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second is responsible for thedeath of the diseased ones and for causing 
the premature decay of the wood. All bark and timber beetles are, 
therefore, more or less destructive in their habits, their power of de- 
struction depending more than anything else perhaps upon their num- 
bers. 
Nature has provided plant life with the power, to a certain extent, 
of resisting the attack of enemies and with natural means of healing 
wounds, recovering from disease, and other injuries occasioned by 
severe drought, cold, etc. Therefore, in order for a single species of 
insect enemy of a tree to attack and kill it it must not only infest a 
vital part, but must occur in sufficient numbers to overcome all resist- 
ance. This is especially the case with destructive Scolytids, which, to 
accomplish this end, must enter the bark or wood of living trees, where 
they meet with the flowing sap, which offers the greatest resistance and 
most difficult to overcome. Therefore, no single species of Scolytid 
bark beetle can cause the death of large or small forest trees unless 
occurring in immense swarms. In fact, it is doubtful if any single 
species could overcome the resistance thus offered by vigorous, healthy 
trees without the assistance of numerous species of Scolytids and other 
insects which always come as reénforcements after the first attack is 
made. Hence, to cause a widespread devastation of timber, numerous 
species must work in concert. One species makes the primary attack 
and causes at once an unhealthy condition of the bark and tree. This 
diseased condition, if ever so slight, attracts other species to the affected 
tree. One or more kinds will attack the bark and wood at the base, 
others attack the bark at different points on the trunk, others infest the 
large and small branches, while still others enter the bark and wood of — 
the terminal twigs, until the infested trees may be the hosts of twenty- 
five to forty species of Scolytids, each aiding the other in making the 
conditions favorable for the perpetuation of their species, and all con- 
tributing to the death and premature decay of their host. 
Thus, through certain favorable conditions (the increased numbers 
of the species which are capable of existing in the green bark of living 
trees being the most favorable), an invasion may be started which in a 
few years results in the loss of millions of dollar’s worth of property. 
The fact that the primary attack of one species makes the conditions 
favorable for the increase of others, which in turn contribute te the 
increase of the first, is an important feature to be considered, in our 
effort to discover methods of checking or preventing the ravages of 
this class of insects. If the numbers of those making the primary 
attack can be reduced below their power of causing a diseased condi- 
tion of the trees, the trouble of which they are the primary cause must 
end. If, on the other hand, their undue increase can be prevented, — 
invasions by them can not occur. 
Thus, it is evident that, before considering a remedy against an — 
Invasion of Scolytids, we must discover the species to blame for the pri- 
