• TABLE OF CONTENTS
HIDE
 Front Cover
 Table of Contents
 Introduction
 The black scale
 The red or orange scale
 The yellow scale
 The purple scale
 The cottony cushion scale
 Soft brown scale
 Hemsipherical scale
 The greedy scale
 The oleander scale, the citrus...
 Red spiders
 Silver mite
 Thrips
 Aphis
 The orange tortrix
 Fuller's rose beetle
 Diabrotica soror
 Serious citrus fruit pests not...
 Spraying for citrus fruit...
 Fumigation
 Inspection and quarantine
 Back Matter






Group Title: Bulletin
Title: Citrus fruit insects
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00095561/00001
 Material Information
Title: Citrus fruit insects
Physical Description: 3 p., p. 443-512 : ill. ; 23 cm.
Language: English
Creator: Quayle, H. J ( Henry Josef ), 1876-
Donor: unknow ( endowment )
Publisher: Agricultural Experiment Station
Place of Publication: Berkeley, Cal.
Publication Date: 1911
 Subjects
Subject: Citrus -- Diseases and pests   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by H.J. Quayle.
General Note: Cover title.
General Note: At head of title: University of California publications. College of Agriculture. Agricultural Experiment Station, Berkeley, California.
General Note: Florida Agricultural Experiment Station bulletin 214
 Record Information
Bibliographic ID: UF00095561
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 14048265
lccn - a 34001007

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Table of Contents
        Table of Contents 1
        Table of Contents 2
    Introduction
        Page 443
        Page 444
    The black scale
        Page 445
        Page 446
        Page 447
        Page 448
        Page 449
        Page 450
        Page 451
        Page 452
        Page 453
        Page 454
        Page 455
        Page 456
        Page 457
        Page 458
    The red or orange scale
        Page 459
        Page 460
        Page 461
        Page 462
        Page 463
        Page 464
    The yellow scale
        Page 465
    The purple scale
        Page 466
        Page 467
        Page 468
    The cottony cushion scale
        Page 469
        Page 470
        Page 471
        Page 472
        Page 473
        Page 474
    Soft brown scale
        Page 475
        Page 476
        Page 477
    Hemsipherical scale
        Page 478
        Page 479
    The greedy scale
        Page 480
    The oleander scale, the citrus mealy bug
        Page 481
        Page 482
        Page 483
        Page 484
    Red spiders
        Page 485
        Page 486
        Page 487
        Page 488
    Silver mite
        Page 489
    Thrips
        Page 490
        Page 491
        Page 492
    Aphis
        Page 493
    The orange tortrix
        Page 494
        Page 495
        Page 496
        Page 497
        Page 498
    Fuller's rose beetle
        Page 499
        Page 500
    Diabrotica soror
        Page 501
        Page 502
    Serious citrus fruit pests not yet established in california
        Page 503
        Page 504
    Spraying for citrus fruit insects
        Page 505
    Fumigation
        Page 506
        Page 507
        Page 508
        Page 509
        Page 510
    Inspection and quarantine
        Page 511
        Page 512
    Back Matter
        Page 513
        Page 514
Full Text





COLLEGE OF AGRICULTURE
AGRICULTURAL EXPERIMENT STATION
BERKELEY, CALIFORNIA I




CITRUS FRUIT INSECTS

BY H. J. QUAYLE


BULLETIN No. 214
(Berkeley, Cal., May, 1911)

SACRAMENTO
W. W. SHANNON - - SUPERINTENDENT OF STATE PRINTING
1911









EXPERIMENT STATION STAFF.


E. J. WICKSON, M.A., Director and Horticulturist.
E. W. HILGARD, Ph.D., LL.D., Chemist (Emeritus).
W. A. SETCHELL, Ph.D., Botanist.
LEROY ANDERSON, Ph.D., Dairy Industry and Superintendent University Farm Schools.
M. E. JAFFA, M.S., Nutrition Expert, in charge of the Poultry Station.
R. H. LOUGHRIDGE, Ph.D., Soil Chemist and Physicist (Emeritus).
C. W. WOODWORTH, M.S., Entomologist.
RALPH E. SMITH, B.S., Plant Pathologist and Superintendent of Southern California
Pathological Laboratory and Experiment Station.
G. W. SHAW, M.A., Ph.D., Experimental Agronomist and Agricultural Technologist,
in charge of Cereal Stations.
E. W. MAJOR, B.Agr., Animal Industry, Farm Manager, University Farm, Davis.
F. T. BIOLzTTI, B.S., Viticulturist.
B. A. ETCHEVERRY, B.S., Irrigation Expert.
GEORGE E. COLBY, M.S., Chemist (Fruits, Waters, and Insecticides), in charge of
Chemical Laboratory.
H. J. QUAYLE, M.S., Assistant Entomologist, Plant Disease Laboratory, Whittier.
W. T. CLARKE, B.S., Assistant Horticulturist and Superintendent of University Exten-
sion in Agriculture.
H. M. HALL, Ph.D., Assistant Botanist.
C. M. HARING, D.V.M., Assistant Veterinarian and Bacteriologist.
JOHN S. BURD, B.S., Chemist, in charge of Fertilizer Control.
E. B. BABCOCK, B.S., Assistant in Agricultural Education.
W. B. HERMS, M.A., Assistant Entomologist.
J. H. NORTON, M.S., Assistant Chemist, in charge of Citrus Experiment Station, River-
side.
W. T. HORNE, B.S., Assistant Plant Pathologist.
J. E. CoIT, Ph.D., Assistant Pomologist, Plant Disease Laboratory, Whittier.
C. B. LIPMAN, Ph.D., Soil Chemist and Bacteriologist.
R. E. MANSELL, Assistant in Horticulture, in charge of Central Station grounds.
A. J. GAUMNITZ, M.S., Assistant in Cereal Investigations, University Farm, Davis.
E. H. HAGEMANN, Assistant in Dairying, Davis.
B. S. BROWN, B.S.A., Assistant in Horticulture, University Farm, Davis.
F. D. HAWK, B.S.A., Assistant in Animal Industry.
J. I. THOMPSON, B.S., Assistant in Animal Industry, Davis.
R. M. ROBERTS, B.S.A., Field Assistant in Viticulture, University Farm, Davis.
J. C. BRIDWELL, B.S., Assistant Entomologist.
C. H. McCHARLES, B.S., Assistant in Agricultural Chemical Laboratory.
N. D. INGHAM, B.S., Assistant in Sylviculture, Santa Monica.
E. H. SMITH, M.S., Assistant Plant Pathologist.
T. F. HUNT, B.S., Assistant Plant Pathologist.
C. 0. SMITH, M.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier.
F. L. YEAW, B.S., Assistant Plant Pathologist, Vacaville.
F. E. JOHNSON, B.L., M.S., Assistant in Soil Laboratory.
CHARLES FUCHS, Curator Entomological Museum.
P. L. HIBBARD, B.S., Assistant in Fertilizer Control Laboratory.
L. M. DAVIs, B.S., Assistant in Dairy Husbandry, University Farm, Davis.
L. BONNET, I.A., Assistant in Viticulture.
S. S. ROGERS, B.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier.
B. A. MADSON, B.S.A., Assistant in Cereal Laboratory.
WALTER E. PACKARD, M.S., Field Assistant, Imperial Valley Investigation, El Centro.
M. E. STOVER, B.S., Assistant in Agricultural Chemical Laboratory.
P. L. McCREARY, B.S., Laboratory Assistant in Fertilizer Control.
E. E. THOMAS, B.S., Assistant Chemist, Plant Disease Laboratory, Whittier.
ANNA HAMILTON, Assistant in Entomology.
MRS. D. L. BUNNELL, Secretary to Director.
W. H. VOLCK, Field Assistant in Entomology, Watsonville.
E. L. MoRRIS, B.S., Field Assistant in Entomology, San Jose.
J. S. HUNTER, Field Assistant in Entomology, San Mateo.
J. C. ROPER, Patron, University Forestry Station, Chico.
J. T. BEARSS, Foreman, Kearney Park Station, Fresno.
E. C. MILLER, Foreman, Forestry Station, Chico.













CONTENTS.


INTRODUCTION. PAGE.

THE BLACK SCALE (Saissetia oleae Bern.) --------------------------- 445
Life history ------------------------------ 449
Seasonal history ------------------------------------------ 451
Distribution and spread----------- -------------------------- 452
Parasites and predaceous enemies-
Scutellista cyanea Motsch. ------------------------- --------------.456
Other enemies --- ------ ------------------- 459
Control ----- ------------------ 459

THE RED OR ORANGE SCALE (Chrysomphalus aurantii Mask.)------ 459
Life history ---------------------------460
Seasonal history ------------------------------------ ------- 462
Food plants ---------------- -------- 463
Distribution and spread -------------------------- 463
Parasites-
Aphelinus diaspides How. ------------ --- -- 463
Predatory enemies-
Rhizobius Lophanths Blaisd ---------- ---- 464

THE YELLOW SCALE (Chrysomphalus aurantii var. citrinus Coq.) ---------465
Distribution ----------------- -------------------- 465
Life history ---------------------------465
Parasites -------------- -- ------- ---- -- 465
Control --------------------------------------------------------- 466

THE PURPLE SCALE (Lepidosaphes beckii Newm.) ---------------------466
Life history -- --- ---------------- 466
Seasonal history --- --- --- -- 468
Natural enemies -- --------- ---- ----------------------- 469
Control ------------------ ----------------------------- 469

THE COTTONY CUSHION SCALE (Icerya purchase Mask.) -------- 469
Present status in California-----------------------470
Life history annd habits ------------------------- 472
Natural enemies ------------------------------------- 472

SOFT BROWN SCALE (Coccus hesperidum Linn.) ----------------------475
Life history ---------------------------------------------------- 476
Natural enemies --- ------------------------------------------ 476

HEMISPHERICAL SCALE (Saissetia hemisphaerica Targ.) ------- 478
Natural enemies --------------------------------- ----- 478

THE GREEDY SCALE (Aspidiotus rapax Comst.) -------------480

THE OLEANDER SCALE (Aspidiotus hederae Comst.) ------ ----- 481

THE CITRUS MEALY BUG (Pseudococcus citri Risso.) -----------481
Life history and habits---------------------------------- ----- 483
Natural enemies -------------------------------- ------------- 484
Control --------------------------------------------------------- 484










CONTENTS-Continued.
PAGE.
RED SPIDERS (Tetranychus mytilaspidid Riley) 485
(Tetranychus sexmaculatus Riley) ---- 485
Life history and habits ------- ----_ 486
Control __ -------------- 487

SILVER MITE (Phytoptus oleivorus Ash.)------------------- 489
Life history and habits -- -- ----- 489
Control ----- 490

THRIPS ------ -- ------490
Life history and habits 493
Control --------------- 493

APHIS (Aphis gossypii) ----- --- -- --- 493

THE ORANGE TORTRIX (Tortrix citrana Fern.) -----------------------494
Life history and habits ----- 495

PULLER'S ROSE BEETLE (Aramigus fUlleri Horn.) -_ -- 499
Life history, habits and control--------- ---- 499

DIABROTICA SOROR ------------ 501

SERIOUS CITRUS FRUIT PESTS NOT YET ESTABLISHED IN CALI-
FORNIA ---------------------- 503
The Orange Maggot (Trypeta ludens Loew.) 503
The Citrus White Fly (Alerodes citri R. and H.) -- 504

SPRAYING FOR CITRUS FRUIT INSECTS 505

FUMIGATION ---- -------- 506

INSPECTION AND QUARANTINE ------------------- 511










CITRUS FRUIT INSECTS.
By H. J. QUAYLE.

INTRODUCTION.
That insect pests are one of the important factors in the citrus fruit
industry of southern California is shown by the fact that more than
half a million dollars are expended annually in their control. This
amount includes only what is actually expended in fumigation and
spraying, and does not take into consideration the loss of fruit from im-
properly treated trees or trees not treated at all. The cost of fumigation
in one county alone amounts to $200,000 annually. Furthermore, each
county maintains a horticultural commissioner, and many of them a
corps of inspectors, primarily on account of insect enemies, who are
charged with the quarantine and inspection work, the cost of which in
some of the counties may run as high as $25,000 annually. That all of
this vigilance is necessary seems to be warranted from the thirty years'
experience of the most important citrus fruit section of the United
States.
It has been estimated that the average cost of fumigation per tree,
taking the whole of the citrus belt, amounts to about 30 or 40 cents,
which means an expense of approximately $30 to $40 per acre, and this
is done on an average about every other year. This is intensive insect
fighting, but when the improved market value of the fruit is considered,
it is money judiciously spent with such a valuable crop as the orange or
lemon.
Commercial citrus culture in California is confined to seven counties
south of the Tehachapi mountain range, namely, Santa Barbara, Ven-
tura, Los Angeles, Orange, Riverside, San Bernardino, and San Diego;
and the two counties north of this range, namely, Tulare in the upper
San Joaquin Valley, and Butte in the upper Sacramento Valley. The
southern counties form a section contiguous to the coast line, and which
has a coast climate, excepting the Riverside-Redlands district, which
approaches the interior conditions on account of its distance from the
ocean (60 to 75 miles), without being separated by a well-defined
natural barrier. The San Joaquin and Sacramento Valley citrus dis-
tricts have the typically interior climate which is characterized by
hotter summers than that of the more equable coast counties.
These general climatic differences appear to account for the differences
in the insect pests, not only of the northern and southern sections, but
also within the latter section itself, since even here there is a wide range
of variation. However, it is not safe to speak too confidently of the
influence of climate on insect distribution. Time has changed a num-






444 UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.

ber of ideas to correspond with the facts as they exist to-day. It had
been asserted that California need have no fear of the citrus white fly,
yet this pest got a fairly good foothold in a part of the State least
unsuited to it, according to theory. It was also held that the black scale
would not exist in the Riverside section, yet it occurs there and attacks
citrus trees. Likewise, the purple was supposed not to become a pest
in arid California, and, if it did become established, it would be limited
to a narrower range than its distribution at the present time indicates.
In general, however, it may be said that the black scale thrives best
in sections near the coast, as shown by its prevalence in the citrus belt
from Santa Barbara to San Diego, and also on deciduous trees in the
coast counties of the north. The interior valley citrus sections are not
troubled with the black scale, though it may occur there on such plants
as the olive and oleander. The purple scale, thus far, is limited to the
coast counties, occurring with the black, but not of such wide distribu-
tion. The red and yellow scales occur both near the coast and in the
interior, though they are considered the more typical scales of the
warmer interior sections.
Aside from the scale insects mentioned, the next most general citrus
tree pests are to be found among the spiders and mites. The Florida
red spider and the six-spotted mite are widely distributed, while the
silver mite of the lemon is restricted to a limited section in San Diego
County. The mealy bug has become a rather serious pest in certain
limited sections in Ventura and San Diego counties, and also smaller
infestations in other counties. The soft brown, cottony cushion, and a
few other scales sometimes occur in considerable numbers over small
areas, but are not usually considered permanent pests. A species of
thrips has recently come into prominence as a pest in the San Joaquin
section. The orange tortrix is the only insect that burrows into the
orange itself to any extent, and this fortunately has not become a very
important pest thus far. Other insects which attack the fruit occasion-
ally are grasshoppers, katydids and cutworms. Other biting insects
attacking the leaves only are Fuller's rose beetle and the common
Diabrotica.
A couple of dozen species will thus cover all the insects of economic
importance attacking citrus trees in California, and of these, practically
all of the control work is directed against but four of the scale insects,
the black (Saissetia olece Bern.), the red (Chrysomphalus aurantii
Mask.), the yellow (Chrysomphalus aurantii var. citrinis Coq.) and the
purple (Lepidosaphes beckii Newm.). The present publication is
intended to give a popular account of all those species likely to be
considered of economic importance, together with their chief attendant
parasites or enemies. This will include a discussion of their life history
and habits, mainly, since the principal reliance for control, which is






CITRUS FRUIT INSECTS.


fumigation, is discussed in separate publications from this station and
also the Department at Washington. A brief outline of spraying and
fumigation is, however, appended at the close of this bulletin which gives
the essential facts for these operations. The control of those pests which
are not handled by fumigation or spraying is given at the close of the
discussion of each species.
Most of the photographs were made by Professor R. W. Doane of
Stanford University, who assisted in the investigation of citrus fruit
insects during the summer of 1910, while the drawings are the work of
Miss Anna Hamilton.


THE BLACK SCALE.
(Saissetia olece Bern.)
The Black Scale (Saissetia olece Bern.) ranks first among the citrus
pests of southern California.
This statement is based upon the
amount of control work actually
directed against it, and its wide
distribution throughout the cit-
rus belt. The purple scale and
the mealy bug may be more diffi-
cult insects to control, but their
distribution is not so general as
that of the black. In the county
horticultural commissioners' re-
ports tabulated on next page, the
black scale is given first place in
three counties, Los Angeles, San-
ta Barbara, and Orange. The sec-
ond in two others, Ventura and
San Diego. While the mealy bug
is given first place in Ventura, it
will be noticed that most of the
control work is against the black.
This scale also has a wider dis-
tribution in San Diego County
than the purple, and should I
probably be entitled to first
place there. Where control work ,A
is directed against the purple, FIG. 1.-Black Scale (Saissetia oleae Bern.)
on orange twig.
and the black is associated with
it, the extra dosage used against the former keeps the black well in
check, otherwise it would have to be reckoned with separately. The


BULLETIN 214]









) UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.



TABULAR STATEMENT CONCERNING CITRUS INSECT PESTS BY COUN


I. Most important scale
insect pest ......-----

II. Seond most Import-
ant ------

III. Third most import-
ant -------

IV. Annual cost fumigat-
ing --------------




V. Annual cost spraying-

VI. Annual cost fumigat-
ing 10 years ago---

VII. Annual cost spraying
10 years ago..---

VIII. Proportion of fumi-
gating and spray-
ing for black scale._

IX. Proportion fumigat-
ing and spraying
for red and yellow--

X. Proportion fumigat-
ing and spraying
for purple ------


XI. Acreage in citrus
fruits 10 years ago_

XII. Present acreage -__

XIII. Other control work--


Riverside.

R. P. Cundliff
Commissioner.



Red.


Yellow.


Black.


$75,000




8,000


20,000


5,000



*30-40%



60-70%



No purple in
county.


16,000

23,389

N. cardinalis
for cottony
cushion.
0. Lecanii for
soft brown.


San Bernardino.

S. A. Pease,
Commissioner.


Red.


Yellow.


Black.


$200,000




10,000


60,000


25,000



33,%



66.%



No purple in
county.


24,000

57,000

Spraying f o r
red spiders.


Los Angeles.

A. R. Meserve,
Commissioner.


Black.


Red.


Purple.


$175,000




5,000


Orange.

Roy K. Bishop,
Commissioner.


Black.


Red.


Purple.


$35,000




1,000


Nearly all.



-







17,800

29,200 12,500

Mealy bug pest Sulfur for red
in certain seec- spider.
tions.


*75% for black in 1910.








BULLETiN 2141


TIES GIVEN BY THEIR RESPECTIVE HORTICULTURAL COMMISSIONERS.


Ventura.

E. 0. Essig.
Commissioner.



Citrus mealy
bug.

Black.


Long-tailed
mealy bug.

Work just begun.
1908-9, 3,000
1909-10, 10,000
1910-11, 20,000

None, except for
mealy bug.

No fumigation
then.

No fumigation
then.


Practically all.



Only two infesta-
tions in county.


C


San Diego. Santa Barbara.

C. H. Stuart, C. W. Beers,
Commissioner. Commissioner. C



Purple. Black.


Black. Purple. S


citrus mealy Yellow.
bug.

$10,000 None.




1,000 One orchard
spray.

nm as ton-day. No records.


Same as to-day.



50%


No records.


None.



None.


No
ci


Butte. Tulare.

Earle Mills, A. G. Schulz,
Commissioner. Commissioner.



Yellow.


oft brown.


$1,500




None.


None.


None.



ne in commer-
al orchards.


100%


1-16 50% None. No purple in
county.


-- -------- 10,000 1,400 1,200

12,000 1 7,000 13,000 1,800

Lime-sulfur for Scutellista does Parasites control Parasites a n d
red spider, goo d wo r k Black. Para- predatory ene-
Predaceous ene- s o me years, sites give excel- mies for cot-
mies: cottony A ls o crypto- lent control of tony cushion
cushion and lae mes on purple, and soft brown.
mealy bug. mealy bugs.


None of the economic
scales yet estab-
lished in commer-
cial groves.

2,000 acres sprayed
for thrips in 1910.


CITRUS FRUIT INSECTS.


<


Sa






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


only sections where the black is not considered a serious pest in the
south are certain sections of Riverside and San Bernardino counties.
The chief injury occasioned by the black scale is not due so much to the
loss of sap through feeding, nor is it due to the poisonous effect on the
plant tissues through the insertion of its thread-like mouth parts. The
black scale excretes large quantities of so-called honey dew which falls
upon the upper surface of the leaves and fruit, and this serves as a
medium for the growth of a fungus known as the sooty mold fungus.
This necessitates the washing of the fruit, which operation alone adds
to the cost of the handling, but the chief injury is due to the wash
water becoming infected with blue mold and other fungi. Since the
fruit comes in contact with the sides of the tank, brushes, elevators, and

















FIG. 2.-Mature Black Scales.
drying racks, it is impossible to escape some abrasion of the fruit, into
which the spores of the fungus readily make their way.
Regarding the washing of oranges, Powell in Bulletin 123 of the
Bureau of Plant Industry, U. S. D. A., says the following:
"' Oranges are washed primarily to remove the sooty mold fungus that
grows in the so-called honeydew exuded by the black scale (Saissetia
olece Bern.). The Valencia orange is sometimes washed to raise the
grade by making the fruit clean and attractive, and the Washington
Navel is occasionally washed with that end in view.
"When the present investigation by the Bureau of Plant Industry
was undertaken, from one third to one half of the oranges of California
were washed, practically all the fruit in some sections being treated
in this way, especially where the growers had been over-confident in the
parasite Scutellista cyanea Motsch, or in the use of oil sprays as a
means of holding the black scale in check."
More detailed and complete publications will follow on the Black, Red and Purple
Scales.






CITRUS FRUIT INSECTS.


Aside from the damage to the fruit, this sooty mold fungus often
forms a complete coating over the surface of the leaf, which greatly
interferes with the natural functions of the leaf by shutting off light.
Light is necessary for the formation of starch and sugar, and conse-
quently the sugar content of the fruit may be reduced as a result of
black scale infestation. The black scale, as already intimated, does
not conspicuously interfere with the growth of the tree. There is
probably no case where this insect has killed a tree, though some of the
smaller twigs may be severely injured. However, the sooty mold
fungus may also have its effect on the general growth of the tree,
because of its interference with the manufacture of sugar which is
necessary for the formation of the living matter (protoplasm) of the
tree.
LIFE HISTORY OF THE BLACK SCALE.
The Egg is almost white in color when first deposited, but later as it
approaches the hatching time it becomes distinctly orange. If the eggs
of this scale are placed end to end in a
single line it will require about 80 to /
equal one inch in length. The number /
laid varies from 300 to nearly 3,000, //
the average being from 1,500 to 2,000.
These will be deposited during a period .
of two months during which time from .- -
25 to 40 will be laid each day. The -
time required for the hatching is from ,,
fifteen to twenty days during the spring ,i
or summer months.
Eggs of this insect may be found at
any season of the year in some section
of the southern California citrus belt, FIG. 3.-Male of Black Scale. x25.
though the great bulk of them are to be found in May, June and part
of July. The time of maximum egg production in 1910 was about the
second week in June. This will vary from year to year, and there
appears during some years to be a more uniform hatch than in other
years. However, practically all the young appear by the middle of
August, or first of September, from that great majority of scales that
mature in the spring.
The young upon hatching from the egg remain beneath the parent
scale for a day or two before emerging. Upon making their way from
beneath the old scale they actively crawl about for a time but almost
always settle within two or three days. A large majority settle on the
leaves or tender twigs. Those settling on the leaves rarely come to
maturity there. As they become partly grown they loosen their hold


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


and migrate to the twigs and branches. The young scales seem unable
to become established, in any large numbers, on the older corky branches.
Once becoming fixed on the twigs they remain, in the case of the females,
throughout their entire existence. This migration from leaves to stems
may occur when the scale is nearly one half grown, but usually takes
place prior to that time.


FIG. 4.-Leaf on right showing sooty mold fungus as a result of Black Scale
infestation. Normal leaf on left.

The female black scale undergoes a couple of molts, but the legs are
not lost in the process, as is the case with the red scale. While the legs
are retained throughout its life they are functionless after the scale is
about one half grown. It is during the growing period, and partic-
ularly as they approach maturity, that the honeydew is excreted. It is







CITRUS FRUIT INSECTS.


this honeydew that the ants, which are so frequently seen on black or
soft.brown scale-infested trees, are after. They do not feed on the scales,
as is often supposed, and neither do they attack the tree itself. The rela-
tion of the ants, therefore, is largely neutral, though indirectly they may
be somewhat detrimental through their protection of the scales from
parasites and other enemies. Again, on the other hand, ants have been
seen abundant enough, especially in the case of the soft brown scale, to
take up all the honeydew as fast as it was excreted so that the fruit and
foliage remained clean.
The adult female, which becomes full grown in eight to ten months,
is hard and leathery in texture, and approximately a solid hemisphere
in shape. As the eggs are deposited beneath, the body itself gradually
becomes hollow, so that when all the eggs are deposited the scale becomes
simply a hollow hemisphere filled with eggs. On the back of the full-
grown scale, and from the time it is half grown as well, there is a distinct
letter H, which is one of the best common characters for distinguishing
it. The color varies from dark brown to jet black, which is darker than
any of the other common scale insects of the orange.
The male of this insect in most localities has not been seen, though
during some years it does occur in considerable numbers in many sec-
tions of southern California. As many as 97 male puparia from which
males had emerged, have been seen on a single orange leaf in San Diego
County. The males occur commonly, also, in Los Angeles and Orange
counties. The puparium in which the later stages of the male insect
is passed is glassy white and resembling in shape a partly grown soft
brown scale. They are much longer and narrower than the female scale
at the same stage. The male which emerged from those transparent
glass-like scales are like those of all scale insects in being active winged
insects. They are, however, weak fliers, and the wind may be an impor-
tant aid in wafting them from one tree to another.

SEASONAL HISTORY OF THE BLACK SCALE.
There appears to be but one complete generation of the black scale in
a year, and the majority of the insects reach maturity in the spring
months. The seasonal history of the scale differs in detail, according
to locality. On citrus trees in southern California there is more or less
overlapping, so that, in some sections, the insects may be found in some
of the stages at all times of the year. Likewise, they may be found in
most of the coast districts as far north as San Francisco. In the interior
valleys, where the seasons are a little more pronounced, more of the
scales come to maturity at a definite time. Young will be found during
the winter months, but they are very few as compared with the early
summer months.
Mortality. The black scale suffers its greatest mortality during the


BULLETIN 214]






452 UNIVERSITY OF CALIFORNIA--EXPERIMENT STATION.

period when the young are active, and again at the molting periods.
Fully 50 per cent in many cases fail to get settled, and often this runs
as high as 95 per cent. They seem unable to become fixed in any large
numbers on stems that are old and corky. This can be explained
because of their delicate mouth-parts being unable to penetrate into
the harder tissue. But in those cases, where they fail to get a foothold
on the leaves, as many do, and where, there seems to be something to
prevent them from settling, the matter is not so easily accounted for.
In addition to this mortality, on account of the insects themselves, they
are, of course, during the active period more likely to be attacked by
enemies and succumb to other outside agencies. During the molting
periods the insects are undergoing a profound physiological change,
and many fail to pass through this critical period.
During the younger stages of the insect there are also likely to be hot
weather periods that kill them off in large numbers. Young black
scales just hatched and placed on soil in the sun, with a temperature of
1080 to 1100 in the sun, died in 1 to 1I hours. At a temperature of
1190 to 122 they died in 15 minutes, and at a temperature of 1300,
died in 5 minutes. In all cases those under the same conditions in the
shade were not affected. It is not uncommon to find as high as 90 per
cent or more of the partly grown young on orange leaves killed by what
appears to be heat or other climatic condition.
While, therefore, a black scale may lay 2,500 eggs, and that would
represent the progeny at the end of the year, this condition never obtains
in nature. After the loss of first settling, the loss during the molts, the
weather, diseases, parasites, and other enemies, the number coming to
maturity is very small as compared with the number of eggs produced.
DISTRIBUTION AND SPREAD OF THE BLACK SCALE.
The distribution of the black scale over the citrus belt of the State
has been given in the introduction. It thrives best in the coast sections,
and the reason for this is the cooler summers. Often here, as indicated
above, hot weather periods bring about considerable mortality, but not
to such an extent as in the interior valleys. The black scale is to be
found in greatest numbers on the underside of the smaller twigs and
branches of the tree. On young trees, one to three years old, they may
occur even down on the trunk, but are very rarely found here in mature
trees. The statement has been made that they occur on the roots of
certain plants, such as the nightshade. While they may get a few inches
below the surface in loose soil, they are still on the stem of the plant and
are not to any extent root-infesting insects. Aside from the citrus trees,
the olive is the one worst infested; in fact, it attacks the olive in prefer-
ence to the orange. It was on this tree that the black scale was first
discovered and named by a Frenchman named Bernard in 1782. The






CITRUS FRUIT INSECTS.


oleander and pepper are also favorite host-plants for this insect in
southern California. The total range of plants attacked is large, and
includes many of the deciduous fruit trees of the State.
Rate of Travel. The spread of this insect, like most other scales, is
dependent very largely upon outside agencies rather than on its own
powers for traveling. It is only three or four days at most when the
scale crawls to any extent, and no very long distances can be covered
by such a small insect as the active larva. Over smooth paper they are
capable of traveling at a maximum rate of 6 feet in an hour. On the
basis of a scale living four days and going at full speed all the time it





















FIG. 5.-Washing oranges to remove sooty mold fungus which grows in the
so-called honeydew from the Black Scale. From Bull. 123, Bur. Plant
Industry, U. S. D. A.

would cover 720 feet. But no scales under ordinary conditions do this,
nor do they have smooth paper to walk upon.
Experiments on the rate of travel of these young scales over smooth
sand showed that they covered a 10-inch strip in from 1 to 13 hours.
Several thousand scales were liberated in the center of a 4-foot circle
of ordinary orchard soil. The first scales reached the edge in 2 hours.
Only a very small per cent of the total number succeeded in getting over
the 2-foot radius of soil. Similar tests were made where the width of
the soil to be traversed was 4 feet, but none came to the edge during
the same day. The finer the mulch the more difficult it is for travel, and
in the compacted irrigation furrows they were found to make much
more rapid progress. While, therefore, there may be some young black


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


scales that will make their way from one tree to another, or possibly
to a second or third tree away, by their own powers of locomotion, this
means of transfer must be considered a rather small factor in the total
spread.
The Wind as a Factor. The wind is one other means of spreading
scale insects about which considerable has been said with but little actual
data presented to support the claims. Wind is an important factor
in aiding the flight of small weak flying insects, as winged plant lice and
the winged males of scale insects; but it is not an important factor in
the spread of the female black scale in any stage. The crawling young
are not often dislodged from the tree by the wind. A strong current
of the air from a foot-bellows, much stronger than the wind blows in
this section, was directed against a twig with numerous active young
black scales. None were dislodged until the twig was brought within
six inches from the mouth of the bellows and even then only a small
proportion were blown off. Once dislodged, they would be carried a
short distance as they were falling. From this and other experiments
it would seem to indicate that it would be very unusual for a scale to be
dislodged from the tree by the wind alone; but once dislodged, they
would alight a short distance further in the direction the wind was
blowing. If the trees were close together, they might alight on an
adjoining tree, but, with the navel orange as ordinarily planted, this
would be exceptional. Of course, the wind is an important means of
transporting the males and insuring fecundation of the females that
might be spread by other means; but in the case of the black scale, where
the male is so rare, this is not of much significance.
Other Agencies. The rapid spread, over a considerable area, of such
insects as the black scale must, therefore, be accounted for in other ways
than their own powers of locomotion, or through the agency of the wind.
Active flying or crawling insects are probably the most important, and
of these, the ladybird beetles must be considered as the worst offenders.
These insects move about among the scales themselves, upon which they
feed, and many instances have been observed where there was a young
scale insect on the backs of these beetles. About 100 of these beetles
were confined for a day in a jar containing black scale infested twigs,
and, upon examination, it was found that the young scales were being
carried around on the backs of the beetles. About one beetle in every
ten or fifteen carried from one to four young scales. These beetles, of
course, fly from one tree to another and the rapid spread of the scale
is thus effected. Other active insects must also be considered as impor-
tant, but less so than the ladybird beetles. Birds, without doubt, also
spread scale insects, for these, resting on scale-infested twigs for a time,
allow abundant opportunity for the active young to crawl upon them.







CITRUS FRUIT INSECTS.


Because of the long flight of birds they would be specially likely to trans-
port them long distances and thus account for isolated scale infestations.
The ordinary operations of man must also le considered as a factor
in the spread of scale insects. Indeed, it has been through the trans-
porting of nursery stock that different species of scale insects have
such a wide distribution over the world. Practically all the scales of
citrus fruits in this State have thus been imported from other countries.
What applies in the exchange of pests between foreign countries, also
applies between different states and also different counties in our own
State.
While nursery stock is the chief means of spreading scale insects long
distances, man may again be responsible, through picking boxes, wagons
and the like, of spreading scales to adjoining sections and different
parts of his own premises. The operations of picking the fruit, through





















FIG. 6.-Drying racks where fruit is placed after washing as a result of Black
Scale infestation. From Bull. 123, Bur. Plant Industry, U. S. D. A.

wagons, picking boxes, clippers, gloves etc., and the movement of teams
in cultivation may all aid in the distribution of the scale over the
orchard. Different articles, such as sticks, boards, rags, and gloves, were
placed in a scale infested tree and allowed to remain for some time, and,
upon examination, had scales crawling over them. The young black
scale will rarely live more than four or five days without food, so that
infested articles, such as picking boxes, if allowed to remain five or six
days or a week before carrying into other groves, there will not be much
danger of infestation.
2-B214


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


PARASITES AND PREDATORY ENEMIES OF THE
BLACK SCALE.
(Scutellista cyanea Motsch.)
By far the most important enemy of the black scale in California is
Scutellista cyanea Motsch, introduced into this State from South Africa
by. the United States Department of Agriculture through Dr. L. 0.
Howard in cooperation with E. M. Ehrhorn and Alex. Craw in 1900.
This insect has become well established in most parts of the State where
the black scale occurs. Little, if anything, therefore, is gained by
distributing a half dozen or a dozen of these parasites in an orchard
where they already occur in considerable numbers, aside from a possible
moral effect. In isolated places, where it does not now occur, of course,
this artificial distribution should be encouraged.
There is often a very great difference in the abundance of Scutellista
in different sections and also in the same sections at different seasons,
it is not uncommon to find as high as 75 to 80 per cent of the scales
parasitized in a certain section, and the following year a low percentage
of parasitism. There is considerable irregularity, therefore, in its abun-
dance, and the black scale still remains the most important citrus
fruit pest in the State. Usually where there is a heavy parasitization
by the Scutellista, the black scale is very abundant oni the tree. Again,
there may be few black scales and fewer Scutellista, indicating that
other factors are at work aside from the parasite.
We are accustomed to judge of the efficiency of Scutellista by the per-
centage of exit holes in the scales, but this is not the only criterion.
The Scutellista is an egg parasite, almost entirely, so that in no way
does it reduce the injury of the generation of scales attacked. The scale
has come to maturity, sucked all the sap, and given off all the honeydew
it would have given off anyway, whether it was attacked by the Scutel-
lista.or not. The efficiency of Scutellista, then, must be judged by its
power to reduce the progeny of the black scale. It may seem that there
ought to be a direct relation between the numbers of exit holes in the
scales and the number of young present. But this is not necessarily
true, for the reason that the Scu'ellista does not always consume all the
eggs. It is not infrequent to find a very high percentage of exit holes,
and, also, a great abundance of young. Cases have been observed
where the percentage of exit holes ran as high as 75 or 80 per cent, yet
on leaves immediately adjoining this, more than 700 young black scales
were counted on each. On healthy trees, and where all conditions are
favorable for the growth of the scale, they grow very large, and a large
number of eggs are deposited, more than enough to bring the Scutellista
larva to maturity. This, together with the fact that the scales left unin-








CITRUS FRUIT INSECTS.


FIG. 7.-Scutellista cyanea Motsch, egg x70; larva x25; pupm, ventral and
dorsal views x20 ; adult x17 ; inverted Black Scale showing four pupme; exit
holes in scales.


BULLETIN 214]


-01 W,ft







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


fested by the parasite will produce 2,9000 or more young, it is easy to
account for the tree becoming infested again the following year. Where
the scales are small, the Scutellista larva consumes all the eggs and the
number of young is greatly lessened. . : .

LIFE HISTORY OF SCUTELLISTA.,
The Egg of the Scutellista is pearly white in color, larger in size than
those of the black scale, among which it is found, and has a long taper-
ing stalk at one end. They are deposited under the black scale during
the egg stage or a little while previous.
iThere may be more than one egg deposited under a single scale
though apparently not by the same Scutellista. While there may be
several eggs under one scale there are not more than two, sometimes
three and very rarely four, Scutellista come to maturity. The total
number of eggs laid is difficult to obtain under field conditions. Judg-
ing from experiments in the insectary on the rate of laying and length
of adult life, we are inclined to put the maximum at about 25 or 30.
The time required for hatching is from five to six days.
The Larva is the familiar white grub-like creature seen upon lifting
the black scale. There is considerable difference in size, depending upon
the size of the scale and number of eggs. As stated above, eggs may be
deposited under scales without eggs, and larva have also been seen
attached and feeding on the scale itself. The larval stage lasts from
sixteen to twenty-one days. The number of eggs consumed during this
period varies greatly. They are able to mature on the smallest number
laid, which is 500 or less, or they may consume 2,000 or more. They
feed by sucking the contents of the eggs, leaving the shells, or the body
juices of the scale itself.
Pupa. Upon completing its growth as a larva, the insect changes
into the resting or pupal stage, at which time it changes to a black
color, and remains in this stage from seventeen to twenty days.,
Adult. The adult is shown in figure 7, and is the common metallic
blue fly-like insect seen walking about on scale-infested twigs. It lives
about ten days in this stage.

SEASONAL HISTORY OF THE SCUTELLISTA.
The life of the Scutellista is, of course, dependent upon the life of the
black scale. Just as the black scale may be found somewhere in all
stages at all times of the year, so will the Scutellista. But, like the scale
on which it is dependent, it is to be seen in greatest abundance in the
early summer. It has been stated that the maximum egg period of the






CITRUS FRUIT INSECTS.


black scale in 1910 was about the middle of June. This was also the
maximum larval period for the Scutellista. And the maximum number
of adults appeared about one month later, or the middle of July.
The egg stage being five to six days and adult life ten to twelve days,
the total life cycle will be from fifty to sixty days. These periods are
under summer conditions, and in winter they go through their develop-
ment much more slowly. Under favorable conditions there may be as
many as four or five generations .in a year in southern California.

OTHER ENEMIES OF THE BLACK SCALE.-
Another egg parasite (Tomocera California) was formerly said to
occur abundantly on the black scale, but it has been of little significance
of late years as compared with the "Scutellista. At the present time it is
most frequently met with in the citrus groves of Santa Barbara County.
Several ladybird beetles feed upon the black scale, among which the-
most important is probably Rhizobius ventralis, Fig. 25. The steel-
blue ladybird beetle (Orcus chalybeus) also occurs abundantly in Santa
Barbara County, where it feeds on the black and also the yellow scales,
the two commonest scales of that section.

THE CONTROL OF THE BLACK SCALE.
Aside from the control by natural enemies, which some growers are
still inclined to rely upon, fumigation, and in some cases spraying are
the standard control measures for this scale. For a brief discussion of
these measures see pages 505-511 of this bulletin.



THE RED OR ORANGE SCALE.

(Chrysomphalus aurantii Mask.)

The red scale is the second most important citrus fruit scale in Cali-
fornia. It is associated with the black in the coast sections, but also
occurs beyond the limits of the black as a pest in the interior. Its man-
ner of injury differs from that of the black in the fact that no honeydew
is given off. The injury from the red scale is due directly to the feed-
ing, whether this is on account of the loss of sap, toxic effect on the
tissues of the plant, interference with the functions of the stomata when
the scale is abundant, or a combination of these causes. It is usual to
speak of the effect in the case of the San Jos6 scale on apple and pear
because of the discoloration it produces in the tissues. But the discol-
oration is not evident in the case of the red scale on citrus trees, though
this toxic effect may be present without producing a discoloration. Of


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


course, there is a discoloration produced on the leaves in the form of
yellow spots, but this is due to the loss of chlorophyl, rather than a
poisonous substance which reddens the tissue about the point of
puncture.
At any rate, the red scale which infests leaf, twig, branch and fruit,
may seriously injure a tree in a very short time. Fig. 13 shows a large
portion of an orange tree killed in two years by infestation with the red
scale. In this respect it is much more virulent than any of the other


FIG. 8.-Red Scale (Chrysomphalus aurantii Mask.) on grape fruit.

scales of citrus trees. Aside from this serious effect on the tree, the red
scale very readily gets on the fruit, thus marring its appearance and
market value.
LIFE HISTORY OF THE RED SCALE.

The Active Young. No eggs are laid by the red scale, so the starting
point in the life history is the active young, which are born alive. These
are the minute yellowish creatures which may be seen crawling around
on fruit and leaves infested with this scale. They appear somewhat
like granules of sulfur. After remaining under the parent scale for a





CITRUS FRUIT INSECTS.


day or two they emerge and actively crawl about for a short time, but
usually settle within one or two days.
The Fixed Young. As soon as they settle they begin the secretion of
white cottony fibres with which they cover themselves. This later be-
comes more compacted and reddish in color, and also contains parts of
two molted skins of the insect. They remain fixed beneath this covering
throughout their entire existence. During the summer months they
come to maturity in about 2 months and in the winter from 3 to 3j
months.
The Adult Female. The red scale is so called because of the reddish
appearance of the mature scale, but the reddish color is almost entirely
in the scale covering, the insect beneath being yellow usually. The
scales are circular and about the size of the head of an ordinary pin.
The young are produced at the average rate of 2 or 3 a day for a period
of two months in summer. During the winter the production of young
is almost at a standstill during the colder or wet weather. But during
a spell of warm weather they may appear in considerable numbers.
Our records of two or three dozen accurately kept for each day during
the production of young, the number varied from 25 to 143 with an
average of 55 for each scale. The emergence of young averaged from
2 to 3 per day. During the colder days the young probably remained
under the parent scale a little longer, so that the maximum or 8 were
probably not born on the same day; though eight would appear for two
or three days in succession.
Development of the Male Red Scale. The red scale undergoes its first
molt in from sixteen to twenty
days after birth. Up to this -
time the males and females
are exactly alike, but from
this stage on they lose- all re-
semblance to one another and
might be taken for different .
insects. The male, after the ,
first molt, becomes elongate,
and it is during this stage
that the characteristic elon-
gated male scale covering is FIG. 9.-Male of Red Scale.
produced. Under this scale it changes to a pro-pupa, then to a true
pupa, and finally to the adult, which is a frail insect with two wings.
While the female thus undergoes but two molts and does not change
materially, the male passes through four molts and emerges as an active
insect from 1l to 2 months from birth.


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


SEASONAL HISTORY OF THE RED SCALE.

There may be as many-as four generations a year in southern Cali-
fornia. While the
young from a single
scale, which will run
from 40 to 80, is not
nearly so large as the
black, the increased
number of genera-
A tions accounts for
them more rapidly in-
festing a tree. The
first great production
of young in the
spring occurs in Mlay
and June and from
that time on to No-
vember they are al-
ways to be found in
FIG. 10.-Red Scale, mature females and young, large numbers. Scales
matured in slightly less time in the interior section at Riverside than
nearer the coast at Whittier.


















FIG. 11.-Red Scale on orange leaf.

The greatest mortality occurs during the active period of the young.
In all our breeding experiments the per cent would average about 40.





CITRUS FRUIT INSECTS.


FOOD PLANTS.
While the red scale is essentially a citrus pest it is known to attack
other plants, including some of the deciduous fruit trees; but in Cali-
fornia it is of little consequence outside of the citrus fruits. A more
or less common weed, in poorly cared for California orchards, is the
nightshade, and this plant is readily attacked by this scale. Ivy is
another often attacked.
DISTRIBUTION AND SPREAD OF THE RED SCALE.
The maximum rate of travel of young red scales over smooth surfaces
is at the rate of 4J feet per hour. The rate of travel over orchard soil,
where there is a fine mulch, is practically negligible. We have not suc-
ceeded thus far in getting them across a 3-inch strip of such soil. If
these young scales are watched closely, they will be seen to nearly always
fall back in their attempt to ascend a small particle of earth. Thus they
are able to make no progress, and one kept under constant observation
did not travel half an inch in two hours. If there is a fine mulch in the
grove, as most are kept in California, there is little danger of the spread
of the red scale as dependent upon their own powers of locomotion. But
here again, ,if the soil is compacted, as in irrigation furrows or after a
rain, they can travel very well.
Other points taken up under the head of "Distribution and Spread
of the Black Scale" also applies for the red.

PARASITES OF THE RED SCALE.
(Aphelinus diaspidis Howard.)
The commonest parasite of the red scale; and the only qne of any
economic significance, is the little chalcid (Aphelinus diaspidis How-
ard). This parasite is well distributed over the citrus belts but since
the highest parasiti-
zation seen during
the past three years
would not exceed 5
or 10 per cent, it is ~--4- :
of little consequence
as a control factor.
The egg of this i /yl
parasite is deposited
beneath the scale, /
and the grub-like
larva upon hatching FiG. 12.-Aphelinus diaspidis How. Parasite on Red and
attaches itself to the Yellow Scales. x39.
scale and sucks the body juices. It is not, therefore, an internal para-


BULLETIN 214]





UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


site, for at no stage is it within the body of the scale insect itself. The
eggs hatch in five to seven days; the larva grows to maturity in twelve
to sixteen days; it is eight to ten days in the pupal stage, and lives as
an adult four or five days. The number of eggs deposited is not large,
and probably will not exceed 25 or 30.


FIG. 13.-Large portion of orange tree killed as result of two
years' infestation of Red Scale.

There are certain of the ladybird beetles that feed on the red scale,
the commonest being a small black species (Rhizobius lophanthe) shown
in Fig. 25. The eggs of this beetle may be laid beneath the scales, but
the larva upon hatching travels about, attacking many different insects.





BULLETIN 214] CITRUS FRUIT INSECTS. 465



THE YELLOW SCALE.
(Chrysomphalus aurantii var. citrinus.)
This scale is very similar in appearance to the red scale, and in the
absence of typical specimens, or considerable material, it is impossible
to distinguish the two. The structural characters of the insects them-
selves are identical. But the scales as seen on the tree are usually not
difficult to determine. The yellow is distinctly lighter in color, lies
flatter upon the leaf, and is often slightly larger in diameter. When
the yellow scale dies, the scale covering becomes darker in color, in
which case they are much more difficult to separate.
But aside from this difference in general appearance there is a
distinct variance in habits. The red scale attacks all parts of the tree,
whereas, the yellow is limited almost entirely to the leaves and fruit.
Leaves may be very badly infested with the yellow, and but an occa-
sional scale on the twigs, while in the case of the red, the twigs and
branches really become infested first. Because of the fact that the
twigs are not attacked its power to injure the tree is not so great, and
it can not be counted as serious a pest as the red.

DISTRIBUTION OF THE YELLOW SCALE.
The yellow scale occurs scatteringly over practically the whole of
the citrus belt in southern California, having much the same distribu-
tion as that of the red; but in the Sacramento Valley citrus section it
appears to occur exclusively, there being no red to the writer's knowl-
edge thus far seen in that section.

LIFE HISTORY.
The life history of the yellow scale is the same in all particulars as
the red, so that it need not be repeated here.

PARASITES AND PREDACEOUS ENEMIES.
The parasite discussed in connection with the red scale also attacks
the yellow. But there is another common parasite of the yellow, and
which, in former years, was said to be a very effective check on this scale.
Many people still believe that the disappearance of the yellow scale in
places where it was once much more prevalent than now was due to the
work of this parasite. There is no doubt that the early reports con-
cerning this parasite were, like many others, greatly exaggerated and
based upon no careful observations. This parasite of the yellow scale
has the scientific name of Aspidiotiphagus citrinus Craw. It is strictly
an internal parasite, living with the body of the scale insect itself, and






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


emerging when about half-grown. At the present time it is most abun-
dant in Santa Barbara County, and counts made show that as high as
25 per cent of the scales may be parasitized.
The control of the red and yellow scales is effected by fumigation,
for which see the close of this bulletin.


THE PURPLE SCALE.
(Lepidosaphes beckii Newm.)
The purple scale was introduced in California upon cuttings from
Florida in 1892. Statements were then made that it would not thrive
in the drier California climate, but it has succeeded very well in many
of the coast sections from Santa Barbara to San Diego. Its eastern
limit at present is in the eastern part of Los Angeles County, and has
not yet appeared in Riverside or San Bernardino counties, nor any of
the northern citrus sections.
The purple scale is the most difficult to handle of the four scales thus
















FIG. 14.-Purple Scale on orange leaf.

far mentioned, because of the resistance of the eggs to fumigation. It
attacks leaf, branch, and fruit, often becoming incrusted on but a
portion of the tree, usually the lower side. Parts of the tree will thus
be badly injured by the dropping of the leaves and the killing of the
branches, but it seldom, if ever, destroys the entire tree. The retention
of the scales on the fruit after it comes into the packing house is another
point against the purple scale.
LIFE HISTORY OF THE PURPLE SCALE.
The eggs of the purple scale are the pearly white oval-shaped bodies,
which are to be seen upon lifting the mature scales. They are almost






CITRUS FRUIT INSECTS.


completely enclosed by the firm scale-covering above and the lighter
cotton-layer beneath, forming a sack with the opening at the posterior
tip, through which the young make their escape. It is for this reason,
largely, that the purple scale eggs are so resistant to hydrocyanic acid
gas on account of the difficulty of the gas reaching them.
The number of eggs deposited is from 30 to 40 extending over a period
of three or four weeks. The eggs hatch in fifteen to twenty days during
the summer months. From the time the eggs first appear until the last
ones hatch, therefore, is a period of about two months, so that about
six weeks or two months ought to be allowed between fumigations, where























FIG. 15.-Purple Scale on orange leaf enlarged.

two treatments are made, as sometimes is done with this scale. The
most eggs are present in the spring or early summer (May and June)
though all through the season they may occur in all stages.
The Young. The young scales upon hatching remain under the
parent but a day or two, and after another day or two of actively moving
about over the plant, they settle down and remain stationary, in the
case of the female, throughout the rest of their lives. They first secrete
a couple of coarse, entangling threads, which serve as protection until
they have opportunity to cover themselves with the permanent scale
covering.
The female undergoes two molts within a period of one to one and a
half months. Eggs will be deposited at the end of two months in sum-


BULLETIN 214]







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


mer, and during winter it is prolonged to three and over. Young will
begin appearing in a little less than three months from the time the
parent was an active young scale. The old scale dies soon after the
production of eggs.
The male purple scale, after molting four times and going through
the usual pro-pupal and pupal stages, emerges as a winged insect after
a period of approximately two months in summer and three months in
the winter season. The scale of the male is long and narrow and easily
distinguished from that of the female.


FIG. 16.-Orange incrusted with Purple Scale.

SEASONAL HISTORY OF THE PURPLE SCALE.
Taking the minimum period from young to young in midsummer at
80 days and the maximum in winter at 120 days, there will appear
during the season between three and four generations of the purple
scale. In the case of warmer dry winters there may be four full genera-
tions in the year. There appears to be a maximum period of eggs and
young in May and June, and again in August and early SepteAber.
The season of greatest mortality is here again coincident with the season
of greatest production of young; but a larger portion of the young suc-
ceed in getting established than is the case with either the red or the







CITRUS FRUIT INSECTS.


black scales. The provision for mortality, as indicated by the number of
eggs produced, is not so great as in the black scale, for the black scale
produces fifty times more eggs than the purple.
NATURAL ENEMIES OF THE PURPLE SCALE.
Aspidiotiphagus citrinus Craw. is the only parasite we have thus far
taken from the purple scale. This is strictly an internal parasite, and
attacks the scale only between the first and second molts. The egg is
deposited within the insect, and there hatches a very minute white
larva with a tail-like appendage, which disappears with the later molts.
The adult makes its way out
through a circular exit hole
in the posterior one third of
the scale. .
This parasite is not gen- --
erally distributed over the -.- -=
localities where the purple ,
scale occurs, and it is only
occasionally that the parasite
will.be met with; but where i
it does occur, the amount of FIG. 17.-Aspidiotiphagus citrinus Craw. x40.
Parasite on Purple, Yellow, and Red Scales.
parasitization may run as
high as 30 or 40 per cent. During the winter months it has taken at
least five days for the eggs to hatch and nine weeks are necessary for its
complete life cycle. In summer it requires much less time.
In addition to this internal parasite several kinds of ladybird beetles
may be occasionally seen to feed upon the purple scale, and the com-
monest of these are Rhizobius lophanthce Blaisd. and Scymnus margi-
nicoiles.
For the control of the purple scale, see discussion on fumigation on
page 506.

THE COTTONY CUSHION SCALE.
(Icerya purchase Mask.)
The cottony cushion scale is a native of Australia and was introduced
into California, probably upon an acacia at Menlo Park, in 1868.
Twenty years later it was widely spread over the State and considered
a very serious menace to the citrus fruit industry. In 1889, the Austra-
lian ladybird -beetle (Novius cardinalis) was introduced through the
efforts of the Division of Entomology of the United States Department
of Agriculture. In a short while it was reported to have the scale under
subjection, and has usually apparently kept it so ever since.
This importation has always been referred to as the most successful
case on record of one insect keeping another under control. In fact, it


BULLETIN 214]







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


has been the stimulus, the support, and the hope for the future, for a
large amount of work along the line of importing one insect to prey upon
another. This has been espe-
cially true in this State, and
while much good work may
have been done, there has not
been approached any such
signal success as seemed to
be the case with cardinalis.

PRESENT STATUS OF THE COT-
TONY CUSHION SCALE IN
CALIFORNIA.
While the cottony cushion
scale is at present a pest of
comparatively little conse-
quence, it is still one of the
commonest insects inquired
about throughout the entire
length of the State where
citrus trees are grown.
While the cardinalis is pret-
ty well distributed over the
State, and often appears un-
aided in an infestation of
cottony cushion scale, yet in
many cases it does not occur,
and neither does the scale
become very abundant. The
checking of the scale in such
cases must be accounted for
through some other factors.
Sometimes, too, the beetle is
slow in getting the scale
under control. On the sta-
tion grounds at Riverside
fifty or seventy-five orange
trees have been infested
with the cottony cushion
scale, as bad as occurred
FIG. 18.-Cottony Cushion Scale on orange when the insect was at its
twig. height, for at least four
years. During this time also the ladybird beetle has been present. The
scale becomes very abundant each spring, when the cardinalis begins





CITRUS FRUIT INSECTS.


work and effectively checks them. The beetles are present in April,
May, and June, and disappear in July. Some young scales are left


FIG. 19.-Young Cottony Cushion Scales on orange leaf. Larva and adult of
the Australian ladybird beetle also shown feeding upon the scales.





S,


FIG. 20.-Different stages in


the development of the Cottony Cushion
Scale.


and those have a chance to multiply and severely infest the tree again
before the cardinalis appears in the spring. This has been the history
of the infestation for the past four years.
3-8214


BULLETIN 214]






UNIVERSITY OF CALIFORNIA--EXPERIMENT STATION.


LIFE HISTORY AND HABITS OF THE COTTONY CUSHION SCALE.
The large fluted cottony mass that is so characteristic of this scale is
secreted only by the female when it is full grown. This is for the
protection of the orange yellow eggs that are deposited within the mass
and which is enlarged as the 500 to 800 eggs are deposited. These
require ten to twelve days to hatch in summer and may be prolonged
to three weeks in winter.
The larvva settle upon the leaves and twigs, arranging themselves
largely along the mid rib and veins of the leaf. In the later stages
they prefer the twigs and branches, or even the trunk. Occasionally,
they develop on the leaves, but very rarely upon the fruit. Unlike the
other scales mentioned, the cottony cushion scale travels throughout the
greater part of its life, or until the egg sack is secreted.
There is a great variation in the time of development of the different
scales, even during the same season.
S- Some will mature in three months,
while others will go four months
S ) and over. There are about three
generations a year in southern
SCalifornia, but on account of the
/ irregularity in development these
are not at all distinct. The season
FIG. 21.-Male of Cottony Cushion of greatest production of young is
Scale. May and June. The injury from
this scale is due to the honeydew given off, and also to the direct attack
upon the tree.

NATURAL ENEMIES OF THE COTTONY CUSHION SCALE.
Novius cardinalis, the Australian ladybird beetle, is the most effective
enemy of the cottony cushion scale, and in most eases may be relied
upon to control it. The adult beetle lays from 150 to 200 orange red
eggs, most usually in the cottony egg sack. These hatch in five or six
days and the larvae begin at once to feed upon the eggs. Later, they
feed upon all stages of the scale and their growth as a larva is completed
in three weeks. The pupal stage lasts about a week, when the adult
beetle, with red and black markings, appears. This beetle is known to
feed only upon the cottony cushion scale, or their own kind, if food
becomes scarce. For this reason, upon the cleaning up of an infestation
of scale, the beetles themselves often die, so that there is cause for
maintaining a supply and sending them out to new infestations.
Another enemy of the scale is the dipterous or two-winged parasite
(Cryptochcetum, iceryce Will.). This is said to have occurred quite
abundantly in former years, but is no longer considered an important






CITRUS FRUIT INSECTS.


aid in the control of the scale. This is a small black fly with green
metallic reflections. The larva lives with the scale and the adult


FIG. 22.-Exudation or honeydew from Cottony Cushion Scale crystallized
and before growth of fungus has started.


FIG. 23.-Pupse of N. cardinalis on orange tree.


FIG. 24.-Different stages of the larva of N. cardinalis.


emerges through an exit hole, which characterizes those scales parasi-
tized. Infestations of this scale very often occur with no evidence of


BULLETIN 214]








UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


the parasite, showing that its distribution is not so general as that of
many others. It has been most frequently met with during the past
two or three years in Santa Barbara and Orange counties.
The main reliance for control, therefore, is the ladybird beetle
(Novius cardinalis) and if specimens are not already present among
the scales they may usually be obtained from the State Insectary,
Sacramento.


1


4


- I ,


40x


4.


C


FIG. 25.-Some common ladybird beetles. All enlarged 5 times.
1. Scymnus marginicollis, Mann., feeding on Red and Purple Scales.
2. Rhizobius lophanthbe, Blaisd., feeding on Red and Purple Scales.
3. Scymnus nebulosis, Lee., feeding on Red and Yellow Scales.
4. Rhizobius sp. feeding on Purple Scale.
5. Hyperaspis, 8 notata, on Monterey Pine Scale.
6. Novius koebeli, Oliv., feeding on Red Scale.
7. Rhizobius ventralis, Black, feeding on Black Scale.
8. Orcus chalybeus, Boisd., feeding on Black, Red, Yellow, and Purple.
9. Novius cardinalis, Black, feeding on Cottony Cushion.
10. Cryptolemus montrouzeri, feeding on Mealy Bug.







BULLETIN 214]


475


CITRUS FRUIT INSECTS.


4'V











3 -


















5

FIG. 26.-Some common ladybird beetles, all enlarged five times.
1. Olla plagiata, Casey, feeding on Aphids.
2. Axion plagiatom, Casey, feeding on Black Scale.
3. Hippodamia convergens, Guer., feeding on Aphids and scale insects.
4. Coccinella californica, Mann, feeding on Aphids and scale insects.
5. Hippodamia ambigua, Lee., feeding on Aphids and scale insects.
6. Hippodamia ambigua, Lee., feeding on Aphids and scale insects.


SOFT BROWN SCALE.
(Coccus hesperidium Linn.)

This scale, while seldom occurring in injurious numbers over an entire
orchard, often severely infests an occasional tree or portion of a tree;
but the infestation is usually of short duration, due, in most cases to






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


the efficient work of one or two parasites. This scale is thoroughly
distributed over the world, and attacks a large number of widely dif-
ferent plants. Its injury is due chiefly to the copious amount of honey-
dew given off, and the consequent growth of the
sooty mold fungus. It attacks the smaller twigs
and the leaves.

19 LIFE HISTORY AND HABITS OF THE SOFT BROWN SCALE.
No eggs are deposited by this scale, the young
being born alive, as is the case with the red scale.
The active young soon settle and remain fixed,
-though there may be some movement until it is
about one half grown. They molt twice and come
to maturity, and produce young in sixty-five days
during the summer months. The largest number
















FIG. 28.-Aphycus flavus How. parasite or soft brown
scale. x40.

of young we obtained from a single scale has not
exceeded 30 distributed over a period of thirty to
thirty-five days.' There may be, thus, several gen-
erations in a year, but during the winter their
development is very slow. The young usually ap-
pear abundantly in May, and again in July, and
FIG. 27.-Soft
brown scale also in September, but on account of the overlap-
on orange
twig. ping, many may be present continually during the
summer months. The total number of generations will be between four
and five.
NATURAL ENEMIES OF THE SOFT BROWN SCALE.
There are two common internal parasites of the scale, Coccophagus
lecanii Fitch. and Aphycus flavus How. The former emerges when the
scale is nearly grown or of considerable size, while the latter emerges







CITRUS FRUIT INSECTS.


usually while the scale is still small, not more than half grown. Those
scales parasitized with lecanii may be known when the parasite is in the
pupal stage by the black color which is shown through the scale. The



^.^ -^J ~A --_... _---


S\I




FIG. 29.-Coccophagus lecanil, Fitch, parasite of soft brown and
other scales.

other parasite is yellowish in color, and does not make the scale appear
black. These are strictly internal parasites and the Aphycus is the


FIG. 30.-Soft brown scales with exit holes of
parasites. Partly grown scale shown at top of
figure.
more effective when abundant because the scales are checked before
they attain any size. The scale is often alive for some time after the
parasite has changed to the pupa. Other parasites taken from this scale
are Encrytus flavus and Coccophagus lunulatus.


BULLETIN 214]







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


HEMSIPHERICAL SCALE.
(Saissetia hemisphaerica Targ.)


--
FiG. 31.-Hemispherical scale, Saissetia hemisphaerica,
on leaf of Christmas berry.


absence of the letter H, its lighter
color of brown, and its smooth
shiny surface. Full grown scales
of this species are commonly
found on the leaves as well as the
twigs, and some have the habit
of settling on the very edge -of
the leaf.

NATURAL ENEMIES OF THE HEMIS-
PHERICAL SCALE.
Coccophagus lecanii, the same
internal parasite that attacks the
soft brown scale, also attacks the
Hemisphacrica scale and emerges
from the scale when about one
< half grown. Another parasite,


This is a scale
that is of little con-
sequence as a citrus
tree pest, though it
is commonly found
on such trees in
certain sections as
Santa Barbara and
San Diego. It is
essentially a green-
house scale, but
thrives out of doors
in mild climates.
Here, in California,
it more readily at-
tacks certain orna-
mental plants, as
the Christmas ber-
ry, oleander, and
palm. It is easily
distinguished from
the black, which is
its nearest ally on
citrus trees, by the


*i4r, '^Jr
misphaerica scale on leaf
of orange.







CITRUS FRUIT INSECTS.


Comys fusca, is found commonly in this scale, and this one emerges
when the scale is nearly or quite full grown. Scutellista cyanea, the


FIG. 33.-Hemispherical Scale
on twig of orange.


FIG. 34.-Male puparia of Hemispher-
ical Scale.


Fic. 35.-Comys fusca How., parasite on Hemispherical, Brown Apricot,
and other scales. x18.

egg parasite of the black scale, also occurs occasionally in this scale, as
well as some of the other internal parasites.


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


THE GREEDY SCALE.

(Aspidiotus rapax Comst.)


This scale sometimes infests the twigs
only occurs on the older fruit that may


of citrus trees and also com-
be still remaining on the tree


FIG. 36.-Orange Infested with Greedy Scale (Aspidlotus rapax, Comst.).

from the previous year, or the older tree-ripe lemons. It is thus on the
older fruit that this insect attracts most attention, and so long as it is
confined to such fruit, the injury is of little consequence. But, occa-
sionally, it will also be found on marketable fruit and is often associated
in scattering numbers with other scales. It may be distinguished from
the red or yellow by its lighter gray color and its much greater con-
vexity. The greedy scale infests a long list of plants and occurs more
abundantly on acacia, laurel, and other shade and ornamental trees
than upon citrus trees. The parasite Aphelinus fuscipennis How., has
been bred in some numbers from this scale.






CITRUS FRUIT INSECTS.


THE OLEANDER SCALE.

(Aspidiotus hederc Comst.)

This scale is known as a citrus fruit scale because of its occasional
occurrence on lemons, and goes by the common name of Lemon Peel


FIG. 37.-Oleander Scale (Aspidiotus hederm).
Scale. It does no injury particularly to the tree, and is mentioned
here because it is sometimes met with on the fruit.


THE CITRUS MEALY BUG.
(Pseudococcus citri Risso.)

The citrus mealy bug is widely distributed over the citrus trees of the
State from Chico to San Diego, but it is considered an important pest
only in certain restricted localities, notably in Ventura and San Diego
counties. It is also found commonly on the citrus trees of the Sacra-
mento and San Joaquin valleys. It has been known to occur in the
State for the past fifteen or twenty years, but has never been consid-
ered a very serious pest, except recently in San Diego and Ventura and
to a less extent in other counties. The mealy bug is an insect that


BULLETIN 214]







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


approaches the extent of a pest more or less periodically, and in many
cases where it is present for a few years will disappear without any well
known specific causes.
The mealy bug attacks all parts of the tree, leaf, branch, and fruit,


FIG. 38.-Citrus mealy bug (Pseudococcus citri Risso). The two figures on
the right show the development of the cottony mass in which the eggs are
deposited.

seeming to delight particularly in the fruit. Masses of the insect with
eggs and young may cluster on the fruit, and in the case of the navel


FIG. 39.-Mealy bug on oranges.

orange, will be sure to be found secreted in the navel end. It also gives
off a very sticky sort of honeydew that makes it exceedingly difficult to
wash the fruit clean, in addition to getting the insects themselves
removed. Hidden in the navel of the orange, they may pass through






CITRUS FRUIT INSECTS.


the washing machine and also the hand cleaning. This also happens on
the lemon, and when this fruit is left in the packing house for curing,
they may continue to breed undisturbed. On account of its habit of
seeking protected places, they congregate at the base of the petiole of the
leaf or stem of the fruit causing the leaves and young fruit to drop
prematurely. Because of the injury to the fruit, from the attacks of the
insects themselves, and also through the vigorous washing and cleaning,
the loss through decay in transit is often very heavy.


FIG. 40.-Mealy bug on lemons.

LIFE HISTORY AND HABITS OF THE MEALY BUG.
The eggs of this insect are laid in a cottony mass which is secreted
by the mature female as the eggs are deposited. The number laid by a
,single individual will be from 350 to 400, and they require about eight
to ten days to hatch during the warmer months and in winter from
fourteen to eighteen days.
The young move about more or less throughout their development.
They may not, of course, migrate very far, for they are usually busy
feeding. The time of development of the mealy bugs varies consid-
erably, taking 22 months from March to May and about 11 months
during the summer. Males have completed their life cycle in two
months in winter and only about one month during the warmer weather
of summer. The females appear to have the habit of producing eggs


BULLETIN 214]





UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


before they attain full size, in which cases they continue to enlarge as
the eggs are deposited.

NATURAL ENEMIES OF THE MEALY BUG.
The mealy bug being a soft-bodied insect and exposed as it is on the
tree, is subject to the attacks of a considerable number of parasites and
predaceous insects. Space will not
1 permit of a full discussion of these
here. There are several different
species of ladybird beetles that prey
upon them, and the one that is to us
best known, and probably the most
important, is Cryptolaemus mon-
FIG. 41.-Hemerobius larva. trouzieri. The larvae of this beetle
are covered ;with cottony tufts, and as they occur among the masses of
the mealy bug, are not readily distinguished from them. The beetle
itself is black in color and tipped with yellowish brown at either end.
The under side is light brown, excepting where the legs arise, which is
black.
Beside the ladybird beetles there are the lacewing Hemerobius and
Syrphus fly larvae, and several internal parasites that attack, the mealy
bug. Professor R. W. Doane, who assisted in this investigation during
the summer of 1910, has observed one Hemerobius larva eat 16 partly-
grown mealy bugs in an afternoon.

CONTROL OF THE MEALY BUG.
This insect is one of the most difficult of all the pests to actually
kill all of its numbers. It is very or quite resistant to fumigation
dosages as ordinarily used on citrus trees, and because of its habit of
congregating in masses or hidden away in the navel of the orange or
other secluded places, it is impossible to reach or kill them all with a
spray. But of the two methods, the experience in San Diego County
and also more recently in Ventura, is that the spray is more effective
than fumigation. The spray that Mr. Essig, Horticultural Commis-
sioner of Ventura County, especially recommends is the carbolic acid
emulsion, consisting of 1 gallon of crude carbolic acid and 8 pounds of
whale-oil soap to 170 gallons of water. The soap and carbolic acid are
dissolved in hot water. Kerosene emulsion, or the kerosene water spray,
discussed at the close of this bulletin, will also give fairly satisfactory
results. But with bad infestations two or three sprayings should be
made at intervals of three or four weeks.






CITRUS FRUIT INSECTS.


RED SPIDERS.
(Tetranychus mytilaspidis Riley.)
(Tetranychus sexmaculatus Riley.)
The species named above are the two common species of red spiders
attacking citrus trees in the State. They occur all over the citrus belt
and in one place or another do considerable injury each year. In the
early spring is when they become most abundant and do most damage.
Later in the spring or summer they largely disappear, although they
may be found on the trees the year around.
The injury caused by the red spiders is due to the consuming of the
plant juices, as indicated by the pale spots where their mouth parts are

















FIG. 42.-The Florida Red Spider. x140.
inserted. This gives a mottled effect to the leaf, and later assumes an
ashy gray or yellowish appearance with but little chlorophyll or green
matter left. Leaves thus affected later fall from the tree. The same
effect is produced on the fruit as regards the grayish or silvery appear-
ance of the rind. Another phase of injury that has become important
in some packing houses during the past year is the breeding of the
spiders and consequent injury to lemons during the curing process.
Both species of red spiders have come into the State from Florida.
These are commonly distinguished by the differences in color and mark-
ings. T. mytilaspidis, or the Florida red spider, is distinctly red in
color, while T. sexmaculatus, or the six-spotted mite, is pale gray in
color with six dark spots. The former does the more injury of the two,
and is more generally distributed. In addition to the differences in the
mites themselves, their habits of feeding are different. The Florida red
spider feeds generally over the entire surface of the leaf or fruit making
a uniform mottled effect, whereas the six-spotted species feeds largely


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


on the under side of the leaf and is confined to restricted areas. These
are usually along the mid rib, and extend outward and forward in the
direction of the cross veins. These spots are pale colored with old cast
skins and black specks on the surface, and covered usually with a web.
On the upper surface the leaf is swollen upward, corresponding to the
depression on the lower surface, and the area is smooth and pale yellow-
ish in color.
LIFE HISTORY AND HABITS OF THE RED SPIDER.
What follows on the life history has been worked out for T. mytilas-
pidis, but the other species is probably very similar.
The eggs are minute, nearly-spherical, red bodies, occurring singly
















FIG. 43.-Orange leaf with area in center showing work of the Florida
Red Spider.

on the leaf and held in place by an upward projecting stalk with
radiating guy threads extending down to the leaf. They require ten
days to hatch during May, when they are most abundant. From 0 to
6 or 7 eggs will be deposited each day after egg laying begins. This
will continue for about four weeks, and the average number laid each
day will be 2 or 3. Many of the spiders do not lay for the full period
so that the number of eggs deposited will range from 30 to 75.
The young mite at once begins to feed and comes to maturity in
twelve days, during which time it has molted three times at intervals
of three days each. The young mite as it hatches from the egg has
but six legs, but during the first molt it acquires another pair, making
eight, which is the usual number for most spiders and mites. In
twelve days to two weeks they are depositing eggs, which is continued
for a month longer. The entire life cycle, therefore, will be about forty
days, allowing ten days for the eggs to hatch, twelve days for the devel-
opment of the young and four weeks for adult life. Male spiders,
which are smaller in size than the females, are usually present, but we





CITRUS FRUIT INSECTS.


have determined that eggs may be produced and young hatched without
them.


FIo. 44.-Orange leaf on right showing characteristic feeding areas of six-
spotted mite on lower surface. On left, upper surface of same leaf.

CONTROL OF RED SPIDERS.
The standard remedy for spiders and mites is sulfur. It is usually
applied dry, dusted over the tree. This may be done by hand, but
better by a rotary bellows. In procuring the sulfur, fineness is the
most important consideration. The vapor of sulfur is effective but for
a very short distance, a fraction of an inch, so that evenness of distribu-
tion, instead of large amounts here and there, is more efficient and less
wasteful of the sulfur. There is no stated time for application. It
should be applied just as soon as injury by the spiders is apparent.
This will be some time in the early spring. A temperature of about 750

4-B214


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


is necessary to properly vaporize the sulfur. The higher the temper-
ature above this, the more quickly the sulfur acts. Select, therefore,
days that will have a bright, warm sun in the middle of the day, but


FIG. 45.-Tip of orange twig showing work of six-spotted mite on the leaves.

apply the sulfur in the early morning while the dew is still on the
foliage. If a sulfur spray is desired, use 30 pounds of sulfur and 15
pounds of lime, as milk of lime, to 200 gallons of water, or 1 to 35 or 50
parts of the commercial lime sulfur.







CITRUS FRUIT INSECTS.


THE SILVER MITE.
(Eriophyes oleivorus Ash.)
The silver mite in California is restricted to a comparatively small
section in San Diego County. This, again, is an imported pest, having
come into the State from Florida in 1889. The once familiar russet
orange of Florida was the result of the work of this mite on the rind.
This mite attacks both the foliage and the fruit, but, of course, the
most injury is done to the fruit. The green lemon takes on a decidedly


FIG. 46.-Lemon on right showing work of silver mite.


silvery appearance, which is due to the extraction of the oils and green
matter, or chlorophyll. On account of this silvery effect on the lemon,
which is the principal variety of citrus grown in the section, it is known
here as the silver mite. In Florida it is called the rust mite of the
orange. If the lemons are allowed to ripen on the tree they take on
this russet effect, but not to such a marked extent as is the case with
the orange.
LIFE HISTORY AND HABITS OF THE SILVER MITE.
The eggs are somewhat like the red spider eggs, excepting that they
are pale yellow in color and smaller. They are laid singly or in small
clusters on the foliage or fruit, and hatch in four or five days in summer
and ten to fourteen days in winter. The young mite soon begins to
feed, and after about a week sheds its skin, which brings it to the adult


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


form. A couple of weeks are all that are necessary, therefore, to bring
it from the egg to maturity. This 'T -
will be the period for the warmer .
weather, and in colder weather this [, 1'i i: ';'.,
will be doubled. The adult mite, '
Fig. 47, looks very different from
its near ally, the red spider. It is FIG. 47.-Silver Mite. x320.
more worm-like and has but four legs, while the red spider has eight.
THE CONTROL OF THE SILVER MITE.
Same as for red spiders, page 487.

THRIPS.
Most orange or lemon growers are familiar with the fact that .upon
shaking the blossoms into the hand, there will be likely to be seen
r


FIG. 48.-Work of thrips (Euthrips citri) on fruit.
small yellowish to black insects running about. These are thrips of
which some species are limited almost entirely to the blossoms, while





CITRUS FRUIT INSECTS.


others attack the leaves and fruit and do serious damage. The orange
thrips (Euthrips citri Moul.) causes a leathery, distorted growth, and
gives a pale silvery color to the leaves. On the fruit they often work
around the stem making a very distinct ring, as shown in Fig. 48, some-
times also working down in streaks, as in Fig. 48. Later, they attack
the blossom end where the line of injury is not so distinctly and abruptly
marked off. This injury to the fruit, while not affecting its edible
qualities, decidedly lowers its market value, and such fruit must be
consigned as an inferior grade. The part of the tree attacked is the
tender growth, and, with a severe infestation, the growth of the tree is
considerably interfered with.
The foregoing account of thrips injury is due to the citri species or
regular orange thrips. This species occurs in greatest abundance in













0006.
FiG. 49.-Characteristic rings at stem end of small oranges made by thrips,
(Euthrips citri).
the San Joaquin citrus section. It also occurs in southern California,
and occasionally does some injury in the Redlands district and more
rarely in the other parts of the citrus belt. Its occurrence at Redlands
may be due to the fact that the climate there is more nearly like that
of Tulare County. The same species also occurs in Arizona and does
considerable injury there. However, the only place where it is serious
enough thus far to warrant inaugurating control measures is in the
San Joaquin belt where, during the past year, about 2,000 acres of
orange trees were sprayed.
Another species (Heliothrips hcemorrhoidalis) has been observed
to do even more serious injury than the citri species on a few trees.
In Santa Barbara County three or four cases of a few trees each were
seen to have practically the entire foliage and also the fruit severely


BULLETIN 214]







492 UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.

affected by this species. The leaves were of a mottled pale color and
many had yellowed and dropped off, and the entire surface of the fruit
has a pale silvery color, as shown in Fig. 50. This species has also been


FIG. 50.-Orange on right showing work of thrips
(Heliothrips hmmorrhoidalis).

taken on oranges in Kern County, but we have no report of damage
from that section.
The species commonly occurring in the blossoms of citrus trees are


FIG. 51.-Work of thrips (H. hemorrhoidalis) on orange leaf.

Euthrips tritici Fitch and Euthrips occidentalis. These are common
species widely distributed over the State and attacking various kinds
of plants. Thus far these have done no very serious injury to the fruit
or foliage of the orange tree. They occur in the blossoms for the






CITRUS FRUIT INSECTS.


purpose of feeding on flower parts, and where their numbers are large,
as is often the case, they probably do some injury to the flower and
consequent setting of the fruit. But this injury may never become
serious enough to warrant any attempt at control. The few trees
that were attacked so severely by the hcemorrhoidalis in Santa Barbara
County would certainly warrant spraying. But the most widespread
injury is done by E. citri and the discussion below on control has special
reference to this species.
A certain brown spot that is commonly found on oranges was sup-
posed to be due to thrips, according to a theory that was promulgated
several years ago. Just what is the cause of such spots is not yet
known, but thus far no evidence has been adduced to prove that it is
due to thrips, and it is certainly not characteristic thrips injury.
LIFE HISTORY AND HABITS OF THE ORANGE THRIPS.
Adults of this species appear in the early spring and there is a suc-
cession of broods on to November. In 1910, they first made their
appearance in the Lindsay section about April 15th. By April 22d
they were found commonly feeding upon the more tender leaves.
According to Mr. J. R. Horton of the Bureau of Entomology, Wash-
ington, who has been investigating this species, the period of develop-
ment is from seventeen to twenty-three days and the average life of the
adult about twenty-five days. He has also determined that pupation
does not occur in ground, like its ally the pear thrips, but in rubbish,
old leaves, blossoms, and under bands, in the case of trees so protected.
CONTROL OF THRIPS.
Spraying seems to be the most satisfactory means of combating the
thrips and the spray that has been recommended by the Bureau of
Entomology consists of:
Commercial lime sulfur (33) ------ ----------2 gals.
Black leaf extract -------------2 gals. of 24%, or 14 fluid oz. of 40%.
Water -------------------------200 gals.
The first spraying was done in 1910 on April 25th, and it is necessary
to follow this with a couple more applications at intervals of about
ten days. A strong pressure, 175 pounds, is necessary to reach all parts
of the tree.
APHIS.
(Aphis gossypii.)
Often in the early spring on the tender shoots of citrus trees Aphids
will be found thickly covering the twig and underside of the leaves.
The result of their injury is a curling of the leaves and a checking in
growth of the shoot. Fortunately, these insects never completely
infest a grove, and only rarely an entire tree. Their attack is confined
to a few shoots, usually so that the effect on the whole tree is not so


BULLETIN 214]







UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


serious. Again, they disappear very suddenly in the midst of a maxi-
mum infestation.
Many people attribute this disappearance entirely to a Braconid
parasite which attacks them. But this statement is not always based on


.



*.*,

FIG. 52.-Coceinella abdom-
inalis, Say, feeding on
Aphids. x5.


close observation. When the lice disappear
there is nothing left but the mummies of those
which have been parasitized. The conclusion
is that they have all been thus killed. As a mat-
ter of fact, where there is one mummy left,
there were often a score or more of lice during
the infestation, and, since it is only the mum-
mies that remain, it is not surprising that the
parasite should have all the credit. Diseases
and weather conditions usually must be consid-
ered more important factors in the control of


the plant lice than both parasites and predaceous enemies. But, how-
ever, they disappear, the important thing is that they often do so, and
the grower is relieved of the necessity of inaugurating control measures.
In those few cases where they are present and do much injury, they may
be killed by a nicotine or weak soap or oil spray. In the case of budded
trees, where there is much tender growth, this is sometimes advisable.

THE ORANGE TORTRIX.
(Tortrix citrana Fern.)
Orange growers of southern California have been for a great many
years more or less familiar
with the work of a worm
burrowing into the fruit.
But very little has been
known about the insect
itself or its habits. This
insect was first described in
1889 and has been reported
as doing injury at intervals
since that time.
During the season of
1909-10 it was the cause of
considerable concern in cer-
tain sections of the south-
ern California citrus belt.
It was most abundant in
Los Angeles County, from FIG. 53.-Eggs of orange tortrlx. x14.
Glendale to Covina. In some of the packing houses during the early






CITRUS FRUIT INSECTS.


part of the season the wormy fruit amounted to between 5 and 10 per
cent. The injury is due to the burrows made in the fruit, and those
usually go no deeper than just through the rind. There is considerable
variation in size of the burrows, as shown in Fig. 56. Fruit that is
otherwise sound must be classed as culls on account of these burrows,
and in the worst infested places a special man was delegated to sort
these out in the packing house.
Not only do the holes themselves mar the fruit, but these are the
source of infection for several kinds of decay, including the blue mold,
the navel end rot, and the wither tip fungus. An orange that may
show no outward signs other than the worm hole may be badly infected
with decay in the interior. Such a case is indicated in figures 57 and 58.
The burrows in the fruit also often cause it to drop prematurely,
especially if the fruit is still small, so that all the injury by this insect
is not accounted for in the packing house alone.
This insect attacks a wide range of food plants aside from the orange.
Among those may be mentioned the apricot, willow, oak, wild walnut,
golden rod, and a large number of greenhouse plants. On these plants
the larvar feed upon the leaves
mostly, and these are matted
together by means of silk
threads which it secretes. In
the case of Pelargonium ,.
they also work in the tip and
branches similar to a borer.
LIFE HISTORY AND HABITS OF
THE ORANGE TORTRIX
The eggs are laid on the
leaves, usually the lower sur-
face and also on the orange it-
self. These are laid in masses
of from 10 to 35, and overlap
one another like fish scales.
An individual egg is cream
color, 3/100 of an inch in di-
ameter, disc-shaped, and with
distinctly marked hexagonal ,
net work. Two or three of Fm. 54.-Larva and adult of orange tortrix
(Tortrix citrana Fern.). Larva enlarged
these masses may be laid by a 5 times. Moth about 1H times natural size.
single moth, the total number of eggs varying from 30 to 75. Hatching
occurs in twelve days.
The young larva upon hatching feeds upon the surface of the fruit
at first by making small burrows, but later confines its feeding to a
single burrow. A thin network of silk is often spun about the entrance.


BULLETIN 214]







496 UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.

Larva in the insectary entered the fruit on the underside, where it was
resting on the surface. In the field the most usual place of entry is
where two oranges are in contact or where a leaf is resting upon the
fruit.
The full grown larva is about half an inch long and the color varies
from greenish white to
dark gray, with irregular .
stripes, which show more .
distinctly in the darker
specimens. During the let
growing period the worms i
remain almost continuous-
ly within the fruit, but
upon reaching maturity
they may emerge and
wander about seeking a ,
suitable place for pupa-
tion. If such a place is
not found they will pu- -
pate within their burrow, FIG. 55.-Orange tortrix. Pupal skin in burrow
in fact, this a very com- and moLh which emerged from it.
mon place chosen. The total period necessary to bring the larva to


















FIG. 56.-Squares of orange rind showing the different types of burrows
made by the orange tortrix.

maturity is from fifty-five to sixty days and the pupal period lasts from
nine to twelve days in midsummer.
There is considerable overlapping of broods so that the number is






CITRUS FRUIT INSECTS.


not very well defined. But there is a period in the spring, when the
moths are abundant, and again in the early fall. Moths were common
in May and the first part
of June, and practically
none seen in July and
August. Judging from the
appearance of the worms
and of the moths there are
probably three generations
in a year, in the orange
groves. It has not been un-
common to find the larva of
this orange worm parasi-
tized. Those species that
have been reared are two
new species of Braconids,
not yet described. These,
upon completing their de-
FIG. 57.-Orange showing burrow of orange
development, about the time tortrix. No evidence of decay on outside.

the worm is full grown,
emerge and pupate in a
cylindrical silken cocoon.
As for artificial control
of this insect, spraying
with an arsenical might
be feasible if they became
very abundant, but it is
not likely that this will
ever be necessary. With
the present status of in-
jury the most practical
measure is to pick up and
destroy all dropped fruit
in the field while the
larva is still within its
FIG. 58S.-Same orange as shown in figure 57 burrow, and also the de-
cut into showing infection as result of the
burrow of the orange tortrix. struction of the wormy
culls as they are sorted in the packing house. This is a case where an
insect, that is probably native and accustomed to feed upon other plants,
has adjusted itself to new conditions.


BULLETIN 214]








498 UNIVERSITY OF CALIFORNIA--EXPERIMENT STATION.


FIG. 59.-Oranges showing two stages of decay induced through the burrows
of the orange tortrix. Burrows shown in center of areas.


FIG. 60.-Burrows in fruit and leaf folded by
Amorbia emigratella, Busch, a Central American
insect introduced into Hawaii but hitherto not
recorded from California.






CITRUS FRUIT INSECTS.


FULLER'S ROSE BEETLE.

(Aramigus fuller Horn.)

This is a grayish brown beetle that measures something more than a
quarter of an inch long. It tapers toward the head, which ends in a
short snout. The grayish-brown coloring is due to scales which cover
the body.. These beetles may be seen clinging to a twig, the underside
of a leaf, or at some fork among the smaller branches.
They are nocturnal, and have the habit of feeding at
night, while during the day remain quiet and avoid
the light as much as possible..
The characteristic injury of the beetles on orange
leaves is shown in figure 62. On large trees they feed 7
mostly in the lower and interior part of the tree, this
being due partly to their light-shunning habits. But
it is on newly budded trees that this insect does the '
severest injury. They especially delight in the tender FIG. 61-Fuller's
leaves and often destroy most of the foliage. rose beetle. x4.

LIFE HISTORY AND HABITS OF THE ROSE BEETLE.
The eggs are laid in batches of from 10 to 50, usually in some scar
on the bark of the tree. These require three or four weeks to hatch.
The larva crawls down to the ground and feeds on the roots of the tree.
Usually more injury is done, though not often appreciated, to the roots
by the larva of, this insect than is done by the beetle on the foliage.

CONTROL OF FULLER'S ROSE BEETLE.
The fact that the adult beetle is unable to fly and is dependent upon
crawling alone for the ascent of the tree, makes it easy to prevent their
attack on the foliage. The method most popular with orange growers
is to band the tree trunk with cotton. A band of this about 4 inches
wide is placed about the tree and tied by means of a string on the lower
side of the band. The band is then pulled down over the string so
that it extends out a short distance from the trunk. Tree tangle-foot
makes another excellent barrier.


BULLETIN 214]







500 UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


FIG. 62.-Work of Fuller's rose beetle on orange leaves.


FIG. 63.-Small orange trees banded with cotton for protection against
Fuller's rose beetle.





CITRUS FRUIT INSECTS.


FIG. 64.-Work of white ants in orange wood.


DIABROTICA SOROR.


This is the familiar green beetle with twelve black spots that is to be
seen everywhere and on all sorts of plants. It often does much damage
to the tender, growing shoots of the orange. The lemon foliage is
but rarely attacked. In a grove where orange and lemon trees were
planted alternately, it was ob-
served that no noticeable in-
jury occurred on the lemon,
while all the young growth of
the orange was severely at-
tacked. In the case of budded
trees, they are specially likely
to suffer from the attacks of
Diabrotica. The larva is sub-
terranean and feeds on several
different kinds of plants.

CONTROL OF DIABROTICA.
There are two methods of
handling diabrotica, namely,
jarring and poisoning. If the
trees are small the beetles may
be jarred off on a tarred or
oiled screen in the early morn-
ing while they are still slug- FIG. 65.-Diabrotica soror. xll.
gish. Or the tender growth, where the feeding occurs, may be sprayed
with arsenate of lead, 8 pounds to 200 gallons of water, or 1 pounds
paris green to 200 gallons of water.


BULLETIN 214]








UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


FIG. 66.-Work of Diabrotica soror on orange leaves.


- -~_ I


FIG. 67.-Paper sacks on recently budded orange trees for protection against
Diabrotica. Negative by J. E. Coit.





CITRUS FRUIT INSECTS.


SERIOUS CITRUS FRUIT PESTS NOT YET ESTABLISHED IN CALIFORNIA.
The reader will have noticed that in the discussions of the various
pests in this bulletin, that all the important ones, without exception,
have been imported into this State. We have with us, therefore, prac-
tically all the serious citrus fruit pests excepting the orange maggot
and the white fly; and even the latter got fairly well established in
the upper Sacramento valley a few years ago. A few additional scale
insects might still be imported, but it is probable that none of these
would rank in importance with those that are already here, and on
account of the universal practice of fumigation, these would be con-
trolled along with the others. But such insects as the white fly, the
orange maggot, and other fruit flies would probably necessitate the
inauguration of additional control measures that would greatly increase
our already heavy tax for insect protection.

THE ORANGE MAGGOT.
(Trypeta ludens Loew.)
This is an insect that is a serious pest of oranges in Mexico. The
larva or maggot develops within the fruit similar to the codling moth
within the apple. From 4 or 5 to 15 or 20 of these maggots may occur
in a single orange. The eggs from which these maggots hatch are
deposited on the fruit. About 70 eggs TIT
are laid by a single fly, and these are .. '
distributed over from eight to a dozen r.7 71112'
FIG. 68.-Larva of orange
oranges. When the worm has attained maggot. x4.
its growth it leaves the fruit, which usually 'falls. In case it does not
fall, the maggots drop to the ground. The complete life cycle requires
about three months.
APPEARANCE OF THE ORANGE MAGGOT.
From our point of view it is most important to know what the insect
looks like, especially
the maggot so that in
case it appears, there
will be no delay in 77=
reporting its presence. -"A.- .
The larva or mag- -Y -
got is dirty white in
color and when ma-



FIG. 69.-Pupa of orange
maggot. x4. FIG. 70.-Fly of orange maggot (Trypeta ludens. x3.
5-B214


BULLETIN 214]





UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


ture measures slightly less than one half of an inch long. This is the
stage of the insect that occurs in the pulp of the orange. The pupa-
rium which is the next stage is light brown in color, barrel-shaped and
measures about one third of an inch long. The adult fly is straw yellow
in general color with brownish markings on the wings, which when
spread measure about five'sixths of an inch across.


THE CITRUS WHITE FLY.
(Aleurodes citri R. & H.)
The citrus white fly is one of the most important pests of citrus fruits
in Florida. There it outranks all the scale insects
as a pest and is less amenable to treatment. It was
formerly held that an insect that thrives so well in
a humid climate like that of Florida would not be
likely to become an important pest in our arid Cali-
fornia climate. But such a claim can be no longer
held, since the white fly got a foothold two or three
years ago in certain points in the Sacramento
valley. This, too, in a section that has the typical FIG. 71.-Larva of
dry, hot, interior climate.
The nature of injury of the
white fly is similar to that of
the black, soft brown, and
other unarmored scales; that
is, it is not so much the life of














FIG. 72.-Cast skin of white fly. FIG. 73.-Adult of white fly. x15.
the tree that is threatened, as the injury consequent to the honeydew
and sooty mold. Leaves of trees infested with white fly may be com-
pletely covered with the insects themselves on the under side, together






BULLETIN 214] CITRUS FRUIT INSECTS. 505

with the sooty mold on the upper side, and thus the natural functions of
the leaves are impaired, and fruit from such trees is tasteless and insipid.
The larva of the white fly is shown in figure 71. It is ovel in shape,
slightly less than one sixteenth of an inch long, of a pale greenish
yellow color and lies
very flat upon the leaf.
The adult is a small fly
measuring about one
tenth of an inch long
and covered with a fine
white powder, hence
the name white fly.


SPRAYING fOR CITRUS
FRUIT INSECTS.
Spraying which is
the main reliance for
the control of most in-
sects of deciduous trees
has never been quite
satisfactory with the
citrus tree. On ac-
count of the dense foli- .
age of the citrus tree it
is very difficult to reach
all its parts, and since .
there is no dormant '
period, the application .
of insecticides suffi
ciently strong to kill
all stages of the insects
is not permissible.
Formerly, spraying in
the citrus belt was
more widely practiced '
than at present. Spray- .: '
ing has lost ground
chiefly for the reason FIG. 74.-Leaf infested with white fly.
that growers have come to more generally believe in the better efficiency
of fumigation. Spraying camine into ill-repute also through the injury
due to the old distillate spray, which not only spotted the fruit, but
dropped the leaves in many cases.






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


In spite of the fact that, as a general practice under all conditions,
spraying is out of the question, it still has a limited place in the control
of citrus scales. Eighteen thousand dollars is expended annually for
spraying citrus trees in Riverside and San Bernardino counties. If
there is a uniform hatch of black scale, and they are all small, there is
no doubt but that a thorough spraying will keep them in check. But in
the case of the purple scale, with eggs always likely to be present, very
poor results may be expected. The principal field for spraying is in the
case of young trees infested with the black scale or a few trees about the
dooryard, where it is often difficult to get the work done by fumigation.
The objection formerly held in regard to the injury to the tree and
fruit no longer occurs with the lighter grade of oil used. The distillate
was a 280 gravity oil, and was used at a strength of 2 per cent. The oil
that is now in most general use is a cheap grade of ordinary kerosene.
This is used at a strength of' 10 per cent, the formula being as follows:
Kerosene or water white oil --------------------------- 20 gallons
Water ----------------------------------- 200 gallons
This is applied only with a power outfit with a good agitator which
is necessary to make a mechanical mixture of the oil and water. Where
there are but a few small trees, and a hand outfit is to be used, kerosene
emulsion may be substituted. The formula is as follows:
Kerosene -------------------------------------- 1 gallon
Soap -------------- ------------------------------- pound
Water ------ -------------------------- 15 gallons
Dissolve soap in a gallon of hot water, add 1 gallon of kerosene, and
mix by turning nozzle of spray pump back into mixture, and then dilute
to make 15 gallons.


FUMIGATION.

It is not intended in this general bulletin to discuss all the phases of
the subject of fumigation, but simply to give a few of the more impor-
tant facts. Those wishing a more detailed treatment of the subject
should send to the State Experiment Station for Circulars 11 and 50
by Prof. C. W. Woodworth, and to the Bureau of Entomology, Wash-
ington, for Bulletins 79 and 90 by Mr. R. S. Woglum.
VARIATION OF DOSAGE.
Seven or eight years ago the experiment station had a man in the field
for the purpose of determining the actual practice of scheduling dosage.
Practically all of the fumigating outfits then operating in the State
were visited, and the tented trees accurately measured and the doses
given them by the scheduler recorded. Thus, the dosage and measure-








ments of over 2,000 trees were made, representing the actual practice of
30 fumigators.
From this study it was found that for a 10-foot tree, having the two
dimensions approximately equal, the dosage varied from 2 to 71 ounces.
And for a 20-foot tree the variation was from 7 to 32 ounces. This is
evidence enough, without further comment, in favor of some system of
measurement or accurate calculation of dosage as against the old system
of guessing.
FACTORS IN VARIATION OF DOSAGE.
There are three principal factors that account for the great variation
in dosage: first, there is the inaccuracy of judging the exact size of the
tree, and the consequent dosage; second, there is the difference of opinion
of different fumigators as to the dose a particular sized tree infested
with a particular scale should have. For example, a tree infested with
red scale that measures 20 feet over the top and 30 feet around the base;
one man will say it should have 4 ounces, another 5, another 6, and
another 8. Thus, there may be a variation of 50 per cent for the same
tree and infested with the same insect; third, there is the variation in
dose as the size of the tree varies. We will assume that all fumigators
agree on, say four ounces as the proper dose. for a tree 20 by 30 feet.
Then, for a tree twice that size, the same people will vary their dose
from 10 to 30 ounces. This is a difference in basis of calculation or
variation, as the size of the tree increases or diminishes.
The first two of these factors are easily remedied. The exact size of
the tree can be ascertained by some system of measurement; and there
should be a general agreement as to how much cyanide is necessary to
kill the different scales. But the third factor, namely, varying the
dosage properly according to the size of the tree, is a more difficult and
complicated question.
BASIS FOR DOSAGE.
The first dosage schedule published was based upon the cubic contents.
This, naturally, would be the logical basis for calculation; but in actual
practice it was soon found that a large tree required a dose proportion-
ally less than a smaller tree. This is accounted for through the leakage
of gas, and a small tree has more tent surface per unit of volume than a
larger tree. So many widely different schedules were proposed until
finally actual field practice established a more or less elastic schedule
with the approximate proper variation in dosage according to the size
of the tree.
AREA BASIS.
This has worked out into practically an area basis rather than a
volume basis, that is, trees receive a dose more nearly according to the


BULLETIN 214]


CITRUS FRUIT INSECTS.





UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


area of their tent surface than to the cubic contents of the tented tree.
This basis of dosing a tree according to the tent surface was proposed
by Woodworth of this station in 1903, and it is the one adopted by Mr.
Woglum.
SCHEDULES AND CALCULATION.
The following is a very simple formula by means of which any one
can construct his own schedule. This formula is simply to multiply the
circumference of the tented tree by the distance over the top and point
off two places. The result is the number of ounces of cyanide for the
given tree for the purple scale, or the maximum dosage:
Examples: A tree 20x30------------- --- 6 ounces cyanide.
30x 40 ------- ---------12 ounces cyanide.
This is the schedule for the purple scale and corresponds in general
with Mr. Woglum's schedule No. 1. For the red and yellow scales, or
for the black scale, excepting where it is full grown, reduce this schedule
by one quarter.
Examples: A tree 20 x 30 --------- -------- 6 ounces for purple.
4.5 for red, yellow and black.
30 x 40 ------------12 ounces for purple.
9.0 for red, yellow and black.
SODIUM CYANIDE.
Mr. Woglum has demonstrated that sodium cyanide is equally as
satisfactory as the potassium, both in generating properties and efficiency
in killing the scale; and since it will be apparently cheaper than the
potassium it seems probable that it may sooner or later come into very
general use. Heretofore, the experience with sodium cyanide has not
been satisfactory for the reason, chiefly, that the product was not pure
enough. What has been passing for 98 to 100 per cent sodium cyanide
has been a 98 to 100 per cent purity in terms of potassium cyanide,
whereas, if we accept potassium as a basis of purity, the sodium cyanide
should be 126 to 133 per cent pure. It is unfortunate that this above-a-
hundred per cent purity should have got started, but since we are
accustomed to potassium as a standard possibly it is justifiable. Any-
way, all we need to know is that a pound of chemically pure sodium
cyanide contains about one third more cyanide or cyanogen than the
potassium, and will thus produce more gas.
FORMULA FOR SODIUM CYANIDE.
Since there is more cyanide or cyanogen in a pound of sodium cyanide
than in a pound of potassium cyanide, it will require a proportionally
greater amount of acid. One of the uses of water in the generation of
hydrocyanic acid gas is to dissolve the residual sulphate and thus pre-
vent it from coating the cyanide not yet generated or reached by the






CITRUS FRUIT INSECTS.


acid. In the case of sodium cyanide there is approximately one third
less of the sulphate formed, and consequently the water may be reduced
about one third.
Therefore, the proportions of cyanide acid and water will differ in ease
sodium cyanide is used, and the formula that has been found to be
satisfactory is:
Sodium cyanide 1 part by weight.
Acid ---------------------------- 1---------- parts by volume.
Water ---------------------------------- 2 parts by volume.

It should be noted that in case sodium cyanide is used all dosage tables
should be reduced one quarter.

ADULTERANTS.
The commonest adulterant of cyanides is sodium chloride or common
salt, and this is likely to get into sodium cyanide, particularly in large
amounts. The presence of this salt produces a reaction in which hydro-
chloric acid is formed and this acts in turn directly upon the hydrocyanic
acid gas, thus decomposing it. In order to avoid this adulterant a high
degree of purity should be insisted upon, and this, stated in terms, of the
potassium salt should be 124 to 133 per cent pure.

COMPARATIVE COST OF SODIUM AND POTASSIUM CYANIDE.
A good sodium cyanide can be bought for 27 or 28 cents per pound as
against potassium at about 25 cents. It requires a little more acid for
the sodium so that the acid bill is higher and the cost per pound of
cyanide is higher. But since one pound of the sodium will generate as
much as one and a quarter pounds of the potassium, the cost is really
in favor of the sodium cyanide, and this, if calculated out, will be found
to amount to from 1I to 3 cents per pound.

FORMULA FOR POTASSIUM CYANIDE.
The proportions of cyanide, acid and water that have been found to
produce the greatest amount of gas are:
Cyanide ------__-- ------- 1 oz. avoirdupois.
Acid ---------------------- 1 fluid oz.
Water ---- -----------------------8- 3 fluid ozs.
The water and acid are first placed in an earthenware vessel and the
cyanide added.
EXPOSURE.
The usual exposure is from 45 minutes to 1 hour.


BULLETIN 214]






UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


SEASON FOR FUMIGATING.

The fumigating season extends from August to January. The fruit
is more susceptible to injury until it attains about the size of a walnut.
Fumigation during extremes of temperature (above 700 and below
350 F.) may injure foliage and fruit, or during a high wind.

TENTING MATERIAL.

To secure the tightest possible material is good economy. If maxi-
mum dosages are used with old leaky tents, it may be necessary to reduce
the dosage with the tighter material. And the reduction from the given
schedules should not be made the same for all sizes of trees, because, as
the tenting material becomes tighter, the schedule should approach
more nearly that of the volume basis.

MEASUREMENT OF TENTS.

The distance over the tented tree may be obtained by having the tents
marked according to the Morrill system, or any other, and the distance
around secured by a tape or accurate pacing.
The following tables are based upon the formula given above. The
schedule for the purple scale corresponds in general with that of Wog-
lum's schedule No. 1, and those for the red, yellow and black are on the
basis of three quarters of this schedule:


22 24
2 2
24 3
33
344
4


SCHEDULE FOR PURPLE SCALE.
Circumference trees 16-56 feet.
26 28 30 32 34 36 38 40 42 44 46
(Distance around.)
24 24 3 3 3 34
3 3 34 34 34 4 44
34 4 4 4 44 445 54
4 44 5 54 6 6 6 7
S4 5 5 6 6 7 7 7
5 4 6 664 7 7 8 8 8 9
6 64 7 7 74 8 8 84 9 94
7 74 8 84 9 94 10 10 104
8 8 9 9 10 104 11 111
94 10 104 11 11 12 12
104 11 114 12 13 131
12 124 13 14 141

SCHEDULE FOR PURPLE SCALE.
Circumference trees 40-80 feet.


48 50 52 54 56





10
11 114
12 12J 13
13 14 144 15
14 144 15 154 16
15 151 16 17 174


44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80
(Distance around.)
144 15 154 164 17 174 184 19 20
15 164 17 18 184 19 20 204 214 22
164174 18 19 20 20 214 22 23 24 25
19 19 20 20 21 22 23 24 244 254 26
20 21 214 224 23J424 25 26 261 274 284
22 23 23 24425 26 27 28 281 294 304
24 25 26427 284294. 30 31 32 33 34
S25 264 274 2 294 304 314 324 334 344 35
28 29 30 31" 32 33 34 35 36 37 38
30 31 32 33 34 35 36 37 38 394 404
32 33 344 354 364 374 384 394 40 41 42
344 35 364 384 39 40 41 424 434 444


16 18

2


40 42
131 14
15






CITRUS FRUIT INSECTS.


16 18


SCHEDULE FOR RED, YELLOW, AND BLACK SCALES.
Circumference trees 16-56 feet.
20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
(Distance around. )


1 1 1 1 1 14 2 2 2
1 1 1, 2 2 2 2J 2k 2k
1 2 2 24 3 3 3


24
3 3
3 34 4
4 4; 4* 54
4 4 5" 5 54
5 5 6 6 64 6k
54 6 6 6* 6k 64 7
6 6% 6k 7 7 74 8 8*
64 64 7 7 8 8 9 9 91
6 7*8 8* 9 9 91 10 104 11
7 8 84 9 94 10 104 10 11 1y 12
9 9 9k 10, 10 11 114 12 124 13


34 ]
36
38
40 -
42
44 o
46 S
48
50 S
52
54
56


SCHEDULE FOR RED, YELLOW, AND BLACK SCALES.
Circumference trees 40-80 feet.
44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74
(Distance around.)
10k 11 I11 12 12w 13 13M 14 15
11k 12 124 13 134 14 15 15 16 16
12 13 13 14 15 15 16 16 17 18 18'
13 14 15 15 16 16 17 18 18 19 19
15 152 16 16% 17 18 184. 19 19% 20% 21
16 17 17 18 19 19" 20 21" 21" 22 221
18 19 191 201 21 22 22 23 24 24 244
19 191 20, 21 22 221 23- 24 25" 254 26
21 21" 22 23 24 24k 254 26 27 274
224 23 24 244 25k 26 27 27' 28*
24 244 25; 26k 27J 28 --: 29
251 26i 27 28J 29 'I 301.


76 78 80


30
304 314
32 33,


INSPECTION AND QUARANTINE.

In most of the counties of the citrus belt there are special ordinances
pertaining to the quarantine of certain citrus fruit pests. The grower
or nurseryman should consult his county horticultural commissioner
regarding these before making any interchange of nursery or other
stock. The section of the state law relating to the duties of county
boards of horticulture, approved March 6, 1909, is given below:
Section 2322a. It shall be the duty of the county horticultural commissioner in
each county, whenever he shall deem it necessary, to cause an inspection to be made
of any premises, orchards or nursery or trees, plants, vegetables, vines, or fruits, or
any fruit-packing house, storeroom, salesroom, or any other place or article in his
jurisdiction, and if found infected with infectious diseases, scale insects, or codling
moth, or other pests injurious to fruit, plants, vegetables, trees, or vines, or with their
eggs or larva, or if there is found growing thereon the Russian thistle or saltwort,
Johnson grass or other noxious weeds, he shall in writing notify the owner or owners,
or person or persons in charge, or in possession of the said places, or orchards or
nurseries, or trees, or plants, vegetables, vines, or fruits or article as aforesaid, that
the same are infected with said diseases, insects or other pests, or any of them, or
their eggs or larve, or that the Russian thistle or saltwort, Johnson grass or other
noxious weeds is growing thereon, and require such person or persons, to eradicate
or destroy the said insects, or other pests, or their eggs or larvm, or Russian thistle
or saltwort, Johnson grass. or other noxious weeds within a certain time to be therein
specified. Said notices may be served upon the person or persons, or either of them,
owning or having charge, or having possession of such infested place or orchard, or
nursery, or trees, plants, vegetables, vines, or fruit, or articles, as aforesaid, or
premises where the Russian thistle or saltwort, or Johnson grass, or other noxious
6-B214


52 54 56


BULLETIN 214]








UNIVERSITY OF CALIFORNIA-EXPERIMENT STATION.


weeds shall be growing, or upon the agents of either, by any commissioner, or by any
person deputed by the said commissioner for that purpose in the same manner as a
summons in a civil action; provided, however, that if any such infected or infested
articles, property or premises as hereinabove specified belong to any non-resident
person and there is no person in control or possession thereof and such non-resident
person has no tenant, bailee, depositary or agent upon whom service can be had; or,
if the owner or owners of any such articles, property or premises' can not after due
diligence be found, then such notice may be served by posting the same in some
conspicuous place upon such articles, property or premises, and by mailing a copy
thereof to the owner thereof at his last known residence, if the same is known or can
be ascertained. Any and all such places, or orchards, or nurseries, or trees, plants,
shrubs, vegetables, vines, fruit, or articles thus infested, or premises where the
Russian thistle, or saltwort, or Johnson grass, or other noxious weeds shall be grow-
ing, are hereby adjudged and declared to be a public nuisance; and whenever any
such nuisance shall exist at any place within his county, and the proper notice
thereof shall have been served, as herein provided, and such nuisance shall not have
been abated within the time specified in such notice, it shall be the duty of the county
horticultural commissioner to cause said nuisance to be at once abated, by eradicating
or destroying said diseases, insects, or other pests, or their eggs, or larvae, or Russian
thistle or saltwort, or Johnson grass or other noxious weeds. The expense thereof
shall be a county charge, and the board of supervisors shall allow and pay the same
out of the general fund of the county. Any and all sum or sums so paid shall be and
become a lien on the property and premises from which said nuisance has been
removed or abated in pursuance of this chapter. A notice of such lien shall be filed
and recorded in the office of the county recorder of the county in which the said prop-
erty and premises are situated, within thirty days after the right to the said lien has
accrued. An action to foreclose such lien shall be commenced within ninety days
after the filing and recording of said notice of lien, which action shall be brought in
the proper court by the district attorney of the county in the name and for the benefit
of the county making such payment or payments, and when the property is sold,
enough of the proceeds shall be paid into the county treasury of such county to
satisfy the lien and costs; and the overplus, if any there be, shall be paid to the
owner of the property, if he be known, and if not, into the court for his use when
ascertained. The county horticultural commissioner is hereby vested with the power
to cause any and all such nuisances to be at once abated in a summary manner.











STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION.



REPORTS.

Report of the Viticultural Work during the seasons 1887-93, with data regard-
ing the Vintages of 1894-95.
Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viti-
cultural Report for 1896.
Report of the Agricultural Experiment Station for 1898-1901.
Report of the Agricultural Experiment Station for 1901-03.
Twenty-second Report of the Agricultural Experiment Station for 1903-04.



BULLETINS.


Reprint. Endurance of Drought in Soils of
the Arid Region.
No. 128. Nature, Value, and Utilization of
Alkali Lands, and Tolerance of
Alkali. (Revised and Reprint,
1905.)
133. Tolerance of Alkali by Various
Cultures.
147. Culture Work of the Sub-stations.
149. California Sugar Industry.
151. Arsenical Insecticides.
153. Spraying with Distillates.
159. Contribution to the Study of Fer-
mentation.
161. Tuberculosis in Fowls. (Reprint.)
162. Commercial Fertilizers. (Dec. 1,
1904.)
165. Asparagus and Asparagus Rust
in California.
167. Manufacture of Dry Wines in
Hot Countries.
168. Observations on Some Vine Dis-
eases in Sonoma County.
169. Tolerance of the Sugar Beet for
Alkali.
170. Studies in Grasshopper Control.
171. Commercial Fertilizers. (June
30, 1905.)
172. Further Experience in Asparagus
Rust Control.
174. A New Wine-cooling Machine.
176. Sugar Beets in the San Joaquin
Valley.
177. A New Method of Making Dry
Red Wine.
178. Mosquito Control.
179. Commercial Fertilizers. (June,
1906.)
180. Resistant Vineyards.
181. The Selection of Seed-Wheat.
182. Analysis of Paris Green and
Lead Arsenic. Proposed In-
secticide Law.
183. The California Tussock-Moth.
184. Report of the Plant Pathologist
to July 1, 1906.
185. Report of Progress in Cereal
Investigations.


No. 186. The Oidium of the Vine.
187 Commercial Fertilizers. (Janu-
ary 1907.)
188. Lining of Ditches and Reservoirs
to Prevent Seepage and Losses.
189. Commercial Fertilizers. (June,
1907.)
190. The Brown Rot of the Lemon.
191. California Peach Blight.
192. Insects Injurious to the Vine In
California.
193. The Best Wine Grapes for Cali-
fornia; Pruning Young Vines;
Pruning the Sultanina.
194. Commercial Fertilizers. (Dec.,
1907.)
195. The California Grape Root-
Worm.
197. Grape Culture in California;
Improved Methods of Wine-
making; Yeast from California
Grapes.
198. The Grape Leaf-Hopper.
199. Bovine Tuberculosis.
200. Gum Diseases of Citrus Trees in
California.
201. Commercial Fertilizers. (June,
1908.)
202. Commercial Fertilizers. (Decem-
ber, 1908.)
203. Report of the Plant Pathologist
to July 1, 1909. *
204. The Dairy Cow's Record and the
Stable.
205. Commercial Fertilizers. (Decem-
ber, 1909.)
206. Commercial Fertilizers. (June,
1910.)
207. The Control of the Argentine Ant.
208. The Late Blight of Celery.
209. The Cream Supply.
210. Imperial Valley Settlers' Crop
Manual.
211. How to Increase the Yield of
Wheat in California.
212. California White Wheats.
213. The Principles of Wine-making.




'- -


CIRCULARS.


No. 1. Texas Fever.
5. Contagious Abortion in Cows.
7. Remedies for Insects.
9. Asparagus Rust.
11. Fumigation Practice.
12. Silk Culture.
,15. Recent Problems In Agriculture.
What a University Farm Is For.
17. Why Agriculture Should be Taught
in the Public Schools.
19. Disinfection of Stables.
29. Preliminary Announcement Con-
cerning Instruction in Practical
Agriculture upon the University
Farm, Davis, Cal.
30. White Fly in California.
32. White Fly Eradication.
33. Packing Prunes in Cans. Cane
Sugar vs. Beet Sugar.
36. Analyses of Fertilizers for Con-
sumers.
39. Instruction in Practical Agricul-
ture at the University Farm.


No. 46. Suggestions for Garden Work in
California Schools.
47. Agriculture in the High Schools.
48. Butter Scoring Contest, 1909.
50. Fumigation Scheduling.
51. University Farm School.
52. Information for Students concern-
ing the College of Agriculture.
53. Announcement of Farmers' Short
Courses for 1910.
54. .Some Creamery Problems and
Tests.
55. Farmers' Institutes and University
Extension in Agriculture.
58. Experiments with Plants and Soils
in Laboratory, Garden, and
Field.
59. Tree Growing in the Public
Schools.
60. Butter Scoring Contest, 1910.
61. University Farm School.
62. The School Garden in the Course
Sof Study.


A..




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