ST P A
September 1942 E-577
I MR[AU OF
THE SUGAR-BEET ROOT APHID AND SUGGESTIONS
TO AID IN CONTROLLING IT IN CALIFORNIA
By M. F. Bowen, Division of Truck Crop and Garden Insect Investigations
The sugar-beet root aphid, or root louse, (Pemphigus betae Doane)
is a serious pest of sugar beets in California and other sugar-beet-growing
areas of the Western part of the United States. In the central valley area
of California the damage appears to be most prevalent in the peat soil of
the islands of the south delta of the Sacramento River, but beets grown
in other parts of the State also have suffered severe injury in some years.
Nature of Injury
The beet root aphid, or root louse, as it commonly appears on the
roots of sugar beets and other plants, is a small, wingless, yellowish-
white aphid, which feeds almost entirely on the underground parts of the
plants. Occasionally during the winter months aerial colonies have been
observed on the leaves of beets growing in the greenhouse, but this departure
from the normal subterranean habitat is unusual. Like other aphids, it
feeds by piercing the plant tissues with its beaklike mouth parts and
sucking the plant juices. The feeding causes a general weakening of the
plant that results in a decrease in the yield per acre and also causes a
reduction in the sugar content of the beet. Yellowing of the plant and
wilting of the leaves often accompany heavy infestation by this insect.
These symptoms, however, are not reliable indications of root-aphid damage,
inasmuch as nematodes, and various diseases, such as southern sclerotium
rot, also cause the plant to wilt, and yellowing of the leaves may be
induced by excessive irrigation, by curly-top disease, or by a nitrogen
deficiency in the soil. Therefore the only certain method of recognizing
root-aphid damage is to examine the roots of the plants. The presence of
root aphids is readily determined by the appearance of a bluish-white
moldlike substance on the roots of the beets and in the surrounding soil.
This substance is secreted by the insect, and the abundance of it is a fair
indicator of the severity of the infestation.
Aphid populations in beet fields are relatively light during the
spring and early summer, but under favorable conditions enormous numbers
may develop before fall. As many as 200 "lice" per square inch have been
observed by the middle of October on beets where the infestation was excep-
tionally heavy. Frequently the infestation is spotted, and in some fields
these spots can readily be distinguished by a yellowish cast in the leaves
of the infested plants that contrasts with the darker green of the rest of
Under field conditions the root aphid seldom kills the plant upon
which it fees, the injury being more of the nature of stunting or retarding
the growth of the plants. However, potted beets at the laboratory have
been killed by this insect. In such cases the leaves wilt as though the
plant were suffering from lack of water, the roots become shrunken and
flaccid, and eventually the whole plant dies.
The life cycle of the sugar-beet root aphid, like that of most aphids,
is very complex, involving sexual and asexual reproduction and the develop-
ment of winged and wingless forms of the mature insect. Different parts
of the life cycle are completed on different host plants.
The life cycle of this insect in California is not yet fully under-
stood. A brief summary of its life history, as worked out by Parker (3) in
Montana, follows: The winter is passed chiefly in the egg stage on poplar,
although some wingless females successfully overwinter in the soil. The
eggs hatch in the spring, and the young aphids develop into wingless females
(stem mothers), each of which gives birth to many living young, in a gall
formed on the under side of the leaves of poplar (primary host). The young
of the stem mothers develop into winged females (spring migrants), which
emerge from the gall and fly to the beet fields, where they deposit young.
Sugar beets and other plants (secondary hosts) are infested during the flight
from poplar. Several generations of wingless females are produced on the
roots of beets during the summer. In the fall some of the aphids on the
beets develop wings (fall migrants). These winged females return to the
poplars, on which they deposit tiny males and females, which are the true
sexual stage in the life cycle of the root aphid. The males and females
mate, and the latter lay fertilized eggs on poplar, thus completing the life
The poplars Populus balsamifera L. and Populus angustifolia James
serve as pri.ary hosts throughout their range, but neither of these trees
is known to grow in the central valley of California. Other species of
poplar, however, are common in this area.
Under the climatic and host-plant conditions of central California,
it seems highly probable that the life cycle of the root aphid may differ
from that given above. General observations in 1940 and 1941 have shown
thait it may survive and reproduce asexually throughout the year on the
roots of dock and sugar beets without the formation of a sexual generation.
However, in the fall of both years winged forms developed on the roots of
beets late in October and in November, and these apparently migrated from
the beet fields into the canyons and foothills on the west side of the
San Joaquin Valley, where they were found on cottonwood-poplar and willow.
The winged aphids on beets, and also those captured on willow and cottonwood,
were determined by E. 0. Essig, of the University of California, as PePhigu
betae Doane. This strongly suggests that cottonwood-poplar, willow, or some
other primary host may be involved in the life history of this species in
California, although, as stated previously, such hosts may not be necessary
to maintain the species. Experiments are planned to determine the possible
role of primary hosts in California, Winged females have been observed
to emerge early in April in cages placed over infested dock. Under condi-
tions that obtain in California, the production of winged forms on dock and
sugar beets could serve to facilitate the spread of this species to its wild
host plants as well as to sugar beets, without a spring movement from poplars
such as occurs in Montana (3), Utah and Colorado (2), where the winters are
longer and much colder than in California.
The sugar-beet root aphid feeds on the underground parts of a wide
variety of plants. Essig (1) gives the following list of food plants:
Alfalfa, aster, beets, docks, flax, many wild grasses, goldenrod, knotweed,
lambsquarters, poverty weed, wheat, and yarrow. With further study of this
insect it is likely that other hosts will be found.
Undoubtedly the most important damage to cultivated crops occurs
on the sugar beet, which is a favored host. Several species of perennial
dock (Rum ex spp.) are perhaps the most important of the wild host plants
in the central valley of California. These plants are widely distributed
and generally infested by the root aphid, which survives and asexually
reproduces on them from year to year.
No completely satisfactory control for the sugar-beet root aphid
is known. Since it is a subterranean insect, control by chemical methods
is difficult or impracticable at the present time. Cultural methods of
control seem to offer the greatest promise. Observations made in 1940 and
1941 in the island section of the south delta of the Sacramento River indi-
cate that the aphid causes more injury to beets following beets than where
beets follow potatoes, wheat, barley, corn, beans, tomatoes, or other crops.
Table 1 gives the percentage of infested fields on land planted to beets
1 year as compared with the percentage of infested fields on land planted
to beets 2 or more years in succession. It also gives the average percentage
of infested plants found in the infested fields of the two rotation classi-
fications for the years 1940 and 1941.
Table 1.-Fields and plants infested by the sugar-beet root aphid on land
planted to beets 1 year as compared with those infested on land planted
to beets 2 or more successive years
Infested fields on land Infested plants in infested
Year planted to beets fields planted to beets
1 year 2 years or more 1 year 2 years or more
Percent Percent Percent Percent
1940 29 88 32 73
1941 ** 27 92 18 34
Figures based on the examination of 15 plants in each of 22
* Figures based on the examination of 50 plants in each of 48
The foregoing figures show that 1-year fields are less likely to be
infested than are 2-year fields. It should be noted that the figures
relating to infested fields for the 2 years are not comparable because
a larger number of plants per field were examined in 1941 than in 1940.
it is likely that all fields are infested to some extent, the root aphid
just being so scarce in some that it was not found in the sample.
Although the infestation was heavier in 1940 than in 1941, the data
for both years indicate that infested fields were found about three times
as often on land where beets followed beets in the rotation as on land where
beets followed some other crop. The data for both years also show that the
root aphid was approximately twice as prevalent in the infested 2-year
fields as it was in the infested 1-year fields.
The following cultural practices are recommended as aids in control-
ling the damage caused by the root aphid:
(1) Arrange so that beets do not follow beets in the crop rotation.
This is good farm practice for reasons other than the smaller amount of
aphid damage in 1-year fields.
(2) Avoid planting beets on land where dock (Rumex sp.) was abundant
the previous year. Dense stands of dock infested by the root aphid have
been observed growing in grass land and pastures and in fields of alfalfa.
Even when such land is plowed in the fall, the root aphid will survive on
the fleshy roots of the dock and infest beets when they are planted.
(3) Confine livestock in fields after harvest to clean up the old
beets remaining in the field. This is practiced by some growers, and has
the advantage of utilizing a valuable source of feed, besides removing plants
upon which the root aphid lives during the winter.
(4) Plow the land and keep it free from weeds and grasses by thorough
cultivation at intervals for several weeks prior to planting.
(5) Kill dock plants along road sides, ditch banks, canal levees,
fence rows, and other waste, abandoned, or uncultivated areas that may
serve as outside sources of infestations in beet fields.
It is emphasized that the foregoing recommendations apply only to
the central valley of California and other areas where similar conditions
prevail. They are not applicable to areas where the winters are long and
cold, and where "lice" overwintering in the soil are considered a very
minor source of infestation compared with the flight of winged aphids from
poplars to sugar beets that occurs in the spring.
Some information now available suggests that the time of preparing
the seed bed in the spring, or the time of planting, may affect the amount
of damage caused by the root aphid, but these and other possible aids to
control must await further investigation before definite recommendations
concerning them can be made.
(1) Essig, E. 0.
1926. Insects of western North America. The Macmillan Co. 1035 pp.,
, illus. (See p. 261.)
(2) Maxson, A. C., and Knowlton, G. F.
1929. The Tribe Pemphigini (Aphididae) in Utah. Ent. Soc. Amer. Ann.
22: 251-271, illus.
(3) Parker, J. R.
1914. The life history of the sugar-beet root-louse (Pemhigus betae
Doane). Jour. Econ. Ent. 7: 136-141.
UNIVERSITY OF FLORIDA
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