80 INSECTS AND HUMAN WELFARE 



The age of individual trees may exercise a considerable 

 influence upon the amount of damage caused by insects. It 

 may be stated, with few reservations, that where old or well- 

 matured trees occur among very healthy and vigorous young 

 specimens, that the former are almost always more liable to 

 attack. Thus from an entomological standpoint, the felling 

 and removal of the older and more mature trees in a forest 

 that contains individuals of mixed ages, is a very wise and 

 satisfactory practice. Even though the younger trees are less 

 readily killed by insects, their growth may be temporarily 

 checked, and a part of the increment to the forest by rapid 

 growth may be lost. However, if the fully matured trees had 

 borne the brunt of the attack, they would quite possibly have 

 succumbed altogether, and have served, in addition, as breed- 

 ing places for a much larger brood of insects to attack the 

 remaining trees the next season. The relation which this 

 bears to proper forest management is at once evident, for the 

 utilization of mature trees, or those which have ceased to grow 

 at a satisfactory rate, tends to eliminate the ones which 

 should be removed solely upon entomological grounds. In 

 this way the application of methods devised with little or no 

 reference to insects, is a procedure which the entomologist 

 can heartily recommend. 



Aside from the general preference exhibited by insects for 

 the older trees in a forest, there are some species which select 

 distinctly vigorous trees, saplings, or even seedlings, and 

 these are not amenable to even partial control by the ordi- 

 nary cultural methods. One of these, the white pine weevil 

 (Pissodes strobi), attacks saplings or small trees, and owing to 

 its habit of killing the leaders or terminal shoots produces a 

 deformation of the otherwise straight trunk of the white pine. 

 A number of the weevil eggs are placed by the parent beetle 

 within the tender bark near the tip of the tree, and the result- 

 ing colony of larvae work their way downwards beneath the 

 bark. They usually pass the first lateral shoots before be- 

 coming fully grown, and destroy the part through which they 

 have burrowed. Consequently, one of the lower side branches 



