68 



without discovering anything but perfectly sound wood. On peeling- 

 downward there was found, 2 or 3 feet below, the beginning of a burrow 

 containing a pair of beetles. They had tunneled completely through 

 the bark, but had barely touched the wood. Continuing operations 

 large numbers of embryo burrows were disclosed, some containing one 

 beetle, some a pair. In a space 15 inches long by 5 wide no less than 

 eight burrows were discovered. They were in all stages of develop- 

 ment, from a mere hollowing in the bark containing a single beetle, to 

 a tunnel 2 or 3 inches long, and in these cases, also, there was usually 

 but one inhabitant, though it was not rare even then to find the male 

 still accompanying his spouse. 



The eggs were found in groups of four to six, in little cells or chambers 

 in the substance of the bark close to the entrance to the burrow. Con- 

 tinuing down the tree, every stage of development might be observed, 

 until when near the base the parent beetle would be found dead at the 

 end of her burrow, while her progeny were fast approaching maturity and 

 numbers of the smaller Scolytidre were entering the breach thus made 

 to continue the work of destruction. In one or two cases the complete 

 larval excavations were found surrounded by perfectly sound wood, and 

 the following description is taken from a field note: First, a gallery is 

 excavated in the bark, running vertically up the tree for a distance of 

 from 3 to 4 inches, and sometimes making a sharp semicircular turn at 

 the further extremity. At the beginning it is two or three times the 

 breadth necessary to allow the beetle to pass through, but after the 

 eggs are deposited in the tiny cells prepared for them the whole space 

 is filled with bits of wood packed solidly together, and through this 

 mass a tunnel is excavated barely large enough for passage. It is these 

 tube-like structures that are so characteristic and which are so readily 

 identified after the trees are long dead. 



The eggs were only found in some of the young colonies in cells near 

 the entrance, but it is evident that they are laid at intervals the whole 

 length of the excavation. The young larvae would each start a some- 

 what crooked mine in a different direction from the cluster of eggs. 

 Sometimes these would coalesce later on and several larva? would be 

 engaged in making one broad excavation, filling in the space after them 

 as they progressed. When full grown they would have traversed a 

 distance of from 3 to 4 inches, and the area covered by them would 

 spread out in a fan shape on each side of the parental gallery. The 

 whole space beneath the bark would in some cases be occupied. In 

 others there would be quite large areas of sound wood, but this was 

 being rapidly eaten away by the smaller Scolytids. 



That the Dendroctonus is the primary cause of the death of the tree 

 there is practically no room for doubt. That in some cases, at least, 

 they are the first insects to appear in the affected trees is sure, and 

 from the conditions existing in the dead and dying groups, where the 

 insects obviously spread from one tree to another, hardly any other 



