56 REPORT OF No. 19 



beneath the trees was covered with the old droppings from the caterpillars. 

 This plantation has been repeatedly sprayed in previous years, but the in- 

 sect is very far from being exterminated. Its ravages in the Province of 

 Quebec are graphically described by Dr. Fyles in another part of this Ee- 

 port. 



Spittle insects (Aphrophora) were abundant this summer on some 

 Scotch Firs and also upon grass in pasture fields — no doubt different species. 

 The masses of white froth, resembling spittle, were very conspicuous, each 

 one containing the strange larva which produces it. The adult bugs were 

 to be found in numbers on the Fir trees later in the summer. ■ No serious 

 damage was done in either case, though no doubt an extensive attack must 

 reduce the vitality of a tree, and in a pasture the presence of the frothy 

 masses would be very distasteful to the feeding cattle. 



The Fall Web-worm was very abundant again this year. It is so con- 

 spicuous and so easily got rid of, a whole colony at a time, that there is 

 surely no excuse for its increase and prevalence. The very unsightliness of 

 the webs, with their foul masses of excrement and cast-off caterpillar skins, 

 ought to be enough to cause every one with a spark of tidiness in his com- 

 position to clear at least his own trees and induce his neighbors to follow his 

 example. 



INSECT GALLS OF ONTARIO.* 

 By Tennyson T). Jarvis, Ontario Agricultural College, Guelph 



I am under obligations to numerous friends and correspondents who 

 have aided me in this work. I am especially indebted to Mr. W. R, Thomp- 

 son, 0. A. College, for the assistance he has rendered in the preparation of 

 this work. I am under obligations to the Department of Entomology, Wash- 

 ington, D.C., Dr. Bethune, Dr. Fletcher, Prof. Lochhead, Mr. J. Eaton 

 Howitt, Mr. C. W. Nash and Mr. Douglas Weir for the assistance they have 

 given me. 



Among the many curious phases of insect life, and among the many 

 wonderful illustrations of the effects of evolution upon organized structure."* 

 with which we meet in the study of entomology, there are few examples 

 which present such varied and interesting peculiarities of structure and de- 

 velopment as do insect galls. Varying as they do from such simple mal- 

 formations as the curled leaves produced by the work of aphids to such 

 beautiful and complex structures as the oak-apples and oak twig-galls, they 

 present a succession of types which show in a peculiar and wonderful manner 

 the changes in structure of insect and plant induced in the struggle for 

 existence. A gall may be briefly defined as a malformation of plant tissuo 

 induced by mechanical or chemical stimulus or by some other unknown 

 cause. These are sometimes produced by fungus, but those with which we 

 have to deal are produced in different ways by the work of insects. The habit 

 of gall-making seems to have arisen at different times and in entirely differ* 

 ent orders and families of insects, and even a branch of the order Acarina 

 has acquired this gall-making habit. In each case, however, it has developed 

 along lines which depend directly upon the structure of the insect, so that 

 in many cases the classification of the insect can be considerably simplified 

 by an examination of the gall. For instance, the Cecidomyiid, having an 

 ovipositor incapable of piercing, lays its eggs upon the surface of the leaf, 



* See plates at beginning of volume. 



