FAMILY SCOLYTIDAE 515 



fortnight in the pupal and immature beetle stages, the generation taking 

 about two months to complete from egg to perfect insect. It will be 

 understood from the above that numbers of the beetles will mature and 

 leave the tree together, and this is what actually happens, and explains 

 the state of affairs seen in the second and fourth trees alluded to above. 

 In the first and third the insects maturing were those from the first 

 set of eggs laid in the spring of 1905. In the second and fourth we find 

 beetles all more or less in the same stage, i.e. the egg-laying one (especially 

 in the case of the second tree), the reason being explained by the fact 

 that they had left the tree in which they had been bred, and flown in a 

 swarm to the one in which they were found. 



Further investigations were made into the life history in November 

 of the same year, and reports were submitted to me on the subject in 

 following years. It has been mentioned that the insect passes through 

 three, and often four, life-cycles in the year, and it has been shown that eggs, 

 the eggs of a second generation, were being laid in the trees in the latter 

 part of June, and that some of these had already developed into grubs. 

 Beetles from this generation issue from the trees about the end of July, 

 and lay the eggs of a third generation in fresh trees at the commencement 

 of August. This generation matures towards the latter part of September, 

 issues from the trees, and lays the eggs of a fourth generation in other trees. 

 The progress in the development of this latter generation will depend 

 entirely on the weather. In the case of the earliest-laid eggs, i.e. those 

 laid by the descendants of the beetles who got the first start in 

 the spring, the larvae hatching from them proceed as far as the beetle 

 stage and pass through the winter as beetles, whilst those of the later 

 ones may winter as grubs. This I found actually to be the case in 

 November 1905, as I took both beetles and grubs in the trees. In any 

 case a certain number may have proceeded as far as the pupal stage when 

 the first cold snap catches them, and will probably be killed during 

 the winter. 



The relation of this bark-borer and of its companion rhlocosinus zhvbi 



(p. 496) to the chilgoza forests of Zhob and the Suli- 

 Damage Committed TJ n r -j 1 i 



in the Forest nuui ^ an S e generally is of very considerable interest. 



The preservation of these forests in this region has 

 a two-fold importance : 



( i) To preserve and increase the water supply. It is a fact which it would 

 be difficult to gainsay that the springs which exist on thr Shinghiir Range, 

 and which give water to the valleys on either side, are practically entirely 

 dependent upon the hills remaining covered with the chilgoza tree. Poor 

 as is this covering in parts, it is assisted by an undergrowth of such plants 

 as ephreda, berberis, ash, cotoneaster, spiraea, wild almonds, dog-rose, etc. 

 It is improbable that any of these would be found upon the area in the 

 absence of the chilgoza forest. 



r. K 2 



