185 



Dli. HOPKINS: TliaL is not Uiiowii. We have no way of 

 detei'miiiin<; how far I hey will i;(). I tut lh(!y liav<; winj^s and tan 

 fly. There is no reason wliy (lu;y shonhi not; j^o lonj^ distances. 



DK. KEED, of Vii-iiinia: I wonld like to ask how many of 

 these insects are borers in llu; chesinnl (hat would inllict any 

 wound in the hark which would be larj^e enough to allow infec- 

 tion by a fnngns? 



DR. HOPKINS: There are a number of insects which may 

 cause wounds which will give entrance to the spores. \Vlieu the 

 insects hatch from the eggs, they are almost microscopic; there- 

 fore, the burrows made going into the bark will hardly give en- 

 trance to the siK)res unless there is a flow of saj) from these small 

 wounds, which sometimes hapijens. .My observation in Virginia 

 and the section south of \Vashington indicates that there is a 

 disease, possibly a bacterial one, which does get into these minute 

 wounds, on account of a small amount of the sap oozing out, 

 and in that wa^^ it works into the cambium. This is only a pos- 

 sibility which has been suggt^sted time and time again to me l)y 

 my observations ; perhaps it acounts for the fact that great num- 

 bers of dead trees in the South, do not show any traces of insects. 

 The trees die and the bark falls off and yet they show no evi- 

 dence of insects. Of course, the majority of dead trees do show 

 such evidence. We have had a man down in North Carolina in 

 1903-1904 studying the insects, and trying to determine the cause 

 of the extensive death of the timber in that state, and there was 

 no doubt that a great many of the trees were killed by insects, 

 but that insects were not the cause of all of the trouble. 



DR. REED : Is ther(> any part of the tree which is invariably 

 attacked by these insects, or does it occur generally on the 

 tree? 



DR. HOPKINS : The principal point of attack, the most vital 

 part of a tree, is the middle trnnk. We have found, in the study 

 of insects which kill trees, that they attack the middle portion 

 of the trunk. They girdle the tree at that point. The two- 

 lined chestnut borer does this especially. Other insects attack 

 all parts of the tree inclmling the leaves, and some of them are 

 associated with the chestnut blight, as has been determined by 

 Mr. Craighead, who has been carrying on work under my instruc- 

 tion here in Pennsylvania. 



