REPORT OF THE STATE ENTOMOLOGIST 1903 167 



DISEASED AND DYING TREES AND INSECT ATTACK 



The connection existing between diseased and dying trees and 

 insect depredations is not only one of interest, but also of con- 

 siderable importance, since in some instances at least serious 

 depredations have origin in a group of diseased or dying trees. It 

 is well known for example that certain species exhibit a decided 

 preference for trees in this condition, and when breeding there- 

 from in very large numbers are liable to attack healthy trees, if 

 nothing more suitable is within reach. It is very likely for ex- 

 ample that the more serious injuries by the elm borer, Saperda 

 tridentata Oliv., and the elm snout beetles, M a g d a 1 i s 

 armicollis Say and M . b a r b i t a Say, begin in this manner. 

 These three insects can at least complete their transformations in 

 dead tissues and are known to work in those which are living, and 

 it seems very likely that in some cases they first attack a sickly 

 limb or tree, and then after becoming abundant are able to kill 

 others which show no signs of lowered vitality. The same is true 

 of certain bark borers belonging to the genus Tomicus which oper- 

 ate exclusively in coniferous trees. Our largest species known as the 

 coarse-writing bark beetle, Tomicus calligraphus Germ., 

 usually breeds abundantly in diseased bark and instances have 

 come under our observation where this species not only ran a feAV 

 galleries in living tissues, but evidently took part in a primary 

 attack on a tree in apparently normal condition. It was assisted 

 in this work by a smaller pine bark beetle, Tomicus pini Say, 

 which operates in the thinner bark, about the middle portion of 

 the trunk and on the larger limbs. This latter species very likely 

 has more to do in killing trees than the form previously mentioned, 

 but evidence at hand indicates that the larger as Avell as the 

 smaller may have an important part in this destructive work when 

 conditions are favorable. The destruction of trees by insects 

 breeding from a few dying ones was well illustrated in the sum- 

 mers of 1900 and 1901, at which time a number of pines in the 

 vicinity of Albany began to look unhealthy. Investigation showed 

 that they were infested with bark borers, and later in the season 



