46 MICHIGAN ACADEMY OF SCIENCE. 



A DISEASE OF THE WHITE BIKCH. 



BY JOHK LARSEX. 



The beetle Agrilus auxins, one of the Buprestida', is causing great 

 I'avages among our shade birches, both the white and also the cut- 

 leaved variety. 



A tree that has been attacked does not die the first season but seems 

 to live during several seasons, the beetle doing its work each season. 

 Infected trees very often have last year's leaves remaining upon 

 branches that have sutfered severelv. The death of the trees begins 

 at the top and proceeds downwards. In trees that are nearly dead 

 only a few of the lowest branches bear leaves tardily in the spring 

 only to wither soon. The burrowing of the larv?e weakens the limbs 

 to such an extent that many of them break from their own weight. 

 Trees may be found where nearly all the limbs hang down broken. 



The trees are usually first attacked towards the top Avhere the limbs 

 are from three-fourths to one and one-half inches in diameter and 

 usually only in badly affected trees are the burrows found towards the 

 base in the trunk of the tree. 



Aside from the apjiearance spoken of the presence of the beetle 

 is shown by narrow swollen ridges on the bark which often on the 

 smaller limbs run spirally for some distance. Cutting through these 

 a burrow is always found just beneath the surface. The burrows follow 

 no definite direction in the limbs but may be found running zigzag in 

 any direction, sometimes running upwards, then doubling to again run 

 downwards; sometimes near the bark, then turning inwards even run- 

 ning straight through the center of the limb to the opposite side. The 

 smaller the limb the sfraighter usually is the course upwards or down- 

 wards of the burrows. 



The burrows are sometimes found in twigs onlv one-fourth inch in 

 diameter where they run straight in the center. In the trunk they do 

 not penetrate deeply but twist around among and through each other 

 making it impossible to trace them for any distance as they often 

 form a complete network. In the trunk they do not form regular ridges 

 but irregular swellings; in the smaller limbs and twigs no external sign 

 is shown. The smallest limb upon which ridges were found was one-half 

 inch in diameter. No ridges are found except where the burrow has 

 cut the cambium. 



During the early period of the investigation leading to this paper in 

 the early spring of 1899, "Bulletin No. 19, New Series," of the Agri- 

 cultural Department at Washington came to hand. This furnished 

 the identity of the beetle and data of its distribution. The bulletin 

 speaks of the birches in Buffalo, N. Y., and in Detroit, Mich., as having 

 suffered very severely. Aside from this the observer has found most 

 of the trees here in Ann Arbor suffering more or less severely and 

 many of them dead. The same was found to be the case in various 



