Purple scale and Florida red scale as insect pests of citrus in Florida

Material Information

Purple scale and Florida red scale as insect pests of citrus in Florida
Series Title:
Bulletin University of Florida. Agricultural Experiment Station
Thompson, W. L
Griffiths, James T. ( James Thompson ), 1914-
Place of Publication:
Gainesville Fla
University of Florida Agricultural Experiment Station
Publication Date:
Physical Description:
40 p. : ill., 1 map ; 23 cm.


Subjects / Keywords:
Citrus -- Diseases and pests -- Florida ( lcsh )
Scale insects -- Florida ( lcsh )
Purple scale ( lcsh )
City of Orlando ( local )
City of Gainesville ( local )
Armor ( jstor )
Insects ( jstor )
Pests ( jstor )
bibliography ( marcgt )
non-fiction ( marcgt )


Bibliography: p. 37-40.
General Note:
Cover title.
General Note:
"A contribution from the Citrus Experiment Station"--T.p.
Bulletin (University of Florida. Agricultural Experiment Station) ;
Statement of Responsibility:
W.L. Thompson and J.T. Griffiths, Jr.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
027116174 ( ALEPH )
18254254 ( OCLC )
AEN6196 ( NOTIS )


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September, 1949


(A Contribution From the Citrus Experiment Station)

Purple Scale and Florida Red Scale as

Insect Pests of Citrus in Florida

Single copies free to Florida residents upon request to

Bulletin 462


J. Thos. Gurney, chairman, Orlando
N. B. Jordan, Quincy
Thos. W. Bryant, Lakeland
J. Henson Markham, Jacksonville
Hollis Rinehart, Miami
W. F. Powers, Secretary, Tallahassee


J. Hills Miller, Ph.D., President of the
Harold Mowry, M.S.A., Director
L. O. Gratz, Ph.D., Asst. Dir., Research
W. M. Fifield, M.S., Asst. Dir. Admin.
J. Francis Cooper, M.S.A., Editor3
Clyde Beale, A.B.J., Associate Editor"
W. W. Mosher, Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager2
Geo. F. Baughman, M.A., Business Manager3
Claranelle Alderman, Accountant2

Frazier Rogers, M.S.A., Agr. Engineer3
J. M. Johnson, B.S.A.E., Asso. Agr. Engineer3
J. M. Myers, B.S., Asso. Agr. Engineer
R. E. Choate, B.S.A.E., Asst., Agr. Engineer'
A. M. Pettis, B.S.A.E., Asst. Agr. Engineer: 2

Fred H. Hull, Ph.D., Agronomist'
G. E. Ritchey, M.S., Agronomist2
G. B. Killinger, Ph.D., Agronomist2
H. C. Harris, Ph.D., Agronomist'
R. W. Bledsoe, Ph.D., Agronomist
W. A. Carver, Ph.D., Associate
Darrel D. Morey, Ph.D., Associate
Fred A. Clark, B.S., Assistant
M. N. Gist, Collaborator2

R. B. Becker, Ph.D., Dairy Husbandman'
E. L. Fouts, Ph.D., Dairy Technologist"
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M. Veterinarian'
L. E. Swanson, D.V.M., Parasitologist
N. R. Mehrhof, M.Agr., Paultry Husb.'
G. K. Davis, Ph.D., Animal Nutritionist'
R. S. Glasscock, Ph.D., An. Husbandman"
P. T. Dix Arnold, M.S.A., Asst. Dairy Husb.3
L. E. Mull, M.S., Asst. in Dairy Tech.
Katherine Boney, B.S., Asst. Chem.
J. C. Driggers, Ph.D., Asst. Paultry Husb.2
Glenn Van Ness, D.V.M., Asso. Poultry
S. John Folks, B.S.A., Asst. An. Husb.2
W. A. Krienke, M.S., Asso. in Dairy Mfs.3
S. P. Marshall, Ph.D., Asso. Dairy Husb.3
C. F. Simpson, D.V.M., Asso. Veterinarian
C. F. Winchester, Ph.D., Asso. Biochemist3

C. V. Noble, Ph.D., Agri. Economist"
R. E. L. Greene, Ph.D., Agri. Economist
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
D. E. Alleger, M.S., Associate
D. L. Brooke, M.S.A., Associate
M. R. Godwin, Ph.D., Associate
H. W. Little, M.S., Assistant
Tallmadge Bergen, B.S., Asst.
Orlando, Florida (Cooperative USDA)
G. Norman Rose, B.S., Asso. Agr. Economist
J. C. Townsend, Jr., B.S.A., Agr. Statistician2
J. B. Owens, B.S.A., Agr. Stat:stician.
J. F. Steffens, Jr., B.S.A., Agr. Statistician'

Ouida D. Abbott, Ph.D., Home Econ.'
R. B. French, Ph.D., Biochemist

A. N. Tissot, Ph.D., Entomologist
L. C. Kuitert, Ph.D., Assistant
H. E. Bratley, M.S.A., Assistant

G. H. Blackmon, M.S.A., Horticulturist'
F. S. Jamison, Ph.D., Horticulturista
H. M. Reed, B.S., Chem., Veg. Processing
R. A. Dennison, Ph.D., Asso. Hort.
R. K. Showalter, M.S., Asso. Hort.
Albert P. Lorz, Ph.D., Asso. Hort.
R. H. Sharpe, M.S., Asso. Hort.
F. S. Lagasse, Ph.D., Asso. Hort.2
R. J. Wilmot, M.S.A., Asst. Hort.
R. D. Dickey, M.S.A., Asst. Hort.
Victor F. Nettles, M.S.A., Asst. Hort.4
L. H. Halsey, B.S.A., Asst. Hort.

W. B. Tisdale, Ph.D., Plant Pathologist'
Phares Decker, Ph.D., Plant Pathologist
Erdman West, M.S., Mycologist and Botanist
Howard N. Miller, Ph.D., Asso. Plant Path.
Lillian E. Arnold, M.S., Asst. Botanist

F. B. Smith, Ph.D., Microbiologist':'
Gaylord M. Volk, Ph.D., Chemist
J. R. Henderson, M.S.A., Soil Technologist:
J. R. Neller, Ph.D., Soils ChemlsL
Nathan Gammon, Jr., Ph.D., Soils Chemist
C. E. Bell, Ph.D., Associate Chemist
R. A. Carrigan, Ph.D., Asso. Biochemist3
H. W. Winsor, B.S.A., Assistant Chemist
Geo. D. Thornton, Ph.D., Asso. Microbiologist"
R. E. Caldwell, M.S.A., Asst. Chemist"
Ralph G. Leighty, B.S., Asso. Soil Surveyor
V. W. Cyzycki, B.S., Asst. Soil Surveyor
R. B. Forbes, M.S., Asst. Soils Chemist
W. L. Pritchett, M.S., Asst. Chemist*
Jean Beem, B.S.A., Asst. Soil Surveyor
Walter J. Friedmann, M.S.A., Asst.
O. E. Cruz, B.S.A., Asst. Soil Surveyor

'Head of Department.
2 In cooperation with U. S.
3 Cooperative, other divisions, U. of F.
4On leave.



J. D. Warner, M.S., Vice-Director in Charge
R. R. Kincaid, Ph.D., Plant Pathologist
W. H. Chapman, M. S., Asso. Agron.
L. G. Thompson, Ph.D., Soils Chemist
Frank S. Baker, Jr., B.S., Asst. An. Husb.
W. C. Rhoads, M.S., Entomologist
Mobile Unit, Monticello
R. W. Wallace, B.S., Associate Agronomist
Mobile Unit, Marianna
R. W. Lipscomb, M.S., Associate Agronomist
Mobile Unit, Chipley
J. B. White, B.S.A., Associate Agronomist
Mobile Unit, DeFuniak Springs
R. L. Smith, M.S., Associate Agronomist

A. F. Camp, Ph.D., Vice-Director in Charge
W. L. Thompson, B.S., Entomologist
J. T. Griffiths, Ph.D., Asso. Entomologist
R. F. Suit, Ph.D., Plant Pathologist
E. P. Ducharme, M.S., Asso. Plant Patho.4
R. K. Voorhees, Ph.D., Asso. Horticulturist
C. R. Stearns, Jr., B.S.A., Asso. Chemist
J. W. Sites, M.S.A., Horticulturist
I. O. Sterling, B.S., Asst. Horticulturist
J. A. Granger, B.S.A., Asst. Horticulturist
H. J. Reitz, M.S., Asso. Horticulturist
Francine Fisher, M.S., Asst. Plant Path.
I. W. Wander, Ph.D., Soils Chemist.
A. E. Wilson, B.S.A., Asso. Biochemist
J. W. Kesterson, M.S., Asso. Chemist
R. N. Hendrickson, B.S., Asst. Chemist
Joe P. Barnett, B.S.A., Asst. Horticulturist
J. C. Bowers, B.S., Asst. Chemist
D. S. Prosser, Jr., B.S., Asst. Horticulturist
R. W. Olsen, B.S., Biochemist
F. W. Wenzel, Jr., Ph.D., Supervisory Chem
Alvin H Rouse, M.S., Asso. Chemist
L. W. Fayville, Ph.D., Asst. Chemist

R. V. Allison, Ph.D., Vice-Director in Charge
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane
J. W. Randolph, M.S., Agricultural Engineer
W. T. Forsee, Jr., Ph.D., Chemist
R. W. Kidder, M.S., Asso. Animal Husb.
T. C. Erwin, Assistant Chemist
Roy A. Bair, Ph.D., Agronomist
C. C. Seale, Asso. Agronomist
N. C. Hayslip, B.S.A., Asso. Entomologist
E. H. Wolf, Ph.D., Asst. Horticulturist
W. H. Thames, M.S., Asst. Entomologist
W. N. Stoner, Ph.D., Asst. Plant Path.
W. A. Hills, M.S., Asso. Horticulturist
W. G. Genung, B.S.A., Asst. Entomologist
Daniel W. Beardsley, B.S., Asst. An. Husb.


Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
D. O. Wolfenbarger, Ph.D., Entomologist
Francis B. Lincoln, Ph.D., Horticulturist
Robt. A. Conover, Ph.D., Asso. Plant Path.
R. W. Harkness, Ph.D., Asst. Chemist
Milton Cobin, B.S., Asso. Horticulturist


William Jackson, B.S.A., Animal Husband-
man in Charge-


W. G. Kirk, Ph.D., Vice-Director in Charge
E. M. Hodges, Ph.D., Agronomist
D. W. Jones, B.S., Asst. Soil Technologist
E. M. Kelly, B.S.A., Asst. An. Husb.


R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. W. Wilson, Sc.D., Entomologist
Ben. F. Whitner, Jr., B.S.A., Asst. Hort.


C. E. Hutton, Ph.D. Agronomist'
H. W. Lundy, B.S.A., Associate Agronomist



G. K. Parris, Ph.D., Plant Path. in Charge

Plant City

A. N. Brooks, Ph.D., Plant Pathologist


A. H. Eddins, Ph.D., Plant Path. in Charge
E. N. McCubbin, Ph.D., Horticulturist


A. M. Phillips, B.S., Asso. Entomologist2
John R. Large, M.S., Asso. Plant Path.


J. R. Beckenbach, Ph.D., Hort. in Charge
E. G. Kolsheimer, Ph.D., Entomologist
David G. Kelbert, Asso. Horticulturist
E. L. Spencer, Ph.D., Soils Chemist
Robert O. Magie, Ph.D., Gladioli Hort.
J. M. Walter, Ph.D., Plant Pathologist
Donald S. Burgis, M.S.A., Asst. Hort.


Warren O. Johnson, B.S., Meterologist2

1Head of Department.
-'In cooperation with U. S.
SCooperative, other divisions, U. of F.
On leave.


INTRODUCTION .-----. --------- -- ---- 5

HISTORICAL NOTES .---------------------- .------- -- 5

LIFE HISTORY OF PURPLE SCALE .-------------------------- 6

LIFE CYCLE OF RED SCALE -....- -.. ..... .----- 12

INJURY CAUSED BY SCALE ------- ..------ -- ----- 16


Reproductive Capacity ---..... ------ -- 19

W weather .. .... .. ....- --- -- ---- 20

Tree Health ..------.. ---------------- -------- 23

Residue .- ---. .. ..... ...---------------------- 26

Entomogenous Fungi .. ... .----------- ----- 27

Parasites and Predators -.....------------------ -.- 29

SCALE CONTROL -.-....._--- ----------------- -. 32

Materials ......--- ------------------- 32

Method of Application ..-....- .. .-------------------- 33

time of Application --....-..-------------- --- 33

Effects of Oil Sprays on Trees-------- 34

SUMMARY .---.-------------- ------ 36

LITERATURE CITED ---- --- --------- ------..... 37

Purple Scale and Florida Red Scale as

Insect Pests of Citrus in Florida


Two scale insects, purple scale, Lepidosaphes beckii (Newm.),
and Florida red scale, Chysomphalus aonidum (L.), have been
major pests of citrus in Florida for many years. Since 1885,
when Hubbard (23) first described these scales as feeding upon
citrus in Florida, entomologists have waged battle against them.
Recommendations for control have changed through the years,
erroneous ideas have arisen and been discarded, but the insects
have managed to survive, to multiply, and to remain as major
problems facing all citrus growers in the state. Although both
insects are found in citrus areas throughout the world, the
present work will be confined to a consideration of these pests in
Florida. It is impossible, in the paragraphs which follow, to
trace all of the history and to acknowledge all of the information
contributed by a multiplicity of workers and writers, but it is
intended that certain representative papers will be mentioned
so as to illustrate the basic information which has proved to be
correct through these many years.

Historical Notes
The facts concerning the early history of purple scale and
its introduction into Florida are rather obscure. Purple scale
was first adequately described by Comstock (6) in 1880, and in
his report he credits Glover with a statement to the effect that
this scale was present on lemons imported into Jacksonville in
1855. However, Hubbard (23), writing in 1885, questioned the
validity of Glover's determination and appeared to believe that
the description was actually one of chaff scale, Parlatoria per-
gandii (Comst.) In any case, Hubbard considered the purple
scale to be a pest of minor importance in 1885 (23), stating that
it was often confused with long scale, Lepidosaphes gloverii

1 Entomologist and Associate Entomologist, respectively, Citrus Experi-
ment Station, Lake Alfred, Florida.

Florida Agricultural Experiment Stations

(Pack.), and that it was of little economic importance. Prior
to about 1895, few references to purple scales appear in Florida
citrus literature, and it has been only during the last half cen-
tury that purple scale has been considered a major pest. At
present it is rated as the worst single pest of citrus trees in
Florida. It causes large crop loss and more actual tree damage
than any other single pest.
The Florida red scale was first described by Linne (25) in
1758. Ashmead (1) first reported it in Florida on a sour orange
tree which had been imported and planted near Orlando. In 1881
or 1882 (1) it was found at San Mateo, where it had been trans-
ported on lemons which were shipped from Orlando to San Mateo
for packing. Since that time, this scale has been reported from
considerably more than 150 different host plants in Florida.
Comstock (6) predicted that it might well be a serious pest some
day, and as early as 1897 Webber (72) stated that Florida red
scale was the worst enemy of citrus. Today, it periodically
causes damage in the central part of the citrus belt, and con-
tinues as a very serious pest, particularly in the coastal areas
and in Highlands County below Sebring.

Life History of Purple Scale
The most comprehensive description of the life cycle of the
purple scale is Quayle's (32) account, in 1912. This work was
performed in California, but, in general, it applies to Florida
conditions. The insect passes through several stages in its life
cycle, all of which are outlined below.
Egg Stage.-The eggs are elongate and pearly white in color.
In summer they hatch in about 15 to 20 days, but during cool
winter weather hatching may be delayed for a considerable
Crawlers.-The crawler emerges from the egg and for a short
time is present as a free living individual. It is considerably less
than 1 mm. in length, is oblong shaped, and white in color with
a brown posterior tip. It moves about and appears actively to,
avoid both deep shade and bright sunlight and to tend to climb
against the pull of gravity (66). In general, males are more apt
to settle on upper surfaces and females on the lower surfaces of
leaves. Usually, within 24 hours the crawler finds a satisfactory

Purple Scale and Florida Red Scale as Pests of Citrus 7

place and attaches itself to a leaf, twig, or fruit, where it will
secrete its waxy scale covering.
First Stage Scale.-As soon as the crawler has settled, it
begins to form its scale armor. From its anterior end it secretes

A 8




-- Imm.

Fig. 1.-Stages in the life cycle of purple scale. A, Early first stage;
B, molting upon completion of first stage; C, early second stage; D, molting
upon completion of second stage; E, early third-stage female; F, immature
third-stage female; G, mature third-stage female; H, full-grown armor of
male. a, Area occupied by first-stage armor; b, area occupied by armor
grown during second stage; c, area occupied by armor grown during third
stage. 1, Boundary of first-stage armor; 2, boundary of second-stage armor.

Florida Agricultural Experiment Stations

coarse cottony threads which extend over and around the insect
(32). Smaller threads are next secreted from the posterior end.
These form a closer net over the insect and finally the entire
crawler is covered. It now appears as a little cottony individual
with two horn-like anterior projections on either side (see Fig.
1). Tannish wax then replaces the cottony materials and the
armor takes on a ribbed appearance. At this stage the armor
varies from a dark purplish to a tan color, and usually shows
flecks of red and yellow. It is approximately 0.3 mm. long and
the scale is now ready for its first molt. In Florida this first
stage period probably extends over about 18 to 20 days (66). At
this stage the molting scale may be recognized by the charac-
teristic shape and purple color, and when it is turned over the
scale remains attached inside the armor. The insect completely
fills the armor, and its ventral or under side appears as a shiny
brownish membrane. As the molt is accomplished this under-
membrane is ruptured, the scale actually slips out of its old skin,
and the cast skin is incorporated into the armor, where it then
appears as a shiny ovate brown area lining the inside of the

Second Stage Scale.-During this period the scale grows and,
in so doing, extends itself and the armor posteriorly. A living,
healthy scale is a bright pearly white in color and is entirely
without appendages. Since in the case of the purple scale, almost
all growth is in a posterior direction, the armor takes on an
elongate appearance (see Fig. 1). It is during this stage that
eye spots begin to develop in the male, and this is the first time
that it is possible to differentiate between males and females.
In the case of the female, after about 15 to 20 days (66) a
second and last molt is undergone, If an armor is overturned at
this time it is found that the female adheres to the armor, and
the under side is again covered by what appears to be a shiny
brownish membrane. The membrane is actually the under side
of the old skin, which will be shed. This molt is accomplished in
similar fashion to the first, and now a second segment of cast
skin is incorporated into the armor. The presence or absence of
this incorporated cast skin on the inside of the armor makes it
easily possible to tell whether or not a female has entered third

Purple Scale and Florida Red Scale as Pests of Citrus 9

Prepupa and Pupa Stage of Male Scale.-In the case of the
male, a second molt occurs about 10 to 12 days (32) after the
first one, and the prepupa stage is entered (see Fig. 2). The

Fig. 2.-Purple scale, development of the male. 1, Second stage; 2 and
3, third stage or prepupa, 2, with exuvia still attached; 4, fourth stage or
pupa; 5, adult. (Courtesy Dr. H. J. Quayle and the Comstock Publish-
ing Co.)

Florida Agricultural Experiment Stations

prepupa is purple in color, and the beginnings of appendages may
be noted. In about another 10 days the true pupa is formed.
This is a quiescent stage in which the wings and legs are fully
formed. At this time the male armor is as large as it will ever
be. It is more narrow than that of the female of the same age
and it has a definite band of purple across the posterior end.
After a final molt, the male emerges as a winged, free living
Adult Male.-Under summer conditions the winged male
emerges in about 50 to 60 days after hatching (32). The male
has only two wings. It is yellowish in color with spots of purple
pigment scattered about. The posterior tip of the abdomen is
characterized by a long projecting style.
Third Stage or Adult Female Scale.-Following the second
molt, the female continues to grow posteriorly and the armor
finally becomes 3.6 to 3.9 mm. long. The female is able to lay
eggs about 15 days after fertilization (32) or about 65 to 75 days
after hatching under summer temperature conditions. Egg
laying continues for about three to four weeks, and more than
30 to 40 eggs are usually deposited. As the eggs are laid the
female gradually becomes smaller and smaller and the eggs re-
place a considerable portion of the area within the armor for-
merly occupied by the young adult female. At the time of her
.death, she occupies only a relatively small,area at the anterior
end of the armor, The armor of the mature female is brown in
color and readily shows the lines of demarcation of the armors
of the first and second stages (see Fig. 1). A good comparison
is thus afforded as to the relative size in different stages.
Under Florida conditions a complete life cycle takes less than
three months in summer. Well defined periods of crawler ac-
tivity are reported by various authors as occurring in March
and April, June and July, and again in September aild October
(23, 32, 50, 65, 67, 69). Griffiths and Thompson (18) showed
that oviposition and subsequent periods of crawler activity could
be forecast for purple scales. Although the actual date varies
somewhat from year to year, pronounced periods of oviposition
are readily recognized. Following such a period most of the
scales are initially in first stage. Shortly thereafter the majority
of the scales are in second stage. Thus, regular sequences are

Purple Scale and Florida Red Scale as Pests of Citrus 11

set up, as illustrated in Fig. 3. The sequences seem to be simi-
larly timed throughout the citrus area.
Figure 4 shows the changes in percent of purple scale in first
and second stages from the fall of 1946 to the fall of 1948.
Dates on the graph indicate times when maximum number of
scales were present in first and second stage. The graph is
based on averages from counts taken in groves scattered over
the citrus producing areas, and no account was made for geo-
graphical distributions. Location did not appear to affect ma-
terially the percentage figures. The graph illustrates the fact
that purple scale usually has three generations per year, and
that under summer conditions a generation takes approximately

Fig. 3.-Changes in the percent of purple scales in each stage during a
nine-week period in 1948.

Florida Agricultural Experiment Stations

100 Spring Spring,.
Growth Growth


C0 40
--- Estimated

20 1947 1948
Sept. Jon. May July Sept. Mar. May July
20 3 I 5 3 20 25 25
Fig. 4.-Changes in the average percentage of purple scales in first and
second stages from the fall of 1946 through the fall of 1948.

eight weeks. It also means that forecasts can be made at the
time when maximum numbers of scale will be present in first and
second stages.
Life Cycle of Red Scale
In general, the life history of the Florida red scale is similar
to that of purple scale. However, this scale grows faster, is
more prolific, and enlarges in all directions so as to form a round
armor, rather than an elongate one. Mathis (26, 27) has pre-
sented excellent accounts of the life history of this pest under
Florida conditions.
Egg Stage.-The egg is ovate and a shiny lemon yellow in
color. It usually hatches within 24 hours after being laid, but
under cold weather conditions it may be delayed for 48 hours or
more (27). This is substantiated by unpublished observations
by the authors where they noted numerous eggs under an armor
in cold weather, but only a very few in warm weather. This
indicated that under summer conditions the hatch is extremely
rapid. Just before hatching the egg flattens, the covering breaks
at the anterior end, and the crawler emerges (27).
Crawler Stage.-The crawler is a bright lemon yellow, 0.15 to
0.20 mm. long, and is oval in shape. Its anterior and posterior
une odwahrcniin tmyb eae o 8huso

Purple Scale and Florida Red Scale as Pests of Citrus 13

ends taper to a narrow point, while in comparison the middle of
the abdomen is quite broad. The crawler wanders about over a
leaf or fruit and usually settles within a period of about two
hours (27). As in the case of purple scale, males prefer the top
side of the leaf and females the under side. Work by Mathis
indicated that while light is a factor in causing females to settle
primarily on the under side of the leaf, and while both light and
gravity affect males, there is some other unknown factor in-
volved in the high percentage of males found on the upper side
of the leaf.
First Stage Scale.-After settling, the insect fastens its
mouth parts to the leaf or fruit and begins to rotate with its
mouth parts as a pivot, and at the same time it secretes white
waxy threads over itself. Within two hours a white cap obscures
the larva, and this stage is commonly called the white cap stage
(see Fig. 5). It measures about 0.15 mm. in diameter. About 24
hours after settling, the white cap takes on a purplish grey color
at the margins, with the white center remaining as a nipple-like
structure. More wax is secreted about the margins by the ro-
tating larva, and when molting starts the armor has a charac-
teristic brown color around a lighter colored central area and is
about 0.3 mm. in diameter. If turned over at this time the larva
will be found adhering tightly to the armor. The under, or
ventral, side is very shiny and has, at times, a reddish tinge.
This ventral membrane is actually the old skin. It ruptures and
disintegrates, except at the margins, and the upper or dorsal part
of the cast skin is incorporated into the armor. This gives a
characteristic tan color to the area of the armor originally occu-
pied by the first stage scale. Under Florida conditions (27) this
stage of development was found to range from as low as 15 days
in warm weather to 46 days in cool weather. In summer, most
individuals would complete this stage in a little over two weeks.
Second Scale.-Inside the armor the scale continues as
a lemon colored individual. It grows, rotates, and secretes more
armor. As the armor is enlarged the new portion has a dark
purplish color. The outer margin of this area becomes lighter
(see Fig. 5,c) as the molting process begins, and the female
armor takes on a definitely ringed appearance (see Fig. 5).
During the early part of the second stage, as during the first

Florida Agricultural Experiment Stations



S= Imm.

Fig. 5.-Stages in the life cycle of Florida red scale. A, White cap
stage; B, early first stage; C, molting upon completion of first stage; D,
early second stage; E, late second stage; F, full-grown armor of male; G,
early third stage with ringed effect which appears during molting process;
H, immature third-stage female; I, mature third-stage female. a, Area
occupied by first-stage armor; b, inner portion of second-stage armor which
retains dark color; c, outer portion of second-stage armor which becomes
reddish brown during molt; d, area occupied by armor grown during
third stage. 1, Boundary of white cap area; 2, boundary of first-stage
armor; 3, boundary of second-stage armor.

Purple Scale and Florida Red Scale as Pests of Citrus 15

stage, removal of the armor leaves the scale in place on the leaf
or fruit, and inside the armor can be seen a brown shiny area
due to the incorporation of the first stage skin. When the molt-
ing process begins the scale again adheres to the armor and the
under side takes on a characteristic shiny appearance. The
armor is about 0.5 mm. in diameter and attains a definitely
reddish cast at this time so that the stage is easily recognizable.
When an armor is removed immediately after the molt has been
completed the scale appears to be quite desiccated. Apparently,
considerable water is lost during the molting process. The time
spent in this stage varied between 11 and 36 days, depending on
temperature, with about two weeks being an average, under
summer conditions (27).
During the second stage, as with purple scale, the male be-
gins to differentiate. According to Mathis (27), the eye spots
begin to appear about five days after the first molt. The armor
of the male is a dark purple color with a greyish apron at the
posterior end. The male passes through both prepupal and pupal
stages, but these are of short duration and the males begin to
appear as free living individuals about 15 days after completing
their first molt. The prepupa is still yellow in color, but the pupa
takes on a brownish to purplish tinge. The second, third, and
fourth molts are pushed out from under the armor (27) and are
not incorporated into it. The armor of the mature male measures
about 0.5 mm. by 0.7 mm.
Adult Male Scale.-This individual has only two wings, and
the body ends posteriorly in a style. It is a light orange yellow,
with a dark brown band around the thorax. The average length,
including the style, is about 1.74 mm. (27) and the wing expanse
measures about 1.36 mm.
Third Stage or Adult Female.-During this period the female
grows and the armor is expanded to measure from 1.5 mm. to
more than 2.0 mm. in diameter. Inside the armor the area
occupied by the second stage skin is easily recognized (areas a,
b and c in Fig. 3). It has been shown that fertilization is neces-
sary (37), but little is known concerning the time or the actual
process. In any case, eggs are deposited in from two to four
weeks following the second molt, and the oviposition period may
last up to eight weeks (27). Mathis stated that from 30 to more

Florida Agricultural Experiment Stations

than 300 eggs were laid by a female. He reported an average of
145 eggs laid on fruit, as compared with only 80 on leaves.
As in the case of purple scales, regular sequences have been
found for Florida red scale generations (18). Figure 6 shows
changes in the percent of red scales in first and second stage
between the falls of 1946 and 1948. As in the case of purple
scale, these figures are based on averages from all over the state.



C 4


--- Estimated


Oct. Jan.
20 3


Mayly Nv. Jan. Ar. June Ju St.
5 1 ,v 20 1 I k Sir5

Fig. 6.-Changes in the average percent of Florida red scales in first and
second stages from the fall of 1946 to the fall of 1948.

Location did not materially affect differences in the stage in
which scales were found. The graph demonstrates that Florida
red scale usually has four generations per year, and that these
may be spaced about six weeks apart in the summer time.

Injury Caused by Scale
Both species of scales produce major damage to citrus trees
in Florida. While some of the injury is obvious, some is insidi-
ous, in that any quantity of scales produce a drain on the vitality
of the tree. The tree thus has to support not only itself, but a
considerable scale population as well. Rolfs (35) stated, in 1904,
that prior to 1900, scales were the worst pests of citrus in


Purple Scale and Florida Red Scale as Pests of Citrus 17

Florida. The situation in the decade following 1938 is certainly
Over a 12-year period Thompson (59) experimented with
Pineapple orange trees which were all sprayed with nutritional
sprays and fertilized in an identical manner. Where scales were
controlled by a single oil spray, the trees produced one box of
fruit more per tree per year than where oil was not used for
scale control (see Fig. 7). Although scales were not always
present in excessive amounts on the plots which did not receive
oil, there were sufficient scales to reduce the crop by one box per

4 A?
I --..LA.-----.

YRS 2934 3S 36 07 08 40 41 42 4 44 45 4
Fig. 7.-Effects of purple scale infestations in reducing yields of
Pineapple oranges from 1934 to 1946.

tree per year. Figure 7 shows yields graphically from 1934 to
1946. As indicated there, prior to 1934 yields had been identical
in both series of plots.
Purple scales are an important factor to be considered when
fruit has to be artificially degreened. Wherever a living purple
scale is present on a fruit, a green spot will remain. Although 4
the scales may be removed in the washing process, green spots
may seriously lower the grade of fruit. In addition, purple scales
often settle under the button, on the stem end of the fruit. In
this position they may so weaken the stem that the fruit will
drop prematurely. This is especially serious during periods of
dry weather or following a severe windstorm. Fruit drop is
often excessive and results in major losses to many growers.
Heavy populations of purple scales on a tree are usually
evidenced by a yellow spotting of the leaves. The yellow
splotches coincide with a pile-up of purple scale, and if severe
enough, the leaves will ultimately drop. When leaves are heavily

Florida Agricultural Experiment Stations

infested purple scales are usually common on the smaller twigs
and branches of the tree. A combination of wood infestation plus
leaf drop often results in the death of considerable wood. Losses
L 1

Fig. 8.-Heavy infestation of purple scales on foliage and twigs. Note
the concentrations of scales along the margins of the leaves at top
center. Leaves were dying and falling off of the twig. The petiole remains
after the leaf has fallen in left center. The roughness on the twigs is
caused by layers of scales. (Photograph by Madge Campbell.)

Purple Scale and Florida Red Scale as Pests of Citrus 19

of wood are often excessive and this may, indirectly, be a grade
lowering factor, since dead wood serves as a source of the
melanose fungus (Diaporthe citri Faw.) which will infect small
fruits during the spring of the year. Thus, excessive numbers
of scales may kill out much of the inside wood and not only
reduce the quality of the crop but also necessitate considerable
expense from pruning operations. Stevens (43), in 1912, claimed
that purple scale on the stem end increased the susceptibility of
fruit to stem-end rot, but he offered no supporting evidence.
Florida red scales may do very serious damage to a tree in a
short time. They infest only the leaves and fruit of the tree,
but they increase rapidly during certain seasons of the year,
and when present in large numbers they will cause leaves to
yellow and drop. Excessive leaf drop often results in the loss of
wood which may be as large as one inch in diameter. If heavy
infestations remain unchecked during the fall and winter months
the following spring growth may be sparse and weak and this
may result in a small crop. When Florida red scales are present
in the spring of the year, they may infest the young fruit. This
produces a pitting of the peel and causes the fruit to mature
with a rough skin. If this is coupled with too many scales
present on the fruit at time of maturity it may be an important
grade lowering factor.

Factors Affecting Abundance of Scales
In 1947, Griffiths (12) discussed the problem of biological
balance in citrus insect populations. There is a multiplicity of
factors at work which may cause an insect population to in-
crease or decrease. Sometimes one factor is more important
than another. Sometimes several factors are of major import-
ance. Although a great deal remains to be investigated in this
field of applied ecology, certain factors have already demon-
strated their importance as agents in affecting the increase or
decrease of scale populations.
Reproductive Capacity.-Griffiths (12), in computing data
taken from Spencer (42), reported that in three generations
Florida red scale could out reproduce purple scale in a ratio of 100
to 7. This was based on the hypothesis of 50% of the maximum
number of eggs laid by a female resulting in settled individuals

Florida Agricultural Experiment Stations

and half of these were then assumed to be females. Red scales
not only laid more eggs and thus had a greater reproductive po-
tential, but also passed a complete life cycle more rapidly than
did purple scale. He stated that, "if it be assumed that a five-
box orange tree has 50,000 leaves, one red scale female in May
could have progeny which would be scattered over those leaves
at the rate of two scales per leaf in October." Actual increases
from less than 0.1 scale per quarter leaf to more than 200 scales
per quarter leaf within a three-month period in one grove (12)
have been noted. This reproductive potential is undoubtedly a
factor in comparing the difficulties encountered in controlling red
as compared with purple scales.
While considering reproductive capacity, Mathis (27) found
that red scales laid more eggs on fruit than they did on leaves.
The full significance of this cannot be determined at this time,
but it suggested that the diet afforded by fruit as compared with
leaves made some difference in the reproductive potential of
those females.
Weather.-Weather is probably the most important single
factor which affects scale population intensities from one year
to the next. Winter temperature extremes are of utmost im-
portance, particularly when Florida red scale populations are con-
sidered. Numerous authors (5, 12, 53, 64, 69, 72) have reported
the fact that freezing temperatures markedly reduced red scale
populations. This is not necessarily attributable to defoliation,
although in the case of some groves this is an additional factor.
Low temperatures actually kill red scale. Griffiths (12) esti-
mated a statewide reduction of 75 percent following the extreme
cold of February, 1947. This, in turn, was reflected by the fact
that in most groves red scales did not become prevalent until
after mid-July of that year. In this connection, it is worth
noting that red scale is a major problem only along the east coast
below Cocoa, in the Lake Placid area of central Florida and in
the coastal sections of Manatee, Sarasota, and Charlotte coun-
ties. Reference to Fig. 92 demonstrates that these areas have
similar cold exposures and that they are definitely warmer areas
than those lying immediately north of them. This fact was

2 From "Pattern of Winter Temperatures in Peninsular Florida, No-
vember 1937 through March 1946," by L. G. Pardue, Jr., U. S. Weather
Bureau, Lakeland, Fla.



310 oR LOWER


ToTALs. NOv. 1937 -MR 1946

o 1 1 **

Fig. 9.-Winter temperature pattern in Peninsular Florida.

S- -j

22 Florida Agricultural Experiment Stations

again demonstrated in the freeze of January, 1948, when Lake
Placid did not suffer from the cold as did Polk County and the
counties to the north. Actual red scale counts (Griffiths, unpub-
lished data) showed reductions in red scales in Polk County and
north, but little or no reduction in the Lake Placid area. Winter
extremes are not the sole reason for the prevalence of red scales
in certain areas, but they are undoubtedly a contributing factor.
Purple scales, on the other hand, show little or no effect from
freezing temperatures (5, 12, 53, 64). Although there is some-
times mortality among eggs and crawlers, little mortality occurs
among settled scales unless excessive leaf drop occurs. Cold
weather definitely slows up the rate of development and is, there-
fore, somewhat of a deterrent to population increases. Although
defoliation may markedly reduce the purple scale population,

Fig. 10.-Florida red scale infestation on grapefruit.
(Photograph by A. F. Camp.)

Purple Scale and Florida Red Scale as Pests of Citrus 23

many live scales may remain on the wood. Thompson (unpub-
lished data) sprayed some completely defoliated trees with oil
following the freeze in February, 1947. There were significantly
less scales the following summer on these sprayed trees than on
those beside them which remained unsprayed. This adequately
showed the importance of the survival of purple scales on the
wood of defoliated trees.
Rainfall is probably not a direct factor in affecting scale popu-
lations. However, Mathis (27) reported a marked mortality in
crawlers and newly settled Florida red scales following a tropi-
cal storm in 1939 and similar results would be expected with
purple scales. Trees suffering from dry weather may also suffer
excessively from scale injury. Dry weather often has been con-
sidered to be a cause of population build-up. It is possible that
this interpretation is erroneous, and that dry weather merely
enhances scale injury because the tree suffering from drought
has less resistance. The factor requires additional study.
The advent of warm temperatures in the spring and cool
temperatures in the fall are of utmost importance. Griffiths (13)
discussed this problem and showed, for example, that in 1946
scales began to reproduce in abundance in late March, approxi-
mately a month earlier than normal. The fall of 1946 was warm
and low temperatures were not experienced until December. The
combination of these two temperature abnormalities resulted in
an extra generation of Florida red scale and at least a partial
extra generation of purple scale. This, in turn, resulted in ex-
cessive purple scale populations in the spring of 1947, but, in
spite of this, the freeze of February, 1947, reduced Florida red
scale to a minimum.
Tree Health.-The general condition of a tree is definitely
related to the relative abundance of scale. This is a complex
problem, and only scattered experimental data are available.
However, these data show the effect of shade, succulence, min-
eral deficiencies, etc., as they may be related to general scale
In 1908 Butler (4) stated that a neglected tree was never
bothered by scale unless it was found in either a barnyard or
chicken yard, and that the use of organic sources of nitrogen

Florida Agricultural Experiment Stations

brought up scales. He made further observations to the effect
that scales were a serious pest on succulent shoots following the
1894-95 freeze and that excessive shade was likewise a factor in
scale build-up. Butler probably knew nothing of minor element
(Mg, Mn, Zn, Cu, etc.) deficiencies in citrus, yet he made obser-
vations which actually suggested what happened in the middle
1930's. At that time, with the advent of changes in fertilization,
purple scale became a major instead of a minor pest of citrus.
Thompson (50, 57) partially explained this on the basis of
changes in the type of tree which was then produced. Prior to
the use of magnesium, manganese, copper and zinc as nutritional
elements, trees were often very light of foliage and much of the
foliage was chlorotic, due to magnesium, zinc, or manganese
deficiency. The use of these elements produced more heavily
foliaged and more succulent trees. By actual count, more scales
per leaf were found on moderately foliated trees as compared
with lightly foliated trees. As previously mentioned, purple
scale crawlers seek shaded places to settle. Apparently, semi-
shade affords a more satisfactory environment for them.
Indirectly, heavily foliated trees afford another reason for
scale development. They represent healthy trees which retain
their leaves for longer periods of time, and thus few scales are
lost by an excess shedding of leaves.
Thompson (50, 51, 56, 57) showed that both bronzed (mag-
nesium deficient) leaves and frenched (zinc deficient) leaves had
less scale per leaf than green leaves from the same tree. These
leaves were actually lacking in magnesium and zinc. Whether
it was this deficiency or the resulting chlorosis which made them
less desirable was not determined, but this fact demonstrates
that mineral deficiency and, in turn, general tree health are im-
portant factors in scale increases.
In 1899 Hubbard (22) stated that overfed, succulent trees
were more susceptible to the ravages of insects than hungry
ones. Osburn and Mathis (30) showed that summer cultivation
produced more heavily foliated succulent growth and that these
trees had significantly higher populations of Florida red scale
than did similar trees which were uncultivated during the same
period. The amount of residue was not much greater on leaves
from cultivated than uncultivated trees. They concluded that

Purple Scale and Florida Red Scale as Pests of Citrus 25
the relative vigor and health of the tree was the determining
factor in increased scale. Thus, it appears that general tree
health is concerned with scale infestations and, similarly, that

bt kYI 1
Fig. 11.-Concentrations of purple scale in foliage taken from a tree
which was on an outside row by a roadway. Note concentrations of scales
on petioles, mid-ribs and twigs. (Photograph by Madge Campbell.)

Florida Agricultural Experiment Stations

shade, succulence, and mineral deficiency are also concerned.
The interactions between these factors probably are of the
utmost importance.
Residue.-Residues of any kind on a citrus leaf probably are
a major cause of scale increases. This subject has never been
exhaustively studied, but sufficient evidence has been presented
to establish the importance of residue as a scale-producing fac-
tor. While the chemical nature of the residue may be of sig-
nificance, it has long been recognized in Florida that trees ad-
jacent to clay roads often had much heavier scale infestations
than those farther inside the grove. Thus, inert clay can cause
scale increases.
Two early accounts take note of the fact that purple scale
increased following bordeaux (equal parts of copper sulfate and
lime) applications. Webber in 1897 (72) reported this and at-
tributed the increase of purple, Florida red, and long scale to the
fact that entomogenous fungi were killed. Similarly, O'Byrne
(28) in 1916 noted purple scale infestations following bordeaux
applications for scab control on grapefruit, and Hayman (20)
reported increases in scales following applications of zinc spray.
Thompson (45) experimented with inert residue and found a
very noticeable increase of purple scale following four applica-
tions of hydrated lime in each of two years. He also (50, 52,
54) demonstrated that the amount of lime residue was probably
as important as the amount of copper in the spray in so far as
scale build-up was concerned. With comparable amounts of
copper (52), the spray with the greatest amount of residue re-
sulted in the most scale increase. Similarly, Osburn and Spencer
(31) also found that inert residue brought up both Florida red
and purple scales. Sooty mold (4, 64) also is a factor in scale in-
creases. This may be partially attributable to shade, but the
primary factor is undoubtedly a residue one. In 1948 Griffiths
and Fisher (14) examined the effects of varying the chemical
composition of residues when all were used at the same weights
of materials per 100 gallons of spray. They concluded that all
residue sprays tested resulted in increased purple scale popula-
tions (see Fig. 12) as compared with infestations on unsprayed
controls, and that the chemical composition of the residue ma-
terially affected the duration of the increased population.

Purple Scale and Florida Red Scale as Pests of Citrus 27

Entomogenous Fungi.'-A consideration of entomogenous
fungi is closely associated with the problem of residue. Watson
and Berger (70) listed five species of fungi as being parasitic on
purple scale, and some of these were also supposed to be parasitic
on Florida red scale. Hubbard (23) described a fungus which
he thought was saprophytic rather than parasitic. However,
following Rolfs' (34) work with the red-headed fungus on San
Jose scale, papers by various workers appeared in which fungi
were discussed and the conclusion drawn that several different
species were actually parasitic on the common scale insects of


_J 0 -.-- *


Fig. 12.-Changes in purple scale populations following the use of
different residue sprays in a Pineapple orange block in 1943.

citrus in Florida. A careful review of some of these papers (2, 3,
8, 9, 34, 36) reveals the fact that very little controlled experi-
mental work was actually performed, and the validity of the re-
sults and procedures are undoubtedly open to question. How-
ever, a great many growers have come to believe that particu-
larly the "pink and red-headed fungi" were excellent means for
controlling scales. Actually, there was insufficient data either
to reject or sustain the hypothesis that several species of fungi
are parasitic upon purple and Florida red scales. However, some
work has been performed which has an important bearing on
the subject. The following is a discussion of the facts as they

: The authors are indebted to Miss F. E. Fisher, Asst. Plant Pathologist,
Florida Citrus Experiment Station, for her help in preparing this section
of the bulletin.

Florida Agricultural Experiment Stations

have been presented by various workers and a consideration of
the importance of these fungi as factors in scale insect control.
As early as 1897 bordeaux sprays were recognized as a factor
in scale increases (72). Ziegler (78) in a paper presented in
1935 claimed that red-headed fungus was not a cause of purple
scale mortality and that total spray residue was an important
factor in purple scale build-up. In 1938 Thompson (50) discussed
this problem at some length. He performed a series of related
experiments and found, as noted in the discussion on residue,
that the actual amount of inert residue (copper sulfate, zinc
sulfate, manganese sulfate, lime, neutral metal salts, etc.) was
an important factor in the scale increases. Where a neutral
copper (3 Ibs. per 100 gal.) was compared with bordeaux (6-6-
100), the neutral copper actually caused a greater reduction in
the amount of "pink and red-headed" fungi found associated
with scale, but, in spite of this, there was a greater increase of
scales on the bordeaux plots where the larger amount of residue
was present. The unsprayed control plots had less scale and
more fungus than any of the sprayed plots. Thus, it appeared
from this that copper was not the only important factor in scale
build-up. Holloway and Young (21) attempted to determine the
influence of fungicidal sprays on fungi associated with purple
scale in Florida. They applied high and low amounts of residue,
some of which contained copper and some which did not. They
found more "pink and red-headed" fungi associated with dead
scales where no copper was used and also where low residue was
used. However, in each of the two years, there was no difference
in the number of purple scales following treatments with or with-
out copper, but there were significantly more scales where high-
residue treatments were compared with low. Griffiths and
Fisher (14) found that purple scale infestations, which increased
following the use of copper and zinc-lime sprays, remained at
higher levels for longer periods than did those on unsprayed con-
trols or those following the use of pyrophyllite or wettable sulfur
(see Fig. 9). These two papers emphasize the fact that the
entire problem of the possibility of the presence of parasitic
fungi on scale should be reconsidered and carefully controlled
experimental work performed.
In 1947 Fisher (10) reported finding a new species of fungus
which was definitely parasitic on purple scales. This endopara-

Purple Scale and Florida Red Scale as Pests of Citrus 29

site is a member of the order Chytridiales and is tentatively
placed in the genus Myiophagus (Myrophagus) Thaxter (40).
She also found mycelia of the "pink and red-headed fungi" on
scales killed two weeks previously by oil sprays. Following this
report, Karling in 1948 (24) reported a similar chytrid as para-
sitizing purple scales in both Bermuda and Louisiana. He be-
lieved it to be identical to Myiophtagus ucrainicus (Wize) Spar-
row (40) and stated that a heavy infestation killed as high as 45
percent of the females of purple scale and transformed the con-
tents of their bodies into a mass of golden-orange sporangia.
Whether the species reported by Fisher and Karling are identical
has not been determined, but it does appear that a fungus actu-
ally kills purple scale. In a more complete discussion of fungi
parasitizing purple scales, Fisher et al. (11) also suggested that
there was another fungus attacking scales. This fungus belongs
to the genus Hirsutella and it apparently killed scales which
were in early first stage.
In summary, then, scale increases following the use of residue
sprays may be partially attributable to the physical presence of
the material. However, copper and zinc-lime containing sprays
appear to prolong the duration of the high scale populations.
Neither Holloway nor Thompson was able to demonstrate any
relationship between "pink or red-headed" fungi and scale build-
up following copper sprays, and it appears to be quite possible
that these two species of fungi are primarily saprophytic. It is
possible that the fungi reported by Fisher (10, 11) and by Karl-
ing (24) in purple scales may be found to thrive under similar
conditions to "pink and red-headed" fungi, and if this be true the
latter fungi might be used to indicate the presence of chytridiosis.
However, this is purely in the realm of conjecture and it is only
intended to point out here that the problem of fungi parasitizing
purple and Florida red scales must be further examined before
complete conclusions may be drawn.
Parasites and Predators.-The role of parasites and predators
in normal scale increases and decreases may sometimes be a very
important one. Griffiths and co-workers (15, 17) found that the
use of DDT on citrus trees in Florida resulted in phenomenal in-
creases in Florida red scale populations. Examination of the
scales demonstrated that the unusual increase was due to the
almost total absence of two hymenopterous parasites and the

Florida Agricultural Experiment Stations

twice-stabbed ladybeetle from the DDT-sprayed trees. Thus,
significant differences in beneficial insect populations were found
when DDT-treated trees were compared with adjacent unsprayed
ones. Purple scales did not increase in this same fashion fol-
lowing DDT, and it seems reasonable to suppose that normal
parasitism may not be as important a factor in the control of
purple scale as it is in the reduction of red scale populations.
Griffiths and Stearns (16) found no detrimental effects to the
parasitism of red scales where airplanes applied DDT at the rate
of 1/4 pound per acre for the control of mosquitoes along the east
coast of Florida.

B 0
~---- I mm.
Fig. 13.-Holes in the armors of Florida red scale caused by the
emergence of parasites and by ladybeetle feeding habits. A, Emergence
hole of Prospaltella aurantii (How.) ; B, emergence hole of Pseudohomala-
poda prima (Gir.); C, hole eaten in armor by twice-stabbed ladybeetle.
x, y, Emergence holes; z, jagged hole eaten by ladybeetle.

Three parasites have been identified from Florida red scales,
Pseudohomalapoda prima (Gir.), Prospaltella arantii (How.),
and Aspidiotiphagus lounsburyi (Gerl. and Paoli). The last two
parasitize nearly-mature males and second-stage female scales.
Although their tiny emergence holes (see Fig. 13) are usually

Purple Scale and Florida Red Scale as Pests of Citrus 31

found in the armors of mature males and of molting second-stage
females, in rare instances they are present in third-stage female
armors. Here the female had completed its molt before succumb-
ing to the parasite. P. prima is found in nearly-mature female
scales and in females which are already laying eggs. No work
has been done on the relative effectiveness of each of these, but
all are probably important. Mathis (27) noted higher parasitism
in the fall than at any other season, and this is substantiated by
unpublished data of the authors. This fact is partially explained
by normally higher scale populations in the fall. The authors
have noted, however, that, where excessive red scale populations
were experienced in the spring of the year, parisitism was also at
a high level.
In the case of purple scale, at least one parasite is present in
Florida. This one has been observed for many years, but the
authors have been unable to rear specimens for positive identi-
fication. Although it is found primarily in males and second-
stage females, emergence holes are sometimes present in the
armors of mature females. The authors have rarely found it in
any abundance, even where purple scales were present in heavy
infestations, and it may be of minor importance as a scale check.
The twice-stabbed ladybeetle (Chilocoris stigma Say) is
probably of major importance as a factor in the biological con-
trol of scales, and it is probably more important in Florida red
scale than in purple scale control. Apparently, both the mature
beetles and the larvae tear jagged holes (see Fig. 13) in the
armors of scales so as to get at crawlers, eggs, and the scales
themselves. The hole cut by the ladybeetle is very rough as
compared with that by the emergence of a parasite, and the two
may be readily differentiated (see Fig. 13).
Several species of the order neuroptera, commonly called
aphis-lions and trash bugs, are present on citrus (6) and prob-
ably are actively predaceous on scale crawlers. The trash bugs
pile the dry skins of their victims as well as other trash on their
backs as they move along. Mathis (27) fed the larva of one such
trash bug, Chrysopa lateralis, 12 mature females in one hour.
A number of different mites are often found about collections
of scales. Watson (70) thought that some were occasionally
predaceous, but that they acted more as scavengers than as

Florida Agricultural Experiment Stations

predators. He stated that they often increased following oil
sprays when dead scales were abundant.
Speare (41), Watson (70), and Thompson (49) mention two
lepidopterous larvae which are of interest in their relationships
with scale populations. Watson thought the pyralid moth, Lae-
tilia coccidivora Comst., was predaceous on mealybugs, but
Speare believed it to be only a scavenger. In any case, the larva
of this moth, as well as the pink scavenger bollworm, Pyroderces
rileyi Wlsn., is often associated with scales and/or mealybugs.
They have a very doubtful value as predators, and there can be
no question that the larvae often attack the rind of the fruit. In
occasional instances, the damage to a crop may be severe. In
the spring of 1948 there was excessive fruit damage on Valencia
oranges caused by the pink scavenger worm.

Scale Control
Materials.-Materials used for scale control have varied
through the years. In early days fish oil soap and kerosene
emulsion were commonly used. After 1930, when trees were
suffering from nutritional deficiency, Thompson (46) reported
satisfactory control of purple scales with regular applications of
lime-sulfur, and Yothers (75, 77) had mentioned a similar phe-
nomenon. At present scale control is accomplished by the use of
emulsified petroleum oils. These are usually applied at rates
varying between 1.2 and 1.7 percent, but the standard recommen-
dation is for an emulsion containing 1.3 percent actual oil. The

% Oil Gallons of Various Stocks To Be Diluted to 100 Gallons of Spray
in to Make Percentages of Oil in Spray Mixture Listed Below
Stock 1.0% 1.2% 1.3% 1.4% 1.5% 1.6% 1.7%

100 1.0 1.2 1.3 1.4 1.5 1.6 1.7
99 1.01 1.21 1.31 1.41 1.51 1.61 1.72
98 1.02 1.22 1.33 1.43 1.53 1.63 1.73
97 1.03 1.24 1.34 1.44 1.55 1.65 1.75
92 1.09 1.30 1.41 1.52 1.63 1.74 1.85
90 1.11 1.33 1.44 1.56 1.67 1.78 1.89
84 1.19 1.43 1.55 1.67 1.79 1.90 2.02
83 1.20 1.45 1.57 1.69 1.81 1.93 2.05
80 1.25 1.50 1.62 1.75 1.88 2.00 2.12
70 1.43 1.72 1.86 2.00 2.14 2.29 2.43
65 1.54 1.85 2.00 2.15 2.31 2.46 2.62

1949 Better Fruit Program, Florida Citrus Commission, Lakeland, Florida.

Purple Scale and Florida Red Scale as Pests of Citrus 33

spray may be made from an emulsified oil, from an emulsifiable
oil, or by adding an emulsifying agent in the tank at time of mix-
ing. Table 1 shows standard amounts of stock material to use per
100 gallons of finished spray material where a given percent oil
emulsion is desired.
Parathion is a new organic insecticide which has shown
promise in scale control (61, 63). No recommendations for its
use have been made as yet, and considerable experimental work
must be completed before it or some other allied compound will
be generally recommended for use on citrus.
Method of Application.-In Florida, oil sprays usually are
applied by either of two methods: a pressure sprayer operating
at 400 to 600 pounds per square inch pressure, or a large power-
driven machine which liberates spray material under low
pressure into an air blast of about 44,000 cubic feet per minute
and at an aperture velocity of about 85 miles per hour. In either
case, sufficient gallonage must be applied to wet thoroughly both
sides of the leaves and all fruit and twigs. With a pressure
sprayer it has been shown (44, 48) that larger nozzle apertures
(7/64" and 8 64") give better results than smaller ones (5 '64").
The small openings produce a mist which is not satisfactory.
Where pressure sprayers are used, the trees should first be
sprayed from the inside out and then from the outside of the
canopy. This is absolutely essential for good scale control.
When power-driven equipment is used, speeds should be about
one mile per hour. As speed increases, the amount of oil de-
posited decreases (44). Redd (29) made oil deposit checks fol-
lowing different types of applications and found that, usually,
an initial oil deposit of 50 to 90 mcg. cm2 gave satisfactory con-
trol. A lower average deposit was apt to give unsatisfactory
control, and a higher one was apt to cause damage to the tree.
An average oil deposit figure is not an altogether reliable crite-
rion, since a few leaves with a heavy deposit would raise the
average on a tree with spotty coverage. Thus, complete coverage
is far more important than average oil deposit. However, the
latter information is a valuable adjunct in ascertaining the
possible effectiveness of an oil spray.
Time of Application.-An attempt should be made to time an
oil application so that one spray will result in a minimum amount
of scales for an entire year. In some instances, two applications

Florida Agricultural Experiment Stations

are necessary, but this will be further discussed below. Although
there have been recommendations (66) in the past for the use
of a single application in the fall of the year, it is now generally
agreed (13, 54, 58) that the optimum time for oil spraying is
between June 15 and August 1 in most years. This has been
established by both experimentation and the study of actual pro-
duction records in large commercial operations. Oils applied
prior to June 1 usually allow too much scale build-up by fall (13,
59, 74). Where possible, it may be desirable to attempt to spray
when most of the scale population is in first or second stage (13,
47, 67).
When heavy populations of scales are present, two oil appli-
cations may be necessary. Very satisfactory control may be ob-
tained with a minimum of detrimental effects by following either
of the three programs listed below:
1. a. A pre-bloom oil emulsion*
b. A summer oil emulsion
2. a. A post-bloom copper oil** spray (1.3% oil and a
neutral copper compound with the copper content
equivalent to 3 pounds of copper sulfate per 100
gallons of spray.)
b. A summer oil emulsion
3. a. An oil emulsion about June 1
b. An oil emulsion about July 20-30.
1.3% actual oil.
** A copper oil spray should always be applied prior to the time that
the fruit is %" in diameter. When fruit is larger than this, excessive
marking may occur.
Effects of Oil Sprays on Trees.-Where oil emulsion sprays
are used injudiciously, damage may result. As mentioned above,
too high an oil deposit (33) may result in dead wood or excessive
leaf drop. This condition usually is brought about by using an
emulsion which breaks too easily and, thus, too much oil is de-
posited on the leaves. An excessive oil deposit rarely occurs
because of overspraying, except when a tree is allowed to dry
and is then resprayed.
An oil emulsion spray is a definite shock to a tree and is best
applied when the trees are in the most vigorous growing con-
dition of the year. During a five-year period there was always
more leaf drop following an application of an oil emulsion than
following either lime-sulfur or wettable sulfur. Oil sprays should

Purple Scale and Florida Red Scale as Pests of Citrus 35

not be applied to weak trees, trees suffering from drought or
during the winter when there is danger of cold weather. After
the freeze of 1947, Thompson (59) reported more severe injury
to trees in oil timing plots which received two summer oil appli-
cations or a single one in October, November, or December, than
to trees receiving either one oil spray between June and Sep-
tember or a post-bloom copper-oil followed by a summer oil spray
(See Fig. 14.) This affords adequate reason for avoiding the
necessity of two summer and or fall oil sprays and of fall oil
sprays of any kind.
Oil sprays also may cause unsightly markings on the fruit if
applied when the fruit is between 34" and 11/2" in diameter (60).
When copper is added to a post-bloom oil spray, this same type
of injury may occur, or a condition known as "star melanose"
may be severe if the fruit is larger than 3" in diameter.
In addition to this type of injury there is the fact that oil
sprays applied in late summer and fall delay fruit degreening
and actually prevent or retard the formation of soluble solids (38,
39, 62). This is especially important on early and mid-season



10 10 n lif- )

SI ) Ln oI ul)1 0l l 0 Ln In-

(o a nF > y
f< < iW 0 0 W


wJ W wJ
Crz z2 ZnD z 0
0ID D= Di DUJ0
< 7 -)< -a c) ->0

Fig. 14.-Pounds of dead wood pruned from orange trees in oil timing plots
after freeze of February 6, 1947.

Florida Agricultural Experiment Stations

fruit, and care should be taken to avoid the necessity of spraying
oil, particularly during August and September.
The problem of degreening fruit is complicated by the use of
oil sprays (39, 73). The application of oil any time after August
1 is apt to delay degreening and to result in longer hours in the
coloring room. This fact is particularly important on early
oranges and grapefruit, and it frequently arises when Valencias
require sprays for scale control in February, March, or April.
Contrary to some prevalent ideas, oil sprays do not cause colored
fruit to green up, rather they delay the breakdown of the green
color in the fruit.
Some evidence has been found to show that November and
December oil sprays may result in lowered production the follow-
ing year. Thompson (55) reported a case in 1941 and in the
spring of 1948 the authors saw two blocks of oranges in Lake
County, in both of which several rows had been oil sprayed in
November. On those rows sprayed in November the reduction
in the amount of bloom and crop set was very pronounced in both
groves. Late fall sprays do not always do this, but they appear
to be dangerous from this standpoint, as well as from the possi-
bility of cold following the application.
Summary of Present Control Recommendations. Where
single oil sprays are to be used, a 1.3 percent oil emulsion should
be applied between June 15 and July 31. This will give maximum
scale control and will result in a minimum exposure to possible
deleterious effects of oil. Where serious infestations are not a
factor, early and midseason fruit should be sprayed before late
oranges and grapefruit. The Better Fruit Program issued
annually by the Florida Citrus Commission should be consulted
for any changes in scale control suggestions and for more specific
recommendations and qualifications.

Historical notes concerning purple scale and Florida red scale
in Florida are presented. The life cycle of both species is de-
scribed and illustrated. The adverse effects of scale infestations
on citrus are discussed and the factors affecting the relative
abundance of scales on citrus trees are considered in detail.
Materials used for scale control, method of application, and
effects of oil sprays on citrus trees are outlined.

Purple Scale and Florida Red Scale as Pests of Citrus 37

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Florida Agricultural Experiment Stations

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Purple Scale and Florida Red Scale as Pests of Citrus 39

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Florida Agricultural Experiment Stations

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