268 PROTECTION AGAINST INSECTS 



So far as possible natural agencies which control insects 

 should be fostered. This will include the protection and aug- 

 mentation in numbers of beneficial insects, mammals, birds 

 and diseases which destroy injurious insects. 



Of these the beneficial insects are apt to be the most effec- 

 tive single natural factor for control. Insect diseases (such 

 as the wilt disease of the gipsy moth ^) may suddenly destroy 

 vast numbers of insects; but such diseases only become 

 virulent when the insect numbers have increased to an enor- 

 mous total. Hence diseases do not check insect epidemics 

 until extensive injury has taken place. Birds may be effective 

 in preventing the start of an epidemic, but will be too 

 few in number to cope with a serious outbreak when once 

 started. 



Dr. Felt ^° says in Volume I, page 25, of his book entitled 

 "Insects affecting Park and Woodland Trees ": "The control 

 of insects, particularly in forests, must be effected very largely 

 through the activity of natural agents, which should be en- 

 couraged in every possible way. It is ordinarily impractical 

 to attempt much in either a preventive or a remedial way, in 

 the forests of the United States." In view of the insect con- 

 trol and prevention work which has been successfully con- 

 ducted by the United States Forest Service and other organ- 

 izations, it would seem that Dr. Felt's last statement presents 

 a pessimistic viewpoint. 



(b) Disposal of slash and other material in which insects 

 find favorable conditions for breeding. 



Insects breed in all parts of the slash but particularly in 

 the larger sized portions. The stumps of felled trees, trees 

 windthrown or broken by snow and standing trees in un- 

 healthy condition, offer good breeding places. Trees already 

 infested with insects but not taken in a logging operation 

 require treatment. 



