!UJ 



THE OTTAWA NATURALIST 



VOL. XXX. OTTAWA, JUNE-JULY, 1916 Xos. 3 and 4 

 AMERICAN INSECT GALLS. 



By E. P. Felt, Albany, N.Y. 



American gall insects constitute an exceedingly interesting 

 assemblage, representing at least five of the larger, and better 

 known orders. It is worthy of note that by far the greater 

 majority of plant galls are produced by members of the dip- 

 terous family, Itonididae, and the hymenopterous family, 

 Cynipidae. Of approximately one thousand insect galls listed, 

 members of the above mentioned groups are responsible for 

 over 90% (nearly 95%), with two pecies of the delicate gall 

 midges producing deformations to every one of the relatively 

 better known gall wasps. The plant lice or aphids come next 

 in the number of species, though they would be outranked if 

 the gall mites, the Eriophyidas, were included in this discussion. 

 The other gall-making Diptera, Hymenoptera, and the Hemip- 

 tera and the gall-making Coleoptera and Lepidoptera are, 

 numerically speaking, of comparatively little importance. 



The numerous gall midges show a diversity of taste not 

 evidenced among the gall wasps. The more than 600 galls pro- 

 duced by the midges occur on plants belonging to 69 botanical 

 families and 202 genera. There is no such specialization, as 

 we shall see later, in the Cynipidae. The larvae of 60 species 

 of midges live at the expense of the Salicaceae; 48 of these are 

 found on Salix; 28 occur tipon the Jtiglandaceae, all but one 

 infesting Carya; 3 7 attack the Fagaceae (31 of these being upon 

 Quercus) ; 52 species produce galls on the Rosacea?, 23 on the 

 Leguminoseae, 18 upon the Vitaceae, and 12 5 on the Compositae. 

 The most obvious concentration of species, aside from those 

 mentioned above, is the 41 species reared from solidago and 

 the 20 to be found upon aster. These figures are approximate, 

 yet taken in connection with the great dive -sity in the structure 

 of these small insect , indicate that this group has been able 

 to maintain itself upon a great many different plants through 

 a considerable physiological adaptability, and that the dis- 

 tinctness of the species has been established by relatively small 

 modifications in structure. 



