THE DESTRUCTIVE GREEN PEA

Circular No.43,Second Series.

United States Department ^of Agriculture, DIVISION OF ENTOMOLOGY.

THE DESTRUCTIVE GREEN PEA

LOUSE.

(XectarophoradestructorJohns.)

RECENT

INJURY.

One

ofthe

most

destructive

and

troublesomeinsects ofrecent years

is alittlegreenplant-lousewhich,

from

itsinjuriestopeas_;is

known

as the destructive green pealouse. Since it first attracted attention

by

itsravagesin

May

of1899ithassteadilyincreasedin injuriousness,

and

hasbeenthe causeofgreatlossintheprincipalpea-growingregionsof thiscountry, especially

where

peas are

grown

forcanning. Itwas, in fact, oneofthe

most

important of allinsectsthatravagedcropsinthe UnitedStates during theseasons of 1899

and

1900,

and

thereappears tobelittleprospect, unlesstheunforeseenhappens, of

any

decreasein 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-louseis one ofunusual size

among

thosefoundinfesting gardens,

and

thelargest ofthegreenspecies

which

attack thepea

and

relatedplants.

The

length ofthe

body

ofwinged,viviparous females

isabout _T³g inch. (4.5

mm), and

the total

wing

expanse about _T⁴_o inch

(9to 11

mm.). The

generalcolor of boththe

winged and

apterousor wingless forms ^is uniform pea-green, the

same

color as the insect's favoritefood^plant.a

aTheeyes areprominentandreddishbrownincolor. Theantennae are lighterthanthe body andthe tuberclesprominent; thejointsaredarkerthantherestofthesegments, the seventhjoint filiformandfuscous. The legsare longandconspicuous; tarsi,distal ends oftibiae,andfemorafuscous. Thenectaries arefuscous at thetips,otherwiseofthesame color asthebod}".

Note.

—

^{Severalmore orless} comprehensive articleshave been publishedonthis insect, notably byMessrs. Johnson and Sanderson, of the Maryland andDelaware Agricultural ExperimentStations, respectively, as well asbythewriter. Theformergaveitthescientific

namewhichisused^here,but thelatterhasrecentlygivenreason toshowthatthisinsect is in reality a European form known as Xectarophora pisi Kalt. The question of the identityofthespecies,as well as other technicaldetails,are necessarilyexcludedinthe pres- entcircular,whichispreparedasanaid to thecorrespondence of this officeandisdrawn, inthemain,from matteralreadymadepublic.

—

^F.H.C.

32365—No.43—06

KANSAS

A

^typical

^winged

^{femaleofthisinsectis}

^shown

^{in figure1with wings}

expanded,

showing

venation ata,

and

alateral

view

ofthe

same

with wingsfoldedin theirnatural position

when

theinsectisat rest orfeed- ingispresented at b.

At

c anapterous or wingless

form

ofthe insect is shown,

and

dillustratesthe

nymph

ⁱⁿitslaststage.

The

structure ofthe thirdantennal^{joint of}the

winged form may

be seenat ehighly magnified.

DISTRIBUTION.

From

the fact that this species

had remained

unrecognized until 1899,

and

has not been

found

elsewhere thaninthe

United

States, the conclusion

was

reached

by some

writers that it is indigenous to this country.

Although

^this

may

be true, there are better reasons for

Fig.1.

—

Nectarophoradestructor:a,wingedfemale; b, same fromsidewith wings folded innatural positionwhenfeeding;c,apterousfemale;d,nymphin last stage;e,third joint ofantennaofwinged form

—

a-d,muchenlarged,e,morehighlymagnified(author's illustration)

.

believing it to

have

been introduced

from

abroad, probably

from

Europe, one beingthat injury of the severitynoted

by

aspecies hith- ertounrecognized as distinct

from

others ofitskind isalmost without aparallelinthe history of

economic

entomology. It seemsprobable, therefore, that

we have

^{in this} pea louse a case analogous to that of the

European gypsy

moth,

which was

presentin thiscountryforabout twenty-five years before it

became

apest.

The

firstnoticeofsevereattackto

pea

thatcanwith positivenessbe attributedto the destructivegreenpealouse

was

reportedto thisoffice in aletter dated

May

16, 1899,

by

Mr.

Thomas

Bridges, Bridges, Ya.

This

was

followed within thenext 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 peasin

New

Jersey.

From

presentinformationit seems that thisinsect hasbeen gener- ally injurious during the years 1899

and

1900, although

somewhat

locally in

some

States,

from Nova

Scotiasouthto

North

Carolina

and westward

to Wisconsin.

At

the time of writing, the insect's occur- rence in destructive

abundance

has

been

noted,

by

correspondentsof 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, Illinois,

and

Wisconsin.^a Injuryto peasinthe State last

mentioned was

notnoticedprior to 1900.

EXTENT OF INJURY AND METHOD OF WORK.

This pealouse duringthefirst season ofits

abundance

overran

and

laid waste fields ofpeas

from Nova

Scotia

and Maine

toVirginia

and

Maryland, inthelast aswell as in

some

neighboringStates destroying about 50 per cent ofthe annual output

and

doing similar injury the following year, in spite ofthe 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

overthe

same

area

was

placedasearlyas

June

15at$4,000,000. Sev- eralcases ofsevere

damage

werereportedinMaryland,in

which

80 or

more

per centofthe.peason farms of500or600 acreswere completely destroyed. Inshort,thepea growersofthe Atlantic region

and

west-

ward

as far asWisconsinsufferedveryseverelosses,

which

gaveriseto the expression thatthiscountry

had

beenvisited

by

averitablescourge.

The

reasons

why

the species has

become

so conspicuous a pest are threefold

—

First,because ofits 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 necessaryevil; 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-

aMr. Sanderson has also recordedthe species (assuming its identity with N.

occurring

m

MinnesotaandNebraska. There isevidence that this species was observed on crimson clover in Delaware asearly as 1890,and hasperhapsbeen present alongthe PotomacRiver since,or prior to, 1886(Bui. No.26, n.s., Div. Ent., U.S.Dept. Agr., pp.58,72).

cultythat has

been

experienced in its treatment, pea growers during the firstyear of its ravages haying

met

withnearlycomplete failure inthe remedialmeasures applied.

Although

garden

and

field peas are the crops

most

injured

by

this plant-louse,sweetpeas, red

and

crimsonclover, aswellasvetches

and

tares^a are affected,

and

in

some

cases

have been damaged. Attack

begins

on

the }^oung 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 thelice,

which

inavery

few weeks

are able todestroy acrop.

Attack

is

seldom

noticeduntil

May

⁶inthe

more

southernStates in

which

the insectisfound,

and

alittlelaterinits

more

northernrange.

The

completelifehistory of thisspeciesisnot

known,

butlike other plant-liceitproduces

many

generationseachyear.

Accordingto present knowledge,thepea lousehibernates

on

clover, particularly crimson clover,

from Delaware

southward. In the Dis- trict of

Columbia

itwinters also

on

vetch.

From

these plants the lice

spread

by

flight in April

and May

^to peas,

which

they attack while young.

As

withother plant-lice

;the females atcertainperiods produce liv- 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

4reachedfullmaturity (winged form)

March

16,ortwelvedays

from

thetimeof birth,

and

reproduced

young

three dayslater.

As an

instance ofthe rapid reproductive powers ofthe insect, Pro- fessorJohnson'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 progenitorof423,912 oftheselice.

NATURAL

ENEMIES.

The

efficiency of natural agents in the destruction of plant-lice is

so well

known

that it has been

hoped

that

some

one or

more

of the

many

^{speciesobservedto attack}the destructivegreenpealouse

would

a

A

considerable number of alternatefood plants has been observedfor Nectarophora pisi Kalt. inEurope.

bThepresentyear(1901)Mr.SamuelR.Haynes,Portsmouth,Va.,reportedthepresence ofthisspeciesin thatlocalityabout April7. Duringthesecondweek ofMaythe writer foundthe insectnumerous oncrimsoncloverandvetchesatWashington, D.C, andMay

14itwasreportedatworkuponpeasinthe DistrictofColumbia, neartheMarylandState line.

increase insuch

numbers

as to

have

aneffect

upon

limitingitsmulti- plication. Inspite, however, of the closestobservation

by

a

number

ofpersons, the naturalenemies

have

been foundtoproduce onlytran- sient relief,

and

thisonlyinlimited areas, as arule late inthe season, after

damage

hasbeenaccomplished.

The

presentlist ofinsects

known

^to attackthisplant-louse includes seven species of ladybirds, or

"lady

bugs'⁷ as they are familiarly termed,^a three species of syrphus flies,⁶ a lace-winged fly,^c a soldier beetle/

and

afewminute four-winged

hymenopterous

parasites/

The

ladybirdsaredestructivebothas beetles

and

larvge;thesyrphus

flies only in the larval condition,

which

^is true also of the lace-wingfly.

The

efficiency of the syr-

phus

flies is greatlycur- tailed

by

the presence of a Braconid parasite/

which

has

been

veryprev- alentduringthe last

two

seasons, sometimes al-

most

completely exter- minatingitshostin

man}

^-

fields. Nearly all of the speciesobservedare well-

known

enemies of other

plant-lice,

and

in factgreatly prefer as hosts the cabbage plant-louse

and

species found on

weeds

to this

pea

louse.

The

spotted ladybird

(Megillamaculata)

and

a lace-wing fly {Chrysopa oculata) are

shown

intheir differentstagesinfigures 2

and

3respectively..

In additionto thenaturalenemiesthat

have

alreadybeen

enumer-

ated,several otherinsectsattackthispealouse,

among

others asmall, red mite (RJiyncJiolophusparvus Banks).

Considering theinefficiency ofallother naturalagencies,if

we

except atmospheric conditions, in the control of this pest, it is

hoped

that a

common

fungous disease of plant-lice,

known

as

Empusa

aphidis,

may become

an important factor.

As

thedevelopmentof thisfungusisde- pendent

upon

rather

warm, humid

weather

and

^isretarded

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. ^bAllograpta obliqua, Syrphus americana, Sphxrophoria cylindrica. cChrysopa oculata. dPodabrus rugosulus. eAphidius washingtonensis,A. fletcheri,Praon cerasaphis, Isocratus vulgaris,

fBassusIsetorius.

Intheabovelistthe speciesofeachclassarenamedinapproximateorderofabundance inMaryland,Virginia,andDistrict ofColumbia,andconsequentefficiencyasdestroyers of theplant-louse inthat region.

Fig.2.—Megilla maculata: a,larva;b,empty pupal skin; c, beetlewith enlarged antenna above—allenlarged, (author's illustration).

6

important inthe limitation of this insect. Itiswithin the

bounds

of possibilitythat 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,

Fig.3.

—

Alace-wingfly(Chrysopaoculata):a,eggs;5,full-grownlarva;c,foot ofsame;d,samedevour- ing pear-tree psylla; c,cocoon;_/,adultinsect;g,headofsame; h,adult,naturalsize

—

allenlarged excepth,whichisnaturalsize(fromMarlatt).

many

years in all likelihood, these enemies

may become more

effect- ive; hence,in

view

of the fact that the extermination of the species evenin alimitedareaisapractical impossibility, anythingthatcan be

done

thatwill destroy the louse without

harming

its insect enemiesis

advisable. Ifthisistobe accomplishedit affords initselfareasonfor the rejection of insecticides,

none

of

which

are in allrespects satisfac- tory.

Kerosene-soap emulsion, a standard

remedy

for plant-lice, care- fullyprepared

and

diluted with about twelve parts of water,

and

aForthe benefitof somepersonswhoare notwhollyfamiliarwith the feeding habits ofthisspeciesitshould be stated that it obtains nourishment by suction,and can not thereforebereachedby meansofinternal orstomachpoisonssuchasParisgreenandother arsenicals.

sprayed

upon

the infested plants

upon

thefirstappearanceof the lice,

and

so appliedthat the leaves are wet on boththe

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 scaldthe plant, particularly while the vines are

young and

tender.

Spraysof whaleoil

and

other soaps

have

been

found

lessuseful.

The

costofthekerosene 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 plantswith

boughs

ofpinewiththeirleaveson,

and

acultivator thenfollows

down

therowsassoonafterwardsas possible.

l^or 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 brushingis necessary every three to sevendays until the crop

isreadyforpicking.

Such

^liceas arenotburiedinthe

ground by

the cultivatorwillbekilled

by

thedust

which

closes theirbreathingpores, while a considerable proportion is destroyed also

by

the force of the brushing. This

method

hastheadvantageofnot beingsodestructive 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 plantedⁱⁿrowstopermit offrequent cultivationsuffer

much

less injury than

when sown

broadcast.

As

soon as the last pickinghas

been made,

infested plantsshouldbe

promptly

destroyed

by

plowingunder.^a

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 littlekeroseneis floating

and which

^are dragged

between

the rows,hasalsogiven

good

results, theinsectsasthey

come

into contact withthekerosenebeingallkilled.

A

^busheloflice

was

caughttoeach row, 125 rods long,inone instance

where

this

remedy was

used. It is

practicable onlyforsmallareas.

Cultural methods.

— ^Of

^cultural

^methods

^{there is testimony to the}

value ofearly planting, the earliest peas seldom being infested, or at leastonly 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 nonemore 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 othermeans hadfailed,thefieldswere brushedandcultivatedeverythird day for a period of two weeks. The previous season peas over the same area were broadcast; sothatitwasimpossible to combatthe pest inthis manner,and as a conse- quence 480acreswereentirelyruined (Bui. 20.n.s.,p.94; Bui.26, p. 57,Div. Ent.,U. S.

Dept.Agr.). ^-

8

may

bethat atmospheric conditions

have had

something to do with

exemption

in the cases

which have come under

notice.

Rotationofcropsisadvisable,

and

it isunwiseto plant peasinsuc- cessiveyearsinthe

same

portionof a

farm

orgarden,orin the vicinity offields ofred orcrimson clover, or otherleguminous plants, such as vetch,

which

are likely toharborthisspecies.

As

has

been

said, this insect passes the winter

on

the plants

men-

tioned,because peas arenot available,

and

^it

might

bepossible to use smallplats of

some

one of

them

astrapcrops.

Crimson

clover

would

probably be best because of its conspicuousness

and

the early start thatitgets in thespring.

On

the trap plants thelice could be killed

by hand

methods, suchasbrushing

from

the plants into

pans and

thus large

numbers

oftheinsects couldbekilled earlyin the season before they

had

opportunitytospreadto peas. ^'y

In

Delaware

ithasbeen

shown

that the practiceofkeepingtheland wellfertilized

and

frequent!}'cultivatedenables thepeas, in spite oflice attack,toproducebettercropsthan

would

otherwisebe

made.

Thesubjectof^{alternatehost}plantsis

an

importantone, sincethepea

,

being

an

annual, is not available as food for this plant-louse during winter,

and

^itis desirable to ascertain all ofitshost plants,

and more

especially weeds, as

some

one or

more

of these

may

be factors of importancein the life

economy

ofthe species. It

might

be necessary inthefuture, shouldthe depredationsof thisinsectcontinue asduring the past

two

years, to limit the growingof clover

and

otherlegumes, as well as other alternate hostplants, if such befound,inthe vicinity of peafields. If all of the principal alternate plantscould be discov- ered this

might

furnish a solution of the

problem

of

how

to deal with this insect.

F.

H. Chittexdex,

Approved:

Assistant Entomologist.

J.

H. Brigham,

ActingSecretary of Agriculture.

Washixgtox,

D.

C, May

23, 1901.

O