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Contribution from the Bureau of Entomology
L. O. HOWARD, Chief

PROFESSIONAL PAPER

April 28, ‘1919

LIFE HISTORY AND HABITS OF THE MEALY
PLUM APHIS.

_ By W. M. Davinson, Scientific Assistant, Deciduous-Fruit Insect Investigations.

CONTENTS.
Page Page
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The mealy plum aphis (Hyalopterus arundinis Fabricius) has been
recognized for many years as an enemy of plums, prunes, and to a
lesser extent apricots in California. Since 1913 it has been espe-
cially severe in some regions, notably those in which artificial control
_ for the pear thrips (Zaeniothrips pyri Daniel) was not practiced.

ORIGIN.

The insect is European in origin, having been first described in
1794 by Fabricius. In North America it is widely distributed. <Ac-
cording to Lowe (8)1 it is present in Australia and New Zealand, Van
der Goot (2) reports it from Java, while the United States Bureau
- of Entomology has records of its occurence in Japan. Specimens —
| in the writer’s collection taken on Arundo in Peru, by Mr. E. W.
| Rust, late of the Bureau of Entomology, appear to belong to this
species but the lack of winged forms prevents certain determination.

HOSTS AND MIGRATORY HABITS.

In California plums and prunes of the domestica type are the
favorite hosts, but apricots and Asiatic types of plums and rarely

1 Figures in parenthesis refer to ‘ Literature cited’? on the final page of the bulletin.
98008°—Bull. 774—19

Reese era S eS CL aH eT

2 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

almonds are attacked also. In Europe grape, peach, and nectarine
are also attacked (Lowe). :

From the deciduous-fruit hosts mentioned the mealy plum aphis
migrates in early summer to plants of the genera Phragmites,
Typha, and Arundo, and in the late fall there is a return migration
to the fruit trees. This is the normal process of migration. Occa-
sionally the writer has seen generations of aphids persist on plum
until September, a habit that Lowe (38) records as net unusual in
New York State The migratory forms are winged aphids and
there are strong indications that they traverse long distances in pass-
ing from host to host, as summer colonies have been found in June
many miles from the nearest winter hosts. Vast numbers of migrants
are produced both in spring and fall, and the production of consid-
erable numbers of summer migrants serves to distribute the species
among the summer hosts. In California Phragmites and Typha are
the known alternate hosts.

INJURY.

In the early summer months the aphids occur on the feliage, oiten
crowding together in great quantities. (Pl. 1.) The lower surface of
the leaf is the preferred location, but the peticles and upper surface
are frequently infested. The young fruit is less commonly attacked.
The infested leaves are generally curled and discolored and glisten
with honeydew deposits. (Pl. IL) The ground beneath the tree is
often sprinkled with the whitish shed skins dropped by the aphids.
The combined effect of myriads of aphids feeding simultaneously on
the tree produces fruit of small size and an early drop. In the years
1915 and 1916 an unusual midsummer apical cracking of green
prunes developed in California. Morris (4), after making observa-
tions in the Santa Clara Valley in 1915, opined that this cracking

|

was due to aphis action. In 1916 the writer made some observations —

in Contra Costa County. He found that whereas on the whele crack-
ing was more general on trees that previously in the season had been
heavily infested with the aphis, it occurred also in other cases on trees
which had escaped infestation. He could not conclude otherwise
than that the aphis was not more than a contributing, or at least not

_ the sole cause of the apical cracking in the prunes.

1 Blakey (i), conducting his observations at Redditch, England, found no certain mi-
gration from the winter hosis, the aphids remaining the year around on fruit trees. In
this connection it is of interest to note that he found the active cycle (from hatching of
stem mother to oviposition) to extend in England from the beginning of May to the
middle of Gctober, 5.5 menths, whereas in California the writer found the cycle to cover
a period of 9 months (Mar. 1 to Nov. 30). The longer growing period enjoyed by the
trees in California is of ccurse responsible for this condition, and it is possible that the
much dryer climate of California is concerned in the summer migration of the species to
plants of a semiaquatic nature. The writer has observed that the aphics tend to remain
on the fruit trees later into the summer in the more humid than in the more arid
localities of California, while the occurrence on May 15 of large colonies on a summer
host at Salton Sea (a very arid region) suggested that the aphids were living on this
host the year around,

sit ie i i et =

THE MEALY PLUM APHIS. 3

SYNONYMS.

~ 1794. Aphis arundinis Fabricius, Ent. Syst., v. 4, p. 212.
1794. Aphis pruni Fabricius, Ent. Syst., v. 4, p. 2138.

3 2

ia 1886. Aphis phragmiticola Oestlund, List Aphid. Minn., p. 44.

\

aC TH,

_ 1911. Hyadaphis umbellulariae Davidson, Jour. Econ. Ent., v. 4, p, 559.

BIOLOGY.

THE EGG.

Size 0.55 by 0.27 mm. The newly laid egg is pale green, covered with con-
spicuous silvery filaments excreted by the oviparous female. It darkens rapidly
and after about 5 days is shining black; the threads, however, remain silvery.

LOCATION ON TREES.

The eggs are laid almost invariably in the axils of lateral buds of
year-old or 2-year-old wood. Rarely more than three eggs are to be
found to a single bud group. Occasionally eggs are placed in small
scars or wrinkles in the bark of twigs.

HATCHING.

In 1916 hatching commenced about March 4, and continued for
about two weeks. At this time most prune varieties were just starting
to leaf, but the Myrobalans were in full leaf; nevertheless hatching
was no earlier on the latter trees than on other plums and on apricots.

THE STEM MOTHER.
DESCRIPTION.

Newly hatched.—Pale green; eyes dark red; antenne and legs pale gray;
dorsum of head with a median longitudinal narrow pale green stripe; beak gray.
Form oval.

Antenne one-fourth the length of the body, 5-jointed. Comparative lengths:
I, 0.03 mm.; II, 0.035; IIT, 0.045; IV, 0.05; V, 0.11 (0.060 plus 0.050); beak
reaching to third abdominal segment, 0.21 mm. in length; cornicles minute
raised pores. Style rounded. Length of body 0.63 mm.; width of body 0.39
mm.

During the first and second instars the color darkens and the dark markings
on the head gradually disappear. The characteristic longitudinal stripes of
darker green appear during the third and fourth instars. There are 8 of these,
1 mediodorsal and 2 dorsolateral. The tarsi, apices of tibie, cornicles, tip of
beak, and distal third of the antennsz of the growing nymph become gray.

After the second molt the nymph assumes an elongate shape, and there
appears on the sides and at the abdominal sutures a pruinose ‘“ meal.” This
“meal” is much more scanty and less conspicuous in the stem mother than in
later forms.

Adult.—Yellowish-green with three longitudinal green stripes on dorsum;
eyes dark red; antenne pale green, distal joint dark gray; cornicles pale, dusky
at apex; tarsi dark gray; style pale yellowish green; apex of beak blackish.
Form elongate oval, comparatively flat; newly molted individuals carinate.

4 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

Antenne on very short frontal tubercles, barely one-third the length of the
body, 5-jointed. Comparative lengths: I, 0.075 mm.; II, 0.06; III, 0.30; IV,
0.14; V, 0.22 (0.08 plus 0.14). Beak, length 0.26 mm., reaching to second coxe;
cornicles, 0.045 mm.; style, 0.17 mm. Cornicies wartlike, style ensiform. Pro-
thorax and all abdominal segments bearing small, pale, lateral tubercles. Body
bearing a sparse, inconspicuous clothing of granular “ meal,” most abundant at
the sutures. Length of body (style included), 2.389 mm.; width of body, 1.06 mm.

HABITS AND LENGTH OF NYMPHAL LIFE.

After hatching, the young aphids seek out buds, often massing on
those most advanced, and contrive to penetrate to the inner portions.
On unopened buds they feed on the tender apical! portions and num-
bers of them die in such situations. Newly-hatched aphids move
awkwardly on rough spiny leaf surfaces and frequently fail to make
headway. This was observed especially in connection with Myroba-
lan plum leaves, and perhaps explains the fact that the stem mothers
on this tree have a high percentage of mortality in their early stages.

After the blossoms shoot out the aphids feed on the petioles or on
the outside of the sepals. in the leaf bud they feed generally on the
under (outer) surface of the unfolding foliage and less abundantly
on the reverse side. A favored point is that at the junction of sepal
and petiole on the flower stalks.

The first stem mothers matured on the plums at time of full bloom
(March 19, in 1916), their growth being the more rapid on forward
trees. On March 25 it was estimated that on the most advanced trees
85 per cent of the aphids were mature, while on the most backward
only 20 per cent were full grown. At this time the mature stem
mothers were on the underside of the leaves; none were remaining on
the fruit stalks. On March 28 virtually ail stem mothers on forward
trees were mature; on most backward trees 50 per cent were still im-
mature. By April 5 no more immature stem mothers were found.

Five stem mothers raised on potted Myrobalan seedlings developed
in from 13 to17 days. This time is perhaps less than in the average
orchard, since the quality of food available for the newly-hatched
aphid is often poor, while the seedlings were well in leaf at the time
the experimental eggs hatched. It should be stated that the tempera-
ture in 1916 during the first part of the development of the stem
mother was higher than usual for that time of year.

REPRODUCTION.

The stem mothers deposit on an average about 4 young a day
during a period of from 3 to 5 weeks. The rate of fecundity rises
rapidly at first, maintains an even zenith for some three weeks, and
then rapidly declines. Stem mothers may live for as long as three
weeks after they have deposited their complement of young.

PLATE |.

Bul. 774, U. S. Dept. of Agriculture.

THE MEALY PLUM APHIS (HYALOPTERUS ARUNDINIS).

Enlarged.

Colony of aphids on lower surface of leaf.

PLATE II.

Bul. 774, U.S. Dept. of Agriculture.

THE MEALY PLUM APHIS.

Infested plum foliage.

THE MEALY PLUM APHIS. 5
THE SPRING FORMS.

Six wingless generations, in the maximum-generation series, were
bred from April to June during 1916. An unusually hot wave oc-
curred June 6, and killed all of the individuals of the seventh and
eighth generations in the cages. It has been determined, however,
that wingless generations may persist on the winter hosts through
the summer as late as September, but apparently they can not pro-
duce true sexes. In the maximum series all second-generation indi-
viduals were wingless, in the third generation 1 out of 29 was
winged, none of the fourth or fifth generations were winged, while
the majority of the sixth and seventh generations were wingless. All
the individuals in this series were bred on Myrobalan plum.

SPRING WINGLESS FORMS.
DESCRIPTION.

Newly hatched.—Pale yellowish-green; eyes dark red; rims of cornicles
dusky. Appendages hyaline greenish-white. Form elongate oval.

Antenne 5-jointed, half as long as body. Comparative measurements as fol-
lows: & 0:03 mm: IF, 0.025; iL, O11; IV, 0.06; V, 0.175’ (0.05. plus 0.125).
Beak reaching third coxe, 0.22 mm. long; cornicles wartlike, 0.025 mm. long.
Style rounded. Length of body, 0.50 mm.; width of body, 0.22 mm.

In the first instar the general color darkens, but it is never as dark as
that of the stem mother; the tarsi, last antennal joint, and tip of beak become
dark grayish-black. After the first molt a conspicuous ‘‘ meal” is secreted in
four longitudinal rows of circular areas on the body dorsum. This “ meal” is
more abundant on the first and fifth abdominal segments than elsewhere. The
three longitudinal green stripes described in the stem mother appear less dis-
tinct in later generations. After the second molt the body is elongate oval. The
aphids have a carinated appearance following each molt.

Adult.—Light green; eyes dark red to black; antennz pale hyaline green,
apex gray; legs hyaline greenish-white, tarsi and tibial apices gray; cornicles
somewhat dusky in apical half; cauda light greenish-white. Beak pale, tip
blackish. ‘‘ Meal” as in larva, increasing with age of insect. Form elongate
oval.

Antennz on frontal tubercles, 6-jointed, two-thirds as long as body; com-
parative measurements as follows: I, 0.085 mm.; II, 0.075; III, 0.89; IV, 0.24;
VY, 0.225; VI, 0.445 (0.105 plus 0.3840). In later generations filament of VI is
longer in proportion than in earlier. Beak reaching second coxe, 0.380 mm.
long. Cornicies imbricated rather inconspicuously, constricted near base, some-
what enlarged in middle, mouth not flaring; length, 0.115 mm. Cauda ensiform,
0.17 mm. long. Body length, 2.2 to 2.8 mm.; width, 1.22 mm. Small, pale, blunt
lateral tubercles occur on the prothorax and on each abdominal segment. Body
armed with very few hairs.

DURATION OF NYMPHAL STAGES.

Records of the development of the wingless forms were made both
on caged trees and in the orchard. Myrobalan and Agen (French)
prunes were used for hosts. The development was similar on both

6 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

hosts, the aphids being retarded on weaker trees. The instars occu-
pied, on the average, equal periods of time, except that the fourth was
slightly shorter than any one of the others.

Forty-five individuals of the second generation were observed dur-
ing the period March 27—May 4, the majority developing during
the period March 30-April 22. The average growing period was 12.6
days, the maximum 18, and the minimum 10.

Between April 11 and May 30, 34 third-generation wingless in-
dividuals developed in an average of 11.8 days, the maximum and
minimum periods being, respectively, 18 and 9 days.

Individual records of generations 4 to 7 were made chiefiy from
the maximum-generation series and might be grouped best in tabular
form as follows:

TABLE I.—Development of spring wingless generations of the mealy plum aphis.
Walnut Creek, Cat., 1916.

|
Developmental pericd.
Number
pare. Dates included. | of indi- |

r viduals. | 4 vers Maxi- Mini-
yereee mum mum.

Days. | Days Days
TV....| Apr.23-May 16 10 9.3 | 14) 9
Wages ae | May 3-May 18 27 11.1 14 10
VI....| May 14-May 27 39 12.7 | 16 11
Vil...| May 26-June 3 10 110 11 | 9

| \

1 june 7, five fourth-instar wingless individuals died because of an excessive heat wave..
Had these matured, the average developmental period would have been slightly length-
ened.

MAXIMUM AND MINIMUM GENERATIONS.

A maximum-generation series of first-born aphids (wingless) is
shown in the table following:

Tasie 11.—Development of maximum-generation series of the mealy plum aphis.

Walnut Creek, Cal., 1916.

Genera-.-

Date of | Develop-
fourth | mental

ee Dini molt. period.
| |
| Days.
| T._._...| Mar. 11 | Mar. 28 17
El eas Mar. 30| Apr. 11 12
Tee eet ajar aly le isefaieg 2S) 13
TVD Apr. 23 | May 38 | 10
Ween May 3] May 14 ii
VE one May 14] May 26 12
VII....| May 27) June 6 9

Thus in the space of 115 weeks seven complete generations occurred. —
Had it been possibie to have continued the series until winter, cer-
tainly 10 more generations would have been preduced. ‘The adults —

THE MEALY PLUM APHIS. 7

usually deposit young within a very few hours after shedding the
final skin.

A minimum-generation series of last-born aphids is indicated
below :

Taste Ill.—Development of minimum-generation series of the mealy plum aphis.
Walnut Creek, Cal., 1916.

Genera- Dalene Develop-
_tlon ¢ a our menta
fndlvid birth. molt. period.

Days
atte Sosnle Safe eeem cic Mar. Lemme eee
ide ott. Apr. 21| May 3 12
EDs ee May 29} June 11 13
NV ceeee| Cully: Pl| Sly 11

These four generations were completed in about four months, or
over a month longer than the seven generations of the first-born
series.

The period of reproduction as indicated in the foregoing table
varied from 20 to 26 days.

REPRODUCTION.

Observations were made on the reproduction of individuals of
wingless generations 2 to 5 inclusive. Adults of the second genera-
tion, for a total reproductive period of from 4 to 5 weeks, averaged
about 4 young daily, producing the first three weeks a daily average
of 6 young. The later generations were less prolific, fourth and
fifth generation individuals not averaging above 24 young per day.
Ten young were deposited within 24 hours on several occasions, but
on no occasion was this number exceeded. The rise and decline in
fecundity was in the main similar to that found in the case of the
stem mother.

HABITS OF SPRING GENERATIONS.

The aphids of the second generation, when newly born, dispose
themselves in groups, close by the parent, on the underside of the
leaf. After the first molt many remove to other leaves and this is
the beginning of the migration from, leaf to leaf and branch to
branch. Second-generation larve and adults prefer to suck the
rib tissues of the leaf. Owing to the rapidity of reproduction and
consequent crowding, the aphids of later generations have little choice
of location and feed at any point on the lower surface of the leaves
or on petioles. If the lower surface of a leaf is entirely occupied
many larvee will be found feeding on the upper surface, in some
cases apparently in preference to seeking other less crowded leaves.

8 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

In 1916 infested prune leaves began to curl at the beginning of
April, such leaves having one or more colonies of adult stem mothers
and first-instar young. As April progressed the leaf-curl became
more and more pronounced and the colonies increased rapidly.

About the middle of the month the most heavily infested leaves
began to have a yellowish appearance in the form of blotched areas
at the points where the aphids were most abundantly settled. On
April 21 a few leaves were found to have their under surfaces quite
covered with feeding aphids, and at the end of the month such leaves
were abundant, While twigs and limbs were covered with a sticky
“honeydew,” and here and there young fruits were coated with this
substance. During May and June this condition was greatly aggra-
vated in the orchards examined.

The spring winged form first appeared April 21, and throughout
May el June increased in numbers, and after the middle of May
there was a corresponding decrease in the numbers of wingless adults
produced. By July 1 the mature wingless individuals had dimin-
ished greatly in quantity and thereafter their numbers dwindled so
that by the middle of August none were to be found. In no instance
in 1916 was an infestation prolonged beyond this date, but in 1914
in the same locality a small but vigorous infestation occurred through-
out September, later becoming annihilated by natural enemies.

In the rearing cages it was found that the transfer of newly born
young was very frequently attended by the loss of the insect, and
in most.cases the adult was transferred when it was desired to make
observations on a new plant. Several transfers of larve and adult
wingless individuals from plum to apricot failed, while others re-
sulted successfully. Infested apricot leaves did not curl as badly
as those of prune and plum.

THE SPRING MIGRANT.
DESCRIPTION.

In the first three instars the nymphs of the migrants do not differ from those
of the wingless spring form, except that the third-instar individuals are some-
what narrower.

Pupa.—tLight green; eyes dark red; tarsi and apex of beak dark gray. On
the bedy ground color is superimposed a narrow dorsomedian stripe of darker
green. Thorax broadened to twice the width of the prothorax. Wing pads
vellowish white. Body with pruinose covering as in wingless nymph.

Adult—Light green; eyes red; antenne light gray, basal portion of third
joint hyaline yellow; head, thoracic lobes, and sternum dark grayish black;
scutellum yellowish brown; prothorax, sides of thorax, and wing insertions
greenish yellow; wings hyaline, stigma and veins gray; legs pale greenish yellow,
apices of tibise and the tarsi dusky gray; abdomen and style pale green or
greenish yellow; cornicles pale at base, dusky at apex. Beak pale, extreme tip
dusky. :

Form elongate, the abdomen with parallel sides.

The dorsum and sides are covered with white pruinose “meal,” on the ab-
domen the “ meal” occurring in transverse bars.

THE MEALY PLUM APHIS. 9

Antenne four-fifths as long as body, on frontal tubercles. Comparative
measurements as follows: I, 0.08 mm.; II, 0.06; III, 0.405; IV, 0.26; V, 0.21;
VI, 0.48 (0.10 plus 0.88). Beak reaching a little beyond anterior border of
mesosternum, 0.26 mm. long. Wings 2.5 mm, long. Cornicles faintly imbri-
cated, shorter than in wingless female, barely twice as long as broad at base,
slightly constricted near base, in length 0.08 mm. Style ensiform, 0.15 mm.
long. Length of body, 1.61 to 2 mm.; width, 0.66 mm.

Lateral tubercles as in wingless form; first antennal joint somewhat gibbous.

Sensoria.—On ITI, 23 to 30; on LV, 4 to 10; on V, 1 to 2; on VI, usual apical
group. Sensoria of unequal size, not at all arranged in longitudinal rows, but
rather in spirals,

DURATION OF NYMPHAL STAGES.

Kight winged spring migrants developed in an average of 144 days,
the developmental period ranging from 18 to 18 days. The winged
form therefore develops more slowly than the wingiless, due to the
increased duration of the fourth instar.

REPRODUCTION.

The migrants commenced to reproduce on the cat-tail rush (Typha)
a few days after they settled. In many cases migrants were found to
settle, remain for several days, and finally die without reproducing ~
and only a small percentage of those settling reproduced. Most of
them remained a few days and then departed. Spring migrants in
only one instance out of 76 deposited young on caged plums. In this
instance the three young born refused to feed on the plum (Myroba-
lan). In this connection it might be said that all attempts to induce
wingless forms of earlier generations to settle on Typha failed. Mi-
grants placed in small dishes and provided with plum and cat-tail
foliage in no instance deposited young and in extremely few instances
did migrants placed on cat-tail deposit young. Unfortunately it was
not possible to obtain Phragmites for similar tests.

The migrants may remain on the winter host foliage for several
days before taking flight, especially if the weather be cool and cloudy.

Field observations indicated that the migrants produced young
at the rate of about five every two days at first, and later at a slower
rate. On Typha it appeared that the maximum number of young
per migrant rarely exceeded 20 and, discounting all migrants which
failed to deposit, averaged not much over five. This must have been
abnormal, as examination of individuals disclosed the presence of
many more embryos than were extruded. It is possible that Typha
does not prove an invigorating food for the migrant and this point
is perhaps elucidated below in the paragraphs on migrations.

MIGRATIONS.

Phragmites and Arundo have long been known as alternate hosts
of the mealy plum aphis; in fact the species has been described as
new from both of these hosts. In California enormous infestations

10 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

have been observed on the former in swampy regions, sometimes
removed many miles from any winter hosts. On the other hand,
Typha grows in abundance close to prune orchards and yet, con-
sidering the enormous production of spring migrants throughout
May, June, and July, the later infestations on near-by Typha are in
the aggregate exceedingly small. The writer has seen clumps of Typha
latifolia, growing not 30 feet from prune trees on each of which
thousands of winged forms were being developed, receive only a
few dozen migrants and perhaps have not over 6 out of 100 blades
colonized by their progeny. It is true that when once established
a colony on Typha increases rapidly, but it is also evident that the
migrant fails to do justice to her reproductive capabilities on this
plant.

That the migrants fly long distances to seek their alternate hosts,
especially Phragmites, is the conviction of the writer.

The spring migrants settle on Typha near the apex of a strongly-
growing blade and station themselves parallel to its long axis. The
wingless forms later take up this same position. After the migrants
have extruded a few young the whitish meal is excreted in greater
abundance. On Phragmites the colonies are similarly disposed. On
three occasions the writer observed heavy summer infestations on
the reed Phragmites communis L. On July 5, 1917, along the banks
of the San Joaquin River about 15 miles west of Stockton, Cal., this
plant was heavily attacked. Among the colonies occurred a few
pupe and winged forms of a winged summer form. Typha latifolia —
growing among the infested reeds was not attacked. On August
13,1917, at Benicia, Cal., clumps of reeds growing in swampy ground
near San Francisco Bay bore heavy infestations of the aphis and
the summer winged form was abundant. Plants of Typha grow-
ing among the clumps of Phragmites were sparingly infested. On
May 15, 1918, heavy infestations were observed on Phragmites com-
munis growing on the west shore of the Salton Sea, in southern
California.

These observations indicate that Phragmites is the preferred
summer host plant.

The summer winged aphids serve to distribute the species among
_ the reeds. They do not differ in appearance or structure from the
spring migrants produced on the winter hosts.

Fall migrants appeared both in 1915 and 1916 on Typha about
October 15, and continued until the end of November. Males ap-
peared the last week of October and throughout November. The
small yellowish pupe of the latter are easily distinguishable on the
cat-tails from the green pup of the fall migrant. Mature fall
migrants remained on the summer host for-a day or two before
departing.

THE MEALY PLUM APHIS. 11

Although migrations from Typha were traced with apparent cer-
tainty in the fall of 1915, in the following year so few fall migrants
were produced on local Typha under observation that they were out
of all proportion to the great numbers of winged forms which began
to appear in the prune orchards near Walnut Creek toward the end
of October, and it was certain that the great majority of migrants
-were coming from a considerable distance.

THE SUMMER WINGLESS FORMS.
DESCRIPTION.

Newly hatched.—Similar to that of spring wingless form, but more yellowish.
Form elongate.

Adult.—In color similar to those of spring wingless, but smaller in size and
narrower in shape.

Antenne about two-thirds body length. Comparative measurements as fol-
lows: I, 0.08 mm.; II, 0.045; III, 0.26; IV, 0.16; V, 0.155; VI, 0.40 (0.08 plus
0.32). Beak reaching second cox, 0.26 mm. long. Cornicles more cylindrical
than in spring wingless form, inconspicuously imbricated, 0.07 mm. long. Style
0.135 mm, long, shaped as in spring wingless form. Length of body, 1.6 to 2
mm.; width of body, 0.65 mm.

Measurements from specimens of what appears to be H. arundinis collected
in April on Arundo in Peru by Mr. E. W. Rust were noticeably greater, but simi-

- lar in proportions.
The lateral tubercles are inconspicuous.

DURATION OF STAGES.

- Highteen first-generation (progeny of migrant) individuals in the
period May 29-August 20 matured on Typha in an average of 14.6
days, the period of growth ranging from 12 to 18 days. Between
June 17 and July 30, 15 aphids of the second and third summer gen-
erations developed in an average of 15.8 days, with a range of from
9 to 18 days, while 17 fourth-generation individuals developing
between July 26 and August 27 averaged 12.2 days, with a range of
from 9 to 16 days. Aphids maturing in September developed in an
average of 14 days. All the individuals recorded above were wingless.
There is apparently a maximum of as many as 10 wingless summer
generations and a mimimum of 3. Molts occurred about as in the
spring wingless forms.

HABITS OF SUMMER WINGLESS FORMS.

Colonies are anes on both sides of the blades, chiefly on the outer
half, occasionally on the basal half of the leaf. a3 September, 1915,
several colonies of over 200 wingless individuals were observed on
single blades of Typha at Walnut Creek, and about the end of this
month the aphids reached their maximum abundance. This latter
condition was repeated in 1916, although the colonies were never as

12 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

large as the year previous. As has been noted, the aphids lie parallel
to the length of the blade. They move off at slight disturbance and
much difficulty was experienced in transferring individuals, owing to
their failure to settle on a new plant.

Toward the end of October the blades frequently turn yellow,
causing the aphids resident thereon to assume a straw-colored ap-
pearance. |

The aphids frequently deposit a little circle of “meal” around
them on the surface of the blade, a habit similar to that practiced on
the same host by a species of white fly. On leaves of Phragmites the
aphids congregate in large masses on both surfaces, lying parallel to
the long axis of the leaf. The central portion of the leaf is colonized
first and as the colony increases in numbers the infested area ap-
proaches the margins.

THE FALL FORMS.

There are three fall forms—the fall viviparous migrant, the male,
and the sexual oviparous female. The first two fly to the winter
hosts, after which the viviparous migrants deposit the sexual ovipar-
ous females.

FALL MIGRANT.

DESCRIPTION.

The immature stages do not differ materially from those of the spring mi-
grant.

The adult insect, aside from being slightly smaller and having the antenna,
legs, and style more dusky, is similar to the spring migrant. Form elongate.

Antenne on somewhat gibbous frontal turbercies, about two-thirds as long as
the body. Comparative measurements as follows: I, 0.07 mm.; II, 0.06; III,
0.39; IV, 0.235: V, 0.175; VI, 0.48 (0.10 plus 0.388). Beak reaching a little be-
yond anterior border of mesosternum, 0.26 mm. in length. Wings 2.6 mm. in
length. Cornicles shaped as in spring migrant, 0.075 mm. long. Style ensiform,
0.16 mm. long. ;

Sensoriation and tubercles as in spring migrants.

REPRODUCTION AND HABITS.

~

The migrants normally locate on the underside of the leaves (of the
winter host), but those that arrive latest in the season often find the
leaves blown off by winds and perforce settle on the twigs. Fre-
quently they feed for several days before producing young. In ex-
perimental cages inclosing Agen (French) prunes and Myrobalan
plums 14 was the highest number of young laid by a single migrant,
and the average was about 8 (excluding about 20 per cent of the indi-
viduals which died without bearing progeny). The migrants were
more prolific on Agen (French) prunes than on Myrobalan plums.
In the field it appeared that from 12 to 35 young sexual females are
produced normally, with an average of about 20, on French prunes.

THE MEALY PLUM APHIS. 13

The young were produced within about 12 days (in the cages mostly
within 7 days) and at a rate of from 2 to 3 a day. The migrants,
after they had extruded their complement of young, remained settled
for as long as two weeks.

MALE AND OVIPAROUS FEMALE,
MALz.
DESCRIPTION.

Pupa.—Noticeably smaller than that of the fall migrant, light yellow in color;
eyes dark red; tarsi and distal antennal joint dusky gray. Form elongate.

Aduli.—Light clay yellow; head, antenne, prothorax, thoracic lobes, scutel-
lum, legs, cornicles, and style brownish-black ; eyes dark red; stigma light green-
ish-gray ; veins of wings brown; abdomen with a dorsomedian longitudinal row
(segments 1 to 5 inclusive) of subcircular gray spots, similar lateral spots on
segments 1 to 8 inclusive, and with cross bars of similar color on segments 6, 7,
and 8; genital plate and organs dark gray; beak pale yellow, tip brownish black.
The male is almost devoid of “ meal.”

Antenne on gibbous frontal tgbercles, three-fourths the length of the body ;
comparative measurements as follows: i, 0.08 mm.; I, 0.07; III, 0.88; IV, 0.25;
V, 0.23; VI, 0.46 (0.09 plus 0.37). Wings 2.38 mm. long. Cornicles vase-shaped,
narrowed ciose to base, faintly imbricated, 0.085 mm. in length. Style conical,
0.10 mm. long. Beak reaching a little beyond anterior mesosternal border, 0.30
mm. long. Length of body, 2.05 mm., width, 0.68 mm.

Circular sensoria are distributed along the antennal joints much as in the
spring and fall migrants. They are much more numerous, there being from 38
to 53 on III, 19 to 29 on IV, 9 to 18 on V, and the usual apical group on VI.

OVIPAROUS FEMALE,
DESCRIPTION.

Newly hatched.—Light green, appendages hyaline; eyes red. Form oval.

The immature females are bright green with a very scant covering of ‘ meal.”

Adult.—Greenish yellow; eyes dark red; distal half of antenne, cornicles, and
tarsi gray; beak pale yellow, tip brown. The coating of “meal” is not so
conspicuous as in the earlier forms, in this respect resembling the stem mother.
Form elongate oval, rather flat.

Antenne not quite half as long as body, comparative measurements as fol-
lows: I, 0.06 mm.; II, 0.085; III, 0.145; IV, 0.06; V, 0.085; VI, 0.245 (0.05 plus
0.195). Beak reaching second coxe, 0.25 mm. long. Cornicles cylindrical, twice
as long as wide at base, faintly imbricated, 0.05 mm. long.

Style conical, 0.08 mm. long. Length of body, 1.18 mm.; width, 0.52 mm.

The thickened hind tibie bear a large number of small circular sensoria.

NYMPHAL STAGES.

For the male the nymphal stages were not observed closely, this
form having been very rare on the cat-tails in 1916. From such
observations as took place it appears safe to say that both males and
fall migrants develop in about three weeks. The development of ovip-
arous females was observed in 1916 on both Agen (/’rench) prunes and

14 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

Myrobalan seedlings. Within the period October 20-November 23, 40
oviparous females matured in an average of 19.1 days, the period
of development ranging from 16 to 22 days. On Myrobalan plum
the development was slightly slower than on Agen (French) prunes.

HABITS AND OVIPOSITION.

The females feed normally on the under surface of the leaves, but
occasionally also on tender stalks, especially of sucker growth. The
males frequently arrive before the females are mature and settle
down beside the immature aphids. Copulation takes place very
soon after the female casts her fourth skin, and a male may copulate
with more than one female. As the males are much less abundant
than the females this practice is probably common and was often
noticed in the cages. Toward the middle of November, 1916, large
numbers of immature females were blown off the trees by winds and
perished. In some orchards this only thinned out the infestation to
a small degree, as plenty of mature females had been observed previ-
ous to the coming of the high winds, but in others wherein the sexes
were not so advanced it destroyed the majority of the aphids. The
oviparous females bear only a scant coat of “meal” and may be
easily confused in the orchard with those of Phorodon humuli
Schrank and Aphis cardui Linneus, both of which are contempo-
raneous with arwndinis. They are less likely to be confused with the
plump reddish-brown oviparous form of Rhopalosiphum nympheae
Linneus.

As a rule the female commences oviposition within 24 hours of
copulation, but this was delayed in some cases as long as 5, and in
one instance 10 days. In cages never more than 2 eggs, and more
often only 1, were laid in one day by a single aphid.

Sixteen females laid an average of 4.1 eggs in the period Novem-
ber 9-December 18. In the early part of this period the average was
6, while toward the end it was 3.5. Not over 7 eggs were deposited
by one female. There was a marked tendency to deposit the eggs
over a long period—as much as three weeks—and the females after
depositing an egg or eggs on the stems generally returned to the leaf,
remaining there until the time for the deposition of the next egg.

he females usually died within a week of depositing their last egg,
but in some cases lived longer, and one aphid lived beyond three
weeks. Jt appeared, however, that those that persisted had not rid
themselves of all their ova, as they did not have the shrunken ap-
pearance of sterile aphids.

NATURAL ENEMIES.

The mealy plum aphis, both on winter and summer hosts, is preyed
upon by a large series of natural enemies. As early as March 17,

1916, a few eggs of Syrphidae and Chrysopidae were observed de- —

Se a ee a ee ee ee ene ee

ie ascealiy

je ath name

THE MEALY PLUM APHIS. 15

posited near the growing stem mothers on plums. Throughout April
lampyrid beetles (Podabrus comes Le Conte, P. binotatus Le Conte
var., and Yelephorus divisus Le Conte) appeared locally. During
May syrphus-fly larvee (especially Catabomba pyrastri Linneus) and
ladybird adults and larve (especially Hippodamia convergens
Guérin) abounded, as did also a few hemerobiid larve. Nevertheless —
these predators made little apparent headway in reducing infes-
tations.

Observations made in June, 1915, indicated that Hippodamia con-
vergens was by far the most beneficial of the ladybirds.

The Typha colonies were preyed on by the larve of Syrphus; those
on Phragmites by beetles of the Hippodamia group and by Leucopis
larvee; and late in the fall the sexual females were attacked by syr-
phids and Triphleps.

Internal parasitism in the writer’s opinion is of very rare occur-
rence. Occasionally he has observed parasitized specimens in nature.

CONTROL SUGGESTIONS.

There are two especially vulnerable periods in the annual life cycle
of the mealy plum aphis—one in early spring when the stem mothers
are growing and the other in late fall when the sexual females are
developing on the winter hosts. Unfortunately at these two periods
the enemies of the aphis are very scarce, but the aphis itself is more
easily destroyed than at other times by artificial substances. Both the
stem mothers and the oviparous females have a scant protective cover-
ing of “meal” and both live for the most part on exposed surfaces of
the plant, whereas the aphids of the spring and summer generations
bear a comparatively thick coating of meal and live in great part in
curled foliage. Contact insecticides, which have litle effect on aphids
of the intermediate generations, easily destroy the stem mothers and
the egg-laying females.

SUMMARY.

The mealy plum aphis in California is a decided pest of plums,
prunes, and, to a lesser degree, apricots. Besides devitalizing the
trees it causes small-sized fruits and early drops, and is probably con-
cerned in a measure with apical cracking of prunes.

In 1916 winter eggs hatched between March 4 and 18 and early
stem mothers began reproduction about March 20. It appeared
that normally from 8 to 5 generations were raised on the winter
hosts, but rarely series of wingless generations persisted until the fall.
The aphids of the earlier generations were mostly wingless hke the
stem mothers, and the individuals of the later generations mostly
winged, and after the middle of June virtually all the insects pro-
duced developed wings.

16 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE.

Migration to the summer hosts, Phragmites and Typha, began the
last week in April and continued until August, the great body travel-
ing in early June. On these hosts about 10 generations took place,
continuing up to November. The vast majority of aphids to be found
during the summer were wingless, but winged parthenoparous ind}-
viduals were also produced on the summer host plants and these
served to distribute the species among these plants. About the middle
of October and for six weeks succeeding, winged sexuparous migrants
and winged males were produced and these flew to the fruit trees.
whereon the sexuparae proceeded to deposit sexual females. The
sexes were most abundant during the forepart of November, and
were to be found as late as the middle of December.

Oviposition took place throughout November and December. the
majority of ova having been placed before December 10. .

The foregoing data are based on observations made at Walnut
Creek, Cal., between August, 1915, and December, 1916.

LITERATURE CITED.
t BrAscy.. 3. G.
1918. The mealy plum aphis. [Hyalopterus pruni.] In Gardeners’
Chronicle, y. 63, no. 1619, p. 1-2, illus.
2. GooT, P. VAN DER.
1917. Zur Kenntniss der Blattlise Java’s. Jn Contributions 4 la faune des
Indes Néerlandaises, dirigées par J. C. Koningsberger, v. 1, fasc. 3,
p. 1-801, illus. Buitenzorg.
Page 125: Hyatopterus pruni.
3. Lows, V. H.
1897. Plant-lice: Descriptions, enemies and treatment. N. ¥. Agr. Expt.
Sta. (Geneva) Bul. 139, p. 645-664.
Page 657: Hyalopterus pruni Fab.
4. Morris, Eart.
1915. Cracking ef prunes. Jn California State Com. Hort. Mo. Bul. v. 4,
no. 10, p. 476, figs. 99-100.

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