourish in both. 

 We know that the habitat of the same species 

 of tree may vary from a comparatively hot 

 dry climate to a hot moist one, as, e.g., the 

 sal {Shorea robusta) in the Central Provinces 

 and in Assam. It would therefore perhaps 

 be natural to expect that an insect which 

 infested the tree in the hot dry climate 

 could also adapt itself to the hot moist one. 

 And this is true of some species, but not of 

 others. For instance, the sal longicorn beetle 

 Hoplocerambyx spinicornis infests this tree both 

 in the Central Provinces and Assam, but the 

 beetle also extends down into the Shan Hills 

 far beyond the distribution limit of the sal, 

 and here attacks the Duahanga sonnatioides 

 and Pentacme suavis. On the other hand, the 

 sal-tree extends into Northern India and 

 forms forests in the Terai in the foothills of 

 the Western Himalaya. The Hoplocerambyx 

 does not, however, follow the sal into this 

 locality, its place being taken by another longicorn, jEolesthes holosericea. 

 As a logical sequence to the distribution of this and other species, which will 

 be dealt with later, it would appear that the distribution of forest insects is 

 limited more by cold and elevation than by heat and moisture. 



Or, to put it in another way, beyond a certain elevation in the Himalaya 

 and other elevated mountainous tracts to the south the forest pests of the 

 plains are rarely found, whereas south of the Himalaya below a certain 

 elevation some pests may have a very wide distribution, both in hot dry and 

 hot moist localities, whilst others will be confined either to the forests in 

 hot dry localities or be restricted to the hot moist areas. We will briefly 

 consider this distribution in the plains. 



Fig. I. — Hoploceratnbyx spinicornis. 

 Newn. S X «. (F.B.I.) 



