718 RosBert MATHESON 
Many opinions have been offered by various workers on the causes or 
factors that influence the production of winged forms in aphids. So 
far all these offerings are mere opinions, one of the most favored being 
the crowding of the insects on the food plant and the consequent reduction 
of the food supply. In all the writer’s work of rearing thousands of indi- 
viduals, crowding was eliminated and yet the percentage of winged forms 
for any one generation did not seem to vary. The question of the pro- 
duction of winged forms in aphids is one deserving deeper study than has 
yet been devoted to it, and the results might prove of great economic 
importance. 
Food plants 
The green apple aphis is very restricted in its host plants, being confined 
to a few very closely related forms. The author has found the species 
on the following food plants: apple (Pyrus malus L.), pear (Pyrus com- 
munis L.), American crab (Pyrus coronaria L.), mountain ash (Pyrus 
americana Marsh and P. aucuparia L.), hawthorn (Crataegus oxyacantha 
L. and other species of Crataegus), and quince (Cydonia spp.). 
Of these food plants the apple is the one most generally attacked and 
injured. Some varieties of apples are more susceptible than others, and 
from the writer’s observations the following appear to be the most sus- 
ceptible to injury: Twenty Ounce, Maiden Blush, King, Fall Pippin, 
Greening, and Baldwin. 
THE ROSY APPLE APHIS 
(A phis sorbt Kaltenbach) 
Altho the species Aphis sorbi was recognized at an early date (1854) 
by Fitch under the name Aphis malifoliae, yet, like Aphis pomz and 
Aphis avenae, it has been and still is greatly confused in the literature. 
Its characteristic work on the apple, and its bionomics, are very different 
from those of either of the other two species named, and had a serious 
study been made of its life economy all this confusion would have been 
avoided. Recently two rather extensive papers on the species have 
been published, so that its work, life history, and distribution are now 
becoming well known. The present paper is based on extensive rearing 
experiments made at Ithaca during the seasons of 1914, 1915, and 1916, 
and the manuscript was practically completed before the publication of 
the reports of Brittain (1915 b) and Baker and Turner (1916 b). 
