protection from beetle-predation in cochineal insects (dactylopiidae

PROTECTION FROM BEETLE-PREDATION IN COCHINEAL INSECTS
(DACTYLOPIIDAE:HOMOPTERA)
Dissertation submitted in partial fulfillment
of the requirements for the degree of Master of Science.
Department of Zoology and Entomology.
Rhodes University.
by
John Frederick Morrison
J anuary 1984
CONTENTS.
Page
ACKNOWLEDGEMENTS.
INTRODUCTION.
2
GENERAL MATERIALS AND METHODS.
10
1. FEEDING EXPERIMENTS WITH THE "WAXY COVERING"
OF THE PREY INTACT.
13
2. THE "WAXY COVERING".
3. FEEDING
EXPERIMENTS
18
WITH
THE "WAXY COVERING"
OF THE PREY REMOVED.
33
4. CHOICE EXPERIMENTS AND FEEDING BEHAVIOUR.
35
5. THE ROLE OF CARMIN I C ACID IN PREVENTING PREDATION.
41
6. THE LONG-TERM EFFECTS ON E. FLAVIVENTRIS
WHEN FED ON DIFFERENT DIETS.
48
DISCUSSION.
66
SUMMARY.
.73
REFERENCES.
74
APPENDIX 1.
87
ACKNOWLEDGEMENTS.
My sincere thanks are extended to Professor V.C.
Moran and Mr.
Walter
and
for
their
supervision,
understanding
G. H.
encouragement
throughout this study.
The
constructive criticisms,
many
of
~ reatly
I
my colleagues,
especially those of Dr
J.H.
Hoffmann · are
appreciated.
gratefully
from
interest and helpful advice offered by
the
acknowledge the co- operation and
staff
assistance
received
of the Rhcdes University Electron Microscope 'U nit,
especial ly
Mr.
A.H.
Universi ty
Department
Hartley,
of
and Dr C.G.
Chemistry
for
Wtiteley of the
assistance
in
Rhodes
chemical
analysis.
Finally I thank my wife for her support,
for her help in preparing this manuscript .
patience , encouragement and
2
INTRODUCTION.
In
South
Mader
Africa the native ladybird beetle
Exochomus
flaviventris
feeds on the introduced cochineal insect Dactylopius
(Cockerell) (Pettey,
Marais,
1950).
It
1943,
has
1946, 1948; Geyer, 1947 a, b; Pettey and
also been reported to feed
austrinus Lindley (Geyer,
Appendix
E. flaviventris
This
1) •
feeds
on
Dactylopius
1947 a; Pettey, 1948), but this appears to
occur rarely in the fi eld (H.G.
camm. ;
opuntiae
on
Zimmermann and H.G.
thesis
attempts
D. opuntiae
in
to
the
Robertson pers.
determine
field
but
why
not
on
D. austrinus.
The
genus
Dac t ylopius
particularly
Opuntia
which
is
host
specific
to
to those of the genus Opuntia (De
cactaceous
Lotto,
1974) .
species have been introduced into South Africa,
have become naturalized (Lansdell,
Annecke and Moran,
1978;
Stirton,
1979;
1923;
plants,
Many
several ·of
Phill ips ,
1940
a·,
Moran and Annecke, 1979).
Some of these have become problem weeds (Phillips,
1940 b; Hattingh,
1958; Taylor, 1969; Neser and Annecke 1973; Zimmermann, 1978 a, b, c,
d;
Zimmermann and Moran,
indica (L.)
(Fig.
(Fig.
(Pettey,
of various species of South American cochineal
Lindley
insects
1948). Of these, Dactylopius opuntiae (Cockerell) (Fig.
been successful in controlling
1946;
De
1) and jointed cactus Opuntia aurantiaca
2) . Attempts to control these weeds have relied largely on the
introduction
has
1982), notably prickly pear Opuntia ficus-
O. ficus-indica
(Pettey,
3)
1943;
1948; 1950; Annecke and Moran 1978), and Dactylopius austrinus
Lotto
(Fig.
4)
has been partially successful as
a
control agent on O. aurantiaca (Moran and Annecke, 1979).
biolog ica l
3
~
o
o
3
3
Fig.
1.
The prickly pear
weed Opuntia ficus-indica in , the
field.
1
-
~
o
3
Fig. 2.
The jointed cactus weed Opuntia aurantiaca in t he field.
4
Fig.
3.
The
o.
cochineal
insect
Dactylopius
on
opuntiae
ficus indica.
",
i
Fig. 4 .
The
o.
cochineal
insec t
Dactylopius
austrinus
on
aurantiaca.
;;::;
3
3
Fig. 5.
The cochineal insect Dact y l opius coccus on O. ficus-indica.
5
Although the cochineal insect Dactylopius coccus Costa (Fig.
also introduced into South Africa (Pettey,
was
1943;
Mann,
5)
was
1969),
it
not introduced as a biological control agent but as a source
cochineal
dye,
dye.
Although
D. coccus
1974).
At
is
present
all Dactylopius species produce
the most suitable for this
in South Africa D. coccus
purpose
of
cochineal
(De
is not found
Lotto,
in
the
field (H.G . Zimmermann pers. comm.).
The
most
conspicuous character of cochineal insects is
thread-like
"waxy
covering"
which
has
been
the
considered
woolly
to
have
protective properties (Mann, 1969; Walter, 1977). The "waxy covering"
of
D. opuntiae
3
(Figs
is
and 4),
similar in appearance to
and
that
these are both different
of
D. austrinus
from
the
powdery
covering of D. coccus (Fig. 5).
In South Africa the native ladybird beetle
was
found feeding on
Q.
on the cochineal insect.
indicated
flaviventris
opuntiae within two years of
becoming established (Pettey,
1969)
~.
et al.
reducing the effectiveness of the insect
control agent.
cochineal
1969; Burger,
that E. flaviventris in high
capable of effectively limiting population numbers of
therefore
the
6)
1946). Both the adults and larvae feed
Two studies (Annecke,
strongly
(Fig .
Q.
numbers
is
opuntiae and
as a
biological
These authors worked in different areas where prickly
pear was the dominant plant,
Q.
opuntiae numbers were low
and many
E. flaviventris were present. They reduced the number of coccinellids
by
means
which
did
of low concentrations of insecticide (2 oz DDT
not
harm
the
cochineal
insects.
per
acre)
A dramatic rise in
6
a
",
w
3
3
i
b
Fig.
6.
The ladybird Exochornus flaviventris adult (a) and larva (b)
feeding on D. opuntiae.
7
Q.
opuntiae
numbers resulted and many large prickly pear plants were
defoliated
and killed.
On the other hand E. flaviventris has
been
rarely observed to prey on D. austrinus in the field.
Differential
predation by
D. austrinus
may
mechanisms ,
be
flaviventris on D. opuntiae but not
~.
influenced
by
two
on
suggested-protect ive
the waxy covering of the cochineal insect (Walter, 1977)
and their carminic acid (cochineal dye) content (Eisner, et al 1980).
D. coccus
because
(Baranyovits,
of
its
reputed
high
carminic
1978) and its peculiar waxy covering,
acid
content
was included in
the investigation .
The
following
determine
Q.
five
lines
of
investigation
were
conducted
to
which factors contribute to the differential predation
opuntiae
and
D. austrinus
by~.
flaviventris
and
reported
on
in
sequence in this thesis.
i)
The
species
ability of
was
covering"
~.
flaviventris to feed on different
investigated .
was
E. flaviventris
In one series of experiments
left intact and in others it
has
Dactylopius
was
the
removed.
been reported to feed on both
"waxy
Although
D. opuntiae
and
D. austrinus in the laboratory (Geyer , 1947 a; b ; Walter , 1976, 1977;
Durrheim ,
1980; Brooks , 1981; Morrice , 1981) there are no reports of
E. flaviventris
laboratory.
feeding
on
D. coccus
in
the
field
or
in
the
8
ii)
The
species
structure
of
cochineal insects was
secreted
waxes
of the wax strands
by
secreted
by
investigated.
plant-feeding
insects
Pol lister (1938) as excretory products.
the
The
were
different
non - cuticular
regarded
by
However they have since been
shown to be specially synthesized by the insect (Brown, 1975; Jackson
and Blomquist,
insects
1976) .
It is therefore reasonable to assume that the
derive some advantage from the wax (Pope ,
1983) as observed
by Broadbent (1951) on "wax covered aphids".
The
"waxy covering" of cochineal insects has been considered by Mann
(1969)
to have general protective properties and
Walter
(1977) showed that the "waxy covering"
E. flaviventris .
result
Selective predation by
~.
more
specifically
reduced predation
by
flaviventris could be the
of differences in the physical properties of the wax (Walter,
1977) or differences in composition of the wax
as shown by
Tulloch
(1970) and Meinwald e t al . (1975) for D. coccus and D. confusus .
iii)
The
choice of cochineal - prey species by
investigated.
of
the
Choice
E. flav ivent ris
was
experiments were done with the "waxy covering"
the cochineal insects intact and when removed.
The behaviour
beetles when presented with each Dactylopius species
of
separately
was recorded.
iv)
The protective properties of the red pigment (carminic acid)
of
the
cochineal
an
insects
anthraquinone (Thomson ,
et al.
were
197 1;
investigated.
Brown ,
1975;
Carminic
Lloyd,
acid
1980).
is
Ei sner
(1980) suggested that it acts like other quinones as a potent
feeding- deterrent to predation, although
Baranyovits (1978) reported
9
that
no biological function has been demonstrated for carminic acid.
Carminic
acid concentration in prey individuals could influence
the
predation pattern of E. flaviventris .
v)
Finally,
entirely,
the long-term
for
two
effects on E. flaviventris of being
generations,
( 1966)
on each
Dactylopius
investigated.
Hodek
specialization
of various predacious coccinellids
noted
that
there are no known monophagous species.
found
to
(Blackman,
the
Okamoto, 1966).
degree
of
varies,
was
food
although
Some aphid species have been
be lethal to some coccinellid species,
1966;
species
fed
but not to
others
D. austrinus may therefore be an
inadequate food (Geyer 1947 a), probably because of its carminic acid
content,
and
this
may
result
E. flaviventris on D. opuntiae.
in
selective
predation
of
10
GENERAL MATERIALS AND METHODS.
A
laboratory
approximately
26°29'E).
E. flaviventris
was
started
from
300 adults collected in the Grahamstown area (33°23'S;
The colony was kept in perspex cages
infestations
in
of
colony
of
(35x35x20cm).
Heavy
Q. opuntiae on Q. ficus - indica cladodes were
the cages as food.
The colony was replaced every six
reduce
any possible inbreeding effects.
colony
was
The
insectary,
maintained and where the experimental work
placed
months
to
where
the
was
carried
out, was programmed to simulate early summer conditions (Day- 14hr at
26(+1)OC and 45%
(~10%)
humidity slowly
changing to 17°C and 90% RH) .
In
each
experiment,
RH; night - 10hr with temperature and relative
newly emerged (maximum of one-day
old)
adult
E. flaviventris were isolated and starved for three days before being
used (unless otherwise stated),
old do not feed (Geyer,
coccinellid
the
to
was
stock
because adults younger than two days
1947 a;
and confirmed in this study).
used in only one experiment and was then
colony.
In
those
experiments
where
Each
returned
continuous
behavioural patterns were recorded, the coccinellids were starved for
a
period
of
facilitating
Only
four days ,
thereby enhancing the "hunger
and
monitoring of the feeding activities.
adult Dactylopius females were used as a food source
experiments
drive"
because the females are conspicuous and
in
sedentary ,
these
and
together with the crawlers form the largest part of the Dactylopius
11
prey
(Geyer,
reported
1947 a).
that
Walter
(1976,
E. flaviventris
1977)
will prey on
and
both
Durrheim
( 1980)
D. opuntiae
and
D. austrinus crawlers and adu lt s in the laboratory .
In a numb er of the experiments the cochineal insects were "de-waxed ".
In
the case of D. opuntiae and
the
"waxy
Q.
austrinus this was done by rolling
covering" off the body of the insect on to a
large
pin.
D. coccus was "de - waxed" by brushing the powdery "waxy covering"
off
with a pa in t brush.
E. flaviventris
was
cochineal
obtained
prey
quantity
and
amount
of
development
presented
in
from
all
cases
growing
plants to
quality of the food source.
food
has
available
been
to
demonstrated .
with
The
an
excess
standardize
importance
coccinellid
Ives (1981)
of
fecundity
showed
that
of
the
the
and
egg
production of Coccinel l a trifasciata Mulsant decreased with declining
food availability,
species
that
reproduction
Baumgaertne et al.
supply
and Frazer et al.
resulted
(1981) suggested , for the same
is optimized when food supply
( 1981 a)
is
high.
noted that access to an unlimited food
in the shortest generation time
for
a
Hippodem ia
species.
All containers used f or housing beetles had ventilation holes covered
with
vials
the
muslin,
and from here on will be referred to
unless otherwise
" tops".
stated had a round paper disc which
floor of the vial to form
could easily walk.
as
a rough su rface on which the
All
covered
beetles
12
In all experiments,
results for male and female E. flaviventris were
recorded separately. On analysis, there was no significant difference
in
any experiment between males and females.
obtained from
Therefore the
results
male and female coccinellids have been combined in all
analyses.
This
study consists of a number of sections (see introduction) .
All
of these sections comprised a number of experiments each with its own
methods,
discussed.
and
these
will
be
described
when
each
experiment
is
13
1.
FEEDING EXPERIMENTS WITH THE "WAXY COVERI NG" OF THE
Th e
PREY INTACT.
ability o f E. f laviv e ntris be e tle s t o f eed on thr ee
Da ctylop ius
s pecie s with the "waxy covering " i ntact.
Experiments
were
would
feed
on adult female cochineal insects of the
being
examined
(~.
E. flaviventris
rlwaxy
designed
opuntiae,
was
coverings!'
to investigate
whether
D. austrinus and
p r esented with cochineal
to
ascertain
the
E. flavivent r is
three
species
D. coccus) .
firstly
insects
effectiveness
with
of
intact
the
I!waxy
60mm)
were
covering ll in preventing predation .
Open - ended
placed
glass
vials (diameter of 25mm and length of
over single laborator y - reared Dactylopius adult females (i . e .
leaving the "waxy covering" intac t ) which were still attached to , and
feeding on,
the host plant (Fig .
introduced
into
observations
penetrated
not.
The
were
each
7) .
A single E . flaviventris
vial and the end sealed
made
to
record
whether
with
a
top .
was
Dai l Y
E. flaviventris
the "waxy covering" and fed on the Dactylopius fema l e
experiment
ran
until E. flaviventris either fed
cochineal insect or died of starvation .
on
had
or
t he
14
",
Fig . 7 .
E. flaviven tris (arrow) confined with a
to
determine
insects
whether
Q.
opuntiae
the beetle will feed
that have the "waxy
on
covering" intact.
female
cochineal
The
plant
host is O. ficus-indica.
The
results are summarized in Table 1.
the
"waxy
cases),
D. austrinus
barrier of
penetra ted
and fed readily on D. opuntiae (39 out of
50
managed to penetrate the " waxy covering" and feed
on
covering",
fewer
E. flaviventris
(9 out of 50 cases) and no beetles penetrated the
D. coccus (0 out of 50 cases).
waxy
15
Table 1.
The percentage survival of
food
different
with
E. flaviventris
sources .
when presented
(N =number
of
beetles
observed) .
:
E. flaviventris
'f, fed and
survived
fed on
N
D. opuntiae
78
50
D. austrinus
18
50
0
D. coccus
50
:
These experiments showed that, in the laboratory , the "waxy covering"
appeared
cove ring"
to prevent predation.
of
different
They also indicated that
Dactylopius species does
afford
the
"waxy
different
degrees of protection.
The
surviva l
times of beetles that could not
penetrate
the
"waxy
covering" of the three Dactylopius species .
The
results
confined
of the previous experiment
was
and additional experiments were done .
the beetles that
recorded.
E. flaviven t ris
Dactylopius
beetles
E . flaviventris
in a vial with a Dactylopius female on a cladode
,,,ere elaborated
of
where
Using
could
same
survive
methods the
on
species was recorded.
length
the honeydew
As a
control,
of
(Fig. 7) ,
The longevity
could not penetrate the intact "waxy
the
was
of
the
cover ing"
time
that
different
vials
containing
were placed on clean cladodes of the host plants
(0. ficus -
ind ica and O. aurantiaca) and no prey was provided.
16
The beetles t hat did no t manage to feed on the cochineal pr ey and the
beet l es
in the cont r o l experiments all died.
However,
the
bee tl es
survived for a va r ied pe r iod of t i me, living for a mean period ( Table
Q.
2) of 7,9 days on
opuntiae ,
7 , 8 days on
when confined with D. coccus.
D. opuntiae and
in
turn
(8,2
Q.
Q.
austrinus and 4,1 days
The beetles that "starved to dea t h" on
aust r inus lived for a similar length of time , this
was similar to the time that beetles lived on honeydew only
days on D. opuntiae honey dew ,
dew and 8,3 days on
D. coccus
lived
Q.
8 , 6 days on D. austrinus
coccus honey dew) .
honey
The beetles confined
(i) approximately half as long (4 , 1 days) as
confined with D. opuntiae and
Q.
austrinus,
with
those
and (ii) the same l ength
of time as beetles that received no food (4,9 days on O. ficus - indica
and 4 , 6 days on O. aurantiaca).
The
Q.
beetles
opuntiae
that
could
not
penetrate
the
"waxy
covering"
and D. austrinus presumably fed on the honeydew
cochineal
On the other hand beetles that were confined
D. coccus
were
covering"
fouled up their tarsi .
unable to get to the honey dew as the powdery
was
not the case in the other cochineal insects.
beetles that were confined with D. austrinus were also
getting
confined
effective
entangled
with
in the "waxy covering",
D. opuntiae became entangled.
!Iwaxy covering'1 barrier against
!.
but
with
" waxy
This resulted in loss of grip
the beetles fell on their backs and were unab l e to right
by
the
insects and therefore lived twice as long as those beetles
that had no food.
This
of
of
and
themselves.
Some of
the
incapacitated
none
D. coccus has
flaviventris
of
those
a
more
predation
than D. austrinus which was shown to be more effective than the "waxy
covering" of D. opuntiae .
17
Table 2.
The
longevi ty of E. flaviventris when unable to
the
cochinea l
prey
provided .
(x=mean
and
penetrate
N=number
of
beetles observed).
Starved to death
Food regime
x- days
alive
i
N
I
I
I
I
No food on
O. ficus-indica
--
,!
4,9
-
I,
15
I
,
No food on
O. aurantiaca
I
!
4,6
-
,
7,9
,
,
7,8
,
4,1
i
i
D. opuntiae
!
-
,
D. austrinus
,
-D.
i
-
coccus
!
!
I
I
:
I
!
!
!
,i
-
i
iI
8,6
I
D. coccus honeydew on
O. ficus-indica
I
I
-
8,3
I
a
study
15
15
the "waxy covering" of Q. coccus
between
t\,o Dactylopius species was investigated next"
by
15
I
I
followed
50
i
8,2
D. austrinus honeydew on
o. aurantiaca
other
41
I
O.
ficus-indica
- --
differences
11
i
!
D. opuntiae honeydew on
The
15
of
the
differences
D. austrinus and that of D. opuntiae.
between
and
the
and
the
this
was
wax
of
18
2. THE "WAXY COVERING".
Differences
in
the
"waxy coverings" between the
three
Dactylopius
species.
In
the previous experiments it was shown that
not penetrate the "waxy covering" of Q.. coccus,
in
flaviventris
~.
and found difficulty
penetrating the "waxy covering" of Q.. austrinus,
but
the "waxy covering" of D. opuntiae with relative ease.
wax
strands
investigated
of
Q. opuntiae,
D. austrinus
could
and
penetrated
The component
D. coccus
were
in an attempt to understand why the "waxy coverings" of
these Dactylopius species differ in their effect on E. f laviventris .
The "waxy coverings" of the three Dactylopius species have
properties
in relation to predation by Exochomus .
appearance of the "way!y covering!! of Q.. opuntiae and
similar,
different
Superficially the
Q.
austrinus
is
appearing woolly and thread - like , whereas that of D. coccus
appears powdery (Fig . 5).
Under
the
scanning ·electron microscope (SEM)
striking
differences
were noted between the "waxy covering" of D. coccus and the other two
Dactylopius
species (Fig ,
8) .
D. coccus (Fig. 8 a, b)
large
number of short tubular
body,
whereas Q.. opuntiae and Q.. austrinus produce long
threads
insect.
(Fig. 8 c, d,)
which
produces
a
wax filaments that lie loosely on the
remain attached to the
filamentous
body
of
the
19
a
C
(300 X)
(300 X)
b
(4000 X)
d
(300 X)
..,
h
Fig. 8.
SEM
micrographs
of
the
"waxy
covering"
D. coccus, c) D. opuntiae, and d) D. austrinus.
of
a),
b)
'"
\
1
~
-
-
- - - - -- - - - -
-
~
20
The
effects of
the
different
"waxy coverings"
on
the
tarsi
of
different "waxy coverings"
on
the
tarsi
of
E. flaviventris.
The
effects
of
the
E. flaviventris
were demonstrated with the aid of SEM micrographs
E. flaviventris
tarsi before and after coming into contact with
of
the
"waxy coverings" of D. opuntiae, D. austrinus and D. coccus (Fig.
9) •
These
the
resu lts
appropriate
were
were
obta ined
by
confining
a
beetle
cochineal insect in a vial for one minute.
with
The
then killed by freezing and the tarsi were 'examined
beetles
under
the
SEM.
The micrographs clearly show that the powdery wax of
clogged
that
in
came
into contact with the other two species
Figs 9 b
in
the
contact with
Q.
(Figs
the
were
the
tarsi
relativ~ly
9 a) show clean E. flaviventris tarsi.
clogging of the tarsal setae by
In Figs 9 c, d,
shown.
coccus became
the tarsal setae of E. flaviventris whereas
clean. SEM micrographs
In
Q.
tarsi of
Q.
coccus wax
is
E. flaviventris that had been
opuntiae and D. austrinus wax for one minute
are
shown. Here there is little entanglement of the tarsal setae.
Could
clogging
adhe~ion
of
the tarsal setae of E. flaviventris
of the setae to the substrate?
affect
Many suggestions have
made as to how the adhesive setae of beetles
~nd
the
been
other animals adhere
to surfaces. Stork (1980 a) regards most of these to be based on poor
morphological and experimental evidence. At present the most probable
mode
of
adhesion
is that proposed by Ruibal and Erns t
(1965)
for
21
a
b
c
d
Fig. 9.
SEM
micrographs
showjng a) clean
E. flaviventris
tarsi.
Tarsi
that have come into contact for one minute with
the
"waxy
covering"
and
D. austrinus d).
of.
D. coccus
b),
(Magnification 600X)
D. opuntiae
c),
22
gecko
tarsi,
Edwards
and Tarkanian ( 1970)
for
Rhodnius
prolixus
o
Stahl, Stork (1983 a) for the housefly and Stork (1980 c, 1983 b) for
a number of beetle species. They propose that the mode of ad hesion is
direct molecular adhesion of the tarsal setae with the substratum and
that
the
cohesion
increase
forces
the adhesion .
Brussels
sprouts
of a thin
fluid
layer
of
made
the
plants
less
adhesive
Coleoptera) ,
beetle
into
tarsi.
The debris prevented the tarsal
con ta ct with the substrate and
thereby
of
to
due
of powdery debris and wax blooms covering the adhesive
the
coming
probably
Stork ( 1980 b) showed that the wax bloom
Phaedon cochleariae (fabricius)(Chrysomelidae;
clumps
would
to
setae
setae
decreased
from
the
direct molecular adhesion .
Because
number
the
of
greatly
tarsal setae are clogged with the
D. coccus
contact points between tarsal setae and
reduced,
wax ,
substratum
the
are
resulting in decreased cumulative cohesion forces .
The powdery wax of D. coccus does decrease the adhesion ., f the tarsal
setae
to
the
substrate
by
clogging
them.
investigation
showed no obvious reasons why
to
Q.
penetrate
D. austrinus .
~.
However,
flaviventris is
opuntiae "waxy covering" more easily than
Therefore
the
differences
in
t his
the
"waxy
between D. opuntiae and D. austrinus were investigated.
that
SEM
able
of
covering"
23
The
physical
properties
and the
structures
producing
the
"waxy
covering" of D. opuntiae and D. austrinus.
The
"waxy covering" of
and
does
that
Q.
opuntiae and
Q.
austrinus
is
thread-like
not entangle the t arsal setae of E. flaviventris
of D. coccus.
as
The beetles find it more difficult to
penetrate
the
"waxy covering" of D. austrinus than that of D. opuntiae
get
entangled
differences
in
the threads of the
between
the
11
waxy
former.
cover ingl!
Are
there
Q.
of
does
and do
physical
and
opuntiae
D. austrinus which make the latter more difficult to penetrate?
The
physica l
properties of the "waxy covering" of
D. austri nus
initial
were
strength
studied
by Walter (1977),
of
"waxy
the
D. aust rinus
was
whereas
elasticity
very
the
similar.
field
showed
elasticity
covering"
who
of
Q.
opuntiae
found
and
that
the
laboratory- reared
nearly twice that of laboratory-reared
Q.
of the "waxy covering" in both
opuntiae
species
The "waxy covering" of D. opuntiae collected
in
the
a significant increase in strength and a decrease
compared to laboratory-reared
Q. opuntiae.
In
i.s
in
contrast
D. austrinus "waxy covering" showed I i ttle difference in strength and
a
small decrease in elasticity between laboratory- reared
collected
cochineal insects (Walter,
1977).
The
and field-
differences
were
attributed to different degrees of compaction of the "waxy covering",
due
to
chemical
be
due
weathering,
as
well as possible
properties of the "waxy covering" .
to
differences in the structures
different
physical
and
These differences could
that
produce
coverings" of the cochineal insects (Hartley et a l. 1983).
the
"waxy
24
The differences in number,
shape,
size and distribution of the wax-
producing
structures are so consistent that they have been
taxonomic
features
species (De Lotto,
produce
the
i n distinguishing between diffe rent
1974).
oute r
"waxy
used
as
Dactylopius
There are three different structures that
covering"
of
Dactylopius,
viz.
setae,
quinquelocu lar pores (wide -r immed or na rrow -rimmed) , and ducts . These
structures
are spread over the whole body surface of
insect (De Lotto,
their
positioning
the
cochinea l
1974) . . The differences in these structures and in
between D. opuntiae,
D. austrinus and
D. coccus
are shown in Fig 10 (Ferris , 1955; De Lotto, 1974) .
~.
opuntiae
has
four types of setae whereas
~.
austrinus
has
only
two. Both these two species have a large number of wide - rimmed pores ,
narrow-rimmed pores and ducts . D. coccus di ff ers from D. opuntiae and
D. austrinus in having no narrow-rimmed pores or ducts ,
setae.
and very few
Ia
25
a
4 types
of setae
.,.'
.'
111
. . ,.' ..
- "',
-'
/,
.
,
\J~.
/,
"
. -. "-
"
,
.
t
. .,
.",
,
"
'\
'
/.'.',~':
..
:; .,
....... ,
.
.'
..
'
,
'. ' .;0._
'
,
,
"
,
,
.
~
,
:
...
'"
..
,
"
,
.
.
.
'
z.;;;It,b';)·,'::'..~
Setae
Du cts
.'
2 types
of sefa e
Fig, 10 ,
a)
the
Q, opuntiae ,
number
and
II
b) Q, au s trinus and c) Q. coccus
dist ribu tion
of
the
"waxy
showing
covering tl
producing structures (from, Ferris, 1955; De Lotto , 1974).
~
26
different
The
components
Q.
structures
different
produce
as shown by the SEM micrographs of the peg- like setae
opuntiae (Fig.
11 a) which produce filamentous components of
" waxy covering" which appear tubular (Fig 11 b, c).
D. coccus
setae produce similar filaments.
(Fig. 12 a)
produce
Q.
and D. austrinus whereas
opuntiae
tubular,
covering"
"waxy
threads
that
filaments (Fig . 12 c),
the
D. austrinus and
The quinquelocular pores
appear
Q.
of
ragged
(Fig. 12 b)
coccus pores ' produce
in
sho r t ,
which are smooth . These differences
were found in an investigation with G. H. Walter and A.H. Hartley that
is still in progress.
While
examining
the
quinque locular pores under the SEM
associated with the pores (Fig.
substrate
to
glands,
(Figs
the ultrastructure of
13
b).
wax-secreting
and described the peg- like setae (Fig . 14) and possible wax -
metabolising
associated
cells .
to
described .
The
margarodids
the
wax - secretory
the
pores
as well
of
appear
Sphaeraspis
the
setae
and
section
The
were
and
a l so
diaspidid
through
the
pores also includes the associated central duct.
The
lined with cuticle and secrets a substance
which
differs
from that secreted by the wax-secreting cells of the setae and
(Fig. 15).
in
Eurhizococcus
and
1978)
1978).
their
similar to those of the
psyllid Anomoneura (Waku,
Foldi,
as
similar
15) which appear
cells
wax - secretory cells
(Pesson
quinquelocular
is
quinque locular
Porphyrophora,
(Foldi , 198 1 ),
Aonidiella
The
wax-secretory cells (Fig.
structure
duct
(1983) examined
ducts
13 a) appeared to produce a rod - like
which the content of the pores adhered
Hartley et al .
the
pores
27
a
C
Fig . 11. SEM
(1000 X)
(400 X)
micrographs of the peg-like setae (s),
a) "de-waxed",
b) and c) with "waxy c·o vering" attached to D. opuntiae .
28
a (4000 X)
b
(4500 X)
.-
"."
Fig. 12 .
SEM
micrograph of the quinquelocular pores (qp),
waxed",
a)
"de-
b) with the"waxy covering"attached to D. opuntiae,
and D. coccus c).
\
'I
29
a
(8000 X)
",
b
(8500 X)
Fig. 13.
A cluster of four quinque locular pores (qp) incorporating a
tubular
duct
(td) a) with the "waxy covering" removed
with the "waxy covering" still attached (w=wax,
thread) .
b)
nt=non-wax
30
I,
.
.
, ~
.'"."
:.'
... ~' .
. , :~
.... .
\,'5; " '.
FiK. 14.
A
section through a seta and its wax-secreting cells (wc),
'''" .
(c=central column) (from, Hartley et al. 1983) .
...
\
t• ••.
_· _
-._
.-
I · ~ .· ' ~'. "".'
Fig. 15.
A
section through a quinqueiocular pore (qp) and its
wax-
secreting cells (wc) and associated tubular duct (td) which
is cuticle lined (cu) (from, Hartley et al. 1983).
To
examine
the structures that produce
the
"waxy
covering",
the
cochineal insects were de-waxed. This was done either mechanically or
by
a
combination
of
mechanical
and
chemical
methods.
In
the
31
mechanical
method a large pin was used to roll
threads off the body.
When necessary,
coch ineal
dissolve
In attempting to "de-
insects by the chemical method
remained and had to be removed mechanically.
to
the
covering"
the remainder of the covering
was then dissol ved off with benzene or hexane.
wax"
the "waxy
a
thread-like
mass
Attempts were then made
"waxy covering" completely using
the
following
methods .
i)
Q.. opuntiae and Q.. austrinus with their "waxy
were
coverings"
intact
benzene ,
carbon
immersed in separate solvents such as hexane,
tetrachloride,
chloroform and ethanol 80% ,
thread - like mass remained,
90%,
and a 100%
The
even after being immersed for seven days
in these solvents .
ii) The thread -l ike mass was still present even after the insects had
been subjected to refluxing solvents for one hour .
This indicates that either a highly
resistant wax is produced by the
cochineal insects,
a non-wax substance is produced.
The
presence,
covering"
could
covering" on the
The
or more likely,
absence ,
or quantity
of this substance in the "waxy
influence the protective properties
of
the
" waxy
cochineal insects.
"waxy covering" of Q. . opuntiae and D. austrinus was mechanically
removed, weighed and immersed in hexane for one hour at 50 oC, and was
agitated every 15 minutes.
The "waxy covering" was removed from
hexane and dried (50 0 C; 10minutes) then weighed again.
the
32
3 the percentage weight loss of the "waxy
Table
In
recorded,
~.
showing
opuntiae
significantly
the
that
a
lost
D. austrinus
mean
of
l ost
29 , 4%.
a
mean
covering"
of
20 . 1%
differences
These
different at a probability of 5% (0 , 05> P < 0 , 0 1 )
was
and
were
with
data transformed using an arcs i ne transformation and testing for
significance by means of at-test .
Table 3.
The
meari percentage weight loss of the "waxy coverings" of
D. opuntiae and
~.
austrinus when placed in warm hexane for
an hour (N=number of replicates) .
N
Mean .% weight loss
-
D. opuntiae
29,4%
20
D. austrinus
20 , 1%
20
The
results
in
Table
hydrocarbon - soluble
3
indicate
matter than
Q.
that
opuntiae .
has more of the non- wax substance than
appears
to
be
produced
by
quinquelocular pores (see Hartley
to
D. austrinus
the
~
Q.
al. 1983),
less.
Therefore D. austrinus
opuntiae.
ducts
lost
This
substance
with
associated
and could be the
the
key
the difference in reducing E. flaviventris predation in these two
Dactylopius species.
It
seems that a greater component of the . non - wax substance
produced
Q.
austrinus
by the ducts reduces beetle predation, wh i ch is shown by
and
~.
opuntiae where the former has more of the
than the l atter.
non- wax
substance
33
3. FEEDING EXPERIMENTS WITH THE "WAXY COVERING" OF THE PREY REMOVED
of~.
The ability
flaviventris beetles to feed on three Dactylopius
species with their "waxy cQverings ll removed ..
The
"waxy
insects,
covering" does afford some protection
but
the
cochineal
if this protection is removed can the contents of
insect
cochineal
to
sustain
the
coccinellid
beetle.
the
This
was
investigated by feeding individual coccinellid beetles exclusively on
"de-waxed"
females of one of the three Dactylopius species.
E. flaviventris
adult
A single
was placed in a glass vial (diameter of
25mm
and length of 15mm) which was sealed with a top. The beetles were fed
every
second day so that a continuous supply of food was
20 beetles were fed exclusively on each of D. opuntiae,
available,
D. austrinus .
and D. coccus.
Observations
the
smooth,
starvation.
and
showed that E. flaviventris could
tough,
This
their
f i rst
recordings
of D. coccus
easily pierced.
and
therefore,
then
In
order
all Dactylopius
presented
to
to
through
and died of
D. austrinus
standardize
species
E. flaviventris.
were
Daily
were made to determine how long E. flaviventris lived
these diets.
presented
was
conditions,
pierced,
cuticle
bite
was not the case with D. opuntiae or
cuticle
experimental
de-waxed
not
in
The experiment was run for 33 days and the results
Table
4.
Although~.
flaviventris survived
on
on
are
both
34
D. opuntiae and
on
Q.
austrinus for 33 days they were unable to
a diet comprised only of D. coccus .
survive
Female beetles that wer e fed
on D. coccus lived a few days longer than male beetles ( 11 ,6 and
8,9
days respectively).
Table 4 .
The
Q.
survival
coccus,
(in
days)
of~ .
flaviventris when
fed
on
D. opuntiae, or D. austrinus (N : total number of
beetles observed).
D. coccus
Mean survival of 10,25 days
N: 10
D. opuntiae
All alive after 33 days
N:10
D. austrinus
All alive after 33 days
N: 10
D. coccus,
even
when de - waxed and pierced ,
E. f lav iventris for any length of time
D. coccus
investigate
an
unsuitable
food
source
was unable
to
(mean of 10,25 days) ,
for
the
sustain
making
coccinellids .
whether E. flaviventris chooses one Dactylopius
in preference to another, choice experiments were carried out.
To
species
35
4. CHOICE EXPERIMENTS AND FEEDING BEHAVIOUR
The
choice
three
by
E. flaviventris when presented
Dactylopius
species
with their
"waxy
simultaneously
covering"
with
intact
or
removed ..
The
experiments
presented
E. flaviventris
could
food
D. coccus
but
that
Experiments
chooses
were
in
the
previous
section
showed
that
survive on D. opuntiae and D. austrinus as
did
conducted
not
to
sustain
determine
the
beetles
whether
at
a
all.
E. flaviventris
one Dactylopius species in preference to another.
In
all
these experiments the coccinellids were reared, from first instar, on
a
species
sprouts.
of mealybug (Pseudococcidae) that was
on
was at the start of each experiment.
starved
for
three
days
prior to
experiment unless otherwise stated.
to minimize
the
All
potato
enriou~tered
Therefore the first time that the coccinellids
Dactylopius
were
reared
coccinellids
commencement
of
the
Small containers were used so as
any possible bias due to searching behaviour.
A choice of prey was presented
to~.
flaviventris by placing a single
coccinellid in a vial (diameter of 30mm and length of 12mm). The vial
contained an EPX foam floor which had three holes,
into which
plugs of cactus (Fig. 16) (extracted with a cork borer) were
three
placed.
Each cactus plug supported a single specimen of a Dactylopius species
(Q.
opuntiae,
water
Q.
austrinus or
Q.
coccus). The foam was kept damp with
so that the plugs of cactus did not dry out.
their
The Dactylopius
species
were
reared in the laboratory with
"waxy
covering"
intact.
Eac.h
vial was turned through 120' to change the orientation
36
of
the
prey
and reduce any
possible
directional
stimuli.
Daily
observations were made on the feeding preferences of E. flaviventris.
Two levels of damage were noted.
firstly minor damage
the coccinellids pierced the cuticle of
encountering
damage
them,
to test the
food
occurred when
cochineal insects,
source.
Secondly,
on first
extensive
was recorded when the beetles fed on a cochineal insect,
and
this could take from one to three days to occur.
I
Top
Mus lin ___ "L--I--7'~::':':':':'::
Beetle
D. opuntiae
f
Vial
D. coccus
D. austrinus
,
~/
Fig.
16.
The choice chamber,
Cactus
EPX foam
with
Q.
opuntiae,
D. austrinus
and
D. coccus as a choice of prey for E. flaviventris.
The experiment was repeated with "de-waxed" cochineal insects as prey
in place of intact cochineal insects. Three depressions were hollowed
out of the foam floor to ' hold the "d e - waxed" cochineal insects, which
were not attached to the host plant.
37
E. flaviventris
showed
a preference for
Q.
opuntiae over the
other
two Dactylopius species when the "waxy covering" was intact and
when
it was removed.
During the experiment many of the prey in
arena were pierced but not necessarily extensively damaged .
5
results
are
extensive ly
shown
damaged
of only those
i.e.
those
cochineal
that
insects
had been
as
on
Q.
the
In Table
that
used
also
food
were
by
E. flaviventris.
Ta ble 5.
The
number
of E. f laviventris
D. austrinus
three
opuntiae,
and D. coccus when given a choice between the
species .
insects
that fed
that
Experiments were conducted with
had
their "waxy covering" both
cochineal
intact
removed .
Prey species
selected
-D.
opuntiae only
"Waxy covering"
intact
removed
19
21
D. austrinus only
4
5
D. coccus only
1
0
D. opuntiae and
D. austrinus
3
4
-D.
D.
1
0
-
1
0
D. opuntiae
D. austrinus and
D. coccus
1
0
30
30
-
-
opuntiae and
coccus
D. austrinus and
D. coccus
-
Total
I
and
D. coccus
was
replicates.
on~.
pierced and extensively damaged in only four
In
of
the
previous experiments the beetles were unable to feed
coccus, but here their ability to penetrate the cuticle of this
appeared
species
to
be
due
to
the
E. flaviventris had a firm grip on the foam, it did
Because
used.
apparatus
manage to pierce
D. coccus from below.
With
the
preferred
"waxy covering" intact or with it removed
Q.
opuntiae to the other two species. Even
E. flaviventr i s
with~.
opuntiae
as the preferred prey species, difficulty was found in observing this
difference
in
difficu l ty
stemmed from the beetles habit of attempting to feed
off
the
prey they encountered.
the
first
an eight-hour
continuous
observation
period.
To overcome this difficulty
were presented with the contents of each cochineal
beetles
individually.
The time for each activity (feeding,
This
species
resting,
wa l kin~
and grooming) was then recorded.
The
of
behaviour
E. flaviventris
when
presented
with
each
Dactylopius species separately.
The
fact
that some of the E. f l aviventris fed on both of
the
l ess
su i table prey species (i.e. D. austrinus and D. coccus) may have been
due to the choice of food being largely determined by the first
encountered
was
by the starved predator.
therefore
Another series of
conducted to observe the behaviour of
single~.
E. f l aviventris.
A
of
which contained the contents of
a
females
petri-dish
prey
experiments
starved
adult
flaviventris was placed in the centre
four
~.
opuntiae
arranged at the four poles around the edge of the dish.
The
39
t ime that the beetles spent
f eeding,
wa l king , r esting , and g r ooming
was r ecorded over a 75-minu t e period .
The procedure was repeated for
beetles
provided
investigation
wi th
D. austr i nus
D. coccus.
and
In
this
all the coccinellids were starved for four days
prior
to the experiment.
The
resu l ts (Tab l e 6) show t hat there was little difference
mean
feeding
on D. opuntiae
times
and
D. austrinus
bet ween
whereas
the
feed i ng time on Q. coccus was notably shorter.
It is therefore clear
that
D. coccus
even
eaten,
when
whereas
the coccine ll ids are starved
both
is
D. opunt iae and D. austr i nus are more
se l dom
readily
consumed.
Table 6.
The mean time (minutes) spent feeding, walking , resting and
grooming
when
by
E. flaviven t ris over a per i od of
the beetles were presented with either
75
D.
minutes
opuntiae,
D. austrinus or D. coccus ( N= number of beetles observed).
I
Mean time (minutes)
Feeding
Wa l king
Resting
Grooming
N
D. opuntiae
5.5 , 30
6 , 85
11 ,2O
1 ,65
15
D. austrinus
-
56,12
9,95
8 , 93
0 , 00
15
D. coccus
36,55
15,23
20,15
4,07
15
-
The r esu l ts of this ,
D. coccus
D. opuntiae
and the previous experiment ,
not acceptab l e to E. f l aviventris as
is
is
show clearly that
a
food
source .
chosen in preference to D. austrinus in a long
term
40
choice
experiment,
although
equal ly readily on either
the last experiment.
Q.
a starved beetle will
initia lly
feed
opun tiae or D. austrinus as indicated by
The role of carminic acid was next investigated
to establish whether the preference for D. opuntiae was linked to the
amount of carminic acid in the body of the cochineal insects .
41
5. THE ROLE OF CARMINIC ACID IN PREVENTING PREDATION.
Carminic acid as a drinking and feeding deterrent.
Carminic
in
acid,
E. flaviventr is
feeding
to
different
Ltd) .
presented
to
whether it influenced
drinking
and
The effect of carminic acid on drinking time
was
investigated by presenting
concentrations
(" purified"
was
concentrations,
ascertain
behaviour .
E. flaviventris
various
solution
carminic acid crystals were obtained from BDH
Chemicals
~.
an
aqueous
carminic
with
acid
A single
of
coccinellids
of
flaviventris was placed in
a
petri-dish
arena
(diameter of 65mm) (Fig: 17) which contained a ring of blotting paper
(width
2,5mm) around the edge.
aqueous
four
carminic
acid solution;
The blotting paper was soaked in
an
The coccinellids were starved
for
days before being introduced into the arena.
behaviour
drinking,
of
E. flaviventris
walking,
was
observed
and
In the arena
the
categorized
as
resting, and grooming . After the coccinellid had
been placed in the centre of the arena the duration of each
activity
was
for
ten
as little drinking behaviour was noted after this time.
The
recorded.
minutes
Observations
in
each case were
continued
same procedures were followed using distilled water (0%) ,
0,5%,
2% ,
Apart from
4%,
8%,
and 16% aqueous
the distilled water controls,
carminic acid
solutions .
a further set of controls were run
soaking blotting paper in an aqueous neutral red
solution.
1%,
by
42
Fig. 17.
The
petri-dish
behaviour
arena
used
to
observe
E. flaviventris
when presented with different concentrations
of
an aqueous carminic acid solution.
aqueous
The
s.
carminic
acid
solutions
discouraged
drinking
by
flaviventris (Fig. 18), and the higher the concentration, the less
time
was spent drinking. Even concentrations as low as 0,5% carminic
acid
had a marked effect on feeding time.
No significant difference
in feeding time was noted between the distilled water and the neutral
red solution.
The increase in walking,
sitting,
and grooming times
with the increase in carminic acid concentration can be attributed to
less time being spent feeding.
43
c.
water
d. water
7. Ct,RMINIC ACID
Fig . 18.
The
time spent drinking, walking,
E . flaviventris
concentrations
when
resting and grooming by
presented
with
of an aqueous carminic acid
different
solution.
The
controls consisted of distilled water coloured with neutra1
red (c. water) and pure distilled water (d. water).
Because
the
carminic acid decreases the drinking time of
effect of carminic acid on feeding times was also
This
was
done
by
weighing the cochineal
insects
E. flaviventris
investigated.
and
adding
appropriate amount of carminic acid crystals (by weight) to the
contents
of
thoroughly
placed
in
the
preferred
mixing
the
the
centre
cochineal
two together.
of
a
species,
A single
petri-dish
~.
which
Q.
an
body
opuntiae,
and
flaviventris
was
contained
the
44
Q.
opuntiae/carminic acid mixture.
were
Four cochineal insect individuals
used in each test and pla ced ,at the the edge of the petri
arena
at equal distances from each other.
beetles
for 010,
0,510,
110,
dish
The feeding times of
the
210, 410, 810, and 1610 carminic acid (over
and above the carminic acid in the body of the cochineal insects) was
recorded .
The
feeding
times
of
E . flaviventris
(Fig.
increasing concentrations of carminic acid,
19 )
decreased
and very little
with
feeding
occurred at concentrations of 410 carminic acid or higher .
GROOM
1.25 -
i," ""','
REST
-
/
)
Hi
)'
VhLK
n?
FEED
L---1
.. '.
.75
<
.S!!
-
»
\)
,...... ,..
,., . . ,>,
.25
3.5
Fig .
19.
The
mean feeding times
Q. opuntiae
carminic acid.
was 20 .
2
4
% CARMINIC ACID
mixed
with
8
16
of E. flaviventris when fed
different
concentrations
on
of
The number of replicates in each experiment
45
Carminic acid therefore decreases the drinking and
E. flaviventr is.
preventing
feeding times for
To establish the possib le role of carminic acid
predation,
the carminic acid concentration of a ll
in
three
Dacty lopius species was determined.
Carminic acid contents of the three Dactylopius species.
The carmin i c acid concentration of the three Dactylopius species
measured
by
means
of
High ,Pressure Liquid
Chromotography
according to Eisner, et al. (1980), with aAl- Bondapak C
water;
2:1;
0.8
ml/min;
ultraviolet detect i on at
Dactylopius females were dried,
in
66% methanol .
18
weighed,
ground
was
(HPLC)
(methanol,
280nm) .
The
and then dissolved
The solution was filtered through a 0,5 urn
membrane before an aliquot Has introduced onto the HPLC
teflon
column.
The
test solution was run against a control standard of purified carminic
acid.
D. coccus
had
the
highest
concentration
D. austrinus the lowest (Table 7) .
insects
the
spectrophotometer
readings than the HPLC,
concentration
7) •
of
of
carminic
acid
and
On a differemt batch of cochineai
results ,
although
shoHing
higher
also recorded that D. coccus had the highest
carminic acid and D. aust ri nus
the lowest
(Table
46
Table 7.
concentrations
The
D.
opuntiae,
and
D.
of
carminic
coccus
by
acid
dry
in D. austrinus,
weight
(HPLC=High
Pressure Liquid Chromotography, Spec=Spectrophotometer) .
1
Species
Carminic acid concentration
I
I
D. austrinus
D. opuntiae
HPLC
Spec
2,8%
5,4%
6,3%
, 10,7%
!
D _ coccus
Eisner
11 ,3%
et
carminic
al.
In
(1980) demonstrated a "feeding deterrent" effect
acid
naturally
15,1%
I
on ants which were "general predators" that
feed on the prey species Dactylopius confusus
did
the natural coccinellid predators of the cochineal insect
not dete rred by
cannot
be
because
carminic acid .
regarded
they
Nevertheless
have
high
data ,
were
E. flavi ventris, a native of Africa ",
as a natural
been
not
(Cockerell).
contrast Baranyovits (1978) suggested with no experimental
that
of
predator
sympatric
concentrations
for
of
of
only
cochineal
about
carminic
insects ,
45
acid
years .
prevented
E. flaviventris from drinking and feeding. As the percentage carminic
acid increased,
acid
was the
Dactylopius ,
the feeding and drinking time decreased. If carminic
only
Q.
factor in
deterring
potential
predators
of
austrinus would be the preferred host as it contains
the lowest concentrations of carminic acid. This is not the case, the
conce ntration of carminic acid is only 2,8% in D. austrinus
with
6,3%
in
Q.
opuntiae.
compared
A marked decrease in feeding time
noted after 4% carminic acid was mixed with D. opuntiae,
was
effectively
47
giving
10,3% carminic acid ,
concentration of D. coccus .
carmin i c
acid
which is similar to the
carminic
acid
This indicates that the concentration of
was too low in
Q. opuntiae and D. austrinus t o deter
feeding whereas in D. coccus the concentration appears high enough to
deter feeding.
Carminic
acid
predation
of
t herefore
the
does not appear to play a major
ro l e
Q. opuntiae and D. austrinus by
long- term
effect
on
in
E. flavivent r is,
E. flaviventris
D. opuntiae and D. austrinus was investigated next.
preventing
when
fed
on
48
6. THE LONG TERM EFFECT ON E. FLAVIV ENTRIS WHEN FED ON DIFFERENT DIETS
Effects on the adults.
In
the
short
difference
term f eeding experiments there appears to
between
D. opuntiae and
Q. austrinus as a
even though Q. opuntiae was preferred in the choice
experiment
was
D. austri nus
therefore
and
be
food
little
source,
expe riments.
An
of
designed to compare
the
suitabi l i ty
Q. opuntiae as a food .source
for
E. flaviventris
over a number of generations .
Six
vials
newly -emerged
E. f laviventris
fema le s were iso lated
in
(di ameter of 25mm and length of 15mm) for 14 days and
glass
fed
"de-waxed"
D. austrinus,
"de-waxed"
D. opuntiae (the pre- oviposition period is 13- 15 days
E. flavive ntr is
Geyer,
wh i le another six were isolated and fed on
1947
a) .
After
the i solation
coccinellids· were each introduced into a vial with four
the
males
that
been
fed the same diet as the females they were enclosed
and
left
for 24 hours during which they mated.
female was isolated in a via l .
Eggs
After
in
period
had
in the vial,
on
with,
mating
each
were laid under the paper
disc
where they were protected from adult predation.
eggs were la i d within seven days the females were mated
If no
again. These
groups and the ir offspring were given an ad li b supply of either "dewax ed 1t D. opuntiae or IIde-wax ed ll
D. austrinus
as food.
49
Daily
the
observations were made to record the longevity of the females,
egg
laying period,
and the number of eggs laid
incubation period of the eggs,
the
female
larva
on
(diameter
day.
The
the eggs developed or not, and
number of eggs that hatched was also
selected
made
~hether
per
recorded.
One
randomly-
was taken from the hatching larvae produced by
each
day
and
was put
into
of 6mm and length of 18mm);
a
smal l
gelatin
each
capsule
daily observations were
then
on these larvae to record larval mortality and the duration
of
each instar.
On
emergence
recorded
of
second
generation (F1) adults,
and six randomly - selected females
sex
ratios
were treated in
the same manner as the parental generation (P1) ,
were
exactly
making sure that no
sib-mating occurred .
Due
to the small number of adult females,
because
is
there
distributed,
the
no
certainty
that
six per
the
generation,
data
was
two-sample Wilcoxon test was used to
data (Sokal and Rohlf,
1969).
and
normally
analyze
the .
Four statistical tests were done
for
each treatment.
i) Beetles fed on
ii) Beetles fed on
Q.
opuntiae, P1 versus F1 generations.
Q.
iii) Beetles fed on
Q.
austrinus, P1 versus F1 generations.
opuntiae (P1 generation) versus beetles fed
on D. austrinus (P1 generation).
iv)
Beetles fed on
Q.
opuntiae (F1 generation) versus beetles
on D. austrinus (F1 generation).
fed
50
Due to four tests being conducted for each treatment,
to
keep
t he
and the desire
significant probability values for each
treatment
at
P=0,05 (*) and P=0 , 01 (**) these probability values had to be divided
by
four
P=0,05
in each test,
and therefore P=0,0125 was
and P=0,0025 for P=0,01 (**) in each
(*)
substituted
test .
This
for
is
a
simplification of the Bonferroni inequality (Mil ler, 1966).
All results for the adul t beetles are grouped together in Table 8.
Table. 8. The
Q.
effect
on
E. flaviventris
of a
diet
comprised
of
opuntiae or D. austrinus for two generations . Only adult
females
are
generation
included
is
labelled
in
the
P1
analysis.
and
The
parental
the second generation F1
(x=mean, and N =number of observations).
Prey
D. opuntiae
species
D. austrinus
Generations
The effect on
x longevity
of adult
P1
(days)
N
TIange
x number
of eggs laid
N
Range
x number
of eggs/egg laying day
N
Range
x egg laying period (days)
N
Range
1 11
6
95 - 124
F1
P1
F1
96
6
66 - 115
92
6
62 - 107
19
6
10 - 3 1
442
268
6
6
270 - 527 106 - 403
438
6
323 - 614
77
6
49 - 103
7
6
0- 19
5
6
0- 15
7
6
0- 25
7
6
0- 32
99
6
78 - 116
83
6
61-97
77
6
59 - 89
15
6
7- 2.4
51
Longevity of adult females.
The
results in Table 8 showed that the longevity of
females
fed
Q.
on
opuntiae
for
the
significantly different from that of the
N.S . ).
that
E. flaviventris
generation
P1
was
not
F1 generation (0,1 >P>0,05
Neither was there a significant difference between P1 beetles
fed
on
D. austrinus
generation
Q.
and
opuntiae
those
(0 , 05>P > 0,025 N. S.) .
beetles fed on
Q.
P1
beetles
However ,
that
fed
on
the longevity of
austrinus was significantly lower
F1
than
that in the P1 generation (P<0,0025 '*) and also si'g nificantly lower
than D. opuntiae ,in the F1 generation (P<O,0025 ").
There
between
is thus no significant difference (P>0,05 N.S.) in
and
P'1
generation
beetles
significant
on
F 1 generation
fed
on
Q. opuntiae
beetles fed on
D. austrlnus.
longevity
There
is,
and
however
P1
a
difference (P<0,01**)' between F1 generation beetles fed
D. austrinus
D. austrinus
is
and the other three groups
less
of
beetles .
sui t able than D. opuntiae
as
Therefore
a
f'lod
for
E. flaviventris. However the deleterious effects are not expressed in
beetles
feeding on
Q.
austrinus for a short period .
The effect
of
different prey on E. flaviventris females was further investigated by
recording
the
total number of eggs laid when P1 and
.f1
generation
beetles were fed exclusively on D. opuntiae or D. austrinus.
52
Number of eggs laid.
The Fl generation beetles that fed on D. austrinus showed a decreased
which was also reflected in their fecundity (Tab l e 8) .
longevi ty,
significant
on
difference between Pl and Fl genepation beetles that fed
D. austrinus
fecund i ty
was
(O,0125>P>O , 0025*)
beetles that fed on
the
A
Q.
shown .
generation
F1
opuntiae also showed a signif i cant decrease in
compared
to
Pl beetles that fed on
(Table. 8,
0,0125> P> 0 , 0025 *)
affected
than
beetles
although
were
that
these
the
same
diet
beetles
were
less
fed
D. austrinus
on
(0,0125> P >0,0025* ) •
There was no significant difference between P 1
generation
that
beetles
fed
on
D. opuntiae
and
D. austrinus
then
analyzed
(0 ,3> P > 0 ,20 N. S . ) .
The
egg-laying
determine
period
and oviposition rate was
to
which was responsible for the decrease in egg production in
the second generation beetles.
Egg-laying period.
The
egg- laying
D. austri nus
generation
generation
period
(Table
fed
on
of
8)
E. flavivent r is
was
Significantly
D. austrinus
coccinellids
fed
F1
generation
shorter
tha n
(O,0 125>P>O , 0025 *).
on
D. austrinus
also
fed
on
the
Pl
The
showed
Fl
a
significantly shorter egg laying period than the F1 generation fed on
Q. opuntiae
(P<O , 0025 ** ) .
between
generation
P1
D. austrinus
There
beetles
(O , 2>P>O , l N. S.),
was
that
or
no
fed
significant
on
Q.
difference
opun tiae
between P1 and F1
or
on
generation
53
E. flaviventris
egg- laying
that
on Q. opuntiae (0,1>P>0 , 0125 N.S.). The
fed
period of F1 generation beetles that fed on
D. austrinus
clearly showed a marked decrease even though the percentage time that
eggs
were laid during the beetles life span was similar
(Table
9).
The oviposition rate was then investigated.
Table 9.
The
percentage time that E. flaviventris laid eggs
the
females ' life
span
when
fed
on
during
Q. opuntiae
and
D. austrinus for the F1 and P1 generations. (N =t otal
number of beetles observed).
Generations
P1
N
F1
D. °Euntiae
87,4%
86,4%
6
D. austrinus
82,4%
79,8%
6
Rate of oviposition.
In
Table 8 no significant difference between any of the
rates was shown. This analysis does not show whether
rate
has
constant or whether it varied over the
oviposition
the oviposition
egg-laying
period
between treatments. Therefore the "five day moving averages" (Turkey,
1977) of the mean numb er of eggs laid per day was plotted in Fig. 20 ,
which
also
summarizes
the
effects
of
the
different
E. flaviventris. Two conclusions were drawn from Fig. 20.
diets
on
54
i) The Pl generation beetles that fed on
Q.
opuntiae and
Q.
austrinus
and the F 1 generation beet les that fed on D. opuntiae 'all laid
eggs
over a similar period of time,
their
and at a similar rate over this,
period of time.
ii)
Fl
beetles fed on D. austrinus laid all their eggs over a
shorter
period
treatments.
although
of
This
time (25 days) than the
resulted
in
a
smaller
females
total
of
egg
much
the
other
production,
the egg-laying rate was the same as for the females in the
other treatments.
The
egg laying rates for number of eggs laid per egg l aying day
similar
for
all
E. flaviventris
treatments,
females
however,
that
fed
signi ficantly shorter longevity,
laid
for
difference
exclusiv~
food
E. flaviventris.
the different
for
two
adult
Fl
D. austrinus
generation
showed
laid a smaller number of eggs ,
a shorter period of time.
between
on
the
As food was
treat~ents,
generations
was
are
the only
a
and
apparent
D. austrinus
unsuitable
as
an
for
55
8
PI BEETLES FED ON Q. OPUNTIAE
6
en
(I I)
4
M",.,.... 10"9.... 11:), of "'d.... ll .. l It day.
M"':>,, egg 10y'n9 po.- ' ",.:! .. 99. 3 day.
1-10><\""''' laying pe .. ' o.:! .. 116 doy.
M"", ........... b" ... of "9S8 1" l d - 441.5 "9SE!J9 loylng .... 1:0 .. 6,5 "'99"/099 loY' ....9 day
2
(i) Ciil)
(ii)
a [J
'V
20
6a
40
80
120
8
FI
BEETLES FED ON Q. OPUNTIAE
6
( I)
(ii>
H,,"'n 10nS."lly of' ..dull .. 96, " day ..
Heor> "'99 laY;"9 pa .. lod " 93,(J day.
(II!) 1040><'''''''' "99 10yl"9 par- loa " 97 dolOI'''
4
(Iv)
H"on ......... b., ... of "9S. l ed.:! .. 267,6 "99-
(v)
E!J9 le'yl"g .. ol ... S.l "99-/eS9 l aying dol'
0
<
2
'"
'-'
'-'
[J
--'
w
(ii)
2[J
0
"0
a::
u.
( )
-"'--.:c:..:.~-..: i \l ( I...
)
II
V
60
40
12[J
8~
113
m
:>:
~,
z
z
8
"
6
u.
'"
(\)
(ii)
H"on 1""S""ll:y of "J"I1: .. 92. 2 do y"
M. a", -99 loylng ? "rlod .. 77,2 day.
(ill) Ho><I"'''''' "'99 10)11'"'9 pc,",o.:!" 99
<i,,}
(,,)
4
d"r.
~ .. on ,",,, .. b.,,...
of "99'" I.,;d .. 438, i'I "9':1"
E9!J 10)'1""9 "a~.o" 7,3 -9'3,,1_99 1"),\1'9 doy
2
0
a
21'!
41'!
60
121'!
8iOl
8
F1 BEETLES FED ON Q.
AU.~:rB I N~?
6
(n
4
(Iv)
(.,)
2
0
101 .. ",., 1""9""ll),
or ..dull"
19, e da y-
(II) 1),,,an -egg l"yl ng porlod a 14,8 doye
(Iii) M"""mu .. "'99 l oying p"riad" 2 4 day"
101""" ,",v .. b.,... of c~39m 1"ld .. 75,5 "99Egg 101'1"9 "al . .. 6, 6 .99 ~ /o99 l" yl"g do)'
(i)
(ii)
\7 V:
iJ
(iil>
'V
20
6a
4 I'!
80
121'!
100
DAYS
F i g . 20.
The
mean
generations
~.
number
of
of
eggs
laid pe r
E. f lav iv entris
day
females
by
Pl
tha t
and
fed
Fl
on
opuntiae and D. austrinus. The longevity of the females,
their
mean
egg laying period and their total
egg
periods are also gi ven. Six replicates in each case .
laying
56
Effect on the immature stages.
The
effect
of
investigated.
mortality,
different
The
the
diets on the
incubation period ,
number
immature
stages
was
percentage egg hatch ,
of larval instars and
their
then
larva l
duration
were
investigated. The results are presented in Table 10.
Table 10. The
effect
on
exclusively
on
generations
(F1
second
~.
flaviventris immature stages
Q.
the
opuntiae
or
D. austrinus
when
fed
for
two
first filial generation and
filia l generation)(N=number of observations
F2
the
and
x
=mean) .
Prey species
D. austrinus
D. opuntiae
Gene rat ions
-
The effect on
x incubation
F1
F2
F1
F2
8
1 16
0,92
9
377
0,81
8
122
0,77
9
175
0,79
N
84
138
89
426
81
151
62
281
'/0 larval mortality
N
15
200
16
200
40
200
100
66
13
81
6
171
5
91
4
168
19
79
2
12 1
-
25
138
1 ,96
30
11 2
2, 11
28
95
2 , 06
-
62
138
51
112
54
95
-
period (days)
N
Standard error
% egg hatch
Number of larval instars
before pupation
% three
% four
'Yo
five
N
Mean period, hatch to pupation
(in days) of larvae with 4 ins tars
N
Standard error
Sex ratio (% females)
N
57
I n cubat i on period and percenta ge egg hatch .
The
incubation
species
period
of
the eggs was not affected
by
(Table 10) or by the period for which the prey
the
prey
species
was
eaten .
Egg hatching, however was affected by these factors . Table 10 shows a
very
similar pattern
stock
was
fed
D. austrinus
~.
and
for the F1 generation
(84,1%,
In
the
F2
generation
beetles
not hatch were divided into categories,
development"
incubation
F2
generations
88,5%,
that
(indicated
period),
by
those
the lack of colour
no
hatching"
E. flaviventris
generations
nowever
fed
that
change
on
"no
the
and those that showed some development but
did
and
fed
11
on
Fig .
no
21 .
The "hatch",
development "
~.
opuntiae
The results
of
"development
eggs
during
the
laid
F1
was
and
These eggs had a hi gher "no
with no hatching" percentage.
development"
F2
that
and
The diet of the parental
stock does appear to influence the percentage egg hatch .
source appears to decreases the percentage egg hatch.
diet on the larvae was investigated next.
by
similar .
eggs hatched when laid by F2 generation beetles
on D. austrinus.
"development
fed
that showed
and on D. austrinus for the F1 generation
fewer
80,8%
during
this analysis are shown in
with
and
The eggs that
not hatch (these developed a red spot (Geyer, 1947 a)) .
of
and
were
percentage egg hatch was lo wer (62,~1o).
austrinus ,
did
flaviventris egg hatch when the parental
on D. opuntiae for the F1
fed
respectively).
for~.
A poor food
The effect
of
58
FED ON Q. OPUNTIAE
Fl
F2 gener(:d~. i on
generotlqn
HATCHEO 83. 8%
HATCHED 88.SX
(
\
~
NO 0[V. 4.4:
Y"'v.
1lD HATCH 7. I:
~/
FED ON Q. AUSTRINUS
F2 generation
Fl generation
HATCHED 62.2X
.~
_ ______
HATCHED Bll. ex
110 oEV. IB.1X
'1>%'6151>'7 . NO
0E'1. 17.SX
OEV. tiD HATCH 9. II
O'V. Nll HATCH IB.3X
Fig . 21 .
The percentage hatch of eggs
fed on D.
fir st
opuntiae or D.
filial
(F1l
of~.
flaviventris that
were
austrinus for two generations, a
and a second fil i al
were classified in
ways;
generation .
Unhatched
eggs
developed
(DEV . l but d id not hatch and eggs that showed no
sign of development.
two
(F2l
eggs
that
59
The effe ct of the different diets on the larvae.
The F1 generat ion mor t ality (Tabl e 10) fo r E . f l av i ven t ris larvae was
higher
Q.
(40%) whe n fed on
opuntiae
(15%).
In
Q.
aus t rinus
com pared with
the F2 g e ne r ation,
l arvae fe d
mor t ali t y was
100%
larvae fed on D. austrinus and no l arvae developed beyond the
i nstar
Q.
(Fig .
opuntiae
22) .
there
On t he othe r hand,
was
only
on
fo r
second
i n the F2 gene r a t ion f ed
a 16% mortality.
In
all
cases
on
mos t
mortalities occurred i n the first insta r (Fig . 22) . The proportion of
first instar deaths is higher in larvae that fed on D. austri nus than
F1
and
F2
larvae
that fed on
Q.
opuntiae .
Only
a
small
pupal
mo r tality was reco r ded (5%) on F1 generation E . flaviven t ris tha t
on D. austrinus
The
(Fig. 22) .
developmental prog r ess o f th e surviv i ng larvae was
recording
the
number
of larval i nstal's and
t heir
followed
duration .
E . flavive nt ris la r vae completed t heir developme n t and pupated
four
instars
fed
(Table 10) and feeding on
did not affect this trend .
Q.
opuntiae or
by
Most.
aft er
D. austrinus
More larvae passed through three
ins ta r s
than five i nstars .
The
mean
dura t ion
development
tha t
fed
in
on
o f la r val development in
those
that
completed
fou r i ns t ars was s hor t est fo r F 1 generation
Q.
opuntiae (Table 10),
was slight l y
longer
be etles
f or
generatio n coccine l lids that f e d on D. aus tr i nus and was longe st
F2
generation coccinellids when fed on
fed on
Q.
Q.
opu ntiae.
F1
f or
The larvae tha t
aust r inus during the F2 generation all died , only 10 l a r vae
survived the first instar and will not be considered further .
60
Fl larva e fed on
g.ogun~1a e
1ST INSTAR 18.2%
1ST INSTAR 56.21J,__
~_
PlPAE 0%
ITll INSTAR 4. 4%
fU'AE B%
2t4J IIlSTAR 3. 4%
4Tll IIlSTAR IB. 2%
3Rll HISTAR B. 7%
21{!
3I<!l IIlST AR 37. 8%
Fl larvae fed on ~ .
I lIST AR 3ll. 3%
F2 larvce fed on g. oU8~rinu9
oustrinu a
1ST IIIST AR 75. 9X
PUP!.E 5.1%
1110 HlSTI.R IS. 1X
4TH IIISTAR 6.3,
2}lD !tiSTAR S. 9%
Fig .
22.
The contribution (as a percentage) to the total
of
each
D. opuntiae
immature
stage
mortality
of E. flaviventris when fed
on
or D. austrinus for the F1 and F2 generat i on s.
61
In
Fig.
23
the
durations of the immature stages
are
shown
more
clearly. Several conclusions can be drawn from Fig. 23.
i)
In each case F2 generation larvae took longer to develop than
F1
generation l arvae when fed the same diet.
ii)
In
the F1 generations,
beetles that fed on
D. austrinus
took
longer to develop than beetles that fed on D. opuntiae.
iii)
The
differences between the treatments are
significant,
except
significant
difference
D. austrinus
in
the
second
between
ins tar
where
statistically
there
was
no
that
fed
on
F1 generation larvae
and F2 gene ration larvae that fed on
is regarded as significant (P <
difference
all
Q,
D. opuntiae
(the
05) when the notches
in
two or more boxes do not overlap (McGill et al. 1978)).
The
Fig .
intervals between moults were similar in all cases,
24,
specific
where
day
is
the cumulative percentage of
plotted.
larvae moulting on
With each consecutive
spreading and flattening of the pattern is noted,
of
larger
deviations
These
differences between
as shown in
the means and the
instar
a
a
slight
this is the result
larger
standa rd
shown in Fig. 23 .
differences
appear
t o be due to the difference in
the
food
value of the two prey species, D. austrinus apparently having a lower
food value for the coccinellids.
62
50,-----------------------------------------------------------,
45
E2l
Fl lorvoe ~e d o n Q.~.
D
F 1 lor-vee fed on Q. f!.
~
f2 lar vae f ed on Q'2-
35
•i;",
30
•
..,o
•,
25
,o
20
L
...o
~
.>
o
L
,5
15
,
i- I . 751 r.;
10
i -S
5
0L-~--~--------------------------------------------------~
1st. i na ter
2no i ne t-or
3rd i "etar
4t.h instor
Pupae
fig. 23.
The
duration
of
the
immature
stages
of
E. flaviventris
that were fed exclusively
(D.o.)
beetles that were
(D.a.).
and
f1
(x=mean,
S=standard
fed
deviation,
observations) (McGill , et al. 1978).
on
only
f1
and
f2
D. opuntiae
D. austrinus
and n=number
of
63
Ii
1~~
.'
90
.'
80
I
7~
M
>
;::
-<
I ,
'"
u
4~
/
10
//
1/ :
I:'
(
I
I .:
!
I'
/
/
/
10
2nd
let
instar
15
3rd
1nator
/ .
I
/
I
i
i
I
I
i
I
I
J
i
/
,I
//Q.Q.
for Fl
-, /g. 9·
for Fl
/
/
/'
/
25
2~
. .'
;
I
J
:
~
0
1/1
I
I
/ .:
~<.
. ('
I
I
I
i
I :
I '
I
inotor
/
:
/
//1
I'
/,
:
/
/
/
ff
2~
0
I
j
J
I
3~
j
Ii.'
I :
...J
:0
:0
.
f
/
, !, .
5~
/ r-I
/. '
: .i
.
/ II ;·
6~
W
I
/
, I ..
I I .:
I
/ ~~/
(.'
/
.
I /
/.
L _/
/
/
/
30
4th
/
/
fo~
D. o.
40
35
45
Pvpce
ineter
DAYS
Fig. 24.
The
~.
cumulative
flaviventris
percentage
immature
of
I
moulting
stages that fed
intervals
on
~.
for
opuntiae
(0 . 0) and D. austrinus (D . a) for the Fl and F2 generations.
F2 1
50
64
The
diet
of
incubation
decreased
larval
the
parental
period of the eggs.
However,
not
appear
to
affect
the percentage
when F2 generation beetles were fed on
egg
the
hatch
D. austrinus.
The
mortality was also higher in Fl generation larvae that fed on
D. austrinus
and
D. austrinus
died.
larval
stock did
ins tars
in the F2 generation all the larvae
Diet
but
does
that
not appear to affect the
the duration of the ins tars
was
fed
on
number
of
shown
to
be
shortest for Fl generation larvae that fed on D. opuntiae · and longest
in the F2 generation .
The sex ratios of adults which as larvae had been fed on
Q.
opuntiae
D. austrinus for the Fl and F2 generations were recorded and are
and
shown
in
E. flavi ventris
and
10.
Table
fed
approximately
(59% females).
generation
could
be
The
and
The
sex
ratio
of
the
Fl
generation
on D. opuntiae was female biased (620/,
corresponded to that recorded by
Geyer
of
females)
(1947 a)
change (towards 50%) in the sex ratio of the
the F2 generation for beetles
due to the difference in
·fed
on
Fl
D. austrinus
quality of food resulting
in
a
greater mortality of female larvae.
Of all the variations in the long term experiments only the following
show a significant difference.
i)
Longevity
of
adults,
with Fl generation beetles
that
fed
on
D. austrinus living significantly shorter than the beetles fed on the
other diets.
ii)
Number
of
eggs laid,
the Fl generation beetles
that
fed
D. austrinus laid significantly fewer eggs than the other beetles.
on
65
iii)
The
egg
D. austrinus
laying period of Fl generation beetles
was
that
significantly shorter than the beet le s fed
fed
on
on
the
other diets .
iv) The percentage egg hatch of the Fl generation females that fed on
D. austrinus was lower than the eggs of females feeding on the
other
diets.
v)
The
l arval
D. austrinus
larvae
was
mortality
of
Fl
and
higher than larvae that
F2
fed
larvae
on
that
~.
fed
opuntiae.
developed beyond the second ins tar in the F2 larvae that
on
No
fed
on D. aust rinu s .
vi)
~.
The
sex
opuntiae
other diets .
ratio
of
the
Fl
generation
showed a bias towards the females,
beetles
that
with no bias
fed
on
on the
66
8.
DISCUSSION.
All
lack
female
scale insects have piercing and sucking
wings.
Adults of the more primitive families tend to be
mob ile and have large,
more
complete
reduced ,
and
and
quite
well-developed legs with numerous setae .
advanced scale insects,
towards
mouthparts
however,
show an increasing
The
tendency
sedentary behaviour with their legs and leg
setae
culminating' in the apodous fema l e pit scale insects (Miller
Kosz tarab,
1979).
The sedentary life of the scale insects
has
made them vulnerable to insect predators and parasitoids.
The coccinellids are one of the general insect predators that prey on
the
Coccidae ,
also
preying heavily on
(Clausen,
1940;
has
well documented (see Hodek,
been
1972;
Rodalia
Icerya
purchasi
al.
Maskell,
1966;
1981 b) .
Coccinellids have
and
Emden ,
also
the
been
vedalia
against cottony-cushion scale,
resulted in one of the
first
biological
Cryptolaemus montrouzeri Mulsant and Cryptognatha
Marshall were also biological
mealybugs
Aleyrodidae
Eastop and van
The introduction of
card ina lis Mulsant,
con trol successes,
nodiceps
et
in bio logical control.
beetle ,
and
De Bach, 1974) . Predation by coccinellids on aphids
Baumgaertner
impo rta nt
Aphididae
cont ro l
coconut scale respectively
successes,
(Taylor,
1935;
against
Clausen,
1940; Hagen , 1962; De Bach , 1964, 1974),
Mann (1969) has proposed that in North and South America the relative
sca rc ity
of
Q.
Arizona)
is
due
indigenous
opuntiae in parts of its natural
to the prevalence of
t o these areas,
var i ous
These predators
range
(Texas
predaceous
and
insects
include the ad ults
and
67
larvae
of
many
mot hs,
of
syrphid and agromyzid fli es,
South Africa,
contro l led
coccinellid species ,
the cochineal insect
Q.
larvae of
and some
severa l
phycitid
neuropterans .
In
opuntiae has been shown to
be
by coccinell id beetles (Annecke,
et
al.
1969 ;
Burger,
1969).
Many
scale
protection.
point
develop
insects
a
wax
secretion
that
serves
as
The scale insects appear to require a hard, high melting
wax to protect them from i n sect predators and from the weather
(Tulloch,
which
1970) .
There
is considerable variation in the manner
the wax is attached to the insect and the form the
when
sec reted.
thick
plates
(Coccidae} .
In
of
Some
wax
takes
some scale insects the females are covered
wax,
as occurs in
some
species
of
in
with
Ceroplastes
species such as the Pulvinaria (Coccidae)
species
and some of the Dactylopius species secrete a woolly mass of wax. The
mealy bug , on the other hand, has a powdery wax covering its surface .
In
some
insect
scale
and
insects a ha rd scale of wax and exuviae
shelters
Diaspididae .
the
insect and its
eggs,
as
c overs
found
the
In these diaspidids the scale is produced by secretions
of loose fibres called the white cap secreted mainly by the
glands
in
the
pygidial
and a glutinous liquid discharged from the anus which fo rms a
homogeneous
mass that toughe ns into the
scale
(Baranyovitz ,
1953 ;
Beardsley and Gonzalez , 1975) .
The
successfu l
appears
covering.
to
predation of Cocc i nellidae against diaspi n e Coccidae
be limited by certain physical chara cters of
the
scale
Species with a relatively thin covering are readily preyed
68
upon
whereas
species
Lepidosaphes,
with a thick
Chionaspis,
and
and
tough
Protaspis,
covering ,
such
as
are relatively free from
attack by members of the coccinel l ids (Clausen, 1940).
The woolly "waxy covering" of
(Fig.
4)
was
p r otect ion
"waxy
shown
Q.
opuntiae (Fig.
by Walter (1977) to afford
from E . f laviventri s (Fig .
covering" of
Q.
of
the
6)
the
predation.
D. austrinus
insects
some
However ,
the
opuntiae was penetrated with greater ease than
that of D. austrinus (Walter ,
properties
3) and
1977;
and this study).
"waxy covering" was also shown to
The
physical
be
different
(Walter, 1977).
The
II
waxy covering" of Q.. opuntiae and Q.. austrinus,
wax"
contain a
substance produced by ducts associated with the
pores,
and
a
setae .
The
different
"non
quinque locular
waxy substance produced by qUinque locular
pores
ahd
proportions of these sUbstances could be
the
reason fo r the difference between D. opuntiae and D. austrinus
"waxy
coverings!!.
In D. coccus no ducts are found (De Lotto, 1974), and the thread - like
components
resul ting
protection
on
to
which
the wax matrix adheres
are
not
present,
in a powdery type "waxy covering" (Fig.
5) .
In
D. coccus
completely
different
against predation is achieved in a
manner to D. opuntiae and
barrier,
D. coccus
Q.
females ,
covered with a powdery wax.
completely
austrinus.
and
their immediate
In the laboratory
protected against predation,
the potential predator (Fig.
Instead of a wooly mass as a
9),
vicinit i es ,
Q. · coccus
fema les
are
are
by clogging up the tarsi of
resulting in a loss of adhesion by
69
the tarsi of t he pr edator to t he s ubstrate.
the
This is very similar
to
wax bl ooms of br ass i c a s wh ich was shown to c l og up the tarsi
of
the mustard beetle Phaedon cochleariae (fabricius)(Stork, 1980 b).
To
the
investigate
whether t he "waxy covering" was the only reason
field observations that E. flaviventris preys
predominantly
D. opuntiae, E. flaviventris was given a choice of prey
(Q .
D. austrinus
showed
and
E. flaviventris
species.
D. coccus).
preferred
Q.
This
experiment
opuntiae to the other two
for
on
opuntiae ,
that
Dactylopius
This preference could be due to the presence of prey toxins
in the less prefer r ed prey .
A multitude of chemical defenses against a variety of animals as well
as microorganisms exist in many arthropods.
There are two
principal
ways in which arthropods may acquire defensive substances,
i) from a
dietary
source
(extrinsic) or ii) by synthesis of the substance
by
the arthropod itself (intrinsic)(Eisner, 1970) .
i)
Eisner (1980) noted that "the acquisition of
defensive
from a dietary source - is wide spread among insects!! .
defensive
substances have been recorded in Coleoptera ,
Neuroptera,
Hemiptera ,
material
The extrinsic
Lepido pt era,
Diptera and Orthoptera (Eisner ,
1970 , 1980;
Rothschild, 1973; Bowers, 1980 , 1981) and in some parasitoids ( Vinson
and
Iwantsh ,
cottony - cushion
poorly
on
1980).
The vedalia beetle was noted not to develop on
scale growing on the ornamental Coccu l us ,
others such as maple and scotch- broom
(De
and
Bach,
does
1974) .
70
Hos t - plant-induced
immunity of an insect to a pa rasite
or
predator
could l ead to false c onclusions as to its effectiveness on feeding on
the specific host or even its presence in a parti c ular a rea.
ii) A large number of intrinsic ch e mica l defense s u bstances have been
recorded and invest i gated (Blum,
of
these
of
1981). The synthes i s of most
products have not been elucidated,
well-known
large
1978,
organic
but most of
compounds with relatively s i mple
them
structures .
a
variety of compounds are found which suggests that
metabolic
pathways
compounds (Blum,
Hymenoptera,
indicate
varied
A
number
defensive
1978, 1981). The varied defensive strategies o f the
Coleoptera ,
the
exist in producing these
are
great
Hemipte r a , Phasmids , to mention but a few,
variation that does
exist .
In
some
predator
species extrinsic defense substances a r e obtained not from plants but
from
intrinsic
examp l e,
defense
larvae
containing
the
of
th e
substances
pyral id
from
their
La~ti l ia ,
anthroquinone carminic aCid,
insect
prey.
feeding
repel
on
ants
For
coccids
with
the
quino ne -rich oral discharge from their cr ops (Eisner et al. 1980).
Carminic
acid,
cochineal
which is probably synthesized in the fat body of the
insect
E . flaviventris
from
(Needham,
1978),
feeding when it was
was
in
shown
h i gh
to
prevent
concentrations.
D. coccus has a high concentration of carminic acid (11%) which could
be
the
reason
experiments.
why
this species was not preferred
in
the
choice
D. austrinus , on the other hand, was recorded as having
the lowest carminic acid concentration (2%) of the three spe'cies and
71
was
also not preferred in the choice
experiments,
thus
indicating
that a low concentration of carminic acid appears not to be important
in predator prevention.
Carminic
acid
parasitoids .
in
low
concentrations
prevent
attacks
by
Moran (1980) points out that there have been no reports
of paraSitism in Dactylopius .
also
could
appear
Other Homoptera with red body contents
to be free from parasitoid attack,
such
as
the
pine
woolly aphid Pineus pini (Macquart) (Bruzas, 1983).
On
investigating
the effect of different Dactylopius
(D. coccus,
D. austrinus and D. opuntiae)
found
D. coccus
that
D. austrinus
could
was
sustain
not
on~.
suitable
at
the beetles for
prey
spec i es
flaviventris, it was
all
only
as
a
one
food
and
generation.
D. opuntiae was the only pre y of the three species that could sustain
the beetles for more than two' generations .
that fed on
Q.
opuntiae a lso showed that
not entirely suitable as a food.
the
that
The F1 generation beetles
Q.
opuntiae, on its own, was
This unsuitability could be due
food source lacking some required nutrient .
all coccinellids were polyphagous ,
Hodek (1966)
and Hagen and Sluss
to
note'd
(1966)
showed that when a Hippodemia species was restricted and only allowed
to
feed
declined
on
the
compared
aphid Terioaphis
to
trifolii
when it was fed a
mixed
(Monell),
diet
its
of
vigor
different
species of prey and non - insect food (honey - dew and pollen).
The
disappearance
establishment
was
of
D. coccus in South Africa after a
unlikely
due to
predation
by
period
of
E . flaviventris.
Likew ise the partial success of D. austrinus as a biological
control
72
agent is unlikely to be due to predation by the beetle . Other factors
such as dispersal (Gunn , 1979) and weather could be responsible.
This
the
study showed that in the laboratory E. flaviventris
"waxy
covering" of Q. opuntiae with greater ease than
Q. austrinus,
most
that
of
and preferred to feed on Q. opuntia which was a better
food source compared to the other two Dactylopius species.
the
penetrated
These are
likely reasons why the beetles feed on D. opuntiae in
field and not on D. austrinus.
the
73
SUMMARY .
i)
D. coccus
is protected against
"waxy coveringrt.
D. coccus.
The
easily penetrated by
ii)
clog
up
D. austrinus
ability
to
the
have
to
D. opuntiae
tarsi
is
fine,
E. flaviventris .
of
relatively
powdery
form
Q. opun t iae
which differ
the beetle from predation du e to
of the "waxy coverings" .
the
provides
flaviventris .
woolly "waxy coverings" ,
protect
properties
due
"waxy covering " of
~
its
though not as effective as that
"waxy covering" of Q. coccus is in a
The
.. hich
flavive ntri s predation by
"waxy coveringll of D. austrinus also
The
against E. flaviventris;
protection
of
~.
in
the
and
their
physical
These differences appear to
number of "non - wax" threads
in
the
"waxy
be
covering",
D. austrinus having more "non- wax" threads than D. opuntiae.
iii)
E. flaviventris
D. coccus
when
Q.
preferred
opuntiae
to
D. austrinus
given a choice of the three cochineal species
or
with
i ntact "waxy cQverings ll and when the IIwaxy cover i ngs" were removed.
iv)
~.
In
high
concentrations
flaviventris ,
preferring
Q.
carminic
acid
prevents
feeding
by
and this could be the reason for the coccinelid not
coccus. In concentration of 4% carminic acid and highe r
litt le feeding appears to occur .
v)
D. coccus
inferio r
food
cannot
sustain ~.
compar ed
to
flaviventris ,
Q.
opuntiae
coccinellids for more than two generations.
D. austrinus
which
was
sustained
an
the
74
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