518 
Journal o f Agricultural Research 
Vo\ XXX, No. 6 
INOCULATIONS WITH APHIS 
ABBREYIATA 
Three genera of aphids have been 
found on potatoes in northeastern 
Maine, represented by Macrosiphum 
solanifolii Ashmead, Myzus persicae 
Sulz., and Aphis abbreviata Patch. 16 
It is well known from previous studies 
by the writers and others that Macro¬ 
siphum solanifolii and Myzus persicae 
transmit virus diseases of the potato 
and other cultivated plants. 17 Aphis 
abbreviata feeds very generally on the 
lower leaves of the potato. By color, 
size, and shape it can be distinguished 
readily from the other species when on 
potatoes. Since Aphis abbreviata has 
been observed on potato plants barely 
12 cm. high, it is apparent that it may 
sometimes be present before it is pos¬ 
sible to eliminate diseased plants even 
in the first roguing. 
During 1923 when Aphis abbreviata 
appeared to be especially numerous in 
comparison with previous years and in 
comparison with the other species, in¬ 
oculation experiments with this species 
were begun. Since the overwintering 
host of Aphis abbreviata was not yet 
definitely known, colonies from potato 
foliage were used for inoculations. 
This procedure resulted unfortunately 
in the introduction of a few individuals 
of Macrosiphum solanifolii , so that the 
positive results with Aphis abbreviata 
in field cages in the first test were not 
conclusive. 
However, later in the season pure 
Aphis abbreviata colonies were secured 
from E. M. Patch, as well as from 
isolation cultures in field insect cages. 
After these aphids colonized on mild 
mosaic caged Green Mountain plants 
for a few weeks, about 300 of them 
were transferred to each of three caged 
healthy Green Mountain hills when the 
plants were about 30 cm. high. At the 
same time transfers from the same 
colony were made to sprouts of three 
healthy Green Mountain half tubers. 
The lateness of the season apparently 
prevented sufficient additional foliage 
growth for the appearance of current- 
season symptoms in the cages. How¬ 
ever, in the greenhouse second genera¬ 
tion plants from a tuber from each of 
the three caged hills showed mild 
mosaic throughout the plants. The 
control plants from the three sister 
tuber progeny were healthy. Of the 
plants grown from three sprouted half 
tubers inoculated with Aphis abbreviata 
from mild mosaic Green Mountain 
plants, two developed mild mosaic 
when about 20 cm. high, while the 
corresponding half-tuber controls, from 
the same tubers as the inoculated 
plants, remained healthy. 
NATURAL SPREAD OF MOSAIC WITH 
CURRENT-SEASON SYMPTOMS 
In 1923 colonies of apterous Aphis 
abbreviata appeared somewhat earlier 
and in greater numbers than those of 
the other species on the disease-propa¬ 
gating plot, the first colonies being ob¬ 
served when the potato plants were 
scarcely 12 cm. above ground. Follow¬ 
ing this, current-season rugose mosaic 
symptoms (pi. 9, A) appeared in 
healthy stock in rows near or adjacent 
to rows of diseased plants. This is 
shown diagrammatically in Figure 1. 
In section W-l, 60 per cent of the four- 
hill tuber units and 23 per cent of the 
hills in the first row (16) on the north 
of three rugose mosaic rows (13-15) 
were rugose mosaic in the upper leaves 
of part or of all of the shoots by July 31. 
The disease also spread to the first row 
on the south and to the second row on the 
north with similar current-season effects 
but to a less extent. The difference 
between the two adjoining rows on the 
north and south indicates transmission 
by insects rather than by root contact. 
Patch, E. M. the buckthorn aphid. Me. Agr. Exp. Sta. Bui. 317: 29-52, illus. 1924. 
17 Schultz,. E. S., and Folsom, D. Op. cit. 
EXPLANATORY LEGEND FOR PLATE 8 
A. —Frame and completed insect cage suitable for 3 potato hills. The cloth is in two pieces, one cov¬ 
ering the four sides and the other across the top with an overlap in the middle and a slit in the center cut at 
right angles to the overlap 
B. —Insect cages used in 1923, each covering 3 potato hills. The top opening (A) facilitates the proper care 
of a large number of cages. The arrangement shown permits the inclusion of the maximum number of 
hills possible with the available light 
C. —Green Mountain tuber unit showing delayed symptoms of rugose mosaic after perpetuation of the 
disease by the seed tuber. The parent hill was partly diseased. This tuber unit appeared healthy on 
July 6, 1923, when other tuber units were obviously rugose mosaic (D), but the apparently healthy leaves 
developed spotting, streaking, and leaf-dropping, and the upper leaves showed typical rugose mosaic 
symptoms throughout by July 30 when this photograph was taken 
D. —Green Mountain tuber unit completely rugose mosaic. This tuber unit was planted next to that 
of C in the same row, and was evidently diseased on July 6 when the other was still healthy. Note the 
greater dwarfing and the absence of leaf-dropping. Photographed on July 30, 1923, to the same scale 
as for D 
