306 INSECTS AFFECTING VEGETATION 



left standing to serve as breeding grounds for the pests. (Bui. 33, 

 N. H. E. S.) 



Bronze Birch Borer. The presence of this insect in birch trees 

 is not easily determined until it has been at work for a year or more. 

 The first intimation one usually has of its presence is the dying of 

 some of the top branches of the tree. The whole tree often suc- 

 cumbs in another year or two. Rarely the trees might begin to die 

 at the top from a condition known as stag head caused by lack of 

 moisture and food materials. A careful examination should readily 

 locate the borer if it is the culprit. Some have tried to save a tree 

 by pruning out the dead branches or top, but without avail for by 

 that time the whole tree usually is infested. 



Sometimes one can determine in autumn whether a tree is in- 

 fested by this insect, even before any branches have been killed. 

 Characteristic reddish or rusty brown spots or discolorations often 

 occur on the white bark of the trunk and larger branches at the 

 point where the insect is preparing to hibernate and transform in the 

 wood beneath. Usually the insect can be easily located by cutting 

 through the bark and into the wood beneath tliese rather conspicu- 

 ous spots. Another peculiarity which characterizes the work of the 

 insect is the ridge which often develops in the bark over the burrow 

 on the branches. Thus, while the insect works in rather an obscure 

 manner, it indicates its presence in the above described characteris- 

 tic and sometimes conspicuous ways. Unfortunately, however, it is 

 usually then too late to save the tree, but much can be done to pre- 

 vent further infestation of other trees. 



This destroyer of white birches is a small, slender, olive-bronze 

 colored beetle nearly half an inch in length (7.5-11.5 m m.). Its 

 general color and the fact that it works mostly in birch trees sug- 

 gested the good popular name of Bronze Birch Borer for the insect. 

 However, it is not in this adult or beetle stage that the insect is de- 

 structive. It is injurious only during its life as a larva or grub 

 when it is a borer. (Bui. 234, Cornell Agr. Exp. Sta.) 



The borer is a slender, flattened, footless, creamy white grub 

 about three-fourths of an inch long when fully grown. Its small 

 head with dark brown mouth-parts is retracted into the wide, flat- 

 tened first thoracic segment giving it a flat-headed appearance. The 

 other segments of the body are not so wide, the second and third 

 thoracic being the narrowest. The caudal end of the body ends in 

 two brown, horny, forceps-like processes with bidentate inner mar- 

 gins. It is this slender creature which is responsible for the killing 

 Of the trees. It may be found in autumn by cutting into the trees 

 beneath the rusty-colored spots occurring on the bark. These grubs 

 make tortuous or zigzag burrows in the sapwood around and across 

 the trunk and branches of infested trees. 



This borer attacks white birches of all sizes from nursery trees 

 to stately monarchs more than a quarter of a century old. All parts 

 of the tree, from branches a quarter of an inch in diameter to the 

 main trunk, may be infested. The top branches are always first at- 



