The alfalfa caterpillar

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Title:
The alfalfa caterpillar
Series Title:
United States. Dept. of Agriculture. Bureau of Entomology. Circular ;
Caption title:
Alfalfa caterpillar (Eurymus curytheme Boisd.)
Physical Description:
ii, 14 p. : ill. ; 23 cm.
Language:
English
Creator:
Wildermuth, V. L
United States -- Dept. of Agriculture
United States -- Bureau of Entomology
Publisher:
Government Printing Office
Place of Publication:
Washington
Publication Date:

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Subjects / Keywords:
Alfalfa caterpillar   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

Statement of Responsibility:
by V.L. Wildermuth.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 029685593
oclc - 28141263
lccn - agr11000494
System ID:
AA00022892:00001

Full Text




LIBRARY -
STATE PLANT BOARP


Issued April 22, P'.ll.


U. S. DEPARTMENT


OF AGRICULTURE,


BUREAU OF ENTOMOLOGY-CIRCULAR No. 133.
L. 0 HOWARD. Entomologist and Chief of Bureau.


THE ALFALFA


CATERPILLAR.


V. L. WILDERM LTII,
Agent and Expert.


WASHINGTON : GOVERNMENT PRINTING OFFICE I11
84054-Cir. 133-11


56
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Pf ?6


/I ,
._. ^ t-^ C ~ *.






















BUREAU OF ENTOMOLOGY.

L. 0. HOWARD, Entomologist and Chief of Bureau.
C. IT. MIARLATT, Entomologist and Acting Chief in Absence of Chief.
R. S. CLIFTON, Executive Assistant.
W. F. TASTET, Chief Clerk.

F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations.
A. D. HOPKINS, in charge of forest insect investigations.
W. D. HUNTER, in charge of southern field crop insect investigations.
F. M. WEBSTER, in charge of cereal and forage insect investigations.
A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.
E. F. PHILLIPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work.
ROLLA P. CUBRRIE, in charge of editorial work.
MABEL COLCORD, librarian.
CEREAL AND FORAGE INSECT INVESTIGATIONS.
F. M. WEBSTER, in charge.
GEO. I. REEVES, J. A. HYSLOP, W. R. WALTON, J. T. MONELL, V. L. WILDERMUTH,
R. A. VICKERY, HERBERT T. OSBORN, agents and experts.
W. J. PHILLIPS, E.O.G. KELLY, GEO. G. AINSLIE, PHILIP LUGINBILL, entomological
assistants.
A. H. KIRKLAND, C. N. AINSLIE, T. D. URBAHNS, T. H. PARKS, E. G. SMYTH.
C. W. CREEL, H. R. WATTS, engaged in alfalfa weevil investigations.
NETTIE S. KLOPFER, ELLEN DASHIELL, preparators.
MIRIAM WELLS REEVES, collaborator.
[Cir. 133]
It







CIRCULAR No. 133.


United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.
L. 0. HOWARD, Entomologist and Chief of Bureau.


THE ALFALFA CATERPILLAR.
(Eurymnus curythicme Boisd.)
By V. L. WILDERMUTH, Agent and Expert.
INTRODUCTION.
The insect under consideration in this circular is the caterpillar
(fig. 1) of one of our most beautiful and common butterflies (figs. 2,
3) belonging to the group known as "the yellows," and is closely re-
lated to the well-known cabbage butterfly. The name "yellows" at
once gives one an idea of the
appearance of the adult, but
this may be misleading, as the
species is polymorphic, the
coloration varying from a Fiu. 1.-The alfalfa caterpillar (Eurymus eury-
bright yellow (very fre- theme): Larva or caterpillar stage. About
y t d, t a twice natural size. (Original.)
quently noticed), through an
orange-sulphur (the most commonly noticed), to a pale white (the
least often noticed).
For some years past the green caterpillars of this butterfly have
been reported from various localities in the southwestern United
States as feeding on, and in some cases doing a large amount of
damage to growing alfalfa (Medicago sativa). It should be men-
tioned here that it is the caterpillar or worm stage of this species that
does the damage, and not the adult butterfly. The latter feeds on
the nectar of the bloom and in no way injures the plant. In fact, the
writer has noticed these butterflies to all appearances springing the
pollen triggers on the alfalfa blossoms while feeding, thus, should
his observations prove correct, benefiting the plant for seed produc-
tion.4 In the year 1906 a correspondent of the Department of Agri-
a Though the author is quite confident of the accuracy of his observations, it
is a case where misconception is exceedingly liable to occur; if correct, however,
the fact is entirely new. See Dr. I. Urban, Verhandlung des Botanischen
Vereins der Provinz Brandenberg, 1872, p. 13; Herman Muller, The Fertiliza-
tion of Flowers, par. 93 and 94, 1873: C. V. Piper, Report of American Breeders'
Association, 1909, Report of Committee on Breeding Forage Crops-F. M.
WEBSTER.
[Cir. 133] 1


Issued April 22, 1911.






THE ALFALFA CATERPILLAR.


culture reported the caterpillar infesting the lucern fields in Big-
horn County, Wyo., and in the year 1907 another correspondent re-
ported it as a "cutworm," damaging the alfalfa at Hanford, Cal.
Thi-: caterpillar is also known to have injured alfalfa in Utah. In
1909 Mr. C. N. Ainslie. of the Bureau of Entomology, found the eggs
and larvae of this
species on alfalfa at
SSpringer, N. Mex.,
aboubut doing no appar-
rou t"! cas 'iebent damage. In the
/ same year Mr. E. 0.
accordi"G. Kelly, also of the
Bureau of Entomol-
e o, ,t found the larva
feeding on alfalfa at
% PWellington, Kans.
X In Arizona, in the
"-" "of a cSalt River Valley
ahi. 2.-rh,_ alfla fa caterpillar (Euurlmlst cour 'theme): and in the Yua
venale in the adult or butterfly stage. One-half e Valley, farmers say
larged. (Original.)
6 $ that on an average
about one year in every three or four the hh worms become sufficiently
numerous to cause considerable damage. In the Sacramento Valley,
and in the irrigated alfalfa regions of south-central California,
according to Mr. W. E. Packard, of the California Agricultural
Experiment Station, the butterflies are quite numerous during certain
years and cause more or le:s
dlalI ingace.
Ihwever, not until alfalfa
began to lbe widely grown ill
the newly irrigated region
in the Iml)erial Valley of
sol thern California did the I
butterfly assume such pro-
portion1s, and appear with
s.lch regularity each season,
as to become a dread to
Ilie farners, particularly to r1,;. -'rih alfaira caterpillar (EurymalO
those confining their efforts c.,r.thcn,) Male in the adult or butterfly
wlholly to alfalfa growing. .ng,. One-half enlarged. (Original.)

It was in 1909, after a season when the larvae had taken all of one
crop of hay, causing a loss of hundreds of dollars on his 320-acre
ranch, as well as a similar loss to dozens of other ranchers in the
valley, that Mr. .1. A. Walton, of the Imperial Valley, wrote the
United States L)epartment of Agriculture asking for a remedy or a
[CI r. 1:3.1






THE ALFALFA CATERPILLAR.


method of dealing with the pest. As no remedy was known, plans
were at once begun for investigating the outbreak and if possible
working out some plans of controlling the same.
This circular is a partial report of the work done by the writer in
the Imperial Valley the past season (1910), and while the investi-
gation is still under way, another year being necessary to complete the
same, it is thought desirable to give to the farmers in the alfalfa-
growing section of the country the information secured, it being of
such a nature as to be of great immediate benefit, if'put to. practical
use, in controlling the pest.
DISTRIBUTION.
According to Scudder, this species is more especially a western
insect, being, as a rule, much more abundilant west of the Mississippi
River than east of it, and althlioughl its range extends eastward it is
rather rarely found east of the Allegheny Mountains. In the West. it
occurs from Mexico northward into the Dominion of Canada, thus
covering the chief alfalfa-growing section of the United(l State-s. It is
especially abul)lndailt. throughout the regions where irrigation is most
extensively followed.
DI)ES RIIO'TN OF THiE SPE:( IES.
A meager description is given here of tlhe various stages of develop-
ment, in order to enable the casual (ob-erver to recognize the different
forms:
The adult (figs. 2, 3).-Tle wing's of the adults vary in color from
yellow to white, being usually a .lulphur-yellow above, with black
outer margins, a consp)iciuous black spot in the center of each fore
wing, and a faint yellowish spot in the center of each
hind wing. The underside of the wings is of a lighter
shade than the upper surface and is the side noticed
when the butterfly is at rest with its wings folded i
above its back. The wing expanse is nearly 2 inches;
in some it is a little less than this and in a few a
little more. "'
The egg.-The eggs (fig. 4) are small, only 0.06 FIG.4.-Thealfalfa
*caterpillar: Egg.
inch long, with from 18 to 20 slightly raised longitu- Greatly Oiar -rgd.
dinal ridges or ribs, broken by cross lines. They are (Redrawn from
elongated, white when laid, but turning reddish Sudde.)
brown after the second day, and are deposited upright, with the
basal end attached usually to the upper surface of the leaf. They
are always deposited on fresh, green alfalfa, and never on dry or
partially matured alfalfa.
The larva.-The full-grown larva (fig. 1) is usually 1 inch long,
sometimes a little over, dark green in color, with a white stripe on
(Cir. 133]






THE ALFALFA CATERPILLAR.


each side, partially broken by black and red dots at each spiracle.
There is often an intermediate, narrower, and less distinct white line
just above each of the lateral lines. In some specimens a black or
dark-green median dorsal line is also present.
The pupa.-The pupa (fig. 5) is yellowish green, has no cocoon,
and is found head end up, attached by two threads, one of them form-
ing a swing, to an alfalfa stalk.

INVESTIGATIONS IN TILE IMPERIAL VALLEY OF SOUTHERN CALIFORNIA.
The investigations were begun by the author about the middle of
March, 1910, and carried on through the summer until late in the fall
of the same year. The writer was at first located on the J. A. Walton
ranch, in the extreme southeastern part of the valley, and later at
El Centro, where the work was carried on in cooperation with Mr.
Walter E. Packard. an agent of the California
\ Agricultural Experiment Station, to whom a great
Amount of credit is due for the assistance and timely
suggestions offered.
The Imperial Valley is a place unique in location
and altitude. It is an irrigated region entirely sur-
L rounded by mountains and desert. The major part
of the valley lies below sea level-some of it, in fact,
S as much as 250 feet below. The weather is warm
most of the year and hot the rest of the year. It
hardly ever rains, and the humidity is usually very
S low. The growing season extends over practically
FI..b alfa the entire year, there being an entire lack of freez-
FIG. 5.-The alfalfa I L_
caterpillar tEuryu ing weather during some winters. On the average
mmu curithere): there is not during the year more than one month
Pupa or chrysalis
stag,,. Twice nat of weather that could be called winter weather.
urnl size. (Origi. The conditions just referred to serve to explain
the imnmene numbers of these butterflies in the val-
ley. The period over which the butterflies are able to continue
bi-reeding without being molested is very long, being from March to
Deceinber. Then, too, nvinig to the very low humidity there is usu-
ally insufficient moistlire tI permit the development of what appeared
to 1b e a ('mlitag'iols (liese,. reenlibling in effect fla/hic'r' of the silk-
woFrI. TIhllis d(iseaset, waIs found to be largely responsible for keeping
this 1tl terfly iII check ill other parts of the State of California and
in solluthlern Arizona.
SEASONAL I 1STOJIY IN TIlE IMPERIAL VALLEY.
On the I"5tl o(f March. 1910, several adult individuals, possibly
ttlults tlat lhad i-sisied from lhilerlIati )Ig J),l)t, were caught in the
act of flyNi ig o'ver alfalfa fields andml placed in a large mosquito-bar
( 'ir-. i ]






THE ALFALFA CATERPILLAR. 5

cage which covered an alfalfa plant. These immediately deposited
eggs. It can be said, therefore, that the hibernating forms issue
between March 1 and March 20. The season of 1909-10 was ex-
ceedingly cold in the valley, while that of 1910-11 was, up to the
middle of February, precisely the reverse, and up to the 8th of this
month larvae had been found present in limited numbers in the
fields. It seems, therefore, probable that during some winters the
species may breed throughout the entire season, as sometimes there
is hardly a frost. Either the larval or pupal stage, or both stages,
would during such winters be merely lengthened, for that is really
what happens in the spring or fall of the year, and thus the insect
could hardly be said to hibernate. However, eggs were being laid
on March 15, and possibly a few days earlier, and these gave rise
to the first or spring generation. This generation was very slow in
developing, requiring about 44 days, the egg stage being 6 days, the
larval stage 30 days, and the pupal stage 8 days. As the weather
became warmer each of these periods gradually lessened until in the
third generation only 22 days were required for complete develop-
ment, the egg stage in this case being 4 days, the larval stage 12 days,
and the pupal stage 5 days. These were the periods of development
for individuals confined in cages; in the field a few days longer,
often as many as four or five, seemed to be required for development
from egg to adult.
The first generation covered the period from March 15 to April
30; the second generation from May 1 to May 28; the third genera-
tion from May 28 to June 20; and the fourth generation from June
20 to July 15. There were thus four distinct generations, the last
being less distinct, than the others. Later in the year the generations
became so largely confused that it was impossible to separate them.
Just as the fourth generation was beginning to pupate, the supposedly
contagious disease before mentioned killed a large majority of the
larvae present at the time, and thus observations along life-history
lines were checked. From this time on, scattering individuals pro-
duced eggs and gradually increased in numbers up to October, after
which time quite a few worms were present in some fields, and often
considerable damage was noted. In fields that had been green dur-
ing August, when the water supply was short in the valley, there
were always more of these caterpillars noticed than there were in
fields that had not been green during the month stated. This was
due to the fact that the worms were able to feed in these green fields,
and therefore in the fall there remained quite a number of adults.
By the middle of October, as the nights became cool, .the larvae and
pupae did not develop as rapidly as during the summer months, and
the species just held its own in numbers up to December 28, 1910,
when all were in the hibernating stage.
[Cir. 133]





THE ALFALFA CATERPILLAR.


TWO CLASSES OF RANCHES-PASTURE RANCHES AND HAY RANCHES.
The alfalfa ranches in the Imperial Valley, Cal., can all be divided
into two classes: (1) Pasture ranches, or those devoted entirely to
the fattening or pasturing of cattle and hogs, and (2) hay ranches,
or those on which the crop is utilized for hay. For convenience we
can look at these separately.
Patsare randcles.-It was noticed early in the summer, and the
writer's attention was called to the fact by a number of farmers,
that ranches devoted to the raising of stock, either cattle or hogs,
were rarely, if ever, seriously affected by the pest. On some dozen
ioeh ranches visited and inspected very few worms could be found,
;ind the butterflies flying over the fields were never numerous. At first
this was considered entirely due to the fact that there was hardly ever
any bloom present for the adults to feed upon and that the greater
part of tlhe field was kept grazed quite closely, making the condi-
tion in pastured fields less favorable for the laying and development
of the eggs. Under such conditions the number of eggs deposited
i- greatly reduced. Many of the eggs laid on the young growth
under such conditions are destroyed by the grazing of the stock, and
the percentage that develops is kept to a minimum. Later in the
,season it was noted that on the stock ranches visited the disease
previously mentioned, which is common to lepidopterous larvae, was
more prevalent than on hay ranches. All the factors determining
this difference have not been ascertained, but the fact itself is quite
s.ignificant.
On some of the ranches coming under the writer's observation the
alfalfa was allowed to grow for some four weeks, or until it reached
the height of about 20 to 24 inches. Cattle were then turned into the
field, and within a few days the alfalfa became trampled. The
groliund and the alfalfa were very moist, there being more or less
dlew present every morning, and droppings from the cattle and hogs
iittirally 1)rolghtt abot a foul condition in thle field, assisting in the
retention of moisture. Whether as a result of these conditions or as
a coincidence, thle contagious disease appeared to the writer to be
imucli more prevalent in these fields than elsewhere.
Hay ruirlw..-It is on ranches and fields from which successive
crops of hay are taken that tlhe height of the damage is reached. In
such fields tlhe conditions for tlie development of the species are as
neatly ideal as possible, and here the worms are ordinarily unmo-
lested in their feeding 1111nd growth. The period elapsing from the
tiMie that one crop is cut until another is ready to harvest so nearly
coincid(es with thle length of the period necessary for the develop-
nent of ainy one generation of tlie butterfly that the cutting of the
li:iy, ;s or(dlinarily carried on, does not reduce their numbers or dis-
til tllheir work, since( thle worm will likely l)be in the advanced stage
[C'ir. 1331





THE ALFALFA CATERPILLAR.


or, perhaps, have passed into the pupal stage before the crop is
cut off.
Many fields observed by the writer were attacked in strips or
patches. Sometimes one border would be almost totally devoured,
while an adjoining plot would not be molested. Again, in other
fields irregular patchlies would be attacked and the rest of the field
not materially injured. In cases where whole borders of alfalfa
were injured, the time and amount of water applied in irrigating
produced an uneven growth, and as the generation of butterflies, on
issuing, chose for egg-laying the strip that was the greenest and
freshest, this strip would be the one damaged. It seems possible to
account for the irregular patches in the same way-that is, consider-
ing that these patches were ones that were held back because of the
condition of the soil. The soil conditions in one part of the field
may be quite different from those in another part of the s.ine field,
and thus a varying growth of the crop re-ilt-. which would be at-
tacked in patches.
FOOD PLANTS.

Besides alfalfa the larva in known to feed upon the two buffalo
clovers. TDifolbimn reflex un and T.. stoln, if' rui,,, wh ichl probably con-
stitute its original native food plants. It al-o feeds upon white clover
(T. reopens and in California on T. t';,,mtat,,i, but is s:lid not to
attack red clover (T. pratcn.se). Other food plants noted by Scudder
are Hosackia, grotind plum (Astrael'i. i'yotrpin), and A. ctal-
aria. The butterfly is known to oviposit on Mi, i1'agl, ,..ia and at
Indio, Cal., on July 1 the writer found larvae feeding on sweet clover
(lMelilotus 7alba), which strangely enough they seeini'd to prefer to a
patch of alfalfa growing close by. Eggs were al--o observed to. be
very numerous upon the leaves of the sweet clover at thle -ame time.

INSECT ENEMIES.

The white eggs of tachinid flie-; were always in evidence wherever
any larva, were to be found, and the young of tlie.se de.-troy quite a
large number of worms. In one instance it was noted that as many as
15 per cent of the worms had tachinid eggs on them. Because of the
supposedly contagious disease, as shown in a following paragraph,
little success resulted from rearing these parasitic flies. Five speci-
mens were reared from the larvae of Eurymus. These were all of the
species EtupJioro era (laripennis Macq. (fig. 6). One specimen, de-
termined by Mr.D.W.Coquillett,of this bureau,as .1a.wierea sp., was
reared from the pupa of Eurymus.
Two species of hymenopterous parasites were reared. From the
Eurymus larve several specimens of Lim nerhun. sp.-all females, how.
[Cir. 133]





THE ALFALFA CATERPILLAR.


ever-were reared, while one specimen of Chalcis ovata Say (fig. 7)
was reared from a pupa of Eurymus. It seems from this that the
hymenopterous parasites
are much in evidence, al-
though if the material
SBhad not been affected by
.... ... the supposedly contagious
-, .-.. disease many more might
have been secured.
The cotton. bollworm
/mistaken, for an alfalfa
P caterpillar.-A large
^ green caterpillar known
as the bollworm, Heleo-
-- this obsoleta Fab. (fig. 8),
i that can be distinguished
FiG. 6.-Euphorocra 0(hripen nix, a parasite of the from the Eurymus be-
alfalfa caterpillar: Adult and enlarged antenna of cause it is of a lighter
same; puparium. Enlarged. IFrom hloward.) green color, about one-
en, green color, about one-
fourth larger, and hairy and rough in appearance rather than
smooth, with three black lines traversing its body lengthwise, is quite
prevalent in the Imperial Valley. and is often mistaken for the
alfalfa caterpil-
lar by many *)
farmers. Mr.
E. 0. G. Kelly
and M3r. T. H.
Parks. agents of
the. Bureau ofi ol c
En t oiol og 4 v,
workinli at Wel- -


1909 al,(o noted a r l
this sjxlcies and ft
ref)o'te(l it as
Iteillg (if :1~lC
Fh." ,. 7.-('haheis ora/a, a parasite of the alfalfa caterpillar:
As imtd i ll tlie ,,. li.u b, lparasitized pupa of tussock moth ( Ilrmerocampa
v I I h v. it was if urI,.ix 1151a, : ncitil t ; d, some in proflde ; e, pupal exuvium.
1.Jhrlanrged. Frum Iiivward.)
f1(11111(1itO (1(3 very
little. 4la:n tge I :to il faIft. but tol be a ravenousrllS. CIeniv of the alfalfa
61rfl'.e h ':j z10iltlist-v ha1l1it has also been olserved In Texis )y Quaiintance and
Brus. lit]. .511. lur. l'nt., U. S. Dept. Agr., pp. 79-80, 1lK15.
[Cir. l:;:l]





THE ALFALFA CATERPILLAR.


caterpillar, never eating alfalfa as long as it could find the larvae or
pupae of Eurymus around.
One of these larvae ate 5 larvae of the Eurymus during a single day,
and on May 25 the writer counted many dozens of pupal cases in the
field that had the contents eaten out. Each case had an irregular
opening eaten into it; sometimes the end of the abdomen would be
eaten away, and again the opening would be on the side, often the
entire side being destroyed. Upon further search the larvae of Helio-
this were found in the act of devouring the pupae and were thus
responsible for the damage.
OTHER NATURAL ENEMIES.
Larval disease.-The most common natural enemy observed was a
supposedly contagious disease which there has not yet been an oppor-
tunity to carefully study. This was prevalent all over the valley
and is present at all seasons. It destroys both the pupa and larva.
but more often the larva. The worms when attacked by the disease
turn a lighter green, become sluggish, and in a day or two are nothing
but a soft, decayed mass, usually found hanging to the alfalfa stalks.
The development of the disease apparently depends upon moisture,
as it is more often noticed in moist fields. The fact that it does not
at all times keep the worms in
suppression is without a doubt """
due to the fact that the climate -_ ."
of the Imperial Valley is very
dry. Larvae brought to the '; .Bolworm (cihi .lc), an
la or to I F 'i ; 8.- Bolkvorrm (Hcliiifhhi enb --ilcta), an
laboratory for rearing of insect ,.n,.iiy ,'f the alfalfa .:,terpillar. Twic.
parasites and for life-history natural size. (Original.)
studies in a large percentage of cases died of the disease a.s s)onl as
confined. A quantity of worms sent to Berkeley, Cal., by Mr. Wil-ie,
of the Imperial Valley hortictiltiral conimis:-ion, for experimental
rearing of parasites, all died of the dli-ease, either before reaching
their destination or the day after. During the first week of July the
humidity was exceptionally high for the Imperial Valley, and at the
time about 95 per cent of tlhe larva- in the valley succumbed to disease,
thus saving a hay crop for a great many of the farmer-, )but stopping
experiments almost completely. It is probable that this disease has
occurre(l in years past, and it may occur in future years, at some time
during the summer season, in s-iiuchl abundance as to destroy a brood,
as it did in the past year (1910).
It seems to be partly due to this disease that the alfalfa cater-
pillar does not appear in such large numbers in other regions of the
Southwest, notably in alfalfa regions in Arizona. H-ere there seems
to be greater humidity and more moisture, and the disease is able to
keep the number of worms reduced to a minimum.
[Cir. 1331






THE ALFALFA CATERPILLAR.


It is the intention of the Bureau of Entomology to repeat these
observations and experiments in the Southwest during the summer of
1911. and in order to do so the bureau would be glad to cooperate
with any farmers who wish to put their farms or ranches under a
riird system of control. The greater the number of farmers follow-
ing this plan the greater the beneficial results that may be expected.

METHODS OF CONTROL.
INSECTICIDES.

In (lealiiig with insect pests affecting cereal and forage crops it
has proved po-sible in only a few instances to control them by the
u-e of any of the various insecticides or poisons. The reason for this
lack of success lies largely in the fact that such crops are distributed
over a wide area and the expense of application of any insecticide as
a control measure is necessarily high, while a lack of thoroughness is
likely to arise when one tries to keep the expense of treatment down
to an economical basis.
Since the alfalfa hay is fed to stock, it is not possible to use any
of the arsenical poisons against the caterpillar of the alfalfa butter-
fly. A few experiments were tried by using pyrethrum or buhach."
As tlins is not a poison, and since its fatal effect upon the larvfe of
butterflies i, produced extern-lly through their breathing pores,
there would thus be no danger to stock. Pyrethrum was used in one
case at full strength, and in another instance it was diluted with equal
proportions of flour. An application was made by dusting this sub-
itance from a cheesecloth sack, following the primitive method of
:pplyingf Paris ,reen to potato vines, at the rate of 3 pounds of
pyrethrum to the hlialf acre, which in the case of diluted material
would make 11 pounds of pyrethrum to the half acre. This first
ti-. was tried on July 8, and no results were obtained, because of the
fact that just two days later practically all of the worms in the field
where tlhe test was being made were destroyed by the malady before
miientionjed. The same experiment was repeated, however, on Septem-
ber 22, and in this case al-o the results were negative, not a cater-
pillar being killed. It would seem, therefore, that the application
was not siffliciently heavy to kill the worms, and that to have
increased thle a:mouit of pyret lirtn applied might have resulted in
the eradication of lthe pest : lbut as thlie cost of pyrethrulm at the rate
of 3 pounds to the acre is already nearly $2, without considering the
expense of application by hand, this would be out of consideration
from an economist point of view. However, the excellent results
obtained through thie use of pyretlrunm in the case of other insects
wrill ji-i'fy f'iilher experimentationn along this line, and it may be
pos-ibl- to use it in tlie smaller fields.
[ 'ir. 1:!:!1


10





THE ALFALFA CATERPILLAR.


SYSTEM OF CROP CULTURE.

For the reasons just given the control problem, in dealing with
this alfalfa pest, resolves itself to one of the method of handling the
crop. Not long after the Bureau of Entomology began observations
in the Imperial Valley the writer was informed by well-to-do ranchers
that not all alfalfa fields or even all ranclbes were affected by the
caterpillars, there being apparentlyy certain conditions regulating the
devastation. One cause for thi.,, as noted earlier in this paper, was
the presence of stock in certain fields, but even in hay ranches there
was a variation in the numberr, of tlhe caterpillar-. Accordingly
there was outlined a series of experiments in which, in certain fields
under observation, definite methods of management were tested to
see whether some of then would not reduce or perhaps entirely elimi-
nate the damage. Before describing the conditions existing in these
fields it would be well to consider, fir-:t. the conditions existing in
certain other alfalfa fields not under the direction of the agents of
the bureau which utffercd greatly because of thle pc.t, the owners
often losing an entire crop. The first fact noted was that the cater-
pillar damage in such fields seemed to be correlated with the condi-
tion of the soil. A field seriotily (lanlaged often revealed a poor
soil; at least, a soil not well adapted to alfalfa culture, and conse-
quently producing a slow-growing crop. Of course, not all the fields
damaged were of such poor soil, for some of the very be-t alfalfat
fields were seriously ravaged, but in these latter cases this was at-
tributable to other factors, suchl as time and careless manner of cut-
ting and time of irrigation. The sandy loams or light soils are tlie.
best for alfalfa l)roductionl, and consequently least damaged. A
heavy soil can be greatly improved and the growth of the alfalfa
increased by deep plowing and thorotLighlily preparing the seed bed
at time of seeding the crop and then renovating the alfalfa yearly by
disking or by the use of an alfalfa renovator.
The worst conditions noted were those in which the attack of the
caterpillar was due to delayed cutittinig of the hay crop and due quite
often to the fact that many of the ranchers were trying to cultivate
more land than it is possible for one man to farm successfully. With
such ranchers some of tlhe following defects are observable in their
treatment of the hay crop: First, there is often insufficient water
used to provide for the prompt development of the alfalfa crop. An
abundance of water is very necessary, as it enables the alfalfa to make
faster growth, and thus the farmer can reap his crop sooner and be-
fore the caterpillars have effected much damage. Second, the crop
is not cut early enough in the majority of cases-about 90 per cent--
that is, the alfalfa is too far advanced in bloom when cut, and this
delayed cutting enables the caterpillars to mature successfully. The
[Cir. 133]


11





THE ALFALFA CATERPILLAR.


alfalfa should be cut just when it is beginning to bloom. Other
noticeable factors which tended to hamper control measures were that
at haying time the crop was cut high, the turning corners were left
ragged, and the ditch banks and borders poorly mowed, if at all, and
thus the caterpillars that were present and had not gone through to
the adult stage had a large amount of material upon which to de-
velop, and soon did so, so that the butterflies from these were ready
for the next crop. These places would also afford bloom which would
naturally attract the butterflies.
For fields in which good cultural conditions were to be created and
in which methods were to be inaugurated that would not further the
development of the caterpillars, 10 locations were selected and used
as a basis of work. From what was said in the previous paragraph
it will be readily seen that the thing to be done in these fields was to
put them under a system that would remedy all or part of the defects
noted in other fields.
As has been mentioned before in this paper, four generations of
caterpillars were observed in the Imperial Valley the past year
(1910). A large part of the damage was due to the caterpillars of
the third and fourth generations, the first and second not being
numerous enough to assume any serious aspect. The task, then, was
to keep their numbers below the point at which they could do any
considerable damage. The time to start this control work was natur-
ally with the earlier generations. The ten fields mentioned (no two
of which had had the same conditions of culture previous to that
year, and which had all suffered more or less damage the year before,
namely, in 1909) were given what might be termed clean culture, or
careful management. Just as soon as possible after removing a crop
of hay, using the methods to be described later, the field was irrigated
thoroughly, thus starting the growth quickly. The field was again
irrigated as soon as the dry condition of the crop required, and thus
the growth was forced and not allowed to be checked. It takes about
28 days to produce a hay crop in the Imperial Valley, a little longer
than this in the spring and fall, and a few days less in warmer
weather. It also takes just as many days as has been shown under
" seasonal history" for the butterflies to develop from egg to adult.
Now if the crop of hay be forced by frequent watering, or because
of good soil conditions, the worms will not have gone into the rest-
ing stage at time of cutting, but, instead, will still be feeding on the
green alfalfa, and when the hay is cut and removed conditions are
rendered unfavorable for their development and their food supply
will be correspondingly reduced. Therefore, the hay should be cut
just as it is coming into bloom, which is a few days sooner than it
is generally thought advisable to cut it, as a generation of worms
will take a whole field in a short time. Thus not only will the hay
[(Cir. 133]


12





THE ALFALFA CATERPILLAR.


Sbe saved, butthe-major portion of the larvae, finding a lack of the
food necessary for their complete development, will ultimately perish.
To bring about this condition, however, it is necessary to mow the
field carefully, leaving no high stubble. The turnrows, borders,
and ditch banks should also be closely mown, as this will not only
reduce the supply of food for the larvae but also that of the butter-
flies, as such plants will afford considerable bloom. In two cases in
the writer's experiments it became necessary to remow the fields
at a cost of from 30 to 50 cents per acre, and then in all cases to
irrigate promptly. As a result of this procedure a large percentage
of the caterpillars failed to develop to the imago or butterfly stage.
Deducting these, together with the larger number that failed to
reach the pupal stage, it will be seen that there were many hundred
less worms to attack the next crop, as each butterfly developing from
them would have deposited at least 100 eggs. In some fields, in-
stead of irrigating immediately after the hay was removed, the
experiment was tried of letting the field go dry for several days,
and thus starving the worms. While this gave good results it was
not as satisfactory as the method of immediate irrigation, for there
was always enough moisture in the field to start the new crop going
and thus provide a little food for the caterpillars.
The complete success of these methods is dependent on cooperation
among the farmers, for the larger the percentage of those who in-
augurate a good cultural system the greater will be the benefit derived
therefrom. The butterflies, however, do not fly very long distances,
and as long as the conditions are favorable for their existence on one
field or on one ranch they will remain there. They may, however,
fly considerable distances when forced to do so for want of food or
for fresh green alfalfa on which to deposit eggs or when driven by
the wind, and thus it is that one farmer can secure, by his individual
efforts, such remarkable results as are reported below.

RESULTS OBTAINED.

Of the ten fields cultivated according to these methods only one was
damaged by the caterpillars up to July 10, the date on which so large
a number of them were killed by the disease previously mentioned.
This one field was damaged because irrigation had been delayed for
nearly two weeks after the cutting of the second crop, owing to a new
ditch which was under construction. Being a thrifty field naturally,
the alfalfa had made a start, assisted by the moisture still present in
the ground, and butterflies coming in from an outside field deposited
eggs on this new growth, thus enabling the worms to destroy the best
of the crop after it was finally irrigated. As a result almost an en-
tire crop was lost. A field adjoining on the south, which had been
[Cir. 133]


13





THE ALFALFA CATERPILLAR.


irrigated immediately after cutting, was not in the least damaged. .
Thi wa, a le-sson in itself, as it indicated the necessity for prompt
work.
I'ROTE(TIVE MEASURES ADVISED.

Ti'his from a comparison o(f observations made in the two classes of
fields it.i- possible to derive the following rules for handling the

D),, not abandon a field because tlhe caterpillars are beginning to
daiti'ige ;iv ay crop). If tie caterpillars threaten the destruction of at
r.OJ(i f al]falfa before tlhe hay can possibly mature, mow it at once,
cittinig it low antd clean, and in :o doing starve a large majority of
tli-, generation oIf worms. thereby protecting the next crop as well as
saviNiig aI part of tlhe one already affected.
(et t<1w raicli in tlie best possible cultural condition. Irrigate
often and1 tldoroiuhly andI as soon after cutting as the crop of hay
.can libt gotten off l tie ground.
(Cult clo-e to the ground and clean, especially along the ditch
hun -. 1,,nhr'-. andit irnrowsv, as well as in the main part of the field.
(Cut the crop early. Wlien just coming in bloom is the proper
time. Watchli foir caterpillars in the early spring crop, and if many
aire ol-sUi'\tl :ul;i11 it grolWl cliit thlie hay a few days before it is in
loonI and tuins save the next crop.
Pasture alfalfa whenever possible, as a minimum amount of dam-
al(re cci s ilil such fields.
-e tile mnethlods just mentioned on early spring crops, no matter
whether anyv worms are noticeable or not. and thus avoid any risk of
hliainl, o, ,veVrloiked them. The satisfactory results must come from .
al ailpli 'catiot to aIn early crop.
Renovate every winter, either by. disking or by the use of an alfalfa
renovator, th]I disturbing any pupa' that may be wintering over, and
1)ptti ig tlie land( and alfalfaI in (con(lition for good growth the follow-
ing :lpring.
Tliese mtietliodls. while they will probably be of value in other see-
t iionsll have been tried only in the Imperial Valley of California, and
the3 are not -pecifically reco nmended for sections where climatic
and other conditions differ from those found in this valley.
Approve. SIVERTY OF FLORIDA


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14