72 ENTOMOLOGICAL SOCIETY OF ONTARIO. 



bark beetles, which, aided by timber beetles, not only cause the death of trees, but so 

 damage the wood and hasten its decay that the timber soon becomes worthless, and in 

 this country proves almost a total loss. 



The destructive species of Scolytids may be divided into two classes, one class, 

 including only a limited number, makes the primary attack, or prefers to enter the bark, 

 roots and wood of living trees and other plants. The other class has a preference for 

 injured, unhealthy, or felled treef*, etc., the bark and wood of which these insects infest 

 for the purpose of ^perpetuating their species. The first is primarily to blame for causing 

 the death of trees, or at least a diseased condition, while the second is responsible for the 

 death 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 

 destruction depending more than anything else perhaps upon their numbers. 



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 ir, it must not onlj'^ infest a vital 

 part, but must occur in sufficient numbers to overcome all resistance. 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 is 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 

 ofiered by vigorous, healthy trees, without the assistance of numerous species of Scolytids 

 and other insects which always come as reenforcements 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 contributing 

 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 dollars 

 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 to 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 number of those making the primary attack can 

 be reduced belov/ their power of causing a diseased condition 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, inv&sions 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 primary attack, and become as familiar as 

 possible with its life history and habits, as well as the life history and habits of other 

 species co-operating with it, and also study other causes which might eontribute to or 

 oppose the progress of their destructive work. 



In the consideration of preventive measures against invasions of Scolytids, we must 

 study the habits of the diff^erent species of the family in order to ascertain which of them 

 are capable of causing diseased conditions of trees, or through increased numbers, their 

 death. 



During an investigation of serious trouble caused by these inseets in our state, I have 

 given special attention to these subjects. After discovering the species to blame for the 



