FAMILY SCOLYTIDAE 521 



This beetle was first discovered in the blue pine in June 1902. 



It bores into the boles of large trees, coming in much 



Life History. later than the blue-pine Tomicits. The beetles were 



found boring egg-galleries in the bark in the third 



week of June, when the adults of the first generation of the blue-pine 

 Tomicus, which were plentiful in the tree, were nearly mature, some having 

 already left the bark. It is thus evident that it requires bark less fresh than 

 does the Tomicus. In thus attacking the tree at this stage, and in its habit of 

 infesting old trees, it differs from Polygraphus major, which it resembles 

 in size though not in colour or habits. The insects found in June were 

 probably those of the first generation of the year engaged in laying the 

 eggs of the second generation. The difference in the life history between 

 this and the larger Polygraphus may be summed up as follows : 



P. major was at the time only just maturing as a beetle (first generation) 



in the branches of the blue pine. It was numerous in the tree 



from which Polygraphus nigra was obtained. 

 P. major does not attack the main trunk of the tree ; it attacks the 



tree in a fresher condition, requiring fresh sappy cambium for 



its grubs. The egg-galleries of Polygraphus nigra differ entirely in 



character from those of the large Polygraphus. 



Towards the beginning of November 1906 I again took this insect, and 

 made a more detailed study of its method of attack in the blue pine. These 

 observations modify and supplement some of those given in Departmental Xotcs. 

 Beetles were taken ovipositing in a section of the butt of a large felled 

 blue pine. The section girthed about twelve feet. I was able to confirm 

 my previous observation that the beetle does not enter the tree until it has 

 lost its first freshness, coming in as the generation of Tomicus ribhcti- 

 tropi is leaving the tree. In the case observed in November, the beetles 

 were either just tunnelling into the tree and eating out the egg-galleries in 

 the bast and sapwood, or their egg-galleries were complete and thelarxae 

 already about half-grown. The male beetle, which is smaller than the 

 female, bores in through the bark and eats out a large pairing-chamber <>(" 

 irregular shape about a third by a quarter of an inch. From three to six 

 females enter the pairing-chamber and are fertilized by the male. The first 

 female appears usually to eat out her egg-chamber in a direction parallel 

 to the long axis of the tree; the others may go in tin- sime direction 

 upwards or downwards or at right angles to the direction of the first. 

 The eggs, as usual, are placed in small notches at the sides of the egg- 

 gallery, the larval galleries taking off on both sides of the e.ug-g.dlery, 

 and at right angles to it, as shown in the figure. Only in exceptional cases 

 apparently do the larval galleries develop on one side only of the ei:-- 

 gallery. The pairing-chamber and egg-galleries groove both the bast and 

 sapwood, the latter but slightly. The egg-galleries are almost free of wood- 

 dust, small masses only occurring here and there in them. The larval 

 galleries are eaten out in the bast only. They average from five to six 



