ECONOMIC ZOOLOGY ENTOMOLOGY. 657 



on valuable residence property, have been killed during recent, years and their 

 deadi has been commonly attributed to this pest. In some of the outlying dis- 

 tricts areas of several acres in extent have been completely devastated, leaving 

 the land treeless. 



In this paper the author presents the results of work commenced in the fall 

 of 1913 at the University of Minnesota and continued during 1914 at the Minne- 

 sota Station. 



Members of the black oak group are said to be slightly moi'e susceptible to 

 attack than those of the white oak group, but in localities where infestation is 

 severe none of the species is exempt. It has oftv?n been found that the shoe- 

 string fungus (Armillaria meUea) has apparently been the cause of the weak- 

 ened condition of the trees and that the borers have followed it. 



In 1914 adults were first observeil on June 17 and increased in numbers until 

 thej^ reached their greatest abundance about July 1. The females were oviposit- 

 ing from June 19 to July 13, the eggs being deposited in deep cracks between 

 ridges of the bark on the trunks and larger limbs and especially near the 

 ground. Oviposition is said to have lasted from 1 to 5 minutes, from 1 to 10 

 eggs being laid in a cluster. In the laboratory they hatched in from 10 to 13 

 days. The newly-hatched larvre, which measure from 1 to li mm. in length, 

 were found capable of reaching the cambium layer in 24 hours by burrowing for 

 2:1 nim. " Observations show that burrows made during the first instar often go 

 obliquely across the grain of the wood or with the grain, the larvte being indif- 

 ferent as to whether they go up or down the tree. . . . The burrows measured 

 showed that the larva? had burrowed for a distance of 60 to 135 mm. when the 

 first molt took place. . . . The burrows made during the second Instar meas- 

 ured about 900 fi in width and took about the same course through the cambium 

 layer, but they were about twice as long. At the beginning of the third instar 

 quite a different course was usually found, especially in green bark on the 

 trunks of ti'ees, wliere the burrows were almost always transverse to the grain 

 of the wood. The burrows of the fourth instar were about 2 mm. in width and 

 often attained the length of 500 or 600 mm. Where the bark was thick these 

 burrows were quite generally transverse to the grain of the wood. This condi- 

 tion, as well as the oblique course of some of the smaller burrows, is well shown 

 [in a plate accompanying this article]. 



"At the close of the fourth instar the larva burrows out into the bark, if it is 

 thick enough, and constructs a cell in which it hibernates. Here pupation takes 

 place in the spring. These cells are found in the ridges of the bark on the trunk 

 and larger limbs of the tree and in the wood on small, thin-barked trees and 

 limbs. In constructing the cell the larva burrows out to within a few milli- 

 meters of the surface of the bark, withdraws itself 2 or 3 mm., then turns about 

 to one side and excavates around the posterior portion of its body until an 

 oblong cell has been constructed. . . . From the point where the larva entered 

 the bark to the place it emerged from the wood after the first molt the burrow 

 measures G9 mm. in length and 270 fi in width." 



While the author has not thus far determined the duration of the instars, 

 larvse were found in the first stage from July 21 to August 13, and mature larvae 

 were found in their pupal cells as early as August 7, while the intermediate 

 stage was found throughout this period. It was found that when larvse were so 

 numerous that they confront each other, one or the other is eaten through as if 

 it were merely cambium tissue. Attention is called to the " wide distribution of 

 the burrows on the tree, from the small branches less than an inch in diameter 

 and between 40 and 50 ft. from the ground down even to the roots, where in one 

 case a larva was found constructing a pupal cell 11 in. below the surface of the 

 ground." 



