INSECTS AFFECTIXr, I'ARK AND WOODLAND TREES 47 



estimate of the relative resistance of these trees to insect attack in New 

 York State, specially in the Hudson river valley. The figure 3 has been 

 placed opposite trees which are practically immune from insect injury, 2.5 

 indicates some damage. Trees having one somewhat serious enemy are 

 rated at 2, and those having at least one notorious insect pest at 1.5. 

 Greater likelihood of injuries is indicated by i and still more by .5. The 

 species are arranged according to the comparative injury and the list follows : 



Tulip tree 3 R^d maple ----- 2 



*Tree of Heaven - - - 3 Honey locust - - - - 2 



Hardy catalpa - - - - 3 European linden - - - 1.5 



Gino-ko ------ 3 American linden - - - 1.5 



Red oak ------ 2.5 Horse-chestnut - - - - 1.5 



Scarlet oak- - - - - 2.5 Soft or silver maple - - 1.5 



Yellow oak ----- 2.5 American elm - - - - i 



Oriental plane tree - - 2.5 *Hackberry ----- i 



American plane tree - - 2.5 European elm - - - - .5 



Sycamore maple - - - 2.5 Scotch elm ----- .5 



Norway maple - - - - 2 Cottonwood ----- .5 



Sugar maple - - - - 2 Balm of Gilead - - - .5 



White oak ----- 2 Black locust ----- .5 



■ Bur oak ------ 2 



Those that are starred have been seen only in parks or in such small 

 numbers that the rating can be regarded as provisional only. 



Massing of trees. It is not only advantageous to select trees possessing 

 relative immunity from insect enemies but it is also advisable to avoid plant- 

 ing too many of one variety together. It is a well recognized principle 

 among agriculturists that large areas devoted to a single crop, specially for 

 a series of years, increase the danger from insect enemies and the same 

 applies in the case of shade trees set in parks and along our streets. It would 

 be much better could different varieties be alternated on the same street or 

 at least set in small groups, so that in case a few became badly infested by 

 such a species as the white marked tussock moth, Hemerocampa 



