86 THE REPOKT OF THE No. 36 



beetles. This species bores well into the wood, cutting several side tunnels; each 

 tunnel is cut, usually, by a separate female. The eggs are laid in shallow niches 

 cut in the wood along the sides of the tunnels. The eggs are spindle-shaped and 

 wedged into the niches, one in each, a little above the bottom, and a mass of chips 

 and excrement, on which the ambrosia starts, is plugged into the opening. The 

 larvae deepen the niches until the depth is slightly greater than the length of the 

 larvae when full-grown. In these niches the larvae pupate, and from them the 

 adults push their way through the wall of dust and fungus which has previously 

 blocked tliem in from the tunnel. The chief food of both adults and larvae seems 

 to be a fungus which grows on the walls of the tunnels and niches. The fungus i 

 carried from tunnel to tunnel by the beetles, and stains the walls deep brown o 

 black. The habits of the Ambrosia beetles are very interesting, but I shall not 

 discuss them further at this time. There are two broods of this species in our dis- 

 trict. The first brood was egg-laying this season on May 24th, and matured late 

 in July. By the 6th of August new tunnels were being started in the stumps, and 

 eggs laid for the second brood. Many eggs of the second brood were apparently 

 destroyed by minute nematode worms. 



This species breeds in pine and spruce as well as larch and its tunnels often 

 injure lumber for the most valuable uses. 



Only two of these beetles, D. simplex and /. halsameus, can be considered as 

 seriouR larch enemies, and this is the first time that I have taken halsameiLs from 

 that tree. D. simplex is known to attack and destroy but slightly diseased larches 

 under certain conditions, and those conditions I wish to discuss now very briefly. 

 Previous to this season D. simplex had been rare in that neighborhood, but it came 

 in in fairly large numbers this spring, attracted from a considerable distance by 

 the dying larch bark. Only half the stumps were attacked by the spring swarm,-; 

 but the progeny which matured in midsummer numbered thousands of individuals. 

 These parents of the second brood entered the bark of the remaining stumps, and 

 of the felled larch in the shade in great numbers. They did not attack the dried 

 bark of the cord-wood, nor of the felled trees in the clearing. The individuals o:^ 

 the second brood at present in that swamp must number many thousands 

 Whether or not they are of sufficient number to successfully attack standing trees 

 is a problem which I shall watch with interest next season. 



Tf, after the available dying bark has been utilized by the beetles next springs 

 there are but few individuals left, they will gradually scatter in search of a further 

 supply of bark in such condition. If, however, there are immense numbers in the 

 swamp unable to find bark in the condition which suits them best, they may sue 

 ceed in ovipositing in the bark of but slightly injured, or even healthy, trees, in 

 which case the larvae would probably mature and the trees be killed. "Wlien a few 

 scolytid beetles attack a healthy tree, usually the vigorous flow of sap drives them 

 back before the eggs are laid, and the tree suffers but little. When the number 

 attacking a tree is very great, the many entrance holes and started tunnels check 

 the sap flow so that the beetles succeed in laying their eggs and the resulting larvae 

 develop in the devitalized bark. 



The level of numbers at which a species, usually not injurious, will attack 

 healthy or but slightly diseased trees is known as the Pest Level. 



It will be seen that a slight modification of the method of cutting would have 

 averted any danger from these beetles. If the stumps had been cut longer a few 

 blows of the axe would have removed most of the bark from each. If then all the 

 trunks had been trimmed and left in the open sunlight of the clearing there would 



