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Issued April 25, 1912.

U. S. DEPARTMENT OF AGRICULTURE,

BUREAU OF ENTOMOLOGY—CIRCULAR No. 150.
L. O. HOWARD, Entomologist and Chief of Bureau.

THE RED SPIDER ON COTTON.

BY

E. A. McGREGOR,

Scientific Assistant.

WASHINGTON : GOVERNMENT PRINTING OFRHICE : 1912"

32120°—Cir. 150—12

BUREAU OF ENTOMOLOGY. ;

L. O. Howarp, Entomologist and Chief of Bureau.
Cc. L. Maruatt, Entomologist and Acting Chief in Absence of Chief.
R. S. Cuirtron, Executive Assistant.
W. F. Taster, Chief Clerk,

FP. H. CHITTENDEN, in charge of truck crop and stored product inscet inv estigations.
A D. HopxKIns, in charge of forest insect investigations.

D. HUNTER, in charge of southern field crop insect investigations.

M. WEBSTER, in charge of cereal and forage insect investigations.

L. QUAINTANCE, in charge of deciduous fruit insect investigations,

_E. F. Puriurrs, in charge of bee culture.

D. M. Rocers, in charge of preventing spread of moths, field work.
Roya P. Curis, in charge of editorial work.
MABEL COLCORD, in charge of library.

SoUTiIIERN FIELD Crore INSECT INVESTIGATIONS.
W. D. HUNTER, in charge.

F. C. Bisuorrp, A. H. JeEnniNcS, H. P. Woop, W. V. Kinc; engaged in tick life-
history investigations.

W. D. Pierce, G. D. Smitu, J. D. MircueLrt, Harry PinKus, B. R. Coan, R. W.
MorELAND, cngaged in cotton-boll weeril investigations.

A. C. Morcan, G. A. RuNNER, S. E. Crump, D: C. PARMAN, engaged in tobacco
insect investigations.

T. E. Hottoway, E. R. Barser, engaged in sugar-cane insect investigations.

E. A. McGrecor, W. A. THoMAS, engaged in red spider and other cotton insect
investigations.

J. L. Wess, engaged in rice insect investigations.

R. A. Cootry, D. L. VAN Dine, A. F. Conran, C. C. KRUMBHAAR, collaborators.

Il

Gente a

CIRCULAR No. 150.
Issued April 25, 1912,

United States Department of Agriculture,

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

THE RED SPIDER ON COTTON.

(Tetranychus bimaculatus Harvey.)

By E. A. McGReEcor,

Scientific Assistant.
INTRODUCTORY.

The minute, reddish spinning mite commonly known as the red
spider is rapidly assuming a position of importance among cotton
pests. At Batesburg, S. C., in 1911, it ,
first became noticeable on cotton about
June 1, causing little more than passing
notice at that time among the farmers,
but by the 1st of July it had increased so
enormously that the effect upon cotton
in certain places was most alarming.
Seasons of excessive drought greatly fa-
vor the multiplication of the mites until
the resulting injuries are often so severe
as to cause the death of many plants.

Red-spider infestation is frequently
miscalled “rust” by farmers, since in-
fested leaves soon turn deep red on their
upper surface. Such leaves, however, if
examined underneath, reveal the pres-
ence of the red spiders and the incon-
spicuous webs behind which they are
feeding and laying their eggs.

i
Fig. 1.—The red spider, Tei-
me : : ranychus bimaculatus: Aduit
With the exception of an outbreaks im vy) psiage! Greatly |) entadedtl
Louisiana, reported by Prof. H. A. Mor- — (From Banks.)
gan in 1893, severe occurrence ef the cotton red spider had not

been reported until 1903, at which time complaints of damage came

HISTORY AND DISTRIBUTION.

1This circular is based primarily upon work done at Batesburg, 8. C., in 1911,
under the direction of Mr. W. D. Hunter, but also includes the results of observations
by Messrs. G. A. Runner and H. F. Wilson during the two preceding seasons.

1

2 THE RED SPIDER ON COTTON.

from South Carolina and Georgia.: In 1904 Mr. E. S. G. Titus;
then of this bureau, found severe infestation in fields about Bates-
burg, S. C., and the following year he reported severe injury in
North Carolina, South Carolina, Georgia, and Alabama. Since
then the additional records of Dr. F. H. Chittenden? and Messrs.
G. P. Weldon, D. T. Fullaway, and others establish the presence
of the common red spider in Maine, Massachusetts, New York, New
Jersey, District of Columbia, Virginia, North Carolina, South Caro-
lina, Georgia, Florida, Alabama, Mississippi, Louisiana, Texas, Ohio,
western Colorado, Wyoming, Idaho, Washington, California, and
the Hawaiian Islands.

The red spider was described by Harvey ® in 1893 as Tetranychus
2-maculatus. Harvey considered it. quite distinct from the European
species 7’. telarius L. His types were from Orono, Me. In 1907 Prof.
H. A. Morgan published observations on the cotton mite, and ap-
parently accepted the determination of the species as 7. telarius.
In 1900 Mr. Nathan Banks described the cotton mite under a dis-
tinct name—Tetranychus gloveri—but from the study of additional
specimens has now concluded that the name is synonymous with
Harvey’s 7. bimaculatus. Specimens of red spiders on cotton from
South Carolina have upon two recent occasions been determined by
Prof. A. Berlese as the continental species—7etranychus telarius.
As there seems to be considerable doubt on this point, we shall follow
Mr. Banks in considering the form with which we are dealing as
Tetranychus bimaculatus.

DESCRIPTION.

The typical female (fig. 1) is 0.46 mm, long by 0.24 mm. wide,
broad-oval, widest in front, and the legs are shorter than the body.
Its color is usually brick-red. The typical male is 0.27 mm. long by
0.15 mm. wide, oval-wedge shape, narrowed behind, the legs about
equaling the length of the body, and its color is usually reddish
amber. Individuals of both sexes usually possess on either side of
the body a dark spot, caused by the food contents. This spot may
vary greatly in color, size, and outline. Similarly, depending upon
the host plant and upon locality, the general color of the red spider
is subject to great variation.

The eggs are very minute, but in proportion to the mites they are
large. They are perfectly round, and when first laid are as clear as
water. Each female lays (in the months of June, July, and August)
about 50 to 60 eggs, depositing about 6 per day for a period of about

nine days. Less than 3 eggs or more than 9 are rarely deposited each
1 Cir. 65, Bur. Ent., U. 8S. Dept. Agr., 1905.
2Cir. 104, Bur. Ent., U. S. Dept. Agr., 1905.
3 Ann. Rept. Maine Agr. Exp. Sta. for 1892, Pt. IV, pp. 153-146.

THE RED SPIDER ON COTTON. 3

day in summer weather. During the warmer months the eggs hatch
in about four days after being laid.

The newly hatched red spider, called the larva, is almost round,
has six legs, and is nearly colorless. It begins feeding at once, and
(in summer time) after two days’ activity it becomes quiet, darkens
in color, casts its skin for the first time, and emerges as the primary
nymph with an added pair of legs—making eight.

The primary nymph becomes larger in size and darker in color,
but gives no indication of sex. Feeding continues actively and at the
termination of another two-day period (in summer months) a second
molting occurs which gives rise to'the third stage—the secondary
nymph.

With this last nympnal stage the first indication of sex appears.
As with the preceding stages, two days usually suffice in summer
for the completion of this period, at the end of which time the
skin in shed for the third time and at last the perfectly developed
adult mites appear. At the occurrence of each molt the skin splits in
two, crosswise, and the creature crawls out of the two halves. The
old cast skins are usually to be seen in abundance among the fibrils
of the web.

THE ADULT MALES AND FEMALES COMPARED.

Concerning the relative abundance of females and males it may be
said that there seems to be a predominance of females throughout
the summer, but toward the approach of cold weather the occurrence.
of the sexes becomes more nearly equal. The period of life of the
adult female varies from 17 days in midsummer to several months
in winter. The male is shorter lived. As before stated, the female
is decidedly larger than the male, more rounded behind, and of a
much deeper color, She does not move about much, and when she
does her motion is rather slow. On the other hand, when not mating,
the male is frequently seen moving rapidly about. The body and
legs are well beset with bristles, which are somewhat more con-
spicuous in the males than in the females. The eyes, consisting each
_ of two orbs, one close behind the other, are situated near the front
edge of the body directly over the second pair of legs.

MATING.

Almost immediately upon becoming adult, the red spiders mate
and begin egg laying. The males seem to recognize unfertilized
females with ease. The first eggs are frequently deposited on the
same day upon which the transformation occurs from the last
nymphal to the adult stage.

4 THE RED SPIDER ON COTTON.

PARTHENOGENESIS,

Experiments conducted with unmated female red spiders clearly
proved that they are normally capable of laying eggs, which in turn °
hatch and develop into mature individuals. No tests, however, have
been successfully conducted to determine the sexual fertility of the

latter.
GENERATIONS.

The season of 1911 at Batesburg, S. C., was one of unusual drought
and heat and there were about 17 generations between March 11 and
November 5. The time required for a single generation varied from
85 days in March and early April to 10 days throughout most of
June, July, and August, and to 25 days in the greater portion of
October and early November. The following table presents the
duration of each stage of each of the 17 generations:

TABLE I.—Development of generations of the cotton red spider.

id Incuba- is Nymph |} Nymph} Ovipo-
epee [' Period covered by gerneration. tion serna (1) (2) sitigaeie
period * | period. | period. adult.
Days Days. Days Days Days.

i) eaeoeds Mar ato Aup re Was is ee iia ie ie pe ee As 13 Aig 6 7 35
he aa Apr oto -Apri29) 2: esas oe St See wer 6 3 3 3 15
Siete ete ADr..30) to May Se ie2 o's scig28 Baas ees 6 3 3 2 14
Cae Mayil4ito May 25). Jscs2 92. <se estes se eee 5 3 2 2 12
PbS Mays26:tO SMUG G8 ecu ek oselk Sas e cee 5 3 2 2 12
Gea. LINE bO! MUO, Sse es a ee oe 4.5 2.5 2 2 11
(cea Abbe HT FOG i c-Rel Sees oka + 2 2 2 10
ae! Oe AITOWS LO WUD gine me SMe eps a le ee 4 . 2 2 2 10
Ginan Arvid acter Ye J 8 hae 9 Esp et pec Fach Ne Ss 4 2.5 2.5 2 11
‘tS ae nalayed 9 ORY OSS ers Uo ee 4 2 2 2 10
in bases eta Sy 29 COTATI ES ince ot cre ocr ete ele eee 4 2 2 2 10
ee Agize 8) to pA MY Snape cee a. 2 34 meee ure t 4 2 2 2 10
ils}s adiaeeg AIISS 1S DORAL. eOae eis ote tore caaaer ie eee oe 5 2D 2 2.5 12
eee ATIC SOLO Sep h. Os sae ose wey as sagen Fiori 5 2 2 2 11
i pleats Sept. LOO Sepak se ee = aye ere 5 3.5 3 3.5 15
1G Aes Sent. 25 to,Cb.610 srg. Sate so ede 6 3 3 4 16
gee re Oct: LIMOUNDVa 2 aces ee eee ene eee eee 9 6 5 a7) 25
PAIVETER CL ot a eer tee eet ei eens ate ante 5.9 3.1 Zo | 2.8 14

RELATION OF WEATHER TO BREEDING ACTIVITIES.

The influence of the weather on breeding activity is very notice-
able. Hot, dry conditions greatly favor and hasten development.
while cool, wet weather correspondingly retards it. A female laying
normally about 6 or 7 eggs per day will often upon the oecurrence
of a very hot day, suddenly increase the number to 15 or even more
eggs per day, or upon a chilly day may drop as suddenly to 1 or 2
egos. It is easy then to understand the remarkable rate at which
this pest increases during times of unusual drought.

OBSERVATIONS ON HABITS.

In establishing herself upon cotton the female selects a concave
area between the under veins of the leaf and begins at once to deposit
eggs. These may be attached to the fibrils of the web slightly above
the surface, or, as seems most often the case, they are placed directly

THE RED SPIDER ON COTTON. 5

upon the leaf. The eggs are usually clustered rather closely and
rarely occupy an area greater in size than that of a dime. Feeding
continues interruptedly throughout the period of egg laying and the
affected area of the leaf becomes thickly dotted with the blackish-
ereen puncture marks. Meanwhile a wine-red spot has appeared on
the upper surface of the leaf directly over the young colony, which
spreads as the colony increases and may finally color the entire leaf.
As the eggs hatch the larvee remain close to the place of their birth.
The mites seem of a decidedly social disposition. In a young colony
there is usually little web formed, but where the spiders are very
abundant the web may become quite conspicuous. It doubtless
affords some protection from adverse weather conditions, and upon
several occasions hostile insects have been observed ensnared and dead
among the fibers. New females, after mating, either select an attrac-
tive spot on the leaf, or migrate upward
to a more tempting leaf, or in some
cases may even travel to another plant.

THE VIOLET AS HOST.

When cotton dies or becomes untempt-
ing in the late fall an exodus of red
spiders from the cotton fields occurs in
the effort to find more suitable food
plants. At this time cotton mites may
be easily found on a number of native |
and cultivated plants, prominent among Fic. 2—Diagram showing how vio-
which are cowpeas, tomato, Jamestown = foe erie in. Gatentation in
weed, ironweed, and cultivated violets. adjoining field. The infestation
Most of these plants die after the frosts, thie diagram te typical of shia
but the violet remains somewhat green a, found during 1911. (Orig-
throughout the winter, and it is upon
this plant, probably, that the vast majority of mites overwinter. Out
of many cases of cotton infestation investigated the vast majority
have indicated most clearly that the original source of the pest was
doubtless this innocent pet of the housewife, the English violet.
(See fig. 2.)

OTHER HOSTS.

In all, the red spider has been found in 1911 upon over 50 species
of plants, including weeds, ornamental plants, and garden and field
crops. Upon most of these the pest was only occasionally seen, but
it was found commonly throughout the active season upon the fol-
lowing plants: Beans, cowpeas, dahlia, ironweed, Jerusalem-oak
weed, Jamestown weed, okra, tomato, wild blackberry, and wild
geranium.

6 THE RED SPIDER ON COTTON.
HIBERNATION VERSUS WINTERING.

Some observers have thought that the red spider commonly hiber-
nates in trash or in the soil in cotton fields, but the past season’s
investigations have produced absolutely no evidence to support this
idea. During the early spring, before the active season for the red
spider commenced, trash was several times taken from fields in which
the infestation had previously been severe and examined with great
care. A few minute dormant acarids and other forms were thus
obtained, but no red spiders could be found in such material. Simi-
larly, during December, 1911, ample quantities of trash, etc., from
recently infested fields were carefully examined, but always without
finding any trace of the red spider. That this pest remains more or
less active throughout the winter there can be no doubt. Mr. G. A.
Runner found active adults at Batesburg, S. C., on December 21,
1909. Mr. H. F. Wilson observed red spiders feeding in early Feb-
ruary at the same locality. The writer found all stages on violets on
March 11, and adults as late as December 19, on the same host at
Batesburg. The finding of the active red spiders during the coldest
weather is certainly an additional indication that hibernation does
not take place in South Carolina.

DISPERSION.

How do red spiders become established upon cotton? They have
no wings and their legs are very minute. Close observations reveal
that on the ground they normally travel at the rate of 1 inch per
15 seconds, which, if maintained, would total 480 feet in 24 hours.
Red spiders are doubtless occasionally transferred by dogs, chickens,
other domestic animals, insects, and birds. Strong winds may serve
occasionally to transfer them from plant to plant. It is the writer’s
firm belief, however, that the chief means of dispersion is the red
spider’s own efforts. When once established in a field they may be
further distributed by farm hands and by stock while cultivation is
being carried on. They also spread from plant to plant along the
interlacing branches, but traps specially prepared with “ tangle-foot ”
and placed in the field have proven that individuals commonly craw]
from plant to plant by way of the stalk and the ground.

Since the red spider apparently uses no instinct or intelligence in
finding cotton plants, it follows that the pest must hit upon the cotton
stalks entirely by chance. The result of this haphazard manner of
migration must necessarily result often in the penetration of the
spiders far into the center of fields, thus giving rise to the mistaken
impression that they had hibernated at these points.

Furthermore, as the likelihood of the discovery of cotton by the
spider is doubtless in proportion to the thickness of the “stand,” it

ree ho aS

THE RED SPIDER ON COTTON. fi

should follow that the thick broadcasting of a narrow border strip
along the edge of a field adjoining a source of infestation would serve
as a trap crop to intercept the majority of migrating spiders. This
strip should be plowed in as soon as there seems to be danger of a
general movement to the main field. (For a practical test of this
idea, see under Prevention, p. 10.)

NATURE OF DAMAGE.

‘Cotton seedlings 2 inches high were found infested on May 1, but
not until June 1 did the work of the pest become noticeable. The

RCS

Pos

Fic. 3.—-a@, Cross section of normal cotton leaf; b, cross section of cotton leaf injured by
the red spider. The puncture is near lower right-hand corner. Highly magnified.
(Original. )

presence of the pest on cotton is first revealed by. the appearance on
the upper surface of the leaf of a blood-red spot. As leaves become
badly infested they redden over the entire surface, become distorted,
and drop. The lower leaves are first attacked, but infestation spreads

upward until often only the bare stalk and one or two terminal

leaves remain. Such plants almost invariably die. The injury to
the leaf and the discoloration which follows the feeding of the mites
are easily understood by referring to figure 3, which represents (a)
the appearance of healthy cotton leaf-tissues and ()) the condition
of the tissue after feeding by the pest. As previously intimated, the
worst spots of infestation are usually to be found in close proximity

8 THE RED SPIDER ON COTTON.

to yards with borders of violets. Large fields are probably never
completely damaged, but small fields frequently become wholly
affected. The crop of one 5-acre field near Leesville, S. C., was
probably reduced at least 50 per cent by this pest. Local spots with
from 25 to 100 per cent damage are frequently to be seen.

NATURAL CONTROLLING AGENCIES.

Red spider occurrence was most severe throughout July and was
still at its height on August 1. Within three weeks of the latter
date, however, the pest had become so greatly diminished that it was
hardly noticeable and was doing practically no damage. This
phenomenon indeed happened suddenly, and the agencies which
worked to produce it are unquestionably of great economic value.
The toughening of the leaves at that time may have caused many
mites to desert cotton for other plants, but another factor of much
more importance was the appearance in abundance of several species
of insect enemies.

CLIMATIC INFLUENCES.

As before mentioned, climatic conditions exert a marked influence
upon the welfare of the pest. During times of little rainfall and
high temperature reproduction goes on by leaps and bounds; on
the other hand, long, heavy rains work havoc to the red spider
population. In spite of the fact that the red spiders inhabit the
underside of the leaves, many are washed off by rains and many more
are destroyed by the upward bombardment of sand particles, which
may always be seen coating the lower leaves after storms. From
observations made both early in the season and at the beginning of
winter it is doubtless true that the young stages are killed by freez-
ing weather. This naturally prevents any considerable winter in-
crease, and in addition many adults probably perish.

INSECT ENEMIES.

Hot weather, although favoring red-spider development, also en-
courages the increase of insect enemies, of which several have been
observed. Were it not for these inconspicuous friends of the farmer
the depredation to his crops by the red spider would unquestionably
be far more severe. The following are a few of the more important
beneficial species observed this season at Batesburg, S. C.

Triphleps insidiosus Say (fig. 4), a small anthrocorid bug, was
seen from the beginning of August, and both in the nymphal and
adult stages was probably the most effective enemy of the spider.
Coming upon a red spider like a flash, the adult thrusts its sharp
proboscis through the pest’s back and proceeds quietly to siphon out

THE RED SPIDER ON COTTON. 9

the body contents. The first victim observed was “ drained”
about five minutes, but each succeeding meal was of shorter ae
as the appetite cauatie
satisfied. The actions
of the nymph (fig. 5)
are similar, but the in-
dividuals observed were
seen only to destroy
eges of the spider. In
this operation the pro-
boscis was not inserted
far into the ovum, and
two minutes sufliced for
draining an egg.

A species of Chry-
sopa or lace-winged fly
was seen abundantly Se
throughout most of the Fic. 4.—Triphleps insidiosus, an important enemy of the
summer, the larva of red spider. Much enlarged. (Original.)
which is doubtless very active in reducing the pest.

Two species of thrips, Luthrips fuscus Hinds and EF. occidentalis
Pergande, have been determined this season from cotton. They are
commonly found throughout
the season about red spider
colonies, and may be very in-
strumental in spider destruc-
tion. Scolothrips sexwmaculata
Pergande has been recorded as
an enemy of the red spider by
Pergande and by Duffy.

Lady-beetle larve and adults
of several species were com-
monly seen on infested leaves.
These were usually either
Coccinella 9-notata Ubst. or
Hippodamia convergens Guer.,
but a small black species,
(Scymnus) Stethorus punctym

Pic. 5.—Triphleps insidiosus: Nymph. Lec., was eccasionally observed.

sedis Va ath) jaaete The larger beetles were prob-

ably more intent upon cotton aphides, but the last-mentioned species,

although late in appearing and not very numerous, seems to be more
restricted to the cotton mite than are other species.

10 THE RED SPIDER ON COTTON.

REMEDIAL MEASURES.
PREVENTION.

Control on violets—First among preventive measures against the
red spider is that of its control on violets. In most cases, as before
stated, infested cotton fields upon examination are found to have
near them infested violet borders. In early June of the past season,
in one particular instance, violets adjoining fields of past severe
annual infestation were thoroughly sprayed. It is of great interest
to record that subsequent infestation in these fields was practically
negligible. These and similar observations certainly emphasize the
important part that the violet plays in the seasonal history of the red
spider.

Clean culture—Borders of weeds and underbrush about fields
should be burned or grubbed out. Margining a field close to a spot
which was heavily infested the previous season there was found to
occur a thick border of wild geranium, dock, and other weeds which
at that time contained many red spiders. These weeds were de-
stroyed by burning over them a heavy application of straw. No
spiders appeared in the adjoining cotton throughout the season.

Broadcasted cotton.—An opportunity was accidentally provided of
testing the value of thickly broadcasting cotton at the boundary of
a field as a trap crop for red spiders. This cotton, intended as a
cover crop, intervened between the cotton field proper and a large,
heavily infested border of violets—a former abundant source of
migration. The broadcasted cotton became infested and was later
plowed in. The adjoining field remained free from mites. The suc-
cess of this experiment would strongly indicate that the cotton trap
crop is one of the most practical cultural expedients to be used in
controlling this pest.

Spacing —Experiments at Batesburg, S. C., have shown that the
red spider commonly travels between plants upon the ground. This
shows the futility of spacing as a remedial measure.

Time of planting—The advantages of early or of late planting
are not sufficiently clear to justify serious consideration. It would
seem reasonable, however, to suppose that early planting would en-
able the plants to attain greater size and vigor by the time of the
appearance of the spiders and that this would perhaps assist the
plants in withstanding the weakening effects of the pest.

Rotation.—In an effort to test the rotational value of other crops,
cowpeas, corn, beets, and peanuts were planted in or near infested
areas. In addition, grains, beans, peas, onions, tomatoes, squash,
watermelon, okra, turnip, lettuce, and other yegetables in infested
locations have been observed frequently. Exeepting the grains and
peanuts, the red spider has been seen commonly upon all of these.

THE RED SPIDER ON COTTON. he

On the other hand, should an immune crop be found and employed,
it is extremely probable that the pest would reinvade the fields upon
the return to cotton culture with as great ease and quickness as it
has done during any previous season, providing the sources of infesta-
tion were yet at hand. Rotation, then, does not promise to contribute
toward the solution of the problem.

Effects of fertilizers. —A rather elaborate series of tests with fer-
tilizers was instituted in an attempt to determine whether the various
applications assisted cotton to withstand the injurious | effects of
infestation. Since almost no infestation appeared in these test plats
it was impossible to deduce positive conclusions. It was very notice-
able, however, that plants receiving heavy applications withstood the
very severe drought conditions which prevailed in South Carolina in
1911 conspicuously better than did plants which were not so treated.
It seems reasonable to suppose, therefore, that plants which have

‘been fortified by a liberal quantity of fertilizer will be assisted, upon

occurrence of severe infestation, in resisting its effects. :
REPRESSION.

We have just discussed cultural measures which may help to pre-
vent infestation. We will now consider what may be done to combat
the pest when it has already gained entrance to a field.

Pulling infested plants.—The experiment was made in one field of
pulling up and destroying the first few plants which showed infesta-
tion. In this particular case the operation was repeated three times.
Care was taken to find every plant showing the characteristic red
spots, and these were carried from the field and burned. The result
was most satisfactory, and the pest was completely eradicated.

If infestation has spread until a considerable patch has become
involved it might be advisable, in the case of a large field, to plow
up the affected portion in order to save the balance of the field. Such
a drastic measure, however, should only be resorted to in extreme
cases, and the planter concerned must be the judge of its desirability.

Insecticides——In all, 26 spray combinations were thoroughly tested
under conditions entirely natural. The field used for this purpose
was about 1 acre in extent, arid infestation had become both very gen-
eral and very severe. <A strip through the middle of the field, crossing
each sprayed plat, was left unsprayed to serve as a check. Since no
substance was discovered which could safely be used to destroy all
eggs In one application, it was found necessary to spray twice with
an interval of six or seven days, so as to destroy the hatching larvee.
The killing ability of all these sprays was computed, and the per-
centages range from 100 to 0. Each of the following six combina-
tions (see Table II) was found to be very satisfactory.- These are
presented to indicate the manner of preparation, together with the

12 THE RED SPIDER ON COTTON.

cost of 100 gallons of each. If one of these were to be used in
preference to all others it should undoubtedly be potassium sulphid.
This insecticide commends itself from every standpoint—cheapness,
simplicity of preparation, continued readiness for use, ability to kill
quickly, and safety of foliage. Altogether it seems to be an ideal
red-spider spray. It was found that 100 gallons, when applied as a
misty spray, about sufficed to treat an acre of average-sized cotton.

TABLE II.—Some satisfactory sprays for the red spider.

*
tee Formula and items. > pa Pon
Y | pRotassiam silphid, 3 pounds: at 2b cents: 202 2555 es ee ee ee $0.75 100
Water, 100 gallons.
II | Flowers of sulphur, 15 pounds, at 4 eet Se ARIEL S EE ee $0. 60
Fresh lime, 20 pounds, at 4 cents....... OUCH Ke fas 5. SAS | eee - 80
Water, 100 gallons mg aeee > ties be ii es A iS iy ——| 1.40 100
LETS Mascible‘olls 5 eallpnsvat $ii- cesses al ee sey Ane Lite 5 fad 38 OS ET ee 4S 5.00 100
Water to make 100 gallons (1 to 20).
IV | Potassium permanganate, 164 pounds, at 50 cents..................---------- 8.25 100
Water to make 100 gallons (2 per cent solution).
We4| MaScIble Ol. 24 PallonS<atiele so. 5 ecco ete ee ae ee ee cman ie $2.50
Black-leaf tobacco extract, 40%, 4 gallon, at $1.25 per pound ......... 2.00 ae. a
VI | Flowers of sulphur, 28 pounds, at 4 cents. ..........-...--.-2.--.----- 2
Soft soap, 14 ounces, at 40 cents per pound...-....-..---2----:--.-----
Water to make 100 gallons. 1.50 98

SUMMARY.

The female red spider, appearing to the naked eye like a dot of
reddish ink from the point of a fine pen, lays about 50 or 60 round,
colorless eggs, which hatch in summertime in about four days.

The colorless, newborn spider has six legs, feeds at once, and molts
in two days to the primary nymph.

This first nymphal stage (and all later stages) possesses eight
legs, and has become larger in size and darker in color. In two more
days (in summer) it, in turn, molts to the secondary nymph.

The second nymphal stage lasts two days, at the end of which
time, after molting, the fully formed adult emerges. Mating occurs
at once and egg laying commences immediately afterwards.

Thus, one generation requires in summer weather in South Caro-
lina about 10 or 11 days. There are probably about 15 generations
in an average year in that locality.

The red-spider colonies live on the underside of the cotton leaves,
and their constant feeding causes blood-red spots to appear on the
tops of the leaves. The effect upon the cotton plant is that the
leaves drop, one by one, until usually the plant dies.

The pest increases and spreads most rapidly in hot, dry weather
until (toward the end of July) several acres of a field may become
badly damaged. '

THE RED SPIDER ON COTTON. ilies

Several insects have been discovered which destroy many mites,
and are thus of great benefit to the planter.

At the end of the cotton-growing season most of the red spiders
migrate afoot in search of greener plants, the majority of those
which survive settling ultimately upon the cultivated violet.

RECOMMENDATIONS.

(1) Clean culture——Burn or grub out all weeds and underbrush
about cotton fields and practice fall plowing so far as possible.

(2) Control on violets —Spray or destroy suspected violet plants
in order to remove the sources of red spider infestation.

(3) Broadcasted trap borders.—Thickly sow cotton along mar-
gins of fields at points where infestation has appeared on former
eccasions, and plow these in about June 1, so as to intercept and
destroy the invading mites.

(4) Pulling first infested stalks—Maintain a careful watch of
fields so that the first attacked plants may be detected, removed, and
burned, thus preventing further spread.

(5) Spraying—Apply one of the insecticides recommended above
to the infested portion of a field before occurrence becomes too gen-
eral to prohibit its use. Two applications should be made; the first
to destroy the living mites, and the second, a week later, to kill the
recently hatched individuals which were eggs at the time of the first
spraying.

Finally, the opinion will be ventured that the red spider is not a
difficult pest to combat. Unlike many other pests, it has no wings
and spreads mainly by means of its tiny legs. Migration does not
extend far from its winter quarters. This makes every man’s prob-
lem virtually his own. In other words, rf his infestation has always
come from a certain spot upon his premises, proper attention to this

spot will yield him results in spite of the negligence of his neighbors. >

Approved :
JAMES WILSON,
Secretary of Agriculture.
Wasuinerton, D. C., February 14, 1912.

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