Title Page
 Table of Contents
 List of Tables
 List of Figures
 Literature review
 Results and discussion
 Summary and conclusions
 Biographical sketch

Title: Biology and population dynamics of tea scale, Fiorinia theae Green (Diaspididae: Coccoidea: Homoptera)
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00099245/00001
 Material Information
Title: Biology and population dynamics of tea scale, Fiorinia theae Green (Diaspididae: Coccoidea: Homoptera)
Alternate Title: Tea scale
Physical Description: x, 125 leaves : ill. ; 28 cm.
Language: English
Creator: Munir, Badar, 1938-
Copyright Date: 1980
Subject: Scale insects   ( lcsh )
Fiorinia theae
Entomology and Nematology thesis Ph. D
Dissertations, Academic -- Entomology and Nematology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by Badar Munir.
Thesis: Thesis--University of Florida.
Bibliography: Bibliography: leaves 110-114.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00099245
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: alephbibnum - 000014231
oclc - 06324636
notis - AAB7430


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Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Tables
        Page vi
    List of Figures
        Page vii
        Page viii
        Page ix
        Page x
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
    Literature review
        Page 9
        Page 10
        Page 11
        Page 12
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        Page 19
        Page 20
        Page 21
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        Page 23
        Page 24
        Page 25
    Results and discussion
        Page 26
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    Summary and conclusions
        Page 108
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    Biographical sketch
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Full Text

Fiorinia theae GREEN







This dissertation is dedicated to my father, Choudhry Murad Ali,

whose support, love, and goodwill enabled me to complete this work.


I am deeply indebted tothe Chairman of my graduate committee,

Dr. Reece I. Sailer, for his continuous guidance and advice throughout

the studies. I am also extremely grateful to Dr. T. E. Freeman and

Or. A. B. Hamon for critical review of the first draft of the disserta-

tion; to Dr. T. J. Walker and Dr. S. L. Poe for help and valuable sug-

gestions in the preparations of life tables. I wish to express my

gratitude to Mrs. Helen Huseman for preparing the figures, and to

Miss Mary Davis for her patience and dedication while typing the

dissertation. Last, but not least, I extend my sincerest appreciation

to my wife, Rafia, for her support and enthusiasm during these studies.


ACKNOWLEDGEMENTS .................................................... iii

LIST OF TABLES.. ......................... ...................... .... vi

LIST OF FIGURES.................................................... vii

ABSTRACT............................................................ ix

INTRODUCTION.......................................................... 1

LITERATURE REVIEW....................................... ............ 9

Fiorinia theae Green ................ .......................... 9

General Review............................................. 9
Description............. ...... .............................. 9
Distribution............ .................................... 11
Host Plants................................................ 12
Economic Importance....................... ............... 12
Biology..................................................... 16
Laboratory Rearing.......................................... 16
Natural Enemies............................................ 17
Chemical Control ........................................... 18

Aphytis theae (Cameron)....................................... 18

Description................................................ 18
Redescription.............................................. 19

Life Tables..................................................... 19

METHODS..............................................* .............. 22

Biology........................................................ 22
Parthenogenesis................................................ 23
Population Dynamics ............................................ 23

RESULTS AND DISCUSSION.............................................. 26

Biology..................................... .................. 26
Parthenogenesis................................................ 34


Population Dynamics

General Characteristics of Tea Scale
Populations ......................................... ... 36
Populations of Adult Males ................................. 39
Populations of Mature Females .............................. 44
Introduced Parasites ....................................... 48
Aphytis theae (Cameron) ................................. 48
Aspidiotiphagus sp ...................................... 55
Life Tables ....... ........................................ 57
K-Factor Analysis of Life Tables ........................... 77
Survivorship Curves........................................ 80
Fertility Tables ........................................... 87
Age Composition ............................................ 98
Methodology to Calculate Survival Rates of
Female and Male Tea Scale Populations ................... 104

SUMMARY AND CONCLUSIONS ............................................. 108

REFERENCES CITED .................................................... 110


1. Number of Male and Female Tea Scale, Fiorinia theae, survived
on Camellia japonica at different temperatures............... 115

2. Side Preference of Tea Scale, Fiorinia theae.................... 116

3. Values (log) of Various Mortality Factors (k's) and the
Generation Mortality (K) for Tea Scale, Fiorinia theae,...... 117
at Wilmot Garden, Gainesville

4. Data for the Survivorship Curves. Number of Tea Scale,
Fiorinia theae, per 30 cm2 area of leaves of Camellia
japonica at Wilmot Garden, Gainesville....................... 118

5. Number of Male and Female Tea Scales, Fiorinia theae, per
30 cm2 area of Camellia japonica at Wilmot Garden,
Gainesville.................................................. 119

6. Data for the Age Composition. Number of Live Male and Female
Tea Scales, Fiorinia theae, per 30 cm2 area of Leaves of
Camellia japonica at Wilmot Garden, Gainesville.............. 120

7. Reproductive Value of the Ovipositing Females of the Tea Scale,
Fiorinia theae, at Wilmot Garden............................. 121

8. Number of Female Tea Scale, Fiorinia theae, in 3 cm2 area,
and on Whole Leaves of Camellia japonica at Wilmot Garden,
Gainesville.................................................. 123

BIOGRAPHICAL SKETCH................................................. 125



Table Page

1. Host Plants of Tea Scale, Fiorinia theae ...................... 13

2. Total Fecundity of Tea Scale, Fiorinia theae .................. 29

3. Comparison of Numbers of Male F. theae Adults
Emerged from Colonies on Leaves of Camellia
japonica at Wilmot Garden in 1977 and 1979 .................... 43

4. Number of Mature Females of F. theae in
Pre-oviposition, Oviposition, and Post-
Oviposition Stages ............................................ 46

5. Larval and Pupal Mortality of Aphytis theae
per 30 cm2 of Leaves of Camellia japonica
at Wilmot Garden .............................................. 51

6. Monthly and Annual Life Tables for Tea Scale,
Fiorinia theae, at Wilmot Garden, Gainesville ................. 64

7. Specific and Crude Sex-Ratios of Tea Scale,
Fiorinia theae ................................................ 88

8. Number of Female Tea Scale, Fiorinia theae,
per 30 cm2 Area of Leaves of Camellia
japonica at Wilmot Garden, Gainesville........................ 91

9. Monthly and Annual Fertility Tables for
Tea Scale, F. theae ........................................... 93


Figures Page

1. Adult Populations of Aphytis theae and
Male Fiorinia theae Observed on Leaves of
Camellia japonica at Wilmot Garden, Gainesville............... 40

2. Number of Male Adults of Fiorinia theae, Adults
of Aphytis theae, Larvae of Microweisea coccidivora
and Lindorus lophanthae on Leaves of Camellia
iaponica, and Percent Parasitism by A. theae at
Wilmot Garden, Gainesville ................................... 42

3. Number of Ovipositing Females of Tea Scale,
Fiorinia theae, on Leaves of Camellia japonica at
Wilmot Garden, Gainesville................................... 45

4. Life Cycle and Survival of Different Stages of
Tea Scale, Fiorinia theae Green, at Gainesville.
The Area of Circles is Proportional to the Size
of Populations. Decrease in Size of Circles is
Due to Mortality Occurred Between Successive Stages........... 47

5. Larval and Pupal Populations of Aphytis theae on
Leaves of Camellia japonica at Wilmot Garden,
Gainesville .................................................. 49

6. Average Monthly Rainfall and Minimum Temperature
at Jorhat (India) and Gainesville (Florida).
Data for Jorhat were Obtained from CIBC (Indian
Station), and for Gainesville from Agronomy
Department, University of Florida............................. 52

7. Key Factor Analysis. The Recognition of Key
Factors in the Life Tables for Tea Scale,
Fiorinia theae, by Visual Correlation of Various
Mortality Factors (ks) with the Generation Mortality (K)...... 78

8. General Types of Survivorship Curves.......................... 81


Figures Page

9. Monthly and Annual Survivorhip Curves of
Tea Scale, Fiorinia theae, at Wilmot
Garden, Gainesville.......................................... 83

10. Specific and Crude Sex-Ratio of Tea Scale,
Fiorinia theae, at Wilmot Garden, Gainesville................ 89

11. Monthly and Annual Age Composition of Tea Scale,
Fiorinia theae, at Wilmot Garden, Gainesville................ 100

Abstract of Dissertation Presented to the Graduate
Council of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

Fiorinia theae GREEN



March 1980

Chairman: R. I. Sailer
Major Department: Entomology and Nematology

Tea scale, Fiorinia theae Green, is the most important pest of

camellias and hollies in the eastern United States. Because chemical

control is costly and otherwise less than satisfactory, an attempt was

made to import natural enemies for biological control of this pest. Two

aphelinids, Aphytis theae (Cameron) and Aspidiotiphagus sp., were im-

ported from India and cultured in greenhouses at Gainesville. Both

species attack male nymphs of tea scale. Field releases of A. theae and

Aspidiotiphagus sp. were made in May 1976 and January 1977, respectively.

A. theae was colonized but failed to survive the second winter; Aspidi-

otiphagus sp. seems to have become established.

A mite and a thrips feed on settlers, while male nymphs are preyed

on by 3 species of predators. A local parasite that attacks female nymphs

is very rare and consequently ineffective in population regulation of tea


Biology of tea scale was studied. Development in males and females

is asynchronous, the species being protandrous. Dimorphism is exhibited

in the immature as well as mature stages. Females deposited an average

of 28.82 eggs which were retained under the armor where they hatched in

9-10 days. Male nymphs molt 4 times; females 2 times. Male adults

emerged in 34 days; females began ovipositing in 65 days.

Data generated by field and laboratory studies are utilized to con-

struct 12 monthly and 1 annual life tables. Generation mortality ranged

from 92.65% in April to 96.92% in February, with an annual average of

95.15%. Index of population trend varied from 0.71 to 1.39, with an

average of 0.98. Major mortality factors were dispersion loss at crawler

stage and parasitization of male nymphs by A. theae. Mortality in male

nymphs did not affect the overall population level because of male

biased sex-ratio and polygyny. Survivorship curves and fertility tables

for tea scale were also prepared. Net replacement rate (Ro) ranged from

1.80 in February to 4.45 in May, with an annual average of 2.86. Specific

sex-ratio in the tea scale varied at all stages; there were more males

at nymphal stages but females were more abundant as adults. Crude sex-

ratio indicated a constant preponderance of males. Major cause of vari-

ation in sex-ratio was mortality of the male nymphs by A. theae. Age

composition figures for tea scale were prepared for each month and for

mean annual populations. A schematic representation of life cycle

depicting the salient features of biology and population dynamics of tea

scale was developed. Methods to calculate the survival rates of males

and females are described.


The tea scale, Fiorinia theae Green, is a member of Diaspididae, a

family that contains many damaging and unmanageable pests of perennial

crops and ornamentals. Tea scale is regarded as one of the principal

armored scale insect pests of the world (Beardsley & Gonzalez, 1975).

In North Florida and a large part of the Southeastern United States,

including Alabama, Georgia, and South Carolina, it is placed among the

10 most important pests of nurseries and home landscape plantings

(Dekle, 1965).

Tea scale is a polyphagous insect and at least 43 different ornament-

als and fruit trees are known to serve as its hosts. The most seriously

affected plants are camellias and hollies which are highly desirable

broad-leaf evergreen ornamentals.

Being stenomerous, it feeds only on leaves of the host plants. The

feeding on lower surfaces of leaves invariably results in discoloration

on the upper side, followed by defoliation. Infested camellias assume

an unthrifty appearance and flower poorly. In cases of severe infesta-

tions, dieback of twig terminals occurs and ultimately results in the

death of the plants.

Tea scale is known to have originated in the Oriental region, where

it is associated with tea and related plants. Nowhere in the region from

India to Japan has the tea scale been found to be a serious pest. This

suggests that natural control factors provide effective control of tea

scale in that area. Although a number of natural enemies have been found

in association with tea scale in Florida, they are not effective in keeping

the populations at non-economic levels.

Efforts to control tea scale infestations have, so far, been confined

to chemical control; a number of insecticides have been tested, utilized,

and recommended by various workers. However, chemical control is not a

suitable long-term strategy for suppression of pests such as tea scale.

The fact that tea scale is a pest of ornamentals, normally grown around

homes, offices, and other public buildings, makes use of chemical insecti-

cides undesirable, for more people, especially children, are likely to

come into physical contact with the toxic compounds. Moreover, the nature

of tea scale infestations is such that chemical control does not offer

much promise of success. For instance, camellia and holly plants are

usually quite large and densely foliated, with tea scale colonies located

on the underside of leaves. These characteristics render many insecticides

ineffective because of poor spray coverage. Also, new foliage in some

varieties of host plants is sensitive to certain chemicals. In addition,

chemical treatments are costly, especially for homeowners, and must be

repeated at regular intervals.

Despite the fact that tea scale is a pest of foreign origin, belonging

to a group that provides numerous examples of successful control by intro-

duced natural enemies, and is an unsuitable candidate for chemical control,

no effort was made to introduce exotic natural enemies. Various species

of Aphytis have proved to be key agents in regulating the densities of

numerous diaspid pests of citrus and other crops in various parts of the

world (Rosen, 1973). In Florida similar scale pest problems on citrus

have been eliminated through the action of introduced parasites of the

genus Aphytis, the two most notable examples being the control of Florida

red scale by A. holoxanthus DeBach, and of purple scale by A. lepidosaphes

Compere. These were the circumstances that prompted initiation in 1976

of an effort to introduce parasites of tea scale from India. As a

result of a joint IFAS-ARS-CIBC effort, A. theae and a still unidentified

species of Aspidiotiphagus were obtained and released in Gainesville.

Both species proved specific to male nymphs of tea scale. Although the

limitations of male specific parasites were recognized, it was hoped that

male mortality would be sufficient to prevent fertilization of females

and thus bring about reductions in tea scale populations. Had such

proved the case, it would have been the first example of control through

the agency of male specific mortality caused by parasites.

The initiation of a biological control program and subsequent evalua-

tion of its results require detailed information on the biology, seasonal

history, and population dynamics of the candidate pest species. In

Florida such information for the tea scale was at best fragmentary, and

no attempt has ever been made anywhere in the world to study bionomics

of the species in the detail needed for purposes of biological control.

Post-colonization studies designed to assess the efficacy of intro-

duced natural enemies are very useful in understanding the success or

failure of biological control programs. Such studies provide information

on the role of various mortality factors in regulating the population of

pest species, and, if the previously introduced species are proven inef-

fective, demonstrate the need for introduction of different species of

natural enemies. Although there are many examples of successful biolo-

gical control programs, a larger number have met with failure. Seldom

has it been possible to adequately document reasons for either success

or failure, and in the words of Krebs (1972), "biological control will

remain an art until we can do so" (p. 374).

Biology of tea scale was studied in the laboratory, and observations

on the seasonal changes and population dynamics were carried out at

Wilmot Garden, Gainesville, Florida. The data obtained through these

studies were utilized in the construction of life tables, survivorship

curves, fertility tables, and age composition. These are very convenient

and useful methods to describe the dynamics of populations.

Ecological life tables are one of the most useful methods of descrip-

tion and analysis of population dynamics of an insect. These tables con-

tain a series of sequential measurements that indicate changes in the

population in its natural environment. These measurements, when related

to the mortality factors and presented in the form of life tables, reveal

the presence of successive processes that operate in the populations.

Life tables were initially developed for the quantitative analysis of

human populations. Their importance lies in the fact that each stage in

the life history of a species is affected by different mortality factors

and at different rates.

Life tables for humans and insects fundamentally differ only in

objectives. In human life tables the objective is to determine the average

expected life remaining for an individual and therefore the most important

feature is the ex column. In the case of insects, the major interest lies

in the mortality factors and their rates, and therefore the most important

features are the dx and dxF columns. Life tables for non-human populations

are termed ecological life tables because of the emphasis on mortality

factors and the actual numbers used. The ecological life table is really

an organized summary of the life of a typical cohort of individuals in a

population. It describes in precise detail the stages in the life history

and reveals which contribute most to the population, and at the same time


reveals the mortality factors-- biotic or abiotic-- responsible for

regulation of the population. Trends in populations can be better under-

stood once the causes of mortality during each age interval are quantified.

An ecological life table usually consists of 6 columns. The first

column is labeled x and lists the pivotal age for the age class or age

interval under consideration. For insects it consists of various stages,

i. e., egg, nymph or larva, pupa, and adult. The next column labeled Ix

contains the number of individuals of the original cohort which were alive

at the beginning of age class x. Mortality factors are listed in the

third column which is labeled dxF. The fourth column, which represents

the number of individuals dying during the age interval, is labeled dx.

The fifth column, headed 100qx, is the proportion of individuals dying by

cause listed in dxF expressed as the percentage of 1x. The last column

is labeled 100dx/N1 and gives the percentage of the generation mortality;

in some life tables, this column is labeled sx and records the survival

at age interval x.

Three types of data are used in the construction of life tables:

1) Survival of a reasonably large cohort born more or less simultaneously

is followed at fairly close intervals throughout its existence. Since

this does not involve the assumption that the population is stable in

time, this is considered the best form of information.

2) Age at death is directly observed for a large and reasonably random

sample of individuals in the population. This requires the assumption

that the population is stable in time and that the birth and death rates

remain constant.

3) Age structure is obtained directly from a random sample of population

and the number of dead individuals is inferred from the reduction in the

number of living individuals between successive age intervals. It requires

the assumption that the population has a stable age distribution.

Data for the construction of tea scale life tables were obtained by

the combination of the above techniques in order to avoid unnecessary

assumptions. Death in different age intervals can be accurately deter-

mined because dead individuals remain attached to leaves and can be

easily counted. Because of stable age distribution, all stages are

present simultaneously, thus age structure can be observed directly.

The only assumption made was that the ovipositing females represent the

terminal individuals of a cohort that contained all dead individuals of

each age interval found on the sampled leaves. In view of the fact that

life cycle of the tea scale lasts for about 2 months, and that only new

colonies were sampled, this assumption does not seem unreasonable.

In general, there are 2 types of life tables, the age-specific and

the time-specific. These 2 kinds are different in meaning and form except

under unusual circumstances. The age-specific life tables are also called

cohort, generation, or horizontal life tables, and are constructed on the

basis of data obtained by following a cohort or designated members of a

population with discrete generations. The time-specific life tables are

also called stationary, static, current, or vertical life tables. Data

for these are collected on the basis of a cross-section of a multivoltine

population with overlapping generations.

Among diaspids, life tables are available only for the oystershell

scale, Lepidosaphes ulmi (L.) in Quebec, Canada,where this species is

univoltine and undergoes diapause in the egg stage. Tea scale, on the other

hand, is a multivoltine species and does not undergo diapause at any stage.

Life tables are very useful in understanding the dynamics of animal

and plant populations. Their concise and organized form presents much

information that is otherwise difficult to handle and comprehend. They

also help in determining the survival strategies of species, and evolution

of characteristics, such as fecundity and parental care. Data for life

tables are utilized by population theorists to test the validity of their

conceptual models. Life tables of pest species reveal the most vulnerable

stage in the life history and leads to emphasis on control at that stage

in order to influence survival rates of pests through management strate-


In order to understand the effect that any one environmental factor

has on the trend of a population, a series of age-specific life tables

is required covering a number of generations. The analysis of a series

of this sort enables one to assess the effect of each component of the

environment. A number of different techniques have been used to analyze

life table data. One method in particular is now widely used, namely,

the "K" factor analysis of Varley and Gradwell (1960). The other popu-

lar methods involving regression analysis were developed by Morris (1963)

and Watt (1963).

Adequate sampling techniques to study changes in population density

and interaction of various factors were not available for tea scale, which

is a multivoltine, beisexual, and dimorphic species. Sampling techniques

are further complicated by the fact that distribution of tea scale on

host plants is not uniform. Both interplant and intraplant variations

are large. Many potential host plants are not infested, while on in-

fested plants 1 or 2 twigs may be infested, the rest of the plant being

free of the scale. Invensive survey and sampling of small, arbitrarily

delineated populations on individual plants over time, is therefore


The parasites Aphytis theae (Cameron) and Aspidiotiphagus sp., origi-

nally imported from India and later released in Gainesville, exhibited

a marked preference for male nymphs of tea scale. This necessitated

ascertaining the importance of males in the reproductive biology of tea

scale. Consequently, an experiment was designed to determine if females

were capable of reproducing without fertilization. Results of this

experiment also provided information on relative survival of tea scale

at different temperatures and preference of crawlers to settle on lower

sides of leaves. All information on biology and population dynamics

of tea scale obtained through these studies was summarized in a schematic

representation. The data and information on the biology and ecology of

tea scale obtained in these studies will prove very valuable as a founda-

tion for future attempts to control this pest through importation of

additional enemy species and for comparing results of such attempts.


Fiorinia theae, Green

General Review

The published history of Fiorinia theae Green contains 3 major

landmarks: its discovery as a pest of tea in India by Watt in 1898, a

formal description as a new species by Green in 1900, and comprehensive

studies on its biology in India by Das and Das in 1962. The remainder

of the articles on tea scale contains either original records or reviews

on local and geographical distribution, host plants, descriptions of

female and male armors, and chemical control measures. Borchsenius

(1966), Fernald (1903), Lobdel (1937), Merrill and Chaffin (1923), and

Riddick (1955) included F. theae in their lists of coccids; while

Kuwana (1925) and MacGillivary (1921) presented keys to separate species

of Fiorinia, including theae.


Green's (1900) original description of F. theae was based on speci-

mens from Kangra Valley, India. He stated, "when this insect was first

submitted to me I supposed it to be merely a local form of the world-wide

F. fioriniae. A more critical examination shows me that it is quite

distinct. It differs from fioriniae in the absence of lateral lobes on

the pygidium; in the form of the antenna which has no stout spine, and

in the presence between the antennae of a proboscis-like projection. The

scale also is larger, stouter and more opaque. I now describe the species

under the name F. theae" (p. 3).

He described the female armor as "consisting of the indurated

pellicle of the second stage which completely encloses the adult

insect and is without any secretionary margin. Elongate; narrow;

with a moderately distinct median longitudinal carina. Colour bright

castaneous to dark ferruginous brown, median longitudinal area darkest;

opaque; not revealing the form of the insect beneath. First pellicle

colourless or very pale yellow; projecting from anterior extremity of

scale. Length 1.25 to 1.50 mm. Breadth 0.50 mm" (p. 3-4).

In his description of the adult females, he wrote:

Antennae close together, on anterior margin; each antenna consisting of
an irregular tubercle with a single curved bristle on one side. From
between the antennae springs a stout spatulate process . which is
not chitinous but of the same consistency as the surrounding parts of
the body. Margin of thorax and abdomen with a series of minute spin-
neret ducts opening on to small conical tubercles. Pygidium . with
a conspicuous median cleft, on the margins of which are situated the
moderately large serrate thickenings of the margin; second lateral lobes
obsolete. Spines normal, the dorsal series rather long; one pair spring-
ing from within the median cleft. Circumgenital glands in five groups;
the median and upper lateral groups together forming an almost continu-
ous arch. Median group with 4 or 5 orifices; upper laterals 10 to 13;
lower laterals 15 to 18. A very few circular pores with accompanying
ducts, on dorsal surface, near the margin. Length 0.50 to 0.75mm.
(p. 3-4).

Neither the male scale nor the male armor were represented in the material

examined by Green.

Sasscer (1912) published the first descriptive account of the male

armor. Later, many workers provided descriptions of females and males

and their armor, and keys to separate F. theae from other species of

Fiorinia. Das and Das (1962) were the first workers to describe the

immature stages of tea scale in detail.

Tippins (1970) described the second instar males of F. theae,

F. externa, and F. pinicola, and presented a key to separate these species

on the basis of morphological differences in the second instar males.


Tea scale is widely distributed in the warmer parts of the world

except Africa and Australia. According to Das and Das (1962), it is

present in all of the tea growing districts of India. Tapia (1968)

was the first to record the tea scale damaging camellias in Argentina.

In the United States, Sasscer (1912) stated that tea scale was present

in Alabama, the District of Columbia, Georgia, Louisiana, North Carolina,

and South Carolina, and Lawson (1917) reported it from Kansas. Tea scale

has also been recorded from Japan (Ferris, 1942), China, Taiwan, Mexico,

and Costa Rica (Merrill, 1953), and Sri Lanka (Ceylon) and the Philippines

(Sasscer, 1912).

F. theae is considered to have originated in the Orient. On the

basis of the number of described species, Takagi (1970) concluded that

the origin of the genus was evidently centered in eastern Asia, with most

of the species occurring in India through China to Japan. He stated that

none of the genuine members of the genus was native to the New World and

the Ethiopean region. Commenting on the introduction of the tea scale

in the United States, Sasscer (1912) remarked that "since no (tea) plants

have been introduced from Asiatic regions, all being grown from seed, it is

extremely probable that its (tea scale) introduction was through the agency

of the camellias, which have been for a number of years greatly in demand

as ornamental plants in this country" (p. 10).

Sasscer (1914) reported interception of F. theae at quarantine

in the District of Columbia in a shipment of mango plants from Java.

Host Plants

Tea scale is a polyphagous species and has, so far, been found to

feed on some 43 species of plants in 25 genera belonging to 16 families

(Table 1).

Economic Importance

Watt and Mann (1903) regarded the tea scale as a destructive pest

of tea in India, but Das and Das (1962) disagreed and maintained that

it was destructive only in rare instances. With the exception of

Argentina, where Camellia japonica was reported as seriously damaged

(Tapia, 1968), there are no published records describing tea scale as

a serious pest in parts of the world other than the United States.

Sasscer (1912) reported that in the northwestern Himalayas, tea scale

infestations on the olive, Olea grandulifera, frequently caused leaves

to turn yellow and drop off.

In the United States, specialists on insects of ornamentals are

unanimous in their opinion that scale insects are the most important

group of pests infesting camellias. Tea scale holds a prominent posi-

tion within the group and is, in all likelihood, the most important

pest of camellias (Kouskolekas, 1971). Sasscer (1912) reported that

tea scale was a serious pest of camellias and warranted frequent appli-

cation of control measures. English and Turnipseed (1940) considered

the tea scale as the most important pest of camellias and stated that

infestation by tea scale impaired the vitality of the plant and pro-

duction of bloom, thereby greatly reducing the sale value of the plants.

Merrill (1953) remarked that the tea scale was a serious pest in Florida

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and required frequent application of chemical insecticides. Kuitert

and Dekle (1972) considered it to be the most destructive pest of

camellias and hollies in Florida. Because of the importance of

camellias and hollies in landscape plantings in Alabama, Florida,

Georgia, and South Carolina, the tea scale is clearly one of the 10

most important pests of nurseries and ornamental shrubs in the south-

eastern United States.

Collins (unpublished) claimed that the natural enemies kept tea

scale under control in other parts of the world, and it was because of

the absence of natural enemies that the tea scale was an economic pest

in Florida.

My studies on tea scale, in which infested potted camellias were

held in a greenhouse from which all natural enemies were excluded, con-

firm Collins' view. Within weeks both sides of the leaves on these

plants were densely covered with colonies of tea scale. Subsequent

death of the plants was attributed to the curtailment of photosynthetic

activity of the leaves and ultimate loss of all foliage. Under field

conditions, leaf drop results from the scale infestations, which greatly

depreciates the ornamental value of the plants, but seldom causes



English and Turnipseed (1940) published a partial life history of

F. theae on camellia in Alabama. They stated that each female deposited

10-16 eggs which hatched within 7-21 days. Crawlers settled within 2-3

days and secreted thin white coverings. Later, they secreted great

quantities of white woolly filaments which covered the undersides of

leaves. Nymphs molted within 13-36 days after hatching. Second molt

occurred a week later. The females started laying eggs within 41-65

days, and life cycle was completed in 60-70 days.

Das and Das (1962) carried out comprehensive studies on the biology

of tea scale on potted tea plants in India. They found that pre-ovipo-

sition periods lasted 12-14 days. Females laid 22-43 eggs with an

average of 32.1 eggs per female. Males molted 4 times and completed

development in 22-24 days, while females molted 2 times and completed

the life cycle in 24-27 days. They also described the eggs, crawlers,

nymphs, and adults of both sexes in some detail.

Laboratory Rearing

Accounts of rearing tea scale in the laboratory on artificial hosts

are scanty. Nagarkatti (personal communication, 1977), Collins (unpub-

lished), and Chiu and Kouskolekas (1978) experienced considerable diffi-

culties in establishing laboratory colonies.

Nagarkatti (personal communication, 1977) commented that tea scale

colonies could be established on pumpkin if relative humidity was main-

tained at about 70%. Chiu and Kouskolekas (1978) tested a number of

artificial hosts and found that butternut squash was the most suitable

laboratory host for tea scale.

Natural Enemies

Watt (1898) reported on a fungus parasitizing a tea scale female

which was sent to him by Green,probably from Ceylon. He also commented

that the fungus was not present in India and that "it certainly would

be worthwhile to obtain a supply if the blight (tea scale) becomes

serious" (p. 325).

In the United States, Sasscer (1912) reported that the Darjeeling

tea,which was grown in moist lowlands in South Carolina, was frequently

found covered with a brown fungus which was apparently parasitic on tea

scale and was quite effective in holding the pest in check. He also

listed Chilocorus bivulnerus Muls., Microweisea misella Lec. (Coccinelli-

dae), and Cybocephalus nigritulus Lec. (Cybocephalidae) as predators of

the tea scale.

Das and Das (1962) stated that in India an aphelinid, Aphytis sp.,

parasitized the second instar nymphs. They noticed that about 38% of the

males and 4% of the females in the field were killed by this parasite.

They also reported Scymnus sp. and Jauravia quadrinotata Kapur (Cocci-

nellidae) as predators of the immature stages of tea scale and a fungus

that occasionally attacked second instar female nymphs and mature


Nagarkatti (personal communication) informed that Aphytis sp. and

Aspidiotiphagus sp. parasitized male nymphs, while a species of

Prospaltella attacked the female nymphs of tea scale in India.

In Florida, Collins and Whitcomb (unpublished) conducted a survey

of natural enemies and observed Aspidiotiphagus sp. nr. lounsburyi

(Berlese & Paoli) and Aphytis sp. nr. lignanensis (Compere) (Aphelinidae),

Aleurodothrips fasciapennis (Franklin) (Phlaeothripidae), Chrysopa

bicarnea (Banks), C. claveri (Navas), C. harrisii (Fitch), and

C. rufilabris (Burm.) (Chrysopidae), Cybocephalus nigritulus (Cybo-

cephalidae), Chilocorus stigma (Say), Lindorus lophanthae (Blaisdell),

and Microweisea coccidivora (Ashmead) (Coccinellidae), and a parasitic

fungus, Aschersonia aleyrodis (Webber) (Zythiaceae) associated with

tea scale.

Chemical Control

Of the literature concerning tea scale, by far the largest part

concerns chemical control. English and Turnipseed (1940), and Kuitert

(1949) in Alabama; Tippins (1969) and Kouskolekas (1971) in Georgia;

Kuitert and Dekle (1972) and Vaughan, Short and McConnell (1976) in

Florida; and Das and Das (1962) in India offered suggestions and

recommendations for suppressing the tea scale infestations by means

of insecticides. Kouskolekas (1973) and Kouskolekas and Self (1973)

conducted experiments designed to improve methods of application of

insecticides, while Tippins and Dupree (1973) evaluated the effective-

ness of different types of sprayers.

Aphytis theae (Cameron)


Cameron (1891) described an aphelinid which was "bred from the tea

scale insect Aspidiotus theae from Janygo (India)" (p. 3). His description

was based on a single specimen mounted in balsam that was so flattened that

its exact shape could not be seen satisfactorily. Although he placed the

specimen in the genus Aphelinus, but because of certain peculiarities, he

was confident that on further examination of fresh specimens the peculiari-

ties would prove to be of generic value and that the species would form

the type of a new genus.


On the basis of the original description, Compere (1955) transferred

Aphelinus theae to the genus Aphytis. He stated that Aphytis and

Aphelinus were not closely related to each other. He further elaborated

that members of the two genera differed from each other in basic structu-

ral characters of the abdomen and ovipositor. According to him, Aphytis

and Aphelinus differed also in the manner of oviposition which was cor-

related with fundamental differences in the structural features of the

abdomen and ovipositor. He observed that when Aphelinus oviposited, the

entire ovipositor everted and the whole apparatus swung outward. On the

other hand, when Aphytis oviposited, only the shaft swung downward, but

the other components of the ovipositor did not evert.

Rosen and DeBach (1977) redescribed Aphytis theae from a female

neotype and a male allotype, because the original type was lost, and

the description and figures presented by Cameron were very confusing.

They established the group Funicularis for the species of Aphytis with

5-segmented antenna and reduced mouth parts. The group includes Aphytis

funicularis, A. gordoni, A. ulianovi, and A. theae. A key for the iden-

tification of the 4 members of the new group was also presented.

Life Tables

Life tables were originally devised by demographers to study human

populations. They were used extensively in the field of life insurance

to determine the average expected life of clients. Pearl and Parker (1921)

introduced the life tables to ecologists by studying the population fluc-

tuations of Drosophila in the laboratory cultures. Leopold (1933) was

the first ecologist to recognize the value of the life tables in the

study of natural populations, and although he used the term "life

equation," he was indeed talking about life tables. Pearl and Miner (1935)

attempted to formulate a general theory of mortality of lower organisms

on the basis of life tables. However, they gave up the attempt after

realizing that the environmental detriments of life duration could not,

at least then, be disentangled from such biological detriments as gene-

tic constitution and rate of living. They pleaded for more observation-

al data, carefully and critically collected for different species that

will follow throughout the life of each individual in a cohort. Deevey

(1947) also recognized the difficulty of comparing life tables of dif-

ferent species because the basic data of life tables were sometimes of

the "age-specific" type and sometimes of the "time-specific" type; the

point of origin of life tables was also different-birth for mammals,

egg laying for insects, etc. He was the first worker to apply the life

tables technique to growing populations in nature. His paper includes

many examples of the life table format.

The first life table for an insect species was prepared by Morris

and Miller (1954) for the spruce budworm, Choristoneura fumiferana in

Canada. They were more interested in the causes of mortality at partic-

ular age intervals, and therefore used the stages of life cycle, i.e.,

eggs, larvae, pupae, etc., instead of dividing the age interval into

equal lengths of time. They also added the dxF column to the life table

which listed all quantifiable mortality factors at each age interval.

There are only 3 reviews in the literature that deal with the

development of insect life tables; the monograph by Morris (1963), the

textbook on ecological methods by Southwood (1966), and the review

article by Harcourt (1969).


As for the diaspids, life tables are available for only one species.

Samarasinghe and LeRoux (1966) prepared the life tables of Lepidosaphes

ulmi (L.) which is a univoltine species and undergoes diapause in the

egg stage during winter in Quebec, Canada. Atkinson (1977) proposed a

method of making life tables for Aonidiella aurantii (Mask.) in Swaziland

where the generations of the scale were more or less discrete in spring

but became increasingly overlapped as the season advanced.



The biology of tea scale was studied in the laboratory at 25 1,5 C

and 69 6.5% relative humidity. Colonies of the scale insect were es-

tablished on butternut squash using the method described by Chiu and

Kouskolekas (1978). Infested leaves of Camellia japonica were collected

at Wilmot Garden, Gainesville, Florida. In the laboratory these leaves

were lightly brushed to remove natural enemies, contaminants and male

tea scales, and then placed on cleaned butternut squash. After 4 days

the leaves were removed from the squash. During this interval enough

eggs hatched to allow completion of life cycle observations.

Details of development were obtained by daily removal of 20 indivi-

duals for microscopic examination. However, when nymphs became distin-

guishable as males and females, 10 individuals of each sex were examined

daily. Since the tea scale is a protandrous species, males emerge long

before females become receptive to mating. To ensure fertilization of

females some infested leaves containing abundant males near emergence

were placed around the squash to provide mates as the females became

sexually mature.

Fecundity of the females was estimated by counting the number of egg

shells, unhatched eggs, and eggs still present in the ovaries of 40 field

collected females.

The incubation period was studied by removing the last egg from under

the armor of actively ovipositing females. The removed eggs were kept in

covered plastic dishes for hatching. The incubation period of eggs

allowed to remain under the armor was also studied, Gravid females were

removed from leaves and placed in plastic dishes. Once removed, the

females could lay only 2 more eggs before dying. Laying and hatching

dates were recorded to determine the incubation period under more or

less natural conditions.


To study the possibility of parthenogenetic reproduction by the tea

scale females, 5 potted Camellia japonica plants of uniform size and vigor

were implanted with field collected gravid females. The females were

placed on pieces of cheesecloth and secured on the upper surfaces of.:

leaves with hairpins. Each plant was supplied with 100 females at 20

females per leaf. Plants were kept in different environators indivi-

dually set at temperatures of 15, 20, 25, and 350C. The relative

humidity was about 70%, with a light period of 15 hours and dark period

of 9 hours in each environator. The cheesecloth was removed after 10

days. Males were counted and removed as soon as they could be recognized.

Females were also counted but left on the leaves undisturbed to determine

if they could reproduce without fertilization. The number of immatures

settled on upper and lower surfaces of the leaves was also recorded to

evaluate the site preference. The experiment was repeated a second time,

but only 4 plants were used at temperatures of 15, 20, 25, and 300C.

Population Dynamics

Studies on population dynamics were conducted on the natural field

populations of tea sclae on Camellia japonica at Wilmot Garden, Gainesville,

Florida. The garden covers approximately 5 acres of a 10-acre green belt;

the remaining 5 acres are natural woodland. In addition to numerous

varieties of camellias, azaleas, and hollies, the garden contains many

other groups represented by one or more genera.

Populations of A. theae and male F. theae adults were studied in

the field. Five Camellia japonica plants growing in a row at Wilmot

Garden were selected for regular observations. Each week, 20 infested

leaves on each of the 5 plants were randomly selected and thoroughly

examined with the aid of a 10x lens. The number of A. theae and male

F. theae adults present on the leaves was recorded.

Since both A. theae and male F. theae adults migrate to other

locations, their populations were studied by another technique also.

At regular intervals, 5 infested leaves of C. japonica were picked up

10 times each month from September 1977 August 1978. The leaves were

placed in covered plastic containers, and kept in the laboratory for

7 days, and then placed in the freezer for a day to kill the emerged

adults to facilitate counting. The number of A. theae, male F. theae

adults, mites, thrips, Lindorus, and Microweisea, was recorded. After-

ward, the leaves were lightly brushed to remove male scales and other

contaminants, and an area of 3 cm2 was delineated in the center of each

leaf with a circular corer. The number of mature females present in the

3 cm2 area was recorded.

For studying the population structure of tea scale and its natural

enemies, 10 infested leaves containing new colonies of tea scale were

picked up at random during the month. In the laboratory, a 3 cm2 area

was marked in the center of each leaf and examined under a microscope.

Each tea scale individual was probed and examined to record its age

class (crawler, settler, etc.), sex, and whether it was dead or alive.

The data for life tables were obtained by counting the number of dead

and live individuals of all stages present in a 3 cm2 area per leaf on

10 leaves each month. Ovipositing females were regarded as the final

survivors of a cohort which contained all the dead members in previous

stages. The number of crawlers that settled successfully was obtained

by adding up numbers of all dead individuals backward in time. For

example, the total number of successfully settling crawlers = the number

of live ovipositing females + the number of dead females (preoviposition

stage) + the number of dead female nymphs + the number of male pupae +

the number of dead male nymphs + the number of dead settlers. The

number of crawlers is assumed to be the same as the number of eggs be-

cause all eggs hatch successfully due to protection provided by the

females. The amount of eggs was obtained by multiplying the number of

live ovipositing females in the previous generation with the average

fecundity value (28.82). The number of crawlers lost during dispersion

was calculated by subtracting the number of settlers from the number of




Biology of the tea scale has been studied in some detail by Das and

Das (1962) in India. An earlier less complete life cycle study was

made in Alabama by English and Turnipseed (1940). The following studies

on biology of tea scale were made in the Biocontrol Laboratory at the

Division of Plant Industry, Gainesville, Florida.


There is no recorded account of mating between male and female tea

scale. In the course of these studies, mating was observed only once,

when, during examination of an infested leaf, a male was seen attempting

to mate, but mating behavior could not be recorded in detail.

The male is probably attracted by a sex pheromone emanating from the

raised posterior end of the receptive female. Antennae of the male, which

are well developed and as long as the body, are probably used to detect

the pheromone.

The presence of a sex pheromone has so far been demonstrated in only

two species of armored scale insects. The first suggestion that males of

armored scale insects locate the females in response to sex pheromones

was that of Bodenheimer (1951), who noted the chemotactic response of

California red scale males to virgin females. The conclusive evidence

of the sex pheromones in the California red scale, Aonidiella aurantii

(Maskell), was provided by Tashiro and Chambers (1967). Their results

were confirmed in the laboratory by Rice and Moreno (1969) and in the

field by Rice and Moreno (1970). Later on Moreno et al. (1972) also

demonstrated the presence of a sex pheromone in the yellow scale,

Aonidiella citrina (Coquillett).

Males of armored scale insects are polygamous. Tashiro and Moffitt

(1968) conducted laboratory tests on Aonidiella aurantii and found that

individual males were able to inseminate up to 30 females. The average

number of females fertilized per male was 11.9.


Eggs are extruded from the body of the female, but retained under

the armor, and arranged in 2 rows, probably with the aid of the pygidial

plates and lobes. Before depositing any eggs the female occupies the

greater part of the space under the armor, but as eggs are laid the body

begins to shrivel, ultimately occupying only a small part of the anterior


Das and Das (1962) stated that eggs were deposited singly at intervals,

at a rate of not more than 4 per day; the rate was highest at the be-

ginning but declined gradually. By following the oviposition activity

of a single female they found that 39 eggs were laid in 21 days.

Oviposition by tea scale is typical oviparity. In oviparous insects

the eggs are extruded from the genital tract and deposited outside the

body. In ovoviviparous insects the eggs are retained in the genital

tract until larvae hatch or are ready to hatch. In the case of tea

scale, the eggs are laid outside the genital tract but retained under the

armor. Thus parental care and a suitable incubation environment is pro-

vided for the eggs to a certain extent.


Fecundity of the tea scale was calculated by counting the number of

eggshells, unhatched eggs and eggs still present in the ovaries of 40

field collected females (Table 2). Females lay from 17-43 (average

28.82 7.82) eggs during their life span.

In India, Das and Das (1962) studied the tea scale fecundity by

daily removal of eggs from the posterior part of the armor. Contending

that the method did not appreciably affect the oviposition potential,

they found that the average fecundity of 14 females was 29. They also

counted the eggshells under the armor of 15 females that had met natural

death and recorded 22-43 (average 32.1) eggshells per female. English

and Turnipseed (1940) reported from Alabama that tea scale females laid

10-16 eggs. Vaughan (1975), commenting on this discrepancy between

fecundity figures given by the above authors, noted that Das and Das

(1962) conducted their studies on potted tea plants in the laboratory,

whereas English and Turnipseed (1940) observed natural field populations

on camellias, and believed this explained the discrepancy. However, the

more probable explanation for this discrepancy may relate to the amount

of space under the female armor. This can accommodate not more than 17

unhatched eggs. Room for additional eggs is made when the earlier eggs

hatch and crawlers emerge. The casual observer can easily and errone-

ously conclude that the maximum number of unhatched eggs present is the

actual total fecundity.


The newly laid egg is shiny yellow, more or less oval in shape and

broader at one end. It measures 0.21 mm in length and 0.13 mm in width

at the broadest point. Near hatching, the color changes to dull yellow,

and the pinkish eyes can be seen through the chorion. Shortly before

hatching, the fully formed crawler is visible through the flattened

eggshell. The crawler hatches out by splitting the chorion, and empty

Total Fecundity

Female # # Eggshells #

of tea scale, Fiorinia theae

Eggs OSO* # Eggs ISO** Total Eggs

- outside the ovary
- inside the ovary

Mean = 28.82
Std. Dev. = 7.82

eggshells are pushed to the rear and compressed in rows, one on either

side in the posterior space under the armor.

Incubation Period

The incubation period of the 14 eggs that were removed from under

the female armor ranged from 10-14 days (average 11.2 1.3). In the

case of the eggs that were left undisturbed under the armor, the incu-

bation period for 10 eggs lasted for 9-10 days (average 9.8 0.4). The

latter figures are closer to the natural conditions and indicate that

the female provides not only protection and care but also a suitable

environment to incubate the eggs. The difference in the two incubation

periods was statistically significant at a 95% level.

According to English and Turnipseed (1940), temperature appears to be

an important factor in determining the length of incubation periods.

They recorded an incubation period of 7-21 days for the tea scale. Das

and Das (1962) working in India, reported that tea scale eggs hatched in

4-6 days at 30-32.70C and 73.5-80.7% relative humidity.

Crawler (Free-Living First Instar)

Immediately after hatching, the crawler emerges from under the female

armor through the raised posterior end. It is flat and somewhat oval in

shape, yellow in color, and measures 0.26 mm in length and 0.14 mm in

width. It has 6 well-developed legs and two normal antennae.

After emergence, the crawlers move around for 1-4 days. On finding a

suitable place, they insert the mouth part stylets into the plant tissue

and settle down. Crawlers from the same female tend to settle in close

proximity to each other, forming a new colony.

As in the other diaspids, the crawler represents an important stage

in the life history of the tea scale, since only through crawlers can

infestations actively spread. They are said to be dispersed by other

insects and birds, but the dispersal of crawlers by means of the often

airborne silken mass secreted by male nymphs is also a possibility. Al-

though the amount of dispersion by this method has not been estimated,

some live crawlers were found entangled in masses of gossamer-like waxen

thread flying about on windy days. Another method of dispersal and colo-

nization is, of course, through the transfer of infested host material.

No sex-differentiation can be made at crawler stage. However,

Ferris (1942) believed that some armored scales might exhibit some dif-

ferences at this stage, and Stickney (1934) observed an additional spur

on the legs of the male of first instar larva of Parlatoria blanchardi

Targioni-Tozzetti. Stoetzel and Davidson (1974) stated that sexual di-

morphism in the crawlers of certain aspidiotine species could be differen-

tiated by the difference in the dorsal setal patterns of both sexes.

Settler (Sedentary First Instar)

Soon after successfully inserting their stylets, the crawlers change

into settlers. Both the free-living crawler and the sedentary settler

belong to the same stage, the first instar. In other words, the first

instar has 2 phases, being first motile then sedentary. The first in-

star changes into the second instar (first molt) after 10 days, i. e.,

14 days after hatching. As in other diaspids, the legs disappear and

antennae are much reduced during the first molt.

Second Instar (Male) Nymphs

The second instar nymph is yellowish in color and measures 0.53 mm

in length and 0.25 mm in width. The armor is thin and felted white. The

pale yellow exuvia remains attached to its anterior end. This stage

molts into third instar after about 11 days, i. e., 25 days after hatching.

Third Instar (Male) Prepupa

At this stage the rudimentary wing pads become visible. The prepupa

is 0.68 mm in length and 0.35 mm in width. The armor is almost rectang-

ular with parallel sides. There is a prominent ridge along the mid dorsal

line. One less-prominent ridge is also present laterally on either side.

Because of the presence of the rudimentary wing pads, this stage is termed

a prepupa. The prepupa molts into pupa in 5 days, i. e., 30 days after


Fourth Instar (Male) Pupa

In the beginning, the color of the pupa is yellow like that of the

prepupa, but later the color changes to orange-yellow. Wing pads become

elongated and a conical stylus develops at the end of the abdomen.

The pupa, including the stylus, measures 0.72 mm in length and

0.21 mm in width. Armor is similar to that of the third instar. The

pupa changes into a pharate adult in 2 days, i. e., 32 days after

hatching, and, on day 34, the adult male emerges from under the posterior

end of the armor.

Adult Male

Adult male measures on an average 0.72 mm in length and 0.21 mm in

width, with a wing span of 1.4 mm. It is a gnat-like creature of orange-

yellow color, and has one pair of glassy, white forewings with reduced

venation. The hind pair of wings is represented by a pair of halteres.

A long stylus, or penis sheath, is present at the end of the abdomen.

Tea scale males are probably nocturnal, as are the males of other

armored scales (Bodenheimer, 1951). Since the mouth parts are non-func-

tional, adult males do not feed, their only purpose being to fertilize

the females. According to Das and Das (1962), adult males live for 2-3 days.

Second Instar (Female) Nymph

After the first molt, a thin membranous covering is formed over the

body of the female nymph. As in the male, pale yellow exuvia of the

first stage remains attached to the anterior end of the female armor.

In the early second instar, the body is light yellow and measures 0.59 mm

in length and 0.28 mm in width. This stage lasts for 6 days, i. e., 20

days after hatching. Following the second molt, the skin of the second

instar female is not shed but remains intact, forming a cover that com-

pletely encloses the adult insect which shrinks, thus leaving a vacant

space at the posterior end of the armor.

Female (Mature)

The body of the female starts increasing on day 22 and becomes fully

elongated by day 26.

The covering of the female is at first thin and light yellow in

color, but after sclerotization becomes hard and covered with a thin film

of wax. Sclerotization occurs between day 31-36 after hatching. The

armor is narrow and elongate with a distinct median longitudinal carina,

and is dark brown, the median longitudinal area being the darkest. The

female armor measures 1.2 mm in length and 0.43 mm in width. The yellow

female lies under this protective armor. Because of shrinkage to provide

room under the armor for the forthcoming eggs, the adult female is shorter

in length than the mature nymph.

During maturation, the armor of the female adheres firmly to the leaf

surface. Upon reaching maturity on or about day 46, the posterior end of

the armor becomes slightly raised. This change may be for emanating

pheromones to attract males. Raising of the posterior end may serve some

additional purposes as well, such as facilitating the intromission of the

penis and egression of crawlers.

Eggs become mature in the ovaries in about 62 days after hatching,

and females start laying eggs on or about day 65, completing the life

cycle. English and Turnipseed (1940) reported that tea scale completed

its life cycle in 60-70 days in Alabama. In India, the life cycle was

completed in 24-27 days (Das and Das, 1972).

During the maturation of females, it was noticed that some individuals

had liquified bodies under the armor. No such individual was found when

females had matured. This liquified stage may be an interval of re-organ-

ization of nymphal body into adult body, i. e., an incipient pupal stage.

Comprehensive studies, however, are required to confirm this finding.

The asynchronous maturation of males and females of the same brood

effectively prevents the fertilization of females by males of the same

colony. Males emerge much earlier and are extremely short-lived; when

females of the same brood mature, males are not available to fertilize

the females in the laboratory colonies. To establish successful cultures,

a succession of implantations at suitable intervals, preferably weekly,

is essential to ensure the availability of males to fertilize the females.


Results of the experiments indicated that unmated females of tea scale

are unable to reproduce, because no crawlers developed on any of the plants.

The plant kept at 350C was killed by heat; therefore no plant was used at

this temperature in the replication of the experiment.

Sex-ratio in the absence of natural mortality factors was 1.9:1 at

150C, 1.8:1 at 20 and 25'C, and 1.4:1 at 30C.

A multiple regression analysis of the data indicated that the temper-

ature (15-30C) failed to produce any effect on the sex-ratio.

Relative survival of the immatures at different temperatures was also

evaluated. Maximum survival was observed at 250C, while the lowest survival


occurred at 300C. Data are presented in Appendix 1. Number of im-

matures present on the upper and lower surfaces of the leaves indicated

that the lower surface was preferred by tea scale. Of 865 nymphs ex-

amined, 315 (36.4%) had settled on upper surfaces, whereas, 550 (63.6%)

had settled on the lower surfaces. There were, on an average, 8.75 nymphs

per leaf on the upper surfaces and 15.28 nymphs per leaf on the lower sur-

faces (Appendix 2). A 't' test indicated that the difference in these

values was significant at 95% level of confidence.

Population Dynamics

General Characteristics of Tea Scale Populations

Tea scale colonies, in general, have a whitish appearance caused

by the white armors and the profuse white wax secretions of the males.

This characteristic cottony mass usually occurs on the under side of

the leaves and, in heavy infestations, hangs from the leaves, especially

on the lower parts of the plants.

On camellias the tea scale usually behaves as a stenomorous species

because the only part of the plant attacked is the leaf. However, in

cases of heavy infestations, some individuals may be found on the upper

side of the leaves as well as on the buds. In the greenhouse, where

natural control is non-operative, both lower and upper sides of camellia

leaves became profusely covered with tea scale colonies. In nature, the

upper surface of the leaves is kept clean probably by the rain, sunlight,

and various natural enemies.

During 1977 some 10,589 leaves on 1320 randomly selected twigs of

Camellia japonica at Wilmot Garden were examined for tea scale infesta-

tions. Of these, 1450 (13.69%) were found to be infested. Rate of in-

festation varied from 1.75-88.14% of leaves on individual plants.

Tea scale is a polyphagous species with a host list consisting of

43 species of plants in 25 genera belonging to 16 families. In spite of

the long host plant list, it occurs in high numbers only on camellias

and hollies, and on these plants it exists virtually without any compe-

tition from other phytophagous insects. It may be that on these hosts

it eliminates the competitors, while on other host plants, it is elimi-

nated; for instance, as on Euonymus sp. by Coccus hesperidum and on

Citrus sp. by whiteflies.

The life history is markedly different in both sexes. Except for

the egg and possibly the first instar, all other stages, including adults,

exhibit sexual dimorphism. During most of its life span, tea scale re-

mains attached to the leaf. Only crawlers and male adults are the mobile

stages. Both of these stages, however, last only for a short time. Non-

feeding stages include the egg, crawler, and pre-pupa (third instar male

nymph), and male pupa, while the feeding stages include the settlers

(sedentary first instar), male nymphs, and all stages of the female.

The most conspicuous sign of feeding is the irregular, yellowish

splotches on the upper surface of the leaves. These discolored areas

correspond to the tea scale colonies present directly on the lower side,

and are obviously caused by their feeding on the leaf tissue. On heavily

infested leaves, these splotches coalesce and the entire upper surface

of the leaves becomes mottled or discolored. Sometimes males and females

were found developing on portions of leaf that had earlier been nibbled

by some caterpillars. This obviously means that stylets are inserted

into the vascular strands of the leaf for feeding.

Tea scale is a multivoltine species with several overlapping gen-

erations breeding more or less uninterruptedly throughout the year in

Florida. Though cold weather decreases developmental activity, hatching

does occur during the winter. During any part of the year all develop-

mental stages can be found in the field. In the winter, camellias and

hollies appear to be heavily infested. This is because no new foliage

appears during winter and crawlers must settle on the same leaves near

the mother colonies. Crawler dispersal may also be reduced by effects

of temperature during the cold season. In India, Das and Das (1962) also

found the same pattern of higher levels of infestation during winter.

Tea scale populations are characterized by highly male-biased sex-

ratios and marked sexual dimorphism; the males being white, soft-bodied,

and ultimately emerging as winged adults, while the less conspicuous,

heavily armored females remain in place as neotenic adults. These

attributes would appear well suited to divert attention of predators

away from the less expendable and better protected females. Aspidioti-

phagus sp. nr. lounsburyi is the only native parasite that attacks females

but it is very rare, killing no more than 1.25% of the females by direct

parasitization and destroying about 19% of the females by host feeding.

As a result of diversion of predation to the more numerous soft-bodied

males, and the resistance of the less conspicuous, heavily armored females

to both predation and parasitization, and protection of the eggs during

incubation, the tea scale has developed a remarkably successful strategy

for survival.

Tea scale is a protandrous species, males emerging long before the

females of the same brood become sexually mature. Despite the shorter

developmental period, males molt 4 times while females molt only twice.

This asynchrony in the life cycles of the sexes creates some problems

in the study of population dynamics. In the interest of clarity and

consistency, the following simplified terminology has been adopted:


Crawler free-living first instar nymph

Settler sedentary first instar nymph

Male nymph second and third instar nymph

Female nymph second instar nymph with unsclerotized armor

Male pre-reproductive intact pupa (fourth instar)

Female pre-reproductive second instar with fully sclerotized
armor, pre-oviposition stage

Male reproductive emerged adult (empty pupal armor)

Female reproductive ovipositing female

Populations of Adult Males

The population surveys of adult male tea scale were carried out at

Wilmot Garden during March 1977 through August 1978. Under field con-

ditions, males began to emerge in April when new foliage was appearing

on host plants. Adults were present in fluctuating numbers during April

January, with peaks of population occurring in May, July, and November.

The curves representing the adult male populations shown in Fig. 1

and Fig. 2 do not conform due to the difference in sampling techniques.

In Fig. 2 the curve for adult population indicates the presence of males

throughout the year because of continuous emergence of males from pupae

in the laboratory. In Fig. 1 the curve represents the number of adult

males observed on leaves and shows an absence of males during February -

April, indicating a disruption of emergence from pupae in the field.

Male populations were greatly affected by the destruction of nymphs

due to parasitism following introduction of Aphytis theae and Aspidioti-

phagus sp. During September December 1977, when A. theae was present,

male populations were much smaller than those of the corresponding months

in 1979 when A. theae was no longer present (Table 3). Average number

of adult males emerging from 200 leaves (50 leaves per month) was 650

in 1977, and 1625 in 1979. A 't' test indicated that the difference in

means was statistically significant at 95% level of confidence.


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Comparison of Numbers of Male F. theae Adults Emerged from Colonies on
Leaves of Camellia japonica at Wilmot Garden in 1977 and 1979.

Number of males emerged per 50 leaves
Month 1977 1979

Sept. 295 1439

Oct. 786 2071

Nov. 675 1398

Dec. 843 1591

Total 2599 6499

Mean 650 1625

Populations of Mature Females

Populations of mature females fluctuated through the season. Peak

of population occurred during January (Fig. 3). This peak was the result

of decreased reproductive activity which causes accumulation of females

during winter. The percent of ovipositing females in the total female

population varies from 49.24 in November to 66.48 in April, with an

average of 56.54 6.1%. The number of mature females in pre-oviposition,

oviposition, and post-oviposition is given in Table 4.

Mortality in the mature females occurs mostly in the pre-oviposition

stage by parasitization and host feeding of Aspidiotiphagus sp. nr.

lounsburyi, and ranges from 14.28% in May to 23.94% in October, with an

annual average of 19.7 3.1%.

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Month Pre-Oviposition
live dead

Sep. 77 20 38

Oct. 77 12 51

Nov. 77 53 41

Dec. 77 61 41

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Introduced Parasites

Aphytis theae (Cameron)

A. theae was introduced into Florida from Jorhat, India,in 1976.

It was successfully cultured in a greenhouse and then released at several

locations in Gainesville during May 1976. Population surveys during the

summer indicated that it was rapidly increasing in numbers and dispersing

to other locations. However, with the advent of winter, its populations

started declining, and during late winter only dead pupae were encountered

in the field, indicating that the parasite failed to survive the winter

(Fig. 5).

Re-colonization of A. theae was initiated in March 1977. For this

purpose infested Camellia japonica leaves harboring pupae and adults of

A. theae from the greenhouse culture were securely placed on infested

leaves of C. japonica at Wilmot Garden. Results of intensive surveys

indicated a rapid increase in population numbers reaching a peak in

October 1977. A sudden decline in population occurred during the second

week of November when adults were killed in large numbers by freezing

temperatures at night. The decline in population continued until

January (Fig. 1). No adults were seen in the field during January -

March. However, A. theae adults did emerge in the laboratory from the

50-leaf sample collected in January and March. No adult emerged from

the material sampled in February.

Live larvae and pupae were present in the field during January and

February, but most of the live pupae seen during this period had been

denuded (host scale removed) by the predators. A few eggs were recorded

in March, indicating that A. theae had barely survived the winter of

1977 1978. This seems to have been a consequence of momentum imparted

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by the extremely high numbers of A. theae present in late fall, the small

percent surviving winter mortality being sufficient to maintain a viable


The larger population present in the fall of 1977 may be explained

by the date of re-colonization which was about 6 weeks earlier than the

first release in 1976. This provided time for about 3 more generations

during the 1977 season.

During 1978, adults were not seen in the field until late May

(Fig. 1). The subsequent pattern of population increase was similar to

that of the two preceding seasons; however, intensive survey was termi-

nated in August 1978. No adult of A. theae was seen in the field during

January March 1979, and later observations revealed that A. theae

failed to survive the winter of 1978 1979.

Mortality of A. theae larvae ranged from 0 in September to 57.14%

in February. Average larval mortality was 7.16%. Pupal mortality

ranged from 8.33% in June to 100% in March. The major cause of larval

and pupal death was cold, seemingly accentuated in the case of pupae by

activity of predators which resulted in removal of the protective host

scale cover from many of the parasites. Details of larval and pupal

mortality are presented in Table 5.

The failure of A. theae to survive in Gainesville can be attributed

to the winter weather conditions. A comparison of 20-year averages of

minimum temperatures and rainfall in Jorhat (India) and Gainesville

(Florida) is presented in Fig. 6. The curves for temperature and

rainfall indicate that winters are cooler and wetter in Gainesville.

Another striking feature exhibited by the temperature curves is the

straight line representing the months from December through February

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at Gainesville and indicating a prolonged period of low temperatures.

The corresponding portion of the Jorhat temperature curve indicates that

winter temperatures are somewhat warmer and the period of adverse temper-

atures is of shorter duration. This difference no doubt accounts for

failure of A. theae to persist at Gainesville.

In the field, mating was observed in the morning and forenoon.

In the laboratory, 10 matings lasted for 25-53 seconds with an average

of 39.5 seconds. Egg laying occurs during evening hours. The egg is

deposited under the armor on the dorsal side of the second instar male

nymph. On hatching, the parasite larva migrates to the ventral side

and starts feeding ectoparasitically. On completion of feeding, it

molts into the pupal stage; two black fecal pellets (meconia) are

excreted before the molt. At this stage the head of the parasite pupa

can be seen protruding from under the posterior end of the host armor.

Adults emerge after a week. For emergence, adults do not drill any

holes, but crawl out from under the host armor. The life cycle is com-

pleted in about 2 weeks.

Because of the atrophied mouthparts, adult A. these is not capable

of host feeding.

Aphytis theae exhibits host relationships of more than usual

interest as it shows a marked preference for parasitizing male nymphs

of its host species. While originally collected from tea scale it is

not in any sense restricted to this species. Near the end of the 1977

season it was observed to attack male nymphs of the false oleander

scale, Pseudaulacaspis cockerelli (Cooley) as readily as those of tea

scale. A. theae appears, therefore, to be a representative of a group

of scale parasites that are adapted to exploit the male sex of diaspine

scales. This kind of host-parasite association may represent another

example of resource partitioning (Schoener, 1974) in which other related

parasite species are restricted to the host females. Direct competition

between parasites would thus be minimized by host sex rather than host

species specificity. As an alternative explanation, restriction of a

parasite such as A. theae to males of host species may have evolved

as regulative mechanicism facilitating coexistence of host and parasite.

Such sex specific parasites also afford an interesting opportunity

to investiage the effect of male mortality on host populations. Although

there is no documented evidence that such mortality has significant

generation to generation effects on host populations, two possible

effects can be hypothesized. First, the population of host species will

decline due to reduced mating. This effect would most likely occur if

females were polyandrous and normally the more numerous sex. Secondly,

the host species might in due time evolve a uniparental strain.

Failure of A. theae to produce any effect on tea scale populations

in spite of high male mortality can be attributed to the fact that male

tea scale, like other male diaspids, is polygamous, and normally present

in numbers that considerably exceed the number of females.

Tashiro and Moffitt (1968) proved that males of the California

red scale are polygamous. They found that a single male could fertilize

up to 30 females, with an average of 11.9 females per male.

Effect of A. theae on tea scale populations was studied during

September 1977 through August 1978. This period can be divided into

two parts. First, the period lasting from January through May when

A. theae was inactive due to winter, and second, the period lasting

from June through December when A. theae was active. Comparison of

numbers of live male nymphs in the two intervals was made. On the average,

there were 167 live male nymphs per 30 cm2 of leaf surface present during

January through May, whereas, the corresponding number during June through

December was 80. A 't' test indicated that the difference in numbers of

live male nymphs was statistically significant at 95% level of confidence.

A similar test on numbers of female nymphs present in the respective

periods indicated a statistically insignificant difference.

Comparison of numbers of male F. theae emerging from the colonies

present on 50 leaves during each month of the 2 seasonal periods was

also made. On the average, 1320.8 males per 50 leaves emerged during

January May, and the corresponding numbers during June through

December was 699.2. The difference was found to be statistically sig-


On rare occasions adults of Aphytis sp. nr. lignanensis were found

in the 5-leaf samples. These were probably chance visitors which

happened to be present on the leaves at the time of collection. There

are many Aphytis species attacking different species of armored scales

in Florida, but there is no local species of Aphytis specific to tea

scale in North America. A systematic search of Asian areas where the

tea scale originated would almost certainly reveal a species of Aphytis

adapted to fill this vacant niche.

Aspidiotiphagus sp.

Aspidiotiphagus sp. (Indian) is uniparental species; no males are

present in this species, and unfertilized females produce only female

progeny. A culture was established in the laboratory at Gainesville

using Aspidiotus nerii Bouche as host which was in turn bred on Irish

potato tubers.

To record the duration of life cycle and fecundity, 30 females were

released individually on A. nerii on potatoes. Females were observed

ovipositing, and took 70-140 (average 103) seconds to deposit a single

egg. The progeny started emerging after 28 days. Each female produced

11-41 (average 22.1 8.5) daughters. When Aspidiotiphagus sp. was re-

leased on tea scale on potted camellia in the laboratory, females were

seen ovipositing in both male and female nymphs of tea scale.

Field releases were made in Gainesville during January June 1977.

No data on population dynamics of tea scale were collected during

September 1978 August 1979, but observations were resumed in September

1979 and carried out through December 1979.

During this period, Aspidiotiphagus sp. emerged in abundant numbers.

From a 50-leaf sample per month, 204 Aspidictiphagus sp. adults emerged

in September, 398 in October, 247 in November, and 55 in December. The

percent of parasitism on males was 12.4 in September, 16.1 in October,

15.0 in November, and 3.3 in December 1979. The decrease in numbers was

due to overwintering of the parasite in the pupal stages. All emerging

adults were females. Adult parasites emerge from male nymphs of tea

scale by making a hole on the dorsal side of the armor.

Although re-colonization of A. theae and releases of Aspidiotiphagus

sp. (Indian) were made during the same period in 1977, there was no evi-

dence that the latter had established until September 1979. In the

meantime, A. theae increased rapidly during 1977 1978, and maintained

high population levels until winter. This indicates the superiority of

A. theae as a competitor of Aspidiotiphagus sp., which did not increase

to detectable levels until relieved of competition from A. theae.

Life Tables

In developing the life tables, 5 age intervals are used, namely,

egg, crawler, settler, pre-reproductive, and reproductive. Since tea

scale exhibits distinct sexual dimorphism, nymph, pre-reproductive, and

reproductive age intervals are divided into male and female categories.

Egg. The number of eggs was estimated as the product of the aver-

age fecundity value (28.82) and the number of live ovipositing parent

females. Since the number of such females was not known for September,

1977, it was arbitrarily calculated as the average number of live ovi-

positing females for 11 months (October 1977 August 1978). This is

the only assumed number in the life table figures for September, 1977.

All other numbers in the rest of the life tables are real figures. All

eggs under the female armor hatched successfully and emerged as crawlers.

Crawler. Since crawlers are mobile, their number cannot be

accurately estimated by the sampling method used to calculate numbers

of the sedentary stages. Any other sampling technique employed to esti-

mate the number of crawlers would have been statistically inappropriate.

Because all eggs hatch successfully, their number also represents the

number of crawlers.

A large number of crawlers die before settling. They are probably

blown away by wind, washed away by rain, and lost by misadventure during

dispersal and leaf fall. Their mortality ranged from 62.41% in July to

86.44% in September with an annual average of 77.35%. This high early

mortality is a characteristic of all species with free-living and exposed

individuals. Samarasinghe and LeRoux (1966) found the same trend of

crawler mortality for Lepidosaphes ulmi (L.) in Quebec, Canada.

Settler. These are sedentary individuals with thin armors. As

sex differentiation is not apparent at this stage, the numbers in the

lx and dx columns represent the density of settlers of both sexes. They

are preyed upon by a phytoseiid mite, Iphiseides sp., and a thrips,

Aleurodothrips fasciapennis (Franklin) (Phalaeothripidae).

The extent of mortality caused by each species could not be ascer-

tained. Combined mortality caused by these 2 predators ranged from

16.50% in July to 36.76% in October with an annual average of 24.08%.

Nymph. Dimorphism is quite distinct at this age, and male and

female nymphs can be distinguished from each other.

Male nymphs: This stage includes both second and third instar

nymphs. The major cause of mortality was the temporarily established

introduced parasite, A. theae. The percentage of nymphs parasitized by

A. theae ranged from 8.78 in May to 58.52 in December with an annual

average percentage of 37.47. However, this parasite was not most active

in December as indicated by the rate of parasitism for that month. The

figures were obtained by counting the number of dead nymphs containing

all stages of the parasite, namely, eggs, larvae, pupae, and exuviae of

the emerged adults. Peak numbers of the adult parasite were observed

during October, but populations started declining with the advent of


Major predators feeding on male nymphs are 2 species of coccinellids,

namely, Lindorus lophanthae (Blaisdell) and Microweisea coccidivora

(Ashmead). These are regularly present among the tea scale colonies.

Usually a single larva of L. lophanthae is found feeding on tea scale.

It ploughs through the colonies, denuding and destroying more male

nymphs that it feeds on. This habit of Lindorus probably slows down the

growth rate of Aphytis populations because of indiscriminate destruction

of unparasitized as well as parasitized tea scale nymphs. Most of the

dead pupae of A. theae in winter had been denuded by Lindorus. On the

other hand, 2 or more larvae of Microweisea feed together. This cocci-

nellid consumes the host nymphs individually by making an irregular hole

in the male armor.

The peaks of Lindorus and Microweisea populations more or less

alternated with each other during the season (Fig. 2). This may be

the result of competition between the 2 species. A multiple regression

analysis indicated that variations in the populations of male tea scale

were caused by the activity of these 2 predator species acting together

as well as individually.

A complex of Chrysopa spp. and 2 coccinellids, Cybocephalus sp. and

Chilocorus stigma (Say), which feed on male nymphs, are also occasionally

present among the tea scale colonies. But because of their extremely

low populations and irregular occurrence during the season, these

predators did not play any significant role in the population dynamics

of tea scale. The combined mortality of male nymphs caused by predators

ranged from 3.40% in September to 25.09% in May, with an annual average

of 13.22%.

A considerable number of male nymphs were found dead but the cause

of death could not be ascertained. Diseases and some other physiological

reason may be responsible for this mortality which ranged from 4.76% in

September to 34.31% in February, with an annual average of 14.08%. The

highest rates of mortality occurred during January March indicating

that cold may be the major cause of death in this category.

Female nymphs: This stage includes both unelongated and elongated

nymphs with unsclerotized armor. A local species of parasites,

Aspidiotiphagus sp. nr. lounsburyi (Berlese and Paoli) (Aphelinidae),

attacks the female nymph. It oviposits in the body of the second instar

nymphs, and the larva feeds endoparasitically. Pupae are black and can

be seen through the thin covering of the dead host. A round hole near

one end of the unsclerotized armor is made by the emerging adult. A

few hosts with fully sclerotized armor also contained emergence holes.

This parasite is very rare with rates of parasitization ranging from 0

in May to 3.93% in November with an annual average of 1.57%.

Female nymphs were also parasitized by A. theae. Rate of parasitism

by A. theae on female nymphs ranged from 1.37% in June to 5.06% in July,

with an average of 1.05% during the year. Death in the majority of female

nymphs can be attributed to diseases. Bodies of such nymphs became liqui-

fied under the armor. In later studies, it appeared that liquification

might be due to reorganization of the body tissue preliminary to pupation.

Nevertheless, in the absence of experimental evidence to the contrary,

these nymphs have been assumed dead due to disease. Mortality by this

cause ranged from 11.87% in October to 31.01% in July, with an average

of 21.46% during the year.

Pre-reproductive. Male pre-reproductives: This is the fourth instar

or pupal stage. Although neither A. theae nor predators were found

attacking the pupae, many dead individuals were encountered in the field.

Most of the dead pupae had died as pharate adults. Direct cause of

death was desiccation caused by the denudation of pupae by the predators,

which removed the armors while probing for food but left the pupa intact.

Mortality in male pupae ranged from 4.05% in June to 48.39% in February,

with an annual average of 15.09%. Very high mortality in February

indicates that cold may also be responsible for death of pupae. In

population surveys, the pupal stage is the most appropriate index of

population density. Duration of this stage is very short and, therefore,

the extent of generation overlap is minimal.

Female pre-reproductives: In this stage females have fully sclero-

tized scales. A large number of females were found dead apparently be-

cause of hostfeeding by Aspidiotiphagus sp. nr. lounsburyi. Some of

the dead female nymphs may have died of this cause also. It is possible

that Aspidiotiphagus adults may be parasitizing the nymphs but hostfeeding

on pre-reproductives. Rate of mortality ranged from 18.80% in April to

29.02% in January with an average of 26.21% during the year.

Reproductive. Male reproductive: This stage was sampled by counting

the number of empty pupal armors which indicated the successful emergence

of male adults. Cause of death is recorded in the life tables as senility

which, in fact, means natural death after mating.

Female reproductive: All ovipositing females that survived to re-

produce are included in this category. Generation mortality ranged from

92.65% in February to 96.92% in April with an annual average of 95.15%.

Population trend index (I) is the most practical measure of popu-

lation changes obtained from the life tables. It was calculated as the

ratio of number of eggs in 2 successive generations. Stable populations

have population trend index (I) value equal to 1. A value of (I) greater

or less than 1 indicates increasing or decreasing population trends.

Population trend index (I) of tea scale varied from 0.70 in

November to 1.39 in October with an annual average of 0.98. This shows

that on an average tea scale populations were on decline during the year

1977 1978. This finding is in agreement with the fluctuating popu-

lation trends reported by other workers for all species studied to date.

This should occasion no surprise as all species have good years and bad


To determine the relationship of variation in population trend

index (I), and other variables such as sex-ratio, male and female densi-

ties, and the generation mortality, data were subjected to a multiple

regression analysis. The results of analysis showed that the generation

mortality was the main factor responsible for fluctuations in the values

of population trend index (I).

The column headings of the life tables (Table 6) are similar to those

proposed by Morris and Miller (1954) except that the last column, labeled

as 100dx/Nl represents generation mortality. A brief description of

column headings follows:

x = The age interval

1x = The number alive (1) at the beginning of the
age interval (x)

d F = The factor responsible for the death of indi-
viduals (dx) within each age interval

dx = The number dying (d) within the age interval
stated in the (x) column

100qx = Percentage mortality (dx as percentage of ix)

100dx/N1 = The percentage of generation mortality

The figures in lx and dx columns represent the number of individuals

per 30 cm2 of the infested leaves; figures in other columns were calcu-

lated from these numbers. In d F column, parasites are mentioned in-
dividually by name, whereas, the predators are grouped together. This
dividually by name, whereas, the predators are grouped together. This


is because it is possible to distinguish deaths caused by each species

of parasites, while it is not possible to quantify the damage caused by

the individual species of predators.

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K-Factor Analysis of Life Tables

Varley and Gradwell (1960) described a method of analyzing life

table data that reveals factors responsible for changes in population

density. By this method, the killing power, or k-value, of each mortal-

ity factor is measured by taking the difference between the logarithm of

population numbers before and after its action (Appendix 3). Since a

series of mortality factors act successively in a population, their total

killing power, or K-value, equals the total killing power of the indi-

vidual factors. Its application to tea scale is as follows:

kI = mortality of crawlers during dispersal

k2 = mortality of settlers due to predators

k3 = mortality of nymphs due to parasites, predators,
diseases and unknown causes

k3a = mortality of male nymphs due to A. theae, (contained
in k3)

k4 = mortality of the pre-reproductives due to parasite,
host feeding, and desiccation

Using these k-values, generation mortality (K) can be expressed as

follows: K = k1 + k2 + k3 + k4

The k-values for different age intervals and K-value for each month

(Appendix 3) were plotted in Fig. 7, where the contribution of each

mortality factor to variation in K can be seen by visual inspection.

From the figures it is quite apparent that there are two main types of

mortality factors; the first is for dispersion loss of crawlers (kl) and

the second is the action of natural enemies on nymphs (k3). Both k-values

followed, more or less, the same pattern as did the generation mortality

(K). Action of A. theae is shown separately as k3a, which is similar to

k3 but somewhat lower in magnitude. Since A. theae failed to become

(=kl+k2+ k3+ k4)

Mar May

Figure 7. Key Factor Analysis. The Recognition of Key Factors in
the Life Tables for Tea Scale, Fiorinia theae, by Visual
Correlation of Various Mortality Factors (ks) with the
Generation Mortality (K).







w 0.2

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permanently established, it is no longer operating as a mortality

factor affecting tea scale populations in Gainesville.

Survivorship Curves

A survivorship curve is the simplest graphical description of a

life table and is obtained by plotting the number in the lx column on

the ordinate against age on the abscissa (Fig. 8). Lotka (1925) pointed

out that survivorship curves become more informative if 1x is plotted on

a logarithmic scale. A straight line would indicate a constant mortali-

ty throughout life, while other shapes would measure the different "force

of mortality" at different age intervals. Pearl and Miner (1935) and

Deevey (1947) recognized 3 general types of survivorship curves:

Type I, "the negatively skew rectangular" or convex curve is shown by

members of a cohort which, having been born at the same time, die more

or less simultaneously after a life span characteristic of the species.

In other words, mortality acts heavily on old individuals. Type II is

the "diagonal" curve and represents a constant mortality rate at all age

intervals. That is, there is no greater probability of death at one stage

than at another. Type III, "the positively skew rectangular" or concave

curve indicates very high mortality in the young stages, but the few in-

dividuals which survive to advanced ages have a relatively high probability

of further life. This is the most common type of survivorship curve met

with in animals. Most invertebrates and lower vertebrates exhibit this

trend of mortality. In the higher vertebrates, the survivorship curve

is of Type I because of greater parental care to their offspring.

Most survivorship curves known so far tend to be rather intermediate,

in varying degree, between Type I and Type II. Price (1975) analyzed

the survivorship curves of 22 insect species and found that there were

2 basic types of curves, although intermediates also occurred. In insects,

mortality occurs in distinct stages; therefore, their survivorsip curves

show a number of distinct steps (Ito, 1961).




Figure 8. General Types of Survivorship Curves.

In tea scale, the eggs are retained under the female armor until

hatching. This is a sort of parental care comparable to the higher

vertebrates with Type 1 curves. The shape of the tea scale survivorship

curve (Fig. 9) is somewhat convex in the beginning because of the high

survival of eggs. The latter portion of the curve conforms to the typical

stepped appearance of insect survivorship curves. Survivorship curve for

females shows a consistent pattern throughout the year, while that for

the males indicates variation in the survival which is directly affected

by absence or presence of A. theae. Data for the survivorship curves

are presented in Appendix 4. In the preparation of survivorship curves,

actual numbers were converted to begin at 1000.

The shape of survivorship curves of insect pests helps in determining

the vulnerable stage of each species and may lead to the emphasis of

control efforts on that stage. For instance, in the case of tea scale,

the most vulnerable stage is the female nymph. If a species of natural

enemy can be found that attacks this stage, the tea scale population

can be reduced to non-economic levels.




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Fertility Tables

Knowledge of sex-ratio is a pre-requisite for species fertility

tables. Tanner (1978) stated that sex-ratio can be categorized into

the specific sex-ratio and the crude sex-ratio. The former relates to

the ratio of the numbers of each sex within a particular age group; the

latter is the ratio of the number of each sex in the entire population.

The specific sex-ratio in tea scale varied greatly during different

months because of the differential activity of natural enemies. Aphytis

theae was the major mortality factor acting on the second instar male

nymphs. Populations of A. theae also fluctuated during the season.

During summer months it killed a major portion of male nymphs, but during

the winter period, A. theae was wiped out by prolonged cold. Absence of

A. theae released the pressure on the male nymphs of tea scale, and the

sex-ratio swung further in favor of male sex. For instance, during

March through September, when A. theae was active, the sex-ratio at

nymphal stage ranged from 2.75:1 to 4.87:1, while during October through

February, when Aphytis was inactive or absent, the sex-ratio at nymphal

stage ranged from 6.02:1 to 8.43:1 (Table 7). Data are presented in

Appendix 5.

The effect of fluctuations in A. theae populations was also reflect-

ed by the varying sex-ratio in the subsequent stages of tea scale. Al-

though the specific sex-ratios at the pre-reproductive and reproductive

stages were in favor of females (except during March May in the case

of pre-reproductives, and May and June in the case of reproductives, the

crude sex-ratio consistently remained in favor of males (Fig. 10). A

delayed effect of A. theae on sex-ratio is also depicted by Fig. 10.

The highest proportion of males occurred in February at the nymphal stage,

in April at pre-reproductive stage, and in May at reproductive stage.

Specific and Crude Sex-Ratios of Tea Scale, Fiorinia theae

Sex-ratio (male:female)
Month Nymph Pre-Reprod. Reproductive Crude

Sep. 77 3.53:1 0.12:1 0.17:1 1.03:1

Oct. 77 6.44:1 0.51:1 0.20:1 1.62:1

Nov. 77 6.46:1 0.07:1 0.47:1 2.00:1

Dec. 77 6.32:1 0.16:1 0.26:1 2.22:1

Jan. 78 6.02:1 0.73:1 0.13:1 1.92:1

Feb. 78 8.43:1 0.76:1 0.13:1 2.07:1

Mar. 78 4.87:1 1.31:1 0.56:1 1.97:1

Apr. 78 3.35:1 1.63:1 0.98:1 1.89:1

May 78 2.75:1 1.27:1 1.13:1 1.87:1

Jun. 78 2.78:1 0.07:1 1.10:1 1.67:1

Jul. 78 3.44:1 0.09:1 0.24:1 1.99:1

Aug. 78 3.03:1 0.22:1 0.13:1 1.41:1

0.42:1 1.83:1

Average 4.52:1



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Females of a species are capable of reproducing only during a

certain age span. Much of their life is spent as either immature

(pre-oviposition) or too old (post-oviposition). To estimate the growth

of populations with overlapping generations, it is essential to know the

number of female individuals that are present at each age interval (Table 8)

and the number of female offspring produced by an average female at dif-

ferent intervals in her reproductive life. Once these parameters are

known, the calculation of fertility rate (mx) becomes an easy process.

Fertility rate (mx) and sex-ratio are used in preparing the fertility


A fertility table describes, in a summarized fashion, the net re-

placement rate (Ro) of an average female. Ro is defined as the number

of daughters that replace an average female in the course of a generation.

The usual method of calculating Ro is from tables of age survivorship

(1x) and fecundity (mx). The sum of all products of lx and mx denotes

R A value of R, equal to 1, indicates a stable population; greater

than 1 indicates an increasing population; and less than 1 indicates

a decreasing population.

R is used in the calculation of reproduction or instantaneous

rate of population growth (r). Here r = log Ro/T, where T is the gen-

eration time. According to Price (1975), in the case of populations

with overlapping generations, each month can be considered as a breeding

season. Therefore, for purposes of generation time T of the tea scale

assumed as one month is used. Then r = log Roa/or r = log Ro.

A stable population will have r = 0, while a value more than 0

will indicate an increasing population, and a minus value of r will

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