A STUDY OF THE PLANT LICE 
INJURING THE FOLIAGE AND FRUIT OF THE APPLE 
RosBEeERT MATHESON 
Three specie~ of plant lice — the green apple aphis, Aphis pomi De Geer 
(Aphis mali Fabricius), the rosy apple aphis, Aphis sorbt Kaltenbach, and 
the grain, oat, or apple-bud aphis, Aphis avenae Fabricius — are frequently 
very injurious to the foliage and fruit of apple. Of the three species the 
green apple aphis is undoubtedly the most common and widespread, doing 
considerable injury every year not only in bearing orchards but also in 
young orchards recently set and in nurseries. The greater amount of 
injury wrought by this species is due to the fact that it remains on the 
apple tree thruout the season, whereas the rosy aphis and the apple-bud 
aphis, or grain aphis, migrate in May, June, and early July to other host 
plants. In recent years the rosy aphis has also become very injurious 
and it now probably does as much damage in bearing orchards as does 
the green aphis, if not more. 
DISTINGUISHING CHARACTERS OF THE THREE SPECIES OF APHIDS 
The three common aphids on the apple can be readily separated in 
all the stages of their complicated life histories. From the standpoint 
of the grower it is most essential that he recognize the species as soon 
as they appear in the spring. The first nymphal stages of the stem mothers 
can be separated readily both on color markings and on structural char- 
acters. These characters may be tabulated as follows: 
Species Color Structural characters 
Aphis pomi DeG..... Dark apple green.......... Cornicles cylindrical, about as long as 
a body segment; unguis equal to 
one-half length of segment. 
Aphis sorbi Kalt...... Dark green, with a double] Cornicles long, cylindrical, flanged at 
row of black spots down| tip; unguis distinctly twice as long 
the dorsum; sides with dis-| as base of last segment. 
tinct white pulverulence. 
Aphis avenae Fabr.....| Dark yellowish green...... Cornicles very short, tuberculate: 
unguis distinctly longer than one- 
half of segment. 
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