REPORT OF THE SOCIETY 63 



in a great struggle. Directly or indirectly man suffers from their attacks. On 

 the one hand, lice, fleas and some mites live as real parasites upon man; flies, 

 mosquitoes and other unwelcome guests of our dwellings carry germs of infective 

 diseases. On the other hand, everything that is useful or necessary to man 

 suffers from continual attacks from scores of insects; animals reared for his 

 living or help live under perpetual menace of attack; vegetables, cereals and 

 iruits so indispensable to life, trees giving beauty, shade and various products, in 

 a word, all plants seem to be choice dishes for noxious insects. Damages run 

 up into millions of dollars yearly in this province alone. 



A study of the noxious insects of plants would be a long and arduous task and 

 would over-run the limits of this paper. In fact it would be a long task to review 

 "the insects injurious to trees, therefore we will attempt only to outline the life 

 histories of the more important injurious species on shade trees. 



Insects naturally fall into two groups — external and internal feeders. The 

 external feeders ijiclude caterpillars, plant lice and scale insects. Norwithstand- 

 ing appearances insects of this group are not, generally speaking, the most dan- 

 gerous enemies of trees. Even if a tree be defoliated it possesses the power of 

 recuperation and, in nearly every case, will succeed in putting out new leaves, 

 sooner or later according to its power of resistance, without much appreciable 

 loss. It is quite rare to find a maple, an elm, a poplar or an oak die immediately 

 after the premature disappearance of its leaves due to animal agency. Death 

 follows only after intensive defoliation for three or four years in succession. 

 How^ever, scourges of insects and caterpillars manifest themselves usually with 

 virulence only for three years and return periodically every eight, ten, twelve or 

 fifteen years, or more frequently according to the species. Between two conse- 

 cutive attaks where there has been much damage, the depredations of a leaf- 

 eating insect can be represented by a curve, the highest points being the years of 

 the epidemic, gradually becoming lower to the minimum which would coincide 

 with the middle period of control, and gradually ascending again little by little; 

 the natural enemies of the insects aiding artificial agents tend to combat them. 

 The tree will then show every chance of surviving the assaults of the insect 

 and of returning to the condition before it was attacked. 



Like resistance is not met with among the resin producing trees — which 

 generally show a very great susceptibility. This is due to their inability to 

 make rapidly new foliage, little accustomed to annual renewals and to a physiolo- 

 gical weakness belonging to an organism incapable of recovering from agencies 

 that make for a lessening of its power. Even with essential oils conifers de- 

 prived of foliage show this characteristic weakness. One example will suffice. 

 Canada balsam was practically wanting in our province at the close of the last 

 century — caused by the repeated ravages of the Larch Saw Fly (Nematus Erich- 

 ^onii). Its migration westward is due to a scarcity of victims rather than a 

 pronounced desire for adventures. 



This introduction, dealing with a few examples of leaf eaters is a little long, 

 nevertheless necessary. I shall confine myself to the species which have ac- 



