504 FAMILY SCOLYTIDAE 



or more arms take off, and at some distance from these arms irregular rows 

 of small holes in the wood — the pupating-chambers of the grubs, whose 

 tunnels were made entirely in the bast layer and are therefore not visible 

 in the sapwood. This is the most characteristic appearance of stems 

 and branches attacked by this pest, and by it the presence in the forest of 

 the insect is easily recognizable. The egg-gallery is loosely packed with 

 the wood particles eaten out in excavating it. When she has finished egg- 

 laying the beetle bores a short offshoot gallery from the egg-gallery, in which 

 she dies ; or the female may die at the top of a prolongation of the egg- 

 gallery, no eggs being laid in this portion. In small branches the beetle 

 grooves the sapwood much more deeply, and the egg-galleries are usually 

 much longer than in thicker ones. 



This Folygraphns also infests the spruce in a manner very similar to that 

 in which it attacks the blue pine. The number of generations passed through 

 in the former tree, however, is fewer, owing to the greater elevation at which 

 the fir lives. 



I think also that this is one of the species of Polygraphus which infest 

 the Pinus gerardiana in the Bashahr forests (Sutlej Valley). 



Much more serious, however, than the attacks of the beetle on the 

 spruce is the fact that in areas where the blue pine is scarce it infests the 

 deodar and will attack young green trees, as was evidenced in Jaunsar in 

 1902, in the Simla Catchment Area in igo8, and in the Bre Poorest in Chamba 

 in igog. The bark and wood of the deodar are very much harder than those 

 of either the blue pine or spruce, and because of this a considerable differ- 

 ence is to be seen in the plan of the egg-galleries, for the number of the 

 latter taking off from the pairing-chamber in the deodar is usually two only, 

 and never more than three, and both the egg and larval galleries are shorter, 

 as shown in pi. xlvii. In the deodar the periods occupied in passing 

 through the several generations of the year appear to coincide more or less 

 exactly with those of the deodar bark-borer {Scolytus, p. 568). 



In fevourable years, at the lower elevations at which the blue pine 

 grows, this Polygraphm passes through four full generations and a partial 

 fifth generation in the year. Ordinarily, however, the number of life-cycles 

 during any one year may be taken at three full ones and a partial or wholly 

 completed fourth generation, the periods occupied from egg to mature beetle 

 being roughly from seven to eight weeks, as follcnvs : — 



Generation 1. 



3rd vveek in April Eggs 



4th week in April to end of May Grubs 



End of May to 3rd week in June Nymphs 



2nd week in June to end of June Beetles 



(Iknfkation II. 



3rd week in June ........ Eggs 



4th week in June to 4th week in July .... Grubs 



4th week in July to 2nd week in August . . . Nymphs 



1st week in August to 3rd week in August .... Beetles 



