The army worm (Leucania unipuncta Haw.)


Material Information

The army worm (Leucania unipuncta Haw.)
Physical Description:
Howard, L. O ( Leland Ossian ), 1857-1950
United States. Department of Agriculture, Bureau of Entomology ( Washington, D.C )
Publication Date:

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Resource Identifier:
aleph - 29682054
oclc - 28136969
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Full Text

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-&I No u4. St -11i .
C ,{, U, AI NO. "I..t S .'%L' %t '(.L "I..

United Stiltcs )cllparlIncit of Akriculture,


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(iK'NF'I;M\ APPKEAIl\N E AI* \l|.lllr" l S^ s[y^ --

In hil- I itIlt h- of M: y and June. ml.1 -,,iid I
W il'ri. >u' I-. anI d o0 li'l -ii,,ll .-"'iH i ,1 ',',I. fjP\

ch.0,'r. ( ar.[ occasionally overrun )v) it, 11 it "I "
nakud sirieird caterpillars a1mnit an i111 :ii 'o
t'r Iull" niil a quarter of an inch in ,li,,i .1pi .i.. 1'1
fiull-rrwiin, riillir dark in IjiI"r airi'"" 1ii"
Wt 1nblingl F.i1. 1. '\\t usually travel il ,I'i,' ',VI
from i tnIT I h tlI to aui l lt 'r, lh -tr 1iL, 'i,' II I. I I bI p"
go. Thley have *.,iif .^ + i,,. -1 .I -,. 11. .
and c t11 in,1 i"l t lit i. t ,IotLhy ,.ir- :11141 --i' 1- h ,
sm IIl ,ra iins. r*., -

Ti, airirmy worm seems to he an iiII,',,,'i- .,,' h i
A li,'[ n in-rt and on t liis cuTntin 11, iT m1, 11 S
al111dhlanti in the I'nil .d i .11-. east of ttrhe lc k "/
Miiliuii.. Isolated specimInIs iave been i found 1
in Ki: illihilI d ,! ',ilt i America. anld t ie nmlit IT is -
ieelrn I'ljlriirl-1 in I lIdi: Ja\ ;i A 'ustralia. and N ew
Z/ea:iiliiil. It is nowhere kiown as an cspec I-l. Ki
dr- I rI ,iv, -.1 i *. J- I r \i, O II tSide of the 1 lil t d
Sinir- 'lir r,..=i,, in which it cspe, i-,l[\ '..,irishns
extends fi'i,,i eastern Iowa to \! ll'- and fI.nri /
nruli rn Texas to northern Alabama. KI'r ,i the
B il' I, I-." M.i111,:Il(, ix its sout herly r:irI_',' aI an
in jri,,,- -',., i,.- extends only to northern North j
( ,,r ,l i t ,: t T h m o t h is ,l' i 1 1 , ,i,' l o u t s i d e T
hli,,', limits and fri'i .ni v1 in considerable umi- i+ I.-rw. AwrM
)e,,r-. but the caterpillar does not seem elsewhere 0 ,, ,
to be a f. i, i..i' in .-:t.'ri,,l Ir '. ,- w 1 hc ,
i ; -; -,N, I-,i.

Tle adult insect is a brown moth with a white spot on the center of
each forc-wing. as indicated at Fig. 2. The eggs are very minute and
white in color, round, and are laid in st rings of from 2 or 3 to 15 or 20.
Thely are pushed by hti, ovipositor of the female muth down into the
inner base of the terminal leaf sheaths of grasses or grains. (See also
Fig. 2.) A strong effort is apparently made by the female moth to
conceal them. Tl,yv are laid most abundantly in the thickest tufts of
L!_r:-.S which customarily spring up in pastures over spots where cattle
have dropped. In the vicinity of old fodder stacks the grass usually
411, Mv- high, and this also is a favorite place for egg-laying,. The mot hs
do not confine their (,.g -la ying ,iwrat ions to such localities, however,
and the eggs have been found in old
VOrn't under t he shevat h, and
even under the hark of old cedar posts.
The eggs are hatched in from eight
to ten days and the young caterpillars
feed for a time in the fold of the leaf,
growing ral)idlly, and finally consum-
ing entire leaves.
Under ordinary circumstances, and
when not present in great numbers,
the larve feed miin1\ at night and in
Sdamp cloudy weather, remaining hid-
FIG.2.-T ARMY VoRM Luania un den duri sunshiny days. In this
puncla): Moth above, pupa below. and
eggs in natural position in a grass leaf- respect they resemble in habits the
all natural size. (From Comstock.) closely allied cutworms. They reach
full gr\,wth in three or four wek,. burrow into the around, and
transform to the brown pupae shown at Fi,,. 2. In lthi condition
thwv remain in the summer time on an average about two weeks,
when the moth aurain appears.
The number of :gnerit ions each year varies with the climate and the
season. There are, in the more northern Statcs. two or three genera-
tion and perhaps six in the more southern Statrs.
We have said above that the insect normally feeds by night and
hides by day, and to this habit is due the fact flint. ailthnIugh the army
worm is present every yenir all through the region especially indicated
in a previous pa raIrra1dl. it is only noticed when it becomes excessively
,iiindaint. and this occurs usually only at intervals of several years.
With a favorable succession of seasons the insect multiplies in geo-
metrical ratio. and at last becomes so numerous as tonecesitate mnigra-
tion for food. It then travels and feeds (lIIrinI, both day and night,
and it is Ohwn that the insect becomes very injurious and that reports
of _i. ,.It ,lin-izoe are heard.
Tlw insect passes the winter iiriailly, as do most of the related cut-
S*I II-. inII the hialf-gruowu caterpillar or larval condition. In t hlie South

I l .I, iii IIt I -I' ll I hibernat s sI t m oth iI. and there, is s me -v itdI'nt'e
thait it m Ia pIss the, \inter ,11i ..imi-i ,lly, altl,",-i'it \xceptio Mlly, ill
the it,. state.
The injiiujilrioutlS brood iaily he tii iirsl, scot. nd, or third. The over-
wiuitered larv:a'1 may '. ..i-i, ..ll\ e sI lia u lant 11" l t tlrtil notice,
Il)it in the 11i1 ijril\ of oaes it i the ,ll''- i i._' of le ov rw iiIteIred
ililiiv illual, which caIit alarmi.
li LIi'ie Iil i it may e : said t iat the lit ri ormi a re irte apt Io iinake ill
injiiriu, l- ppeliil' iii e in a rain i>] ii_ or( i early s miier follow]\ i a
seVIl.. Ii of t',oii 'il' ive droI ut Ii. The pleseM sao'l St I) 'Ilers out
tli.'' conditions in the Iti-ierln Satesl ind as a matter o4f flact the
ariliv ll'lriii hlas been lnore ;lii inl.iiil in certain ell tern ectioi thllan
it hi-. beenl sillce ISS.
There is never anit demnand upon this ,,Ili,., for reAmedies for tlie
armi v worml until it is Alii a laA to) bite io do ii\ ililliediaite .A
Th re lare certain old-tinie iile.ii-ii'r, wliich tia lie ail,|le(d to protect
certaiiIl fields from a1viitilii aiiiii,- like the 1l,1". ii-' of a furrow with
it. lerltitliiiilar side toward the field to he proic'tted and the subse-
quent drL.imig of a !,,_', tlirnii.i the fiirl.'>, to keep thle earth friable
and kill the worms which liavi accummi atitie in the ditch, anld another
iis the .ipriikliin-_r of ai strip af paImture or field cr'Ip in ald\llance of an
iarmy with Paris Lrr'ciiI or Liii.iIiI purple in sohution. Ilii ,I.- which(I
the caiiterpillars have already entered there is little which can be done
for their destruction which does not also involve the, destruct ion of the
crop. Tihe. fields many be sprinkled by iieans .,I' a Irtoadtcatt sprayer
willi tin i'eiaiin'l ,ililIi. or tihey ma ie rolled w\ithi a heavy roller
where one is at. hand and the -',innd is level, or a flock of sheep aili be
senil in. which will result in I ri.lii-, almost of tilhe woris byr traiiri[lin.
In the _roli iii ,:lj'nit;y of cases, however, t liese latter imieasiires are
Sunne'essary, for the reason Til 1 nature lir' Ilf aliioIst ailwav takeI s a
|handI in the reduction of the exess-ive numbers of thle iiset, either bIv
1unfaitIrali, weat her condit ion, or by the excessive n1ultiplicatlion of
iluiridl enemies and parasites. o that it is exiriimelv rarely thia we
heir ,f, one army-wormn otitbreak mi ii,'nI \ iel foll, i "I, another.
in 'qci. l',l. therefore, it iiay bye said that, as soon ai the worliim are
di,,.overed to be exceptionally vtinuleroisl in a given field (aldt, as a
matter of falt. ill.,v are at lir'-i almost invariably reNstrictedit to tihe
immediate ui,,i',.,ad of some Ideliil liii ilted, permniilent breed-
il,' planet), all 'iin.r,'iv .Iiamiild be devoted to the protection of the Sur-
rni tnini_, rop] hy the means mnentimoned above, and the destruction
of the wornms in thlie lield first attacked may he safely left to the last.
There are many localities in which the armiy worm is never -,eli. or,
ralither, is never known to be injuirio ,i'. and these localities owe their
exemlptin undoilbliedlv to the unconscious use of preventive llmeas-


ures. Clean cultivat in, rotation of crops, cleaning up fence corners,
close pait iurage, the turning over of waste grri- land in spring or fall
are all preventive measures of great value, since, where these methods
are in v,'guc, the army worm will never be able to get a migratory
start, or, in other words, it never becomes so abundant as to necessi-
tate iigr:rat ion.
Bearing in mind the fact that the insect breeds norinallv in rank
gr such as is usually found along the edges of swamps (not in
swa r i ip. for the insect must have comparatively ,dry earth in which to
pupate) or in accidentally overfertilized spots in pasture lands, and
that it feeds normally only upon true grnisses, the farmer who has
once suffered from armyi-worm attack may easily prevent its recur-
rence by winter burning or by rotation and clean cultiva t ion.
In cases where the worms have already entered a valuable field of
wheat before the farmer has become aware of their l)resewnce, and too
late to render (lit(hiinz of any avail, some little good may be accom-
plished if the majority of the worms are full grown, or nearly full
grown, by the old method of "druggring the rope." Two men, each
having hold of the end of a long rope, are sent through the field and
the rope is dragged over the heads of the grain. The backward jerk
of the stalks jars the caterpillars to the ground. and they are unable to
ascend to the heads again for some little time. This is a laborious
process, however, and has to be repeated almost immediately. It is
only to be undertaken where the number of worms in a field is conm-
paratively small and where these are. as before stated, full grown or
nearly full grown, since in this case they will stop feeding and enter the
ground in a day or two.
There is almost no prominent injurious insect in whose economy
natural enemies play a more important part than the army worn. We
have said above that in the great majority of cases actual destructive
measures against army worms which have once taken full possession
of a grass field are hardly necessary. This is because of the fact that
generally not more than one worm out of a thousand escapes death
from parasitic or predaceous insects. Where the army worm follows
its normal habit and feeds only at night. remaining hidden during the
d(lay under the surface of the ground at the base of sonime tuft of rank-
g.gri in1g gra-.-. it is protected from these natural enemies. but when the
iii,_'riilory instinct drives it forth and perverts its normal habit, caus-
ini,- it to march unprotected during the day, the swift-breeding tachina
flies attack it at olie,.. multiply most rapidly, and in connection with
its other parasites and with the predatory grounmd-b)eetles, reduce its
numbers )once more to the noninjlriii,,s point. We have said this is
generally the case: there may be exception,-, but we have never seen
onle. It is important, however, for the farmer to be able to recognize

thi, a~~l,,nnrL, ,' ,, p -rasitizedl wom. s in this woyv his confidence in
ih v full in Iua l he Ietorled.
\\e, -how at Fi_". tile head andl I1,,,1 **,, i ,n ts 4Of an 1r011 ,w im
h~ean1. rn-.' .:-* ,,f tihe redl-taihed tachil~ii-ly ( \'+nirenr,. ml~i iria Ti,,.
.- ie while, oval, Ie-s than a oI e-sixtect 11h 1i I n inch Iii anl tire
glhedi fast to tIlle skin f t he cat erpi 11.r,
muLu21k oI the huik of tile fro ml _''' A
Fromin half a dozen to li'iy or iwmv of tdi 4lw,
eg"- iiiI\ t1w attached toi a -~ _'. cat. tI illar,
andii froi, each hatch les a \\hi_., t thichi ] 1
Itrt.. heli ,ody of the arm wori 0m1 anlilti- f
h11ml0 l llltinir to cast its skin so Ion Iafter
th1n. e_,.:-, L r, laihd that they do not hliave t ne Ilt'O :l TIK1)T.U. l I N -
to hutclh. The adult tachina-lly riescniuhs pe- ,rm t rh .' iath.o
1 n t1 h r l:r l, c-.-ll \ xcept that it ha- trm ,>h, ,;. w ,,. <
hu\uiiitl't I l++ti ++gg ,ttph-
a re i lip to its abdomien. lHlunlreds and al -m+t -rg4. From
lli oniii I-k of these flies are usually seen
bi.zzin ii bout a field infested by the army worni, and their lres'nce
sh,,uld be welcome to the farmer.
Then extent of the parasitism of the injurious b)rood of the army"
wvIrin iiivY be indicated h. two instances from our plersoal ', ,1ri,'.l .
in I.,.,t I we visited a hS up tract of land planted in tim thv -r:I--. in
ihe vicinity of Portsmouth. Va. A searchl for hours .lliiii.l the hot
part of the day fiild to show a .in1l, worn w which did uot bear tachina
e'gi.,. In 1,-',2 we visited \wheat tiehls in the vicinity of Iluntsvilhle, which were then 1,,ii1_' overrun by thlis insect lHere, alto,112'li a
mnumlber of worms were noticed which did not bear tachina .-'-. they
were destroyed by ,.'r,,i il-beetles to such an extent that when we
atl,,1iiptd.1 to catch an adult mnoth a little later in the season by meansI
of tIrpl lanterns and -11 ',, i- we were unal)ble to secure a -iii'l sWpecimen.
The entire army had been :,i1ii il:dtied, and it is worthy of remark that
in neilltiher of these localities has the a-my, wormin ever been seen since
in injuri,,u, numbers. ,Idt ,,'l, fourteen years have elapsed in t he oe
cas and twelve in the other.
L. 0. Ilow'Ii),


. I IFII( I tillrN ,

WA+IhIN4TON, I). (C., NIt/im ;. 1 N1';.


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