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Insects of Shade Trees and Their Control. 53 
row or by feeding on the sap, depending on whether they feed in the 
dead wood or in the sapwood. Their injury to shade trees is along 
two directions: (1) When their burrows do not kill the tree or limb, 
they admit, on the body of the boring insect or in the moisture that 
penetrates their excavations, diseases which rot and ultimately dis- 
able or kill it: (2) when their burrows in that life-giving layer 
located between the bark and wood extend around the limb or tree, 
the circulation of sap between roots and leaves is arrested and death 
ensues quickly. In the case of timber the burrows also reduce in 
grade the lumber cut from it or make it. entirely worthless. More- 
over, the work of these insects is hidden from view, so that too often 
it is discovered when it is too late to save the tree. For these several 
reasons the presence of borers in trees is particularly dangerous and 
must be guarded against most carefully. 
Because they feed and live most of their lives out of sight they 
are beyond reach of the usual poison or contact insecticides. The 
use of certain preparations, like poisoned miscible oil or kerosene 
emulsion or carbon disulphid, as will be pointed out under the re- 
spective insects, is practicable in a few instances. In the majority 
of cases, however, the healthy trees can be saved only by opportune 
sacrificing of those that are badly infested, or, in some cases, by 
sstimulating the growth and well-being of those just invaded by these 
insects. Protection of shade trees from boring insects rests, there- 
fore, almost wholly on preventive measures. Trees well nourished, 
protected from all manner of injury, and otherwise well cared for 
are more nearly immune to attack by boring insects than those not 
so cared for. In a neighborhood, community, grove, or park where 
a majority of the individuals of a given borer are destroyed the re- 
maining trees will successfully resist attack and be saved thereby. 
SUGAR-MAPLE BORER.* 
How injurious.—In some sections of the country, especially along 
roadsides in New York State, the sugar-maple borer is regarded as 
the most serious enemy of this tree. It attacks trees in full vigor, 
killing large limbs and entire trees. The serious damage is done by 
the grubs, especially when their burrows meet so as to girdle the tree 
or limb. 
Signs of borer presence.—When the borer is present the trees show 
dead limbs here and there; ridges and dead spots appear on the bark 
(fig. 38, 7, 7a), or naked scars on the branches and trunk. especially 
near the base of the larger limbs, sometimes with oval holes three- 
eighths to five-eighths inch in diameter, and “sawdust ” (fig. 33, 6) at 
°8 Plagionotus speciosus Say. 
