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Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

RECEIVED

U.S. Dep't of Agricufture,

: ve MAR 31 1909 » -

LIBRARY ;:

Soa NA NINA NINA A CEN NA
SANTA NE AAA .

CIRCULAR No. 43, SECOND SERIES.

United States Department of Agriculture,

DIVISION CF ENTOMOLOGY.

THE DESTRUCTIVE GREEN PEA LOUSE.

(Nectarophora destructor Johns.)
RECENT INJURY.

One of the most destructive and troublesome insects of recent years
is a little green plant-louse which, from its injuries to peas, is known as
the destructive green pea louse. Since it first attracted attention by
its ravages in May of 1899 it has steadily increased in injuriousness, and
has been the cause of great loss in the principal pea-growing regions of
this country, especially where peas are grown for canning. It was, in
fact, one of the most important of all insects that ravaged crops in the
United States during the seasons of 1899 and 1900, and there appears
to be little prospect, unless the unforeseen happens, of any decrease in
its devastations. On the contrary, it is to be expected that it will
widen its range geographically, as it has apparently already done to
some extent.

DESCRIPTIVE.

This plant-louse is one of unusual size among those found infesting
gardens, and the largest of the green species which attack the pea and
related plants. The length of the body of winged, viviparous females
is about +3; inch. (4.5 mm), and the total wing expanse about +4; inch
(9to1llmm.). The general color of both the winged and apterous or
wingless forms is uniform pea-green, the same color as the insect’s
favorite food plant.¢

a The eyes are prominent and reddish brown in color. The antenne are lighter than the
body and the tubercles prominent; the joints are darker than the rest of the segments, the
seventh joint filiform and fuscous. The legs are long and conspicuous; tarsi, distal ends
of tibiz, and femora fuscous. The nectaries are fuscous at the tips, otherwise of the same
color as the body.

Nore.—Several more or less comprehensive articles have been published on this insect,
notably by Messrs. Johnson and Sanderson, of the Maryland and Delaware Agricultural
Experiment Stations, respectively, as well as by the writer. The former gave it the scientific
name which is used here, but the latter has recently given reason to show that this insect
is In reality a European form known as Nectarophora pisi Kalt. The question of the
identity of the species, as well as other technical details, are necessarily excluded in the pres-
ent circular, which is prepared as an aid to the correspondence of this office and is drawn,
in the main, from matter already made public——?. H. C.

32365—No. 43—06

Z

A typical winged female of this insect is shown in figure 1 with wings
expanded, showing venation at a, and a lateral view of the same with
wings folded in their natural position when the insect is at rest or feed-
ing is presented at 6. At c an apterous or wingless form of the insect
is shown, and d i!lustrates the nymph in its last stage. The structure
of the third antennal joint of the winged form may be seen at ¢ highly
magnified.

DISTRIBUTION.

From the fact that this species had remained unrecognized until
1899, and has not been found elsewhere than in the United States, the
conclusion was reached by some writers that it 1s indigenous to this
country. Although this may be true, there are better reasons for

Fie. 1.— Nectarophora destructor: a, winged female; b, same from side with wings folded in natural
position when feeding; c, apterous female; d, nymph in last stage; e, third joint of antenna of winged
form—a-d, much enlarged, e, more highly magnified (author’s illustration).

believing it to have been introduced from abroad, probably from
Europe, one being that injury of the severity noted te a species hith-
erto cameos as distinct from others of its kind is almost without
a parallel in the history of economic entomology. It seems probable,
therefore, that we have in this pea louse a case analogous to that of
the European gypsy moth, which was present in this country for about
twenty-five years before it became a pest.
The first notice of severe attack to pea that can with positiveness be
attributed to the destructive green pea louse was reported to this office
in a letter dated May 16, 1899, by Mr. Thomas Bridges, Bridges, Va.

3

This was followed within the next few days by reports from Virginia
and Maryland, and soon afterwards injury was recognized in other
States and Canada. During the previous season (1898), however,
this pest was present in some numbers in certain fields in Maryland
and was noticed on late peas in New Jersey.

From present information it seems that this insect has been gener-
ally injurious during the years 1899 and 1900, although somewhat
locally in’some States, from Nova Scotia south to North Carolina and
westward to Wisconsin. At the time of writing, the insect’s occur-
rence in destructive abundance has been noted, by correspondents of
this office, in Nova Scotia, New Brunswick, and Ontario, Canada;
Maine, Vermont, Massachusetts, Connecticut, New York, New Jersey,
Pennsylvania, Delaware, Maryland, District of Columbia, Virginia,
North Carolina, Michigan, Ohio, [llinois, and Wisconsin.* Injury to
peas in the State last mentioned was not noticed prior to 1900.

EXTENT OF INJURY AND METHOD OF WORK.

This pea louse during the first season of its abundance overran and
laid waste fields of peas from Nova Scotia and Maine to Virginia and
Maryland, in the last as well as in some neighboring States destroying
about 50 per cent of the annual output and doing similar injury the
following year, in spite of the vigorous efforts that were made to con-
trol it.

An estimate of the total loss for the year 1899 along the Atlantic
Coast States reached the sum of $3,000,000. During 1900 the loss
over the same area was placed as early as June 15 at $4,000,000. Sev-
eral cases of severe damage were reported in Maryland, in which 80 or
more per cent of the peas on farms of 500 or 600 acres were completely
destroyed. Inshort, the pea growers of the Atiantic region and west-
ward as far as Wisconsin suffered very severe losses, which gave rise to
the expression that this country had been visited by a veritable scourge.

The reasons why the species has become so conspicuous a pest are
threefold— First, because of its ravages to a crop hitherto little trou-
bled by insect attack, if we except the pea weevil, which has always
been present in gardens and fields for upward of a century and has
come to be looked upon as a necessary evil; second, because it isa
species never before noticed, so far as records go, as having been
destructive to peas in this country; third, because of the great diffi-

a Mr. Sanderson has also recorded the species (assuming its identity with N. isi) as
occurring m Minnesota and Nebraska. There is evidence that this species was observed
on crimson clover in Delaware as early as 1890, and has perhaps been present along the
Potomac River since, or prior to, 1886 (Bul. No. 26, n.s., Div. Ent., U. S. Dept. Agr.,
pp. 58, 72).

2

culty that has been experienced in its treatment, pea growers during
the first year of its ravages having met with nearly complete failure
in the remedial measures applied.

Although garden and field peas are the crops most injured by this
plant-louse, sweet peas, red and crimson clover, as well as vetches and
tares* are affected, and in some cases have been damaged. Attack
begins on the young vines; the lice gather in clusters at first under
and within the terminals, and as the leaves become covered they
attack also the stems,and by their numbers and voracity sap the life
of the plant. Whole areas of vines are frequently seen covered with
the lice, which in a very few weeks are able to destroy a crop. Attack
is seldom noticed until May® in the more southern States in which the
insect is found, and a little later in its more northern range.

The complete life history of this species is not known, but like other
plant-lice it produces many generations each year.

According to present knowledge, the pea louse hibernates on clover,
particularly crimson clover, from Delaware southward. In the Dis-
trict of Columbia it winters also on vetch. From these plants the lice
spread by flight in April and May to peas, which they attack while
young.

As with other plant-lice, the females at certain periods produce liy-
ing young. These attain maturity in from ten to fifteen days, and
possibly in less time in the hottest weather. Young that were born
March 4 reached full maturity (winged form) March 16, or twelve days
from the time of birth, and reproduced young three days later.

_ As an instance of the rapid reproductive powers of the insect, Pro-

fessor Johnson’s estimate is interesting. He states that females pro-
duce from 110 to 120 young; and that in one case where lice were
observed on the first of May the fields were abandoned on account of
ravages three weeks later. Calculating from the average number of
insects produced each day, which is 6, one individual would become
the progenitor of 423,912 of these lice.

NATURAL ENEMIES.

The efficiency of natural agents in the destruction of plant-lce is
so well known that it has been hoped that some one or more of the
many species observed to attack the destructive green pea louse would

a A considerable number of alternate food plants has been observed for Nectarophora
pist Kalt. in Europe.

b The present year (1901) Mr. Samuel R. Haynes, Portsmouth, Va., reported the presence
of this species in that locality about April 7. During the second week of May the writer
found the insect numerous on crimson clover and vetches at- Washington, D. C., and May
14 it was reported at work upon peas in the District of Columbia, near the Maryland State
line.

5

increase in such numbers as to have an effect upon limiting its multi-
plication. In spite, however, of the closest observation by a number
of persons, the natural enemies have been found to produce only tran-
sient relief, and this only in limited areas, as a rule late in the season,
after damage has been accomplished.

The present list of insects known to attack this plant-louse includes
seven species of ladybirds, or “lady bugs’’ as they are familiarly
termed,’ three species of syrphus flies,? a lace-winged fly,° a soldier
beetle,? and a few minute four-winged hymenopterous parasites.¢

The ladybirds are destructive both as beetles and larve; the syrphus ©
flies only in the larval
condition, which is true
also of the lace-wing fly.
The efficiency of the syr-
phus flies is greatly cur-
tailed by the presence
of a Braconid parasite,’
which has been very prev-
alent during the last two
seasons, sometimes al-
most completely exter-
minating its host in many
fields. Nearly all of the Fie. 2.— Megilla maculata: a, larva; b, empty pupal skin; c¢,

: i beetle with enlarged antenna above—all enlarged (author’s
species observed are well- — anistration).
known enemies of other
plant-lice, and in fact greatly prefer as hosts the cabbage plant-louse
and species found on weeds to this pea louse. The spotted ladybird
( Megilla maculata) and a lace-wing fly (Chrysopa oculata) are shown
in their different stages in figures 2 and 3 respectively..

In addition to the natural enemies that have already been enumer-
ated, several other insects attack this pea louse, among others a small,
red mite (2hyncholophus parvus Banks).

Considering the inefficiency of all other natural agencies, if we except
atmospheric conditions, in the control of this pest, it is hoped that a
common fungous disease of plant-lice, known as Lmpusa aphidis, may
become an important factor. As the development of this fungus is de-
pendent upon rather warm, humid weather and is retarded by drought,
it is fairly certain that atmospheric conditions, after all, are most

a Coccinella novemnotata, Hippodamia convergens, Megilla maculata, Hippodamia gla-
cialis, Adalia bipunctata, Hippodamia 13-punctata, Coccinella sanguinea. > Allograpta
obliqua, Syrphus americana, Sphxrophoria cylindrica. ¢Chrysopa oculata. 4 Podabrus
rugosulus. ¢ Aphidius washingtonensis, A. fletcheri, Praon cerasaphis, Isocratus vulgaris.
J Bassus letorius.

In the above list the species of each class are named in approximate order of abundance
in Maryland, Virginia, and District of Columbia, and consequent efficiency as destroyers of
the plant-louse in that region.

6

important in the limitation of this insect. It is within the bounds of
possibility that the fungus might be cultivated artificially and be
used, when weather conditions are favorable, in the control of this
pest.

METHODS OF CONTROL.

In some instances natural enemies of this plant-louse have done
efficient service. Seldom, however, do they destroy the insects suf-
ficiently early in the season to save a crop. In the course of time,

Lele

Us

i :

UW ire

— 2 —_———

=

Fia. 3.—A lace-wing fiy ( Chrusopa oculata): a, eggs; 6, full-grown larva; c, foot of same; d, same devour-
ing pear-tree psylla; €, cocoon; 7, adult insect; g, head of same; h, adult, natural size—all enlarged
except h, which is natural size (from Marlatt).

many years in all likelihood, these enemies may become more effect- —
ive; hence, in view of the fact that the extermination of the species
even ina limited area is a practical impossibility, anything that can be
done that will destroy the louse without harming its sect enemies is
advisable. If this is to be accomplished it affords in itself a reason for
the rejection of insecticides, none of which are in all respects satisfac- _
tory:

Kerosene-soap emulsion, a standard remedy for plant-lice, care-
fully prepared and diluted with about twelve parts of water, and

of this species it should be stated that it obtains nourishment by suction, and can not
therefore be reached by means of internal or stomach poisons such as Paris green and other

|
aFor the benefit of some persons who are not wholly familiar with the feeding habits _
arsenicals.

7

sprayed upon the infested plants upon the first appearance of the lice,
and so applied that the leaves are wet on both the under and upper
surfaces, has thus far been found to be the most effective of the
insecticides tried. A stronger solution than that specified is apt to
scald the plant, particularly while the vines are young and tender.
Sprays of whale oil and other soaps have been found less useful. The
cost of the kerosene emulsion remedy, however, and the difficulty of
underspraying, its rapid evaporation, and the necessity of frequent
applications, are such as to hardly warrant its use.

The brush and cultivator method.—The best remedy that has yet
been devised is the growing of peas in rows sufficiently wide apart
as to admit of a one-horse cultivator between them. The lice are
brushed from the plants with boughs of pine with their leaves on, and
a Cultivator then follows down the rows as soon afterwards as possible.
for the perfect success of this method it should be practiced in the
heat of the day, when the ground is dry and hot, and the repetition
of the brushing is necessary every three to seven days until the crop
is ready for picking. Such lice as are not buried in the ground by the
cultivator will be killed by the dust which closes their breathing pores,
while a considerable proportion is destroyed also by the force of the
brushing. This method has the advantage of not being so destructive
to the natural enemies as other means that might be employed, the
louse being more fragile and delicate than any of its insect enemies.
Moreover, peas planted in rows to permit of frequent cultivation suffer
much less injury than when sown broadcast. As soon as the last
picking has been made, infested plants should be promptly destroyed
by plowing under.?

The brush and pan method.—This method, which consists in jarring
| the lice from the vines into specially prepared, long, shallow pans in
| which a little kerosene is floating and which are dragged between the
rows, has also given good results, the insects as they come into contact
| with the kerosene being all killed. A bushel of lice was caught to each
| row, 125 rods long, in one instance where this remedy was used. It is.
| practicable only for small areas.

Cultural methods—Of cultural methods there is testimony to the
_ value of early planting, the earliest peas seldom being infested, or at
| least only slightly injured. Very late plantings of peas to be used
_for canning have also escaped ravages in some instances, but it

a We have abundant testimony to the value of this method, but perhaps none more
striking than that on the farm of Mr. C. H. Pearson, a Maryland pea-grower. During
the season of 1900 a six-hundred-acre pea plantation was practically saved by this
method. After other means had failed, the fields were brushed and cultivated every third
day for a period of two weeks. The previous season peas over the same area were
broadcast; so that it was impossible to combat the pest in this manner, and as a conse-
/ quence 480 acres were entirely ruined (Bul. 20, n. s., p. 94; Bul. 26, p. 57, Div. Ent., U.S.
Dept. Agr:). --

8

may be that atmospheric conditions have had something to do with
exemption in the cases which have come under notice.

Rotation of crops is advisable, and it is unwise to plant peas in suc-
cessive years in the same portion of a farm or garden, or in the vicinity
of fields of red or crimson clover, or other leguminous plants, such as
vetch, which are likely to harbor this species.

As has been said, this insect passes the winter on the plants men-
tioned, because peas are not available, and it might be possible to use
small plats of some one of them as trap crops. Crimson clover would
probably be best because of its conspicuousness ana the early start
that it gets in the spring. On the trap plants the lice could be killed
by hand methods, such as brushing from the plants into pans and thus
large numbers of ile insects could be killed early in the season. before
they had opportunity to spread to peas. ‘

In Delaware it has been shown that the practice of keeping the land
well fertilized and frequently cultivated enables the peas, in spite of lice
attack, to produce better crops than would otherwise be made.

The subject of alternate host plants is an important one, since the pea,
being an annual, is not available as food for this plant-louse during
winter, and it is desirable to ascertain all of its host plants, and more
aseeele weeds, as some one or more of these may be factors of
importance in the life economy of the species. It might be necessary
in the future, should the depredations of this insect continue as during
the past two years, to limit the growing of clover and other legumes,
as well as other alternate host plants, if such be found, in the vicinity
of pea fields. I all of the principal alternate plants could be discov-
ered this might furnish a solution of the problem of how to deal with
this insect.

F. H. CHITTENDEN,

Approved: Assistant intomologist.

J. H. BricHam,
Acting Secretary of Agriculture.

Wasuineton, D. C., May 23, 1901.

O