212 GEOLOGICAIv SURVEY OF NEW JERSEY. 



enter healthy wood, in which, while they may not be able to 

 breed, they may be able to set up a condition of affairs that will 

 afford a proper home for a subsequent horde. 



Meanwhile, further from the injury, but affected by it be- 

 cause of a lessening or interruption of the flow of sap, flat- 

 headed borers have gained a foot-hold. They have begun 

 to form shallow chambers in the sap wood, in which they live 

 one, two or three years, constantly enlarging their field of 

 operations and driving galleries that further interrupt the flow 

 of sap until they are ready to pupate. Then they bore a short 

 distance into the trunk, lie dormant in the pupal stage for a 

 shorter or longer period and finally emerge as adults, ready to 

 reproduce their kind, preferring the tree they themselves fed 

 upon for purposes of oviposition, if it is at all suitable. As a 

 result dozens of galleries replace the few, water gains further 

 entrance here and there and cavities beneath the bark become 

 obvious. These afford shelter to a large series of species that do 

 not directly injure the tree, but by bringing in excrementitious 

 matter favor the development of decay germs. Fermentation 

 sets in, and a host of flies and sap beetles are on hand at once to 

 further the disintegration of wood fibre. Finally a sheet of bark 

 becomes loosened and falls ; then come another lot of borers 

 into the heart-wood : Scolytids or shot-hole borers, round-headed 

 borers, boring caterpillars, goat-moths or Sessiids, and in some 

 instances ants or Termites, though these usually come when 

 the fate of the tree is finally sealed. 



Of course, the progress of the insect attack is slow or rapid, 

 in proportion to the extent of the original injury. If the injury 

 was at all extensive, as a scorching of one side for several feet, 

 two or three years will suffice to doom the tree and place it in 

 control of the scavengers whose duty it is to reduce it to dust. 

 If it was limited, several years may be required, assuming that 

 the tree does not succeed in scarring over the original wound. 



As the trunk becomes the object of primary attack when the 

 injury starts there, the effect on the crown may not be immedi- 

 ately noticeable. But any serious interruption to the flow of sap 

 is bound to have an effect on the area that should be supplied 

 through the injured tract, and at once the insects mark the 

 weakness. Twig borers enter at the tips and kill the young 



