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

Washington, D. C. v y November 4, 1921
EES sea eI ee aia es

; WALNUE HUSK-MAGGOT.’

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a f : stb 9c : f n
By Frep E. Brooks, Hutomologist, Fruit Insect Investigations.
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CONTENTS.

Page Paze
Introduction ________-_ res in Eee Z 1 | Description: of life stages _-_-_--__- 3
Brief description of insect and in- Activities. of the flies. === 4
rip ee ee ee O isthe on. inh 6
SOM YI yes se Se ie 3 8 See JOM Naturah enemics==4 25h re =f. iG
MOUS GUO UO ge ee at ceo ee 2 eEMethods otacontrol= ===. === 2a == 7

Rood plants === ee 3

INTRODUCTION.

The larva of the walnut husk-maggot has long been known to
persons who in autumn have engaged in hulling the nuts of our
native black walnut (Juglans nigra). Soon after the nuts drop, #
large percentage of them are frequently found with the hulls black-
ened and slimy within and containing multitudes of whitish mag-
gots which move actively through the soft pulp. Such infested nuts
are disagreeable to handle, and in hulling the husk sticks to the
inner shell, leaving it dirty and unattractive in appearance GPE IVs
d). Inasmuch as the fruit of the black walnut was not important
commercially in the past this insect did not attract especial attention.
and very few persons, even of those who were familiar with the mag-
gots in the walnuts, ever saw the parent fly. If seen, it was probably
seldom regarded as being in any way connected with the disgusting

1Rhagoletis suavis Loew ; order Diptera, family Trypetidae. A closely allied species,
Rhagoletis juglandis Cresson, has been recorded as attacking the nuts of Juglans rupestris
and J. regia in Arizona and Texas. Several members of the same genus have attracted
considerable attention in North America on account of the destructiveness of the larve
to various kinds of fruit. R. pomonella Walsh, known commonly as the apple maggot
or railroad worm, is an important pest of apples in the northern part of the United
States and Canada. Two species, R. cingulata Loew and R. fausta O. S., attack cherries
over practically the same region, while R. ribicola Doane frequently injures currants and
gooseberries in the Northwestern States.

55813°—21

2 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE.

condition of the nuts. It was not until an interest developed in cer-
tain places in the East in growing the Persian or English walnut
(Juglans regia) commercially that a demand arose for information
regarding this pest. When the Persian walnut trees planted in the
East began to fruit, these maggots attacked the nuts and practically
ruined very promising crops in several localities. The injury to Per-
sian walnuts and the fact that the eastern black walnut, one of the
favorite food plants of the species, is becoming of increasing im-
portance from the standpoint of nut production, have led to the in-
vestigation described herein. The project is not yet completed, but
the outstanding features of the life history and habits of the insect
are now known. Further studies of the species, particularly along
the lines of control, are under way.

BRIEF DESCRIPTION OF INSECT AND INJURY.

The adult of the walnut husk-maggot is a two-winged fly about
the size of the common house fly. The flies appear on the walnut trees
at the time the nuts are approaching maturity and lay clusters of
white eggs in punctures made in the husk with their sharp ovipositor
(Pl. III, e) or in breaks which they may find in the husk of the nuts
(Pl. II, 6, c,d). Apparently no eggs are deposited in the nuts after
they drop. The eggs soon hatch and the resultant maggots rapidly
convert the green tissue of the husk into black pulp. After attain-
ing full growth the maggots enter the ground and pupate, there
being only one generation of the flies annually.

SYNONYMY.

The following data covering the synonymy of.the species were fur-
nished by Mr. B. A. Porter, of the Bureau of Entomology: |
Trypeta suavis Loew, 1862, in Monogr. Dipt. N. Amer., pt. 1, p. 75.
Acidia suavis Loew, 1873, in Monogr. Dipt. N. Amer. pt. 3, p. 235.
Rhagoletis suavis (Loew), 1899, in Coquillett, Jour. N. Y. Ent. Soc.,
Views WieecoUs
DISTRIBUTION.

This fly probably occurs pretty generally over the natural ranges
of the black walnut and the butternut (Juglans cinerea). In 1862
Osten-Sacken? gave its distribution as the “ Middle States.” In
1902 Babb* reared the fly from black walnut at Amherst, Mass.
Washburn, in 1905, listed the species among the flies of Minnesota;

2Lopw, H. MONOGRAPHS OF THE DIPTERA OF NORTH AMMRICA (ed. by R. Osten-Sacken),
pt. 1, p. 75. Washington, D. C. 1862.

2 Bass, G. F. NOTE ON RHAGOLETIS SUAVIS LW., WITH A DESCRIPTION OF THE LARVA
AND PUPARIUM. Jn Ent. News, v. 13, no. 8, p. 242. 1902.

4 WASHBURN, F, L. DIPTERA OF MINNESOTA. . Minn, Agr. Exp. Sta. Bul. 93, p. 118.
1905.

LIBRARY OF CONGRESS
RESENED

NOV 121921

DOCUMENTS DIVISION

3B LR 4 WALNUT HUSK-MAGGOT. 3
=

and Banks,° in 1912, reared flies from butternuts at Plummers Island,
Md. .There are specimens in the United States National Museum
from West Willow and Allegheny, Pa., and Dr. J. M. Aldrich, of
the Museum, has in his personal collection specimens from Blue
Ridge Summit, Pa., and La Fayette, Ind. During the present in-
vestigation the writer has collected or otherwise obtained specimens
from the following localities: Boston, Mass.; Wallingford, Conn. ;
Lockport, N. Y.; West Willow and Washington Heights, Pa.; Co-
lumbus, Ohio; New Windsor, Md.; Washington, D. C.; and French
Creek and other localities in West Virginia.

FOOD PLANTS.

The walnut husk-maggot has been known to attack commonly the
husks of the black walnut (Juglans nigra) and the butternut (/.
cinerea). The writer has reared adults from the husks of the Persian
walnut (J. regia) and Japanese walnut (/. sieboldiana). Of the
foregoing hosts the black walnut and Persian walnut are preferred
to the others, probably on account of the thicker husks.

DESCRIPTION OF LIFE STAGES.

THE EGG.

The egg (PI. II, }, ¢, d) is white, banana-shaped, distinctly curved,
0.9 to 1 mm. in length by 0.2 mm. in width, one end tapering gradu-
ally to a rounded point, the other end tapering more abruptly and
ending in a minute but distinct spur or pedicle. The eggs are placed
in magses compressed closely together (Pl. I, 6, c, 7) im oviposition
punctures extending 2 mm., more or less, beneath the skin of the
nuts. The female will oviposit freely in any fresh puncture which
she may find in the skin made otherwise than with her ovipositor.
Small punctures made experimentally in the husk with a sharp point
usually were found promptly by the females and filled with eggs.
In some cases such punctures would be packed with eggs and the
flies would continue to oviposit on the surface until a small mound
of eggs covered the opening in the skin (Pl. I, d). One artificial
puncture in a black walnut was found to contain 186 eggs and several
punctures made with the ovipositor were found to hold upwards of
60 eggs each. The eggs apparently hatch in from 7 to 10 days.

Oviposition takes place only in the green part of the husk, but
after the maggots hatch and begin to feed the point of attack soon
shows as a black spot on the surface (PI. 1V,@). This spot increases
rapidly in size as the burrows of the maggots penetrate the tissues

5 BANKS, NATHAN. THN STRUCTURE OF CERTAIN DIPTEROUS LARVA WITH PARTICULAR REF-
ERENCE TO THOSK IN HUMAN Foops. U. 8S. Dept. Agr., Bur. Ent., Tech. Ser. Bul. 22,
p. 32. 1912,

4 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE.

o

beneath. Persian walnuts on the trees will often turn black from
this cause during a period of only a few days. Quite often the first
external evidence of the feeding of the larvee within a nut will be a
slight seepage of dark juice from the oviposition wound, which will
flow down and stain the skin of the nut (PI. IV, d).

THE LARVA.

The larva, or maggot (Pl. I, e, 7; Pl. IV, c), is white or creamy
white, and is not stained by the dye-like, semiliquid matter in which
it feeds.. The dark-colored contents of the alimentary canal, how-
ever, give to the immature maggots a brownish appearance. When
full grown they average 10 mm. in length by 2 mm. in width. The
maggots are active and move about rapidly, using in locomotion their
two anal hooks. They often remain in the walnut husk until severe
freezing weather occurs, but take advantage of warm periods in the
late autumn to leave the nuts and enter the ground a short distance
for pupation.

THE PUPA.

The pupa (Pl. I, g, 2) is formed by the shrinkage of the larva
and is pale yellow, cylindrical, tapers slightly from the middle to-
ward the ends, and is 5 mm. in length by 2.5 mm. in width. There
are 11 plainly visible segments, the intersegmental grooves being
shallow but distinct. Each end bears a pair of small, brownish
tubercles and there is a rough, brown spot near one end where the
larval head was retracted. In size, shape, and color the pupa re-
sembles a grain of wheat (Pl. II, 4). The pup are formed in the
ground, anywhere from half an inch to several inches beneath the
surface, and the winter is passed in this stage. Most of the flies
issue the following summer, but a few pupe hold over the second
winter and the adults appear therefrom during the succeeding
summer.

THE ADULT.

The adults of this insect vary considerably in size but average about
¢ mm. in length. With the exception of the eyes, heavy wing mark-
ings, anterior margins of the abdominal segments, and bristle-like
hairs, all of which are dark brown, the color is pale yellow. There
is a hghter longitudinal line on each side of the thorax and the
dorsal surface of the thorax is densely clothed with very short,
yellowish hairs interspersed sparsely with long, stiff, dark-brown
bristles. The head, sides, upper surface of the abdomen, and legs
are covered more or less heavily with brown hairs. (PI. IIT.)

ACTIVITIES OF THE FLIES.

The flies begin to issue from the ground at least as early as the
middle of July in the latitude of West Virginia. In 1920 at French

PLATE I.

Bul. 992, U. S. Dept. of Agriculture.

‘Vd ‘MOTIIM LSAM
*HSNY “DH PP AO SAAOUH) LNNIVM NVISYSd SHL NI LODDVIA-xSNH LANIVAA AHL TOYLNOD OL SLVNASYY GVA] HLIM DNIAVYdS

Bul. 992, U. S. Dept. of Agriculture. PLATE II.

THE WALNUT HUSK-MAGGOT.

a, Genitalia of male and female husk-maggots, male on left; 6 and c, egg clusters in black walnuts
exposed by cutting away the skin: d, egg cluster partJy on the surface of black walnut; e, larve;
jf, jJarva escaping from a black walnut; g, pups; h, resemblance of pupe, above, and grains of
wheat, below. All enlarged.

Bul. 992, U. S. Dept. of Agriculture. PLATE III

THE WALNUT HUSK-MAGGoT.

a, Flies of husk-maggot on black walnut; 6, fly of husk-maggot much enlarged; e, female in the
act of depositing eggs in a black walnut; d, female laying eggs and guarded by a male; e, female
with ovipositor extended. All enlarged.

Bul. 992, U. S. Dept. of Agriculture. PLATE IV.

THE WALNUT HUSK-MAGGOT.

w, Black walnut showing discolored spot on skin made by husk-maggots mining within; b, black
walnut stained by juice flowing from oviposition sear; c, husk-maggots in Persian walnut:
d, black walnuts with husk removed to show difference in hulling between sound and infested
nuts; nut on the Jeft sound, on the right infested. All about natural size.

WALNUT HUSK-MAGGOT. 5)

Creek, W. Va., the first flies appeared in rearing jars on July 16,
and on August 5 the first specimens were recognized definitely on
the trees. Flies, apparently of this species, were seen on trees in both
West Virginia and Pennsylvania several weeks earlier, but no
specimens were captured and identification was not definite. Flies
in rearing jars issued from July 16 to September 8, emergence cover-
ing a period of 55 days. Table I shows the time of emergence of 40
individuals in rearing jars.

TABLE I.—Hmergence of flies of walnut husk-maggot in rearing jars at
French Creek, W. Va., in 1920.

|
Num- | Num-'| Num-) Num- |
Date ber of Date. ber of Date. ber of | Date. ber of |
flies. flies. flies. | flies
July 16... 1 July 31.. He Niort all nS) Aig 29a le sO |
i ee, 0 Aug. 1.. 1 ikoos (8) 30. OF}
Tbe 0 oe 0 tlefe Dal Side: 1
(i alia gut 0 18. 2 || Sept.1..... 0
20... 0 een leat 19... 3 | an Ca 0
Dice 1 See ell ieeoe OLN Die Oe Br. 0
Opdee 0 Gers ee eel O18 0 | Aris rs ell
Tteee 1 7 eae | Deal le Seu Beetle? =O
24. . 0 She 1 ORE ee Ce 0
one 0 || Ouae =| Premed 24° rhe ne 0
pom 1 =. 0 Ree 4 | See lbas a
Fifa 0 || (iS 0 26. . 4- | Oho e--0
sear epee Tare” v9 Dee \an el |
Dee 0 || 13 S228 1 28. 0 Total..| 40
30. - 0 || 1A: 0

Apparently flies are present on the trees several weeks before ovi-
position begins. At first they occupy the foliage chiefly, making
short flights from leaf to leaf and resting quietly for long periods.
During the preoviposition period, as well as later, they may be seen
lapping at the leaves as though extracting food from deposits on the
surface. As the time for the beginning of oviposition approaches
the flies become more active, and both males and females show a
tendency to gather about the nuts. The males habitually select cer-
tain nuts on which an individual will take his stand and often remain
for hours at a time awaiting the coming of the female, combating,
meantime, other males that approach. When a male alights on a nut
already tenanted by another male the original occupant attacks 1t and
usually the two rear up on their hind legs, facing each other, and en-
gage in a brief but animated bout, belaboring each other with their
forelegs. Usually the original occupant is the victor and the would-
be interloper flies away.

A prick made in a walnut with a pin or other sharp point was sure
to be found by a male, who, recognizing it evidently as a suitable
place for the females to come to oviposit, would immediately begin
standing guard over it. In one instance the writer pricked a dozen
walnuts on the lower branches of a tree with the point of a small
nail. Thereafter for several days a male was on guard at each of the

6 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE.

punctured nuts and females were observed frequently to visit these
nuts, where copulation and oviposition took place. In approaching
these nuts the females usually came by easy stages, flying and crawl-
ing near the nut before alighting upon it. When the male would
observe a female approaching he would become much excited, moving
back and forth, whirling around, and raising and lowering the wings
in rapid succession, but remaining near the puncture made with the
nail point. On the arrival of the female upon the nut the male
would usually back away from the nail puncture a short distance
and there remain stationary, with wings elevated above the back,
watching the female intently. When the female would find the
puncture and start to insert the tip of her abdomen into the opening
for the purpose of depositing eggs, the male would spring upon her
and copulation would take place. There would then follow alter-
nating periods of oviposition and copulation, the male sometimes
continuing mounted while oviposition was in progress, and sometimes
dismounting but remaining near by. (PI. III, d.) Frequently there
would be four or five periods of each before the female would fly
away. After this procedure the male was likely to continue on
guard at the same place, for the nail pricks were visited frequently
by ovipositing females.

The flies were observed to be much more abundant on the lower
than on the higher branches of trees, and there was a great differ-
ence in the numbers of flies on individual trees of the same species.
On a group of heavy-laden Persian walnut trees of the variety
known as Hall, at West Willow, Pa., it was estimated that one fly
was present for every two nuts on the trees. The variation in the
numbers of flies on individual trees was followed by a corresponding
abundance or scarcity of maggots in the nuts of each.

Flies were observed to feed upon the juice that flowed from ovi-
position scars and upon the naturally more or less gummy surface
of the nuts. In feeding they would eject from the mouth a particle
of clear liquid onto the surface and after working it over with the
purselike, external mouthparts would swallow it again.

NATURE OF INJURY.

in native black walnuts the eggs of the husk-maggot fly are
usually deposited so late in the season that the resultant maggots
do not prevent the nuts from maturing and dropping normally.
Thus, while apparently all the eggs are laid in nuts on the trees,
the development of the maggots and the blackening of the husks:
which results from their feeding take place chiefly in fallen nuts.
In Persian walnuts, however, eggs appear to be laid earlier in the
development of the nuts. Bearing trees were observed in Maryland
and Pennsylvania, a short time before the crop had ripened, on which

WALNUT HUSK-MAGGOT. (i

a large percentage of the husks of the nuts were blackened through-
out and the surface covered with a gummy exudation from the mag-
got injury within. Some of the infested Persian walnuts drop
prematurely and others hang to the branches until after the
sound nuts have fallen. In nuts that are attacked before maturing
the development is arrested and the kernel becomes unfit for use.
The injury is thus threefold, in that it impairs the quality of the
kernel, causes the husk to stick to the shell in the hulling process, and
blackens and soils the shell, making the nuts unattractive for market.

NATURAL ENEMIES.

Only one parasite of the husk-maggot has been discovered. This
is a hymenopterous species, Aphaereta auripes Prov., reared from
the puparia by Babb (°) at Amherst, Mass. The writer, on Sep-
tember 8, 1920, found a small leaf-bug, determined by W. L. McAtee
as a species of Lopidea, with its beak inserted through the skin of a
black walnut sucking out the contents of a batch of fresh-laid husk-
maggot eggs. An examination of the eggs showed that a number of
them had been punctured and emptied by the bug.

METHODS OF CONTROL.

Experiments in controling the husk maggot with lead-arsenate
sprays were conducted in 1920 in the Persian walnut groves of Mr.
N. H. Baile, at New Windsor, Md., and of Mr. J. G. Rush, at West
Willow, Pa. Only a single application of the spray was made in each
ease. The grove of Mr. Baile consists of about a dozen seedling trees
of various sizes, some of them about 30 years of age. At the time
of the spraying all were bearing heavy crops of nuts. This grove
was sprayed by means of a power sprayer on August 10, with 3
pounds of lead-arsenate paste to 50 gallons of water. The grove of
Mr. Rush consists of 18 trees of named varieties, all of bearing age.
The trees were producing heavily at the time the spray was apphed.
The spraying was done on August 9, using 15 pounds of lead-arsenate
powder to 50 gallons of water. Two trees of the variety known as
Rush, three of Hall, and two of Mayette were sprayed with the lead-
arsenate solution to which enough molasses had been added to give
the liquid a slightly sweetish taste. For treating the Rush grove a
small hand sprayer mounted on a wheelbarrow was used (PI. I).
The trees of both groves had borne the previous season, but the crops
had been injured seriously by the attacks of the maggots.

At the time the groves were sprayed the adults of the maggots
were appearing on the trees and a close examination of the nuts in
the Rush grove disclosed one batch of freshly laid eggs. After the
spraying the Baile grove was not revisited until the nuts were almost

6 Bass, G. KF. op crt.

8 BULLETIN 992, U. S. DEPARTMENT OF AGRICULTURE.

ripe. The Rush grove, however, was kept under close observation
by Mr. Rush and the writer. The flies became very numerous on the
trees of this grove for a period of a few days after the spray was
appled and then decreased in numbers.

Examination and counts of the nuts of the sprayed trees in the
Baile grove just before the crop was gathered showed that 4 per
cent of the nuts had been attacked by the maggots, whereas at least
60 per cent of the crop had been destroyed by the maggots the pre-
vious year. In the Rush grove it was estimated that the condition
was 75 per cent better than the year before when no treatment was
given. No Persian walnut trees were found near either the Baile or
Rush groves that were suitable for use in checking up definite results
of the spraying. However, a comparison of the sprayed nuts with
those produced by the same trees the previous season and with those
produced in other localities the same season, together with the known
abundance of the flies that appeared early upon the sprayed trees,
indicates decidedly beneficial results from the treatment.

Flies confined in roomy wire-screen cages were observed to feed
freely on sweetened water to which sufficient lead arsenate had been
added to give the liquid a milky color. It must be admitted that
these flies succumbed very slowly to the poison. Further tests of
this treatment must be made before it can be recommended unre-

servedly as an effective and sure method of control for this pest.
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