The potato-tuber moth. (Phthorimaea operculella Zell.), A preliminary account

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PAPAALAPAAT:
Issued December 4, 1912.

oS: DERARDMENT OF AGRICULEURE,

BUREAU OF ENTOMOLOGY—CIRCULAR No. 162.
L. O. HOWARD, Entomologist and Chief of Bureau.

THE POTATO-TUBER MOTH.

A PRELIMINARY ACCOUNT.

BY

F. H. CHITTENDEN, Sc. D.,
In Charge of Truck Crop and Stored Product Insect In vestigations.

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1912

BUREAU OF ENTOMOLOG Y.

L. O. Howarp, Entomologist and Chief of Bureau.
C. L. Martarr, Entomologist and Acting Chief in Absence of Chief.
R.S. Currton, Executive Assistant.
W.F. Tastet, Chief Clerk.

F. H. CuirreNnDEN, in charge of truck crop and stored product insect investiyations.
A. D. Hopxrns, in charge of forest insect investigations.

W. D. Hunter, in charge of southern field crop insect investigations.

F.M. Wesster, in charge of cereal and forage insect investigations.

A. L. QUAINTANCE, tn charge of deciduous fruit insect investigations.

E. F. Puriies, in charge of bee culture.

D. M. Rocers, in charge of preventing spread of moths, field work.

Rota P. Curriz, in charge of editorial work.

MaBeEL CoLcorp, in charge of library.

Truck Crop AND STORED PRopuct INsEecT INVESTIGATIONS.
F. H. CHITTENDEN, 17 charge.

H. M. Russet, C. H. Popenoz, Wm. B. Parxer, H. O. Marsn, M. M. Hien,
Frep A. JoHnston, D. E. Finx, Joun E. Grar, A. B. Duckett, eniomological
assistants.

I. J. Conpirt, collaborator in California.

W.N. Orp, collaborator in Oregon.

Tuos. H. Jonsgs, collaborator in Porto Rico.

Marion T. VAN Horn, PAu ine M. Jonnson, Anira M. BALLINGER, preparators.

II

pee COPIES of this publication
may be procured from the SUPERINTEND-
ENT OF DOCUMENTS, Government Printing
Office, Washington, D. C.,at 5 cents per copy

CIRCULAR No. 162. Issued December 4, 1912.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

THE POTATO-TUBER MOTH.'

(Phthorimea operculella Zell.)
By F.'H. Curtrenpen, Sc. D.,
In Charge of Truck Crop and Stored Product Insect Investigations.

INTRODUCTORY.

For many years the potato-tuber moth, known scientifically as
Phthorimea operculella, Zell., has been the worst potato pest in
California. It has now reached the State | ee:
of Washington and menaces adjacent
States. This insect feeds also upon to-
mato, eggplant, and tobacco, which do
not, however, as a rule, suffer much injury.
When it occurs on tobacco it is known as
the splitworm.

The mature moth of this species, which
is quite small and grayish in color, is
shown in figure 1, a; the larva is shown in
band c; andthe pupa in d. Sizes are in-
dicated by the size lines in the figure.

The eggs may be laid upon the leaves or yy. 1.—The potato-tuber moth (Phtho-
onvother parts, ol the plants and) the mi |) 122 eperculelia): 2, Mou; 0, larva,

: E lateral view; c, larva, dorsal view; d,
Mie mealeg pillars Ok awOritis GuICkhy= DOLE Ya pupa. 2 pe seements lof larval on
Denwcen thersuraces son tie leaves on into teed 9 Ctedrawm tomr Riley and

: é 4 : Howard.)

the potato skin, which they mine in every
direction, finally devouring the exterior. It is believed that there
are two or more generations in the course of a summer, and certainly
another one can be producedin store. It thus happens that this insect
belongs to both truck-crop and stored-product insect pests.

An example of injury by this species to potatoes is shown in figure
2. Ataisasection showing the eggs at the top; at b, a badly infested

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dye fli
ded fj /Jp

i The account here given is preliminary in character and issued with the purpose of warning potato
growers and giving general information in regard to remedies. Work has begun on this species and will
continue. :

63079°—Cir. 162—12 1

92 THE POTATO-TUBER MOTH.

potato in section; at the left is a section containing two pits, d and
f, in which the larva has been at work, while at 6 and ¢ are shown
the egg, highly magnified.

od)

DISTRIBUTION.

This species is widespread in its distribution, but in this country,
until the present year (1912), we did not know of its rapid dissemina-
tion. Abroad it is well known in Hawau, all portions of Australia,
New Zealand, Algeria, and many other countries, including southern
Europe. As an enemy to tobacco it has been known for several
years in Florida and in North Carolina, South Carolina, and Virginia.'

The directions for applying remedies
which follow are for the benefit of per-
sons inquiring in regard to means of
control. Which of these should be
used can be best determined by trial in
the different localities under the differ-
ent conditions in which the insect ex-
ists. This applies especially to the
question as to the best material for
fumigation.

EVIDENCE OF IMPORTANCE.

As evidence of the importance of the
pest a few quotations or notes should be
4 made.
er ae Mr. J. E. Graf, working under the

Fic. 2.—Work of the potato-tuber moth:a, direction of the writer, wrote:
Section of tuber, showing eye and eggs :
deposited about it; b, egg in outline; c, In September, 1912, an unusual outbreak of

egg, lateral view; d,f,mines of larvain this pest occurred at El Monte, Cal., due entirely
potato. a, Natural size; 6, c, greatly en- ¢) a combination of circumstances. Thousands
larged; d,somewhatreduced. (Redrawn i 2 : i
from Riley and Howard.) of acres of potatoes were planted in southern Cali-
fornia—mmany more than the market would stand.
This meant that the market was continually clogged and the prices were poor, so that
the crop was worked off very slowly. The tuber moth (Phthorimzxa operculella) is
alwaysiound here, but the crop is generally handled so quickly and carefully that small
lossresults. This year, however, careless work and the leaving of potatoes in the
ground too long have given the insect a tremendous start, and now its ravages are
greater than ever before. A combination of the moth and low prices has so discouraged
many of the growers that they are leaving their potatoes to rot, and as these are becoming
infested there will be a great number of moths waiting for the fall potatoes. * * *

Later, September 17, 1912, Mr. Graf wrote in regard to this species
that two growers near E] Monte, Cal., lost $90,000 and $70,000,
respectively, on potatoes that year. Items of this kind show the
necessity of investigating the problem. .

1 It is somewhat doubtful if the splitworm on tobacco and the potato-tuber moth are the same insect,
although they appear to be identical according to the best authorities on thesubject. This is a matter to
be settled later.

THE POTATO-TUBER MOTH. 3

Aside from numerous similar complaints, including the usual num-
ber from California for the past two years, this species has been re-
ceived from Eagle Lake and Hallettsville, Tex.; San Jose, Costa Rica;
Seattle, Auburn, and Yakima,Wash.; New York City, where it has not
become acclimatized so far as known; Fort Collins, Colo.; and Lari-
more, N. Dak. These records include only occurrences on potato.

In the case of the last report the tuber moth was stated to have
been imported into southern California in potatoes from China. It is
doubtful if the species has been introduced into North Dakota, but
inquiries have been made in regard to the danger of its being intro-
duced there as well as into Minnesota and some other States.

REMEDIES.

The potato-tuber moth is a difficult insect to control. It is not
possible to reach the tuber worms in their mines in the potatoes or in
the stalks or tubers growing in the field, which makes it necessary to
proceed against the pest by other methods. Of these, several must be
employed to insure success.

The first measure consists in the maintenance of clean methods of
cultivation. This implies that all infested potato plants and solana-
ceous weeds, such as ground cherry, bull nettles, horse nettles, and
volunteer potato plants, growing in the same vicinity as the potatoes,
must be destroyed. This can be done by prompt burning as soon
as insect infestation is manifest. The burning of the weeds will
eliminate places for the breeding of the insect or for its successful
hibernation. Domestic animals such as sheep and hogs are valuable
for the destruction of remnants and may be utilized by merely turn-
ing them into the field.

Crop rotation, as in most other cases of insect injury, is desirable
where possible, and the cooperation of all potato growers of the neigh-
borhood is practically a necessity. In certain cases, as, for example,
i a county where many potatoes are grown, it might be possible by
legislation to enforce the discontinuance of potato planting for a year,
requiring at the same time the destruction of the weeds which serve as
food plants. There are several alternate food crops which do not
suffer materially from this insect. About the best of these are
leguminous crops, like beans, peas, cowpeas, alfalfa, and clover.
These possess a dual value, as they all act as soil restorers. Sugar
beets, celery, and crucifers are also good as alternate food crops.
Grains may serve in the same way, as they are not attacked by the
tuber moth. Care in digging is advisable in order not to cut into the
tuber or leave dug potatoes in the field over night where reinfestation
could occur.

FUMIGATION.
“While all of these remedies are of value, the best remedy is the
fumigation of infested tubers with bisulphid of carbon or hydrocyanic-

4 THE POTATO-TUBER MOTH.

acid gas. If bisulphid of carbon is used, it should be at the rate of
3 pounds tc 1,000 cubic feet of air space, including the potatoes;
1 ounce to a barrel of 96 pounds’ capacity would not be excessive.
With an exposure of not more than 24 hours, no harm should be done
to the potatoes for planting. The bisulphid should be evaporated in

Fic. 3.—Fumigator used for stored products infested by insects. (Author's illustration. )

tins, like pie plates, and a cover should be placed on the top of the
fumigating barrel or box so as to make it as nearly air-tight as possi-
ble. At the end of 24 hours the potatoes should be removed, placed
in a fresh barrel, and closed up.

Where it can be conveniently done hydrocyanic-acid gas should
be used in a specially constructed fumigator (see fig. 3), also gas-

THE POTATO-TUBER MOTH. 5

tight. In the case of bisulphid of carbon there is great danger in
bringing the chemical into proximity to fire, such as a lighted lantern
or cigar, for the gas is highly inflammable and even explosive. Then,
too, the bisulphid-of-carbon method costs slightly more than the
hydroevanic-acid-gas method.

Fumigation with hydrocyanic-acid gas, properly performed, is
not dangerous, but 1f improperly performed is decidedly dangerous
to human and other animal life, as the fumes are very poisonous and
are deadly when inhaled in any amount. This gas is more pene-
trating than bisulphid of carbon and can be used by an intelligent
person without trouble, if he first familiarizes himself thoroughly
with the procedure by carefully studying the printed directions or
assisting some one who has had experience in this work. The cubic
contents of the receptacle to be fumigated, on which is based the
amount of chemicals to be used, can be readily computed.

THE CONSTRUCTION OF A FUMIGATOR.

A building, box, or room (see fig. 3) of about 100 to 200 bushels’
capacity suitable for the fumigation of a quantity of potatoes would
contain about 500 cubic feet. A fumigator of this cubic capacity
might be built 8 feet square by 8 feet in height. A good, and perhaps
the best, means of preventing the escape of the gas would be to line
the fumigator with sheet tin, with soldered joimts, and over sheathing.
Another method would be to sheath the room inside, cover the walls,
ceiling, and floor with tarred or heavy building paper, with jomts
well lapped, and cover the inside with matched ceiling boards. The
fumigator should always be equipped with a tight door in which the
joints have been broken, similar to the door of a refrigerator or safe,
and should close with two refrigerator catches against a thick felt
weather strip, which should render it practically gas-tight. Thus
constructed it would furnish sufficient space for the fumigation cf
about 200 bushels of material. There would also be sufficient space
for the apphcation and diffusion of the hydrocyanic-acid gas,' carbon
bisulphid, or other fumigant from the top with a charge more than
necessary for the quantity of potatoes treated.

Approved:

JAMES WILSON,
Secretary of Agriculture.

Wasurneton, D. C., September 30, 1912.

Note.—Fumigation with hydrocyanic-acid gas is considered in Circular No. 112, which will be sent to
anyone who requests it, stating that it is to be used for the potato-tuber moth. j

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