970 
Journal of Agricultural Research 
Voi. XXIII, No. x2 
LIFE HISTORY OF APHIS POMI 
The green apple aphis passes the winter in the egg stage. The eggs 
are placed on the bark of the water sprouts and other terminal growths 
of apple and frequently occur grouped in immense numbers. With the 
unfolding of the buds in the spring, these eggs hatch, and the tiny nymphs 
migrate to the newly developed foliage. 
These “stem mothers’* and the succeeding generations feed upon the 
succulent foliage of apple throughout the summer. There is no migra¬ 
tion to alternate food plants as there is with many species of aphids, and 
the winged forms which are produced serve merely to disseminate the 
species. . 
Reproduction throughout spring and summer is entirely viviparous 
and parthenogenetic. With the approach of fall, males and oviparous 
females are produced, and the over-wintering eggs are deposited. 
There are a variable number of generations during the season, depend¬ 
ing upon environmental conditions. 
methods employed 
This work has been entirely in the nature of a field study, and no at¬ 
tempt was made to modify or control the conditions of temperature or 
moisture. 
The experimental plot was located on the college farm at Corvallis, 
Oreg., about one mile from the Agricultural Building and had an eleva¬ 
tion of approximately 225 feet above sea level. This plot consisted of 
1- and 2-year-old Greening apple trees planted in two rows about 4 feet 
apart with the trees about 3 feet apart in the rows. To the westward 
about 60 to 75 feet distant there was a dense growth of alders along the 
banks of Oak Creek. These trees, being some 35 feet in height, served 
to break the force of the strong, westerly “sea breezes” prevalent during 
the summer months. 
As the aphid eggs hatched, numbers of the nymphs were transferred to 
suitable buds on the experimental trees and here allowed to mature. In 
obtaining nymphs of the later generations, a number of adults would be 
placed on a suitable aphis-free leaf cluster. The following day these 
adults were removed, and the nymphs bom during the 24-hour period 
were allowed to remain. These nymphs were permitted to mature in 
order to obtain the length of the developmental period. The develop¬ 
mental period was reckoned from the day after birth till the day of the 
appearance of the first young, inclusive. 
The trees upon which the experiments were being conducted were 
protected by a special type of cage (fig. 1). This consisted of a cylinder 
of galvanized wire cloth, open at one end. To the open end of this cage 
was attached a cheesecloth skirt. The cage was inverted over the tree, 
and held in position at the proper height by means of a stake set near by. 
The cheesecloth skirt was gathered about the trunk of the tree and tied 
with a cord. A band of cotton batting placed at the proper height on 
the tree rendered a perfect fit between the cloth skirt and the tree, and 
prevented binding of the trunk from the tie-cord. This type of cage is 
easily removed for examination of the aphids, is as readily replaced, and 
has proved quite satisfactory for this work. 
