264 PROTECTION AGAINST INSECTS 



Seed crops are sometimes destroyed by insects working in 

 the cones and seeds. This was the case with the Norway 

 pine seed crop in 191 9, throughout northern New York. 

 Insects interfere with the growing of plant material in nur- 

 series; they may destroy reproduction starting on cutover 

 areas. Numerous species prey on the young and middle- 

 aged stands and are a constant source of annoyance and 

 expense to the forester in producing forest crops. In stands 

 approaching maturity epidemics are Hkely to develop which 

 may destroy the entire stand. 



Every part of the tree has its insect enemies and each 

 species of tree is likely to be attacked by distinct species. 



Insects are classed by Furst ^ on the basis of the part of the 

 tree attacked into : 



Boring insects, which bore into the bark, cambium layer, 



sapwood, heartwood and pith. 

 DefoHating insects, which destroy foHage. 

 Root destroying insects. 

 Bud destroying insects. 

 Seed destroying insects. 

 Insects which produce deformities or malformation. 



Each insect is hkely to prefer or be restricted in its attack 

 to trees of a certain age; either pre3dng upon young repro- 

 duction, upon sapHngs and poles, or upon mature individuals. 



The injury inflicted may be of a physiological or of a tech- 

 nical nature.^ Under the former come injuries such as de- 

 foHation and girdhng which interfere directly with the physi- 

 ological Hfe processes of the tree; while under the latter are 

 included injuries such as those by wood boring insects, which 

 may ruin or reduce the value of the tree for commercial prod- 

 ucts but which do not interfere directly with its growth. 



Insect epidemics are of more common occurrence and of 



