Biol . J . Linn . Soc., 7: 113.146 . With 17 figures
June 1975
Ecology of cotton stainers (Heteroptera:
Pyrrhocoridae) in southern Ghana
B . A . FUSEINI
AND
R . KUMAR
Zoology Department. University of Ghana. Legon. Ghana
Accepted for publication December 1974
An account is given of the ecology of four species of Dysdercus in southern Ghana . Succession
of host plants. host preference and migration is studied Colony structure is examined Natural
enemies are investigated . Mimetic resemblance of the resident predator to a particular species of
host Dysdercus is studied . Experiments on the palatibility of Dysdercus species to mammalian
predators are discussed .
.
.
CONTENTS
Introduction
. . . . . . . . . . . . .
Materials. localities and methods
. . . . . . .
Materials
. . . . . . . . . . . .
Localities . . . . . . . . . . . .
Methods for the determination of host preferences
Methods for the study of colony structure
. .
. . . .
Methods for the study of migration
Methods for the study of natural enemies
. .
Observations and Results
. . . . . . . . .
Host plants
. . . . . . . . . . .
Successionof host plants
. . . . .
. . .
Effect of rain on plants and bugs
Discussion
. . . . . . . . .
Host preference
. . . . . . . . . .
Discussion
. . . . . . . . .
Colony structure . . . . . . . . . .
Coloniesin thesavannazone
. . . .
Colonies in the forest zone . . . . .
Discussion
. . . . . . . . .
Natural enemies
. . . . . . . . . .
Parasites
. . . . . . . . . .
hedaton
. . . . . . . . . .
Invertebrate predators
. . . . .
Vertebrate predators
. . . . .
Discussion
. . . . . . . . .
Summary . . . . . . . . . . . . . .
Acknowledgements
. . . . . . . . . . .
References
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113
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B. A. FUSElNl AND R. KUMAR
INTRODUCTION
Bugs of the genus Dysdercus Guerin-Meneville, 183 1 (Hemiptera: Heteroptera; Pyrrhocoridae) are well known pests of cotton in many parts of the
world. Members of this group are distributed throughout the tropics with each
continent having its own group of species (Pearson, 1958). Ten species of
Dysdercus have been reported from Africa (Pearson, 1958) and five are known
to occur in Ghana. Since the cultivation of cotton on a large scale in Ghana
started in 1968, two species of Dysdercus have already established themselveb
as serious pests. With the cultivation of malvaceous fibre plants such as kenaf
already one of the priorities in Ghana, it is clear that a study of the ecology of
Dy sd ercus species is high 1y desirable .
Several studies on various aspects of the biology, behaviour and other
features of some Dysdercus species have been made by a number of workers.
Of these, mention should be made of the works of Dingle (1972), Doesburg
(1968), Duviard (1972), Fuseini & Kumar ( 1 9 7 9 , Johnson (1963), Kennedy
(1961), Pearson (1958), Whitefield (1933) and Youdeowei (1966, 1967). The
work of these authors throws much light on aspects of the biology of the genus
Dysdercus. However, in general, very little information exists on the details of
colonial populations of Dysdercus species and their fluctuations in size. To
these should be added local problems, for example, the occurrence of wild host
plants, host specificity as well as natural enemies. A knowledge of the aspects
investigated in this work will, it is hoped, assist in evolving long term control
measures against the cotton stainers in Ghana and also contribute further to
our understanding of the ecology of insects in the tropics.
MATERIALS, LOCALITIES AND METHODS
Materials
All the material used in this work was collected by the writers from the field
and a part was reared in the laboratory. Species studied were as follows:
1. Dysdercus superstitiosus (Fabricius)
2. D. fasciatus Signoret
3. D. voelken Schmidt
4. D. melanoderes Karsch
The fifth species D. haemorrhoidalis Signoret is uncommon in Ghana. Only
two specimens of this species were collected in the entire study. The bugs were
fed on seeds of the following plants:
1. Sterculia foetida L.
2. Ceiba pentandra (L.) Gaertn.
3. Hibiscus micranthus L.
4. Sida acuta Burm.
5 . Bombax sessilis (Benth.) Bakh.
6. Ochroma lagopus Sw.
Localities
The distribution of host plants was surveyed in both the savanna and forest
areas in southern Ghana. In the savanna zone, areas near Legon, Achimota,
ECOLOGY OF COTTON STAINERS
115
11.-
10'-
Figure 1 . Map of Ghana showing localities where colonies of Dysdercus species were studied.
9
9'
-
8.
-
7'
-
B. A. FUSEINI AND R. KUMAR
116
Teshie, Ashiaman, Nungua (all in Greater Accra Region) and Kpong in the
Eastern Region; and in the forest zone areas near Aburi, Kade, Koforidua, Tafo
and Krobo Hills (all in the Eastern Region of Ghana) were surveyed (Fig. 1).
Methods for the determination o f host preferences
Thirty adult individuals (15 males and 15 females) of each species of
Dysdercus were used. Two species of seeds were used at a time. These were
crushed and each heaped at one end of a rectangular perspex box, opposite
each other. The box measured 30 x 20 x 10 cm. The 30 insects starved for
some hours previously were released at the middle of the box and the number
feeding on each species of seed was recorded at 30 minute intervals for two
hours. They were disturbed after each recording. This was repeated three times
for each species of bug. Fresh individuals were used for each series, that is, for
each different pair of food given to the insects. There was no weighing of food
supplied but approximately equal volumes were given. For Sterculia foetida
and Ceiba pentandra seeds, two seeds of Sterculia foetida and 20 of Ceiba
pentandra were crushed and given to the bugs. For Bombax sessilis three seeds
were used. Seeds of Hibiscus micranthus and Sida acuta are small, so reasonable
quantities, which were not out of proportion, were used.
1971
1972
Months
.
Fig.2
ECOLOGY O F COTTON STAINERS
117
Methods f o r the study of colony structure
Colonies of the Dysdercus species were mapped in both the savanna and
forest zones. Seven colonies were located in and around the Legon campus,
within savanna zone. A wooded savanna colony on Krobo Hills was also
studied. This area is hilly and thickly wooded but it is within the savanna zone.
In the forest zone (around Koforidua and Aburi) there were originally four
colonies, but these were finally reduced to one by early mortality of the
insects.
Each colony was sampled weekly. In few instances, when sampling could not
be done on the seventh day after the premous sampling date, the day following
was utilised. Where the colonies were not large the estimates of the numbers are
based on actual counts. In colonies where the numbers ran into thousands, only
approximate estimates were made. This was done by counting the bugs in a
measured area and estimating the total number within the colony based on the
number within the measured area. The size of colonies varied from very large to
very small and hence the unit area cannot be given here; it depended on the size
of the colony. Figures 2 to 17 show the numbers recorded in each month.
Months
Fig. 3
Figures 2 and 3. Population changes in D. voelkeri and D. fcrsciotus respectively in colony No. 1
(host plant Sterculia foetida). x, larvae; 0, adults.
B. A. PUSEINI A N D R. K U M A R
118
--
6000-
-
1000
-
500 -
-
VI
n
Y
100-
-
r
&
5
50-
-
z
10
0
-
I
I
Nav
I
Dec
I
I
I
I
Jan
Feb
Mar
Apr
May
Jun
Jul
Methods for the study o f migration
An attempt was made at marking some adults in order to investigate
migratory activity of the bugs. A yellow oil paint was used. Two small circular
marks of the paint were made on the black membranous portion of the hind
wing of a hundred specimens in this experiment.
Methods for the study of natural enemies
Parasites
Egg parasites. Thirty eggs from each of the colonies of the species of
Dysdercus studied were collected and brought to the laboratory where they
were kept in deep, covered, Petri dishes for the emergence of parasites. Each
colony had four replicates. A total of 120 eggs were therefore examined in each
colony for egg parasites.
ECOLOGY O F COTTON STAINERS
119
Figures 4 and 5. Population changes in D. voelkeri and D. fasciutus respectively in colony No. 2.
(host plant-Srerculia foeticfa). Population changes in the resident predator, P. fasciatus are
shown in Fig. 5.
Larval parasites. Fifty larvae were collected from each colony, and kept in
llb Kilner jars and the number of parasites which emerged was noted. For each
colony, on three different occasions, 150 second instar larvae were collected.
These were put into three llb Kilner jars, each jar containing 50 larvae. The
larvae were provided with food and water. Since larval parasites usually emerge
from adults, the larvae were reared to adulthood. The number of parasites that
emerged from the larvae (if any) was noted. In this way 450 larvae in each
colony were examined for larval parasites.
Ectopararites. The number of ectoparasites was noted during each weekly
visit to the colonies in both savanna and forest zone.
Predators
Phonoctonus species (Reduviidae: Heteroptera). Weekly counts of the larvae
and adults of each species were kept. Three species of Phonoctonus were
120
B. A. FUSEINI AND R. K U M A R
encountered-P. fusciutus, P. subimpictus and P. lutescens. In smaller colonies
of these reduviids, total counts were attempted, and in larger colonies,
estimates of the numbers were made, as was done for the stainers (vide supra).
The predator prey relationship between Phonoctonus and the stainers was
studied and the results shown graphically.
These predators have close mimetic association with the stainers. This
resemblance enables the predator to live among the stainers and feed on them.
Some of the species of Phonoctonus more closely resemble some stainers than
others. Experiments were therefore conducted to find out if a particular
Fig. 6
ECOLOGY OF COTTON STAINERS
121
reduviid species prefers the stainer it most resembles. This was done by
isolating the predator in a llb Kilner jar whose floor was covered with soil
about 1%-2 inches deep. Each isolated predator was given four stainers two of
which were of one species of Dysdercus while the other two were of a different
species. Food and water was provided for the Dysdercus species. Daily
recording of stainers eaten by the reduviid was noted. The number of stainers
in the Kilner jar was kept constant by removing those killed and replacing them
with live ones of the same species. Then the species of Dysdercus were changed.
In the end each species of Phonoctonus was presented with all four species of
Dysdercus. After this experiment, each species of Phonoctonus was provided
with one individual at a time of each of the four species of Dysdercus and its
preference noted. The results of this investigation also showed how many
stainers each Phonoctonus predator can eat in a day.
Oecophyllu longinodu (L.) (Formicidae: Hymenoptera). Predation of these
ants on the stainers was observed in the colonies where the ants had their nests.
1971
1972
Months
Fig. 7
Figures 6 and 7 . Population changes in D. voelkeri and D. fasckrtus respectively in colony NO. 3
(host plant-Sterculkr foeffda). Population changes in the resident predator Phonocronus
fasciatus are shown in Fig. 7.
122
B. A. FUSElNl AND R. KUMAR
Fig. 8
The number Of Dysdercus larvae and adults being attacked and carried away
was noted.
Vertebrate predators. Lizards. Faecal pellets of the Agama lizards which
lived on colonized host plants were examined and the number that contained
some parts of Dysdercus was noted.
Another Agama lizard, living in a hedge of plants near the laboratory, was
given both larvae and adults of the four species of Dysdercus reared in the
laboratory to find out if the lizard would eat the bugs willingly. This was a
palatability test.
Another palatability test was done with a mongoose (Gmsarchus obscurus).
A number of the bugs was given to the mammal and its reaction noted.
Zonocerus vanegatus (L.) (Pygomorphidae: Orthoptera) were also given to find
out whether the mongoose would take them as well.
ECOLOGY OF COTTON STAINERS
123
4001
1971
1972
Months
Fig. 9
Figures 8 and 9. Population changes in D. voelkeri and D.fusciutus respectively in colony No. 4
(host plant-Srerculiu foetida).
OBSERVATIONS AND RESULTS
Host plants
Table 1 shows the host plants of the five species of Dysdercus-D.
superstitiosus, D. fasciatus, D. voelkeri, D. melanoderes and D. haemorrhoidalis-found within the area studied. Normally the bugs feed on the fallen ripe
seeds of their hosts. However, they are often observed, feeding on the fruit wall
itself, probably to obtain water and or searching for the seeds inside the fruit.
Their feeding habits explain why these insects are found colonizing plants only
during the period when ripe seeds are available. As the seeds diminish in
abundance, so does the population of the bugs. Potential host plants without
seeds or those with developing fruits were observed to be without bugs even if
the plants had been colonized before.
Succession o f host plants
Since most (if not all) of the host plants produce seeds periodically there is a
succession of colonization by the bugs during the year. Figures 2 to 11
(Sterculiu colonies), Figures 1 3 to 17 (Ceiba colonies) and Fig. 12 (Bombax
B. A. FUSElNl AND R. KUMAR
124
Table 1. Host plants of Dysdercus species in Ghana
Malvaceae
Abutilon mauritianum (Jacq.) Medic.
Gossypium arboreum L.
Gossypium sp.
Hibiscus micranthus L.
H. esculentus L.
H . sabdariffa L.
Sida acuta B u m .
Sida sp.
Thespesia populnea (L.) Soland. ex Corr.
Urena lobata L.
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
Sterculiaceae
Sterculia foetida L.
S. rhinopelta K. Schum.
S. tragacantha Lindl.
F
F
F
F
F
F, P
F
F
F
F
F
F
F
F
F
F
F
Bombacaceae
Adansonia difitata L.
Bombax bucnopozense P . Beauv.
B. sessilis (Benth.) Bakh.
Ceiba pentandra (L.)Gaertn.
Ochroma lagopus Sw.
F
F
F
F
F
Others
Coffea arabica L. (Rubiaceae)
Solanum verbascifolium L. (Solanaceae)
F
Key: F, this study; P, Pearson (1958).
colony) show the rise and fall of the population according to availability of
food. Fruiting and dehiscence periods are shown. The term fruiting as referred
here includes flowering period and the term dehiscence includes the entire
period when seeds are available on the ground beneath the host plant.
Hibiscus micranthus was observed to be colonized by D. voelkeri in the
middle of October 1971. These plants are herbaceous and produce fruits
continuously throughout the year. They were the only host plants which had
ripe seeds at this time. Meanwhile important tree hosts like Sterculia foetida
and Bombax sessilis had developing fruits. The seeds of S. foetida began to be
shed on the ground before those of B. sessilis, so that by the first week of
November 1971, this host plant (S. foetida) was colonized by D. voelken.
Shortly afterwards B. sessilis was also colonized when the fruits were dehiscing
and made the seeds available t o the bugs. At this time, it was observed that the
bugs feeding on the seeds of H. micranthus were decreasing in number, giving
an indication that they were deserting their Hibiscus hosts in preference for the
S. foetida and B. sessilis hosts. Soon, only isolated larvae were found on the
previously heavily colonized H. micranthus hosts.
B. sessilis seeds were first to become scarce. During this period another
ECOLOGY O F COTTON STAINERS
125
important host plant, Ceiba pentandra (Kapok tree) was flowering. Its fruits
were mature by early January. Dehiscence of the fruits started almost
immediately the fruits were mature. This host plant bears fruits at about the
same time in both savanna and forest zones in southern Ghana. There was a
massive desertion of the Dysdercus species which were feeding on S. foetida
and B. sessilis seeds, to their “new” host plant-C. pentandra (Figs 1 3 to 17).
Even in areas where the wind blew C. pentandra seeds to nearby S. foetida and
B. sessilis colonies, the bugs abandoned the old seeds and literally pounced on
the C. pentandra seeds. There are two possible explanations to this behaviour.
First, it might be that the C. pentandra seeds are preferred to other seeds and
secondly, that the food reserves of B. sessilis and S. foetida had been used up.
But the S. foetida and B. sessilis seeds did not shrink, hence there was still more
food within. Moreover, the bugs returned to them after exhausting the C.
pentandra seeds, to confirm the fact that the seeds were not depleted of food
reserves. Massive multiplication of the populations occurred very rapidly on C.
pentandra hosts while there was a substantial decline in populations of S.
foetida and B. sessilis colonies. By the end of January, S. foetida plants began
another cycle of fruiting. There were very few S. foetida seeds available at this
time while B. sessilis was already depleted of its seeds. Therefore the colony of
Dysdercus on B. sessilis had almost disappeared by the end of January.
Meanwhile Dysdercus populations continued to increase in the C. pentandra
colonies in both the forest and savanna zones. The sole species was D. voelkeri
in savanna colonies but in the forest colonies C. pentandra was colonized by
D. melanoderes and D. voelkeri. By March, D. fasciatus was beginning to appear
on the scene within the D. voelkeri colonies in the savanna zone, but its (D.
fasciatus) populations were very low.
Effect o f rain on plants and bugs
The coming of the rains resulted in a mass destruction of the C. pentandra
seeds and shortening of the period of time the seeds could have remained on
the ground. C. pentandra seeds are softer than S. foetida seeds and as a result
begin to rot quickly. This had a deadly effect on the Dysdercus colonies,
particularly those in the forest zone where there was massive destruction of the
bugs (Figs 14 and 15). In the savanna area, because of the abundance of S.
foetida and other host plants the bugs gradually moved back to their old
S. foetida hosts (Figs 2 to 11). This was evidenced in substantial increase in
populations of the bugs in the S. foetida colonies. However, by the last week of
May, S. foetida trees began flowering and their seeds on the ground were
gradually becoming scarce, resulting in decreases in Dysdercus populations
(Figs 2 to 11). This decrease continued in June and July when, in some
colonies, the bugs were no longer present at all, while in others only few larvae
were present (Figs 2 to 11).
Discussion
The host plants of Dysdercus are limited to the Malvales (Pearson, 1958)
which includes the families Malvaceae, Sterculiaceae, Bombacaceae and
Tiliaceae. There are however, families outside these groups on which the bugs
have been found e.g. Solanaceae and Rubiaceae (vide Table 1). Pearson (1958)
has named several host plants of Ghanaian species but was unable to identify
126
B. A. FUSEINI AND R. KUMAR
the species of Dysdercus found on them. This gap has now been filled in this
work.
Pearson (1958) observed that the succession of host plants during the year is
characteristic of each region, and for each species in most equatorial
regions. Where there are two rainy seasons, there is an unbroken succession of
hosts in fruit throughout the year. In drier areas, the stainer's principal
difficulty is to survive by the fruiting of host plants at different times during
the year. This siiccession ranges from the mnua! and perennial herbaceous
ECOLOGY OF COTTON STAINERS
127
hosts to big tree hosts. In Ghana, in November the stainers leave H. micranthus
and move on to tree hosts, S. foetida and B. sessilis as they come into fruiting
at this time. In January and February the stainers move on to C.pentandra.
When none of these tree hosts is fruiting, the stainers return to H. micranthus
which flowers and fruits at all seasons. Hence this plant acts as a host for the
“residual” members of the colonies which have been decolonized as a result of
lack of the preferred food.
Host preference
As mentioned earlier, the bugs appear to have a preference for some species
of seeds rather than others. Field observations support this since it was
observed that D. voelkeri and D. fasciatus quickly abandoned the Sterculia and
Bombax seeds on which they were feeding in preference to Ceiba seeds which
were blown down to the S. foetida and B. sessilis colonies.
Food preference tests were done in the laboratory to find out which species
of seeds were preferred when the insects were given a choice and t o see if
different species of Dysdercus had different host preference. The data obtained
by using the methods described earlier was analysed. Chi-squares were
Figures 10 and 1 1 . Population changes in D. voelkeri and D. fusciutus respectively in colony
5 (host plant-Srerculia foetida).
NO.
B. A. FUSEINI AND R. KUMAR
128
Table 2. Food Preference Tests using D. fusciutus
Species of seed
Numbers of individuals feeding at 30 minute intervals
a
b
C
d
Ceiba pentandra
Sterculia foetida
Totals
15
3
18
Ceiba pentandra
Bombax sessilis
Totals
6
0
6
Sterculia foetida
Bombax sessilis
Totals
10
2
12
Totals
Expectation
19
4
23
85
8
93
46.5
46.6
1
15
3
18
60
4
64
32
32
6
0
6
9
0
9
42
2
44
22
22
25
26
1
0
26
26
xz (1) = 63.76, P > 0.001
11
28
0
12
28
x1 (1) = 24.50, P > 0.001
17
0
17
~ ' ( 1 =) 18.18, P > 0.001
calculated, comparing the observed distribution with the expectation that they
would feed on the two types of seed equally. Results of the experiments are
given in Tables 2 to 5 (the letters a-d represent the numbers of individuals
feeding at 30 minute intervals).
Discussion
The analysis shows that C.pentandru is the most favoured host plant for all
four species of Dysdercus. This confirms the field observations already
mentioned. The next preferred host plant is S.foetida, then B. sessilis followed
by H. rnicrunthus. I t is clear from Table 3 that D. voelkeri shows no distinct
Table 3, Food Preference Tests using D. voelkeri
~
Species of seed
Numbers of individuals feeding at 30 minute intervals
a
b
C
d
~
~~~
~~
Totals
Expectation
22
1
23
51
27
27
17
42
0
0
17
42
2
14
16
3
41
44
22
22
22
22
~~~
Ceiba pentandra
Sterculia foetida
Totals
3
0
3
Ceiba pentandra
Bombax sessilis
Totals
4
0
Bombax sessilis
Sterculia foetida
Totals
1
1
2
Sterculia foetida
Hibiscus micranthus
Totals
6
2
8
Hibiscus micranthus
Bombax sessilis
Totals
5
6
11
4
16
2
10
18
x1 (1) = 42.66, P > 0.001
10
0
x'
10
0
10
(1) = 42.00, P
11
0
11
> 0.001
0
0
7
19
7
19
x1 (1) = 32.80, P > 0.001
3
54
6
0
5
22
39
0
3
5
6
5
2s
44
17
18
40
35
78
x' (1) = 26.28, P > 0.001
5
11
7
9
12
20
~ ' ( 1=
) 0.256,0.90 > P
> 0.80
38
21
21
39
39
ECOLOGY OF COTTON STAINERS
4000
r
129
Fruiting period
Dehiscing period
Seeds absent
5-
-
I
Nov
1971
Dec
Jan
1972
Feb
Mar
Apr
I
May
I
I
I
Jun
Jul
Aug
Months
Figure 12. Population changes in D. voelken and P. fasciaius respectively in colony No. 6 (host
plant-Bombax sessllis).
preference for B. sessilis over H. micranthus (x2(i),
= 0.256, 0.90 > P > 0.80).
This host specificity, together with seasonal changes in host plants fruiting,
explains the succession of host described earlier from H. micranthus plants to
B. sessilis and S. foetida and finally to C. pentandra. C. pentandra seeds are the
most preferred and are colonized even when other host plants have seeds m
abundance. Doesburg (1968) mentions that “besides the ‘common hosts’, each
species has other more or less specific food plants in its cycle”. It therefore
seems that in Ghana the specific wild food plant or preferred host plant is C.
pentandra. Other important wild host plants, such as S. foetida. B. sessilis and
H. micranthus, are what Doesburg terms “common hosts” and are used when
C pentandra seeds are not available.
B. A. FUSEIN1 AND R. KUMAR
130
Table 4.Food Preference Tests using D. superstitiosus
Species of seeds
Number of individuals feeding at 30 minute intervals
a
b
C
d
Ceiba pentandra
Sterculia joetida
Totals
0
Ceiba pentandra
Bomhax sessilis
Totals
0
Botnhax sessilis
Sterctrlia foetida
Totals
5
4
4
3
3
1
6
Totals
Expectation
54
2
56
28
28
29
29
13
20
0
2
15
20
X2 (1)= 24.14,
P > 0.001
17
26
0
11
26
X' (1)= 29.00,P > 0.001
18
0
18
58
1
3
6
9
12
7
X I (1)= 10.32,0.01> P > 0.001
1
13
14
5
33
38
11
0
0
17
0
58
19
19
Colony structure
Nine colonies of Dysdercus species were studied in both the savanna and
forest areas of southern Ghana. Weekly sampling carried out between the
months of November 1971 and July 1972 forms the basis for the study of the
structure of the colonies.
As mentioned earlier, the stainers first colonize herbaceous malvaceous
plants such as H. micranthus and then move on to more preferred host plants
later when these plants have ripe seeds. It.was observed that the stainers never
formed big colonies on the H. micranthus. Numbers on each plant ranged
between ten to forty. These figures were very small as compared to those of the
tree hosts plants where numbers of the stainers in some cases ran into several
thousands.
Colonies in the savanna zone
In the large colonies, there were, in some cases, more than one species in one
colony. In the savanna colonies, Dysdercus voelkeri first appeared and
remained the sole species till late March when D. fasciatus also appeared on the
Table 5 . Food Preference Tests using D. melanoderes
Species of seed
Number of individuals feeding at 30 minute intervals
a
b
C
d
Totals
Expectation
Ceiba pentandra
Sterculia foetida
Totals
7
2
9
6
22
2
0
8
22
X z (1)= 19.31,P> 0.001
26
5
31
61
9
70
35
35
Sterculia foetida
Bombax sessilis
Totals
3
4
7
12
0
12
X a (1)= 10.78,P
8
1
11
19.5
19.5
9
11
34
5
39
Bombax sessilis
Sida acuta
Totals
0
10
0
10
36
4
40
20
20
1
14
3
17
1
Xa
> 0.001
11
1
12
(1) = 12.80,P> 0.001
0
ECOLOGY OF COTTON STAINERS
131
scene. D. melanoderes was rarely present in these savanna colonies. Both L).
voelkeri and D. fasciatus coexisted closely and were observed on several
occasions even copulating though no fertile eggs were produced. They formed
aggregations together and several individuals were often observed feeding on
one seed. On the rare occasions when D. melanoderes were observed in the
savanna colonies, they also formed aggregations with the other species and its
adults were seen copulating with the adults of the other species. I t therefore
seems that there is a very close sympatric relationship between species of the
stainers in a colony.
1
0.voelkeri
, (larvae)
0
Nov.
1971
‘
Dec
’
Jan
Feb
Mar
Apr
May.
dun
Jul
Aug.
1972
Months
Figure 13. Population changes in D. voelkeri and P.firrc&tus in colony NO. 7 (host plant-Ceiba
pentandra).
10
132
3. A. FUSElNl AND R. K U M A R
Colonies in the forest zone
In the forest zone, however, only two species were present in the colonies.
These were D. voelkeri and D. melanoderes. D. melanoderes is a forest species
and was found to be most abundant in the forest colonies. But, very unlike the
savanna colonies, the two species were not in close association. The colony was
in a wet shaded cocoa farm and the host plant was C.pentandra. In this colony,
D. melanoderes was confined within the farm which was bordered by an open,
grassy area along a main road. D. voelkeri was confined to the open grassy area
outside the main colony found within the farm. These two species were never
in close association in this colony. A similar pattern existed in another forest
colony which unfortunately died out very early as a result of a heavy rainfall.
Months
Fig. 14
ECOLOGY OF COTTON STAINERS
133
So from January to May 1972 there was this separation of the two species in
the forest colony. D. voelkeri is essentially a savanna species, while D.
meZanoderes is a forest species. The clear separation in the forest colony very
clearly indicates that D. voelkeri prefers grassy open habitat to the wet shaded
forest conditions. This is confirmed by a similar condition existing in the
wooded savanna colony. Living among the Dysdercus species in a sympatric
association were other pyrrhocorids such as Odontopus sexpunctatus Castel-
Nov
1971
Dec
Jan
1972
'
I
Feb
I
Mar
Apr
May
Jun.
Jul.
Months
Fig. 1 5
Figures 14 and 1 5 . Population changes in D. voelkeri and D. melanoderes respectively in colony
No. 8 (host plant-Ceiba pentundra). Population changes in the resident predator,
P. subimpictus are shown in Fig. 1 5 . A, P. subimpictus.
B. A. FUSElNl AND R. K U M A R
134
\
I
i
i
I
I
I
Larvae
I
I
I
I
- 0
Nov
1971
’
Dec
Jan.
1972
Feb
I
I
.I
I
1
I
I
I
I
Mar.
Apr.
May
\I
I
I
A L
- r
Jun
I
Jul.
Aug.
Months
Fig. 16
nau, Callibaphus longirostris Drury, and Antilochus boerhaviae (Fabricius). 0.
sexpunctatus was found in the savanna colonies and the wooded savanna. It
was never found in the forest colonies. C. longirostris and A. boerhaviae were
found in the forest colonies but absent in the savanna colonies. All these
pyrrhocorids were feeding on the same seeds as Dysdercus. This might have
entailed some form of competition between all members of the Pyrrhocoridae
in the colonies. In one of the forest colonies, C. longirostris died out within 14
days when the seeds on which they were feeding together with Dysdercus and
Antilochus were finishing. A possible explanation to this quick disappearance of
ECOLOGY OF COTTON STAINERS
135
Months
Fig. 17
Figures 16 and 17. Population changes in D. melanodews and D. voelken' respectively in colony
No. 9 (host plant-Ceibo penrondm). Population changes in the resident predator,
P. subimpictus are shown in Fig. 17.
Gzllibuphus might be that it could not compete favourably with the other
pyrrhocorids.
Discussion
In all the colonies, it was observed that adult numbers fell before any
noticeable fall in larval numbers (see Figs 2 to 17). This may be linked with
their migratory activities. Migration in insects is considered to be a distinct
136
B. A. FUSElNl A N D R. KUMAR
behavioural and physiological syndrome (Kennedy, 1961; Johnson, 1963).
Studies of female insects, summarised by Johnson (1963), and supported by
Dingle (1972) and Duviard (1973) show that migration involves an “oogenesisflight syndrome”. Dingle (1972) further states that most migration takes place
prior to egg development and reproduction. This means that migration is
restricted to young adults. It is known (Edwards, 1969, 1970) that flight
muscles in gravid females of Dysdercus species are absorbed and hence they are
unable to migrate by flight. But it seems to us that while this may be true, the
older insects at least the males as well as the larvae also migrate. The results of a
marking-release experiment with D. voelkeri feeding on Ceiba pentandra and
Ochroma lagopus showed that migration also involves older adults. In this
experiment, 100 older male adults were marked at a time the seeds of their
host plant, C.pentandra, were becoming scarce. At the same time, another host
plant, 0. lagopus, at a distance of 280.60m, was shedding its seeds. The
following week 26 marked bugs were recaptured feeding on the seeds of the
Ochroma tree. Marked young females were caught at a similar distance. Gravid
females did not appear to migrate.
It is the belief of some workers, notably Dingle (1972) that the chief
functions of migration are: (1) to allow escape from unfavourable environments and (2) dispersal and colonization of all available habitats. During the
course of the present project, we have observed that migration is certainly a
function of availability of food. It also depends to a greater extent, on host or
food specificity, not just colonizing all “available habitats” as Dingle (1972)
put it. As said earlier, D. voelkeri completely deserted Hibiscus micranthus
hosts when preferred host plants such as Sterculia foetida and Bombax sessilis
began shedding their seeds. In fact, in areas where the Hibiscus plants were not
very far from the “new” host plants, there was mass movement out of the
Hibiscus colonies. This, of course, included larvae as well as adults. Dingle’s
observation that the bugs disperse and colonize all available habitats, probably
applies to bugs which are foraging for a preferred food. The moment a
preferred host is colonized there is a build up of the population followed by a
fall some weeks later (see Figs 2 to 17). This means that emerging adults do not
undergo a short period of flight soon after the adult moult as Dingle (1972) has
observed in Dysdercus nigrofasciatus, D. fasciatus and D. superstitiosus. If this
were the case, most of the colonies would have been shortlived because this
author claimed that migration took place prior to egg development and
reproduction.
I t is, therefore, clear that migration primarily takes place not only as a result
of lack of food, but in search of preferred hosts as well. It is believed that it
may occur in response to a need for a relief in population pressure, a view
which has been supported by evidence of movements of Dysdercus in South
Africa and Malawi (Pearson, 1958). However, it is now known that Dysdercus
species feed better if they are in numbers and an optimum quantity of food is
available. It seems that when a number of individuals feed together on a seed,
they pool a secretion of enzymes on a seed and thus make more food available
to the bugs. Therefore, if food supply of a preferred host plant is optimum, the
bugs in a colony tend to stay together. The present writers have also observed
during the weekly sampling exercise that factors such as tall grasses caused D.
ECOLOGY OF COTTON STAINERS
137
voelkeri and D. fasciatus to migrate or vacate the overgrown colony. In this
particular case the stainers, both larvae and adults, moved out into more open
areas. Galichet (1956)showed that D. voelkeri develop better on bare ground
under host plants in rain forest. In forest clearings host plants have a higher
density of D. voelkeri than in the same forest where there is no such clearing.
The stainers do not form colonies at the same time. It has been observed that
some species appear earlier than others. D. voelkeri is found to be common
species in the savanna zone from November to March when D. fasciatus makes
an appearance. I t is not known why D. fasciatus and D. superstitiosus, both
savanna species, appear late. D. superstitiosus is not very common, and
throughout the period of this project, D. superstitiosus was never found in large
numbers or colonizing a host plant by itself.
The species of Dysdercus have a close sympatric relationship. None of the
species has a separate micro-habitat. They mingle together (if more than one
species comprise a colony), and very often are found forming aggregations.
These habits emphasize that the species are closely related. Other pyrrhocorids
are found living in a close sympatric association with Dysdercus. These include
Callibaphus and Antilochus. These, however, were never observed to form
aggregations with Dysdercus. They lived there apparently because they fed on
the seeds of the same host plants as Dysdercus.
The migratory activities of Dysdercus seem to be more closely related to the
absence of food and also need for a preferred food. Southwood (1960)has
pointed out that species with high levels of flight activity are inhabitants of
temporary habitats. Now that the host plants of Ghanaian stainers have been
listed and their period of fruiting is known, the period of active migration from
one host plant to another can be worked out. Thrs may be of use to cotton
entomologists who are interested in the population dynamics of the stainers
and their control. It is clear that a large scale destruction, in a cotton growing
area, of Hibiscus micranthus which acts as a reservoir of Dysdercus species
should help to break the life cycle of these bugs.
In Ivory Coast, Duviard (1973) has linked the seasonal migration of
Dysdercus voelkeri with the annual displacement of the Inter-tropical Front.
He speculates that a similar phenomenon happens in Ghana as well. However,
he states that migratory period as well as the number of successive phases
decreases with the latitude. According to Duviard’s (1973)interpretation of the
available data, there are three or four migratory phases at Foro-For0 (Ivory
Coast), two or three at Kwadaso (about 169 miles North of Accra) and one or
two at Tafo (about 69 miles north of Accra). Climatic and floral conditions in
southern Ghana are very different from those in Ivory Coast. In Ivory Coast,
Adansonia digitata is the major and preferred host plant of D. voelkeri while
plants such as Sterculia foetida, Hibiscus- micranthus and Bombax sessilis are
absent. Thus according to Dr Duviard (pers. comm.), in wet season, seeds of
Adansonia digitata are available in northern Ivory Coast; therefore, bugs from
southern Ivory Coast perform a mass migration t o the northern part of the
country along with Inter-tropical Front. Climatic conditions in southern Ghana
on the other hand favour a succession of preferred and less preferred host
plants throughout the year. Therefore, it is unlikely that any mass migration of
cotton stainers from southern Ghana to northern Ghana accompanies displace-
B. A. FUSEINI AND R. KUMAR
138
ment of the Inter-tropical Front, at least not from Accra plains though there
would be short migrations from one host plant to another.
Natural enemies
Parasites
The eggs were collected in the field and hatched in the laboratory. But no
parasites emerged from them. However, dipterous parasites did emerge from
adults. All such parasites were found to be dipterous flies, Alophora nasalis
(Bezzi) (Tachinidae), the larvae of which emerged from dead adult stainers.
The stainers had been reared from second stage larvae to adulthood. Since the
first instar larvae are tiny (2.00-2.50 mm long) and the adult flies comparatively large (about 11 mm long), a mere insertion of the ovipositor by the
latter is likely to kill the former. In laboratory the first instar larvae offered to
flies were never parasitized but second instar larvae were parasitized. This
supports Doesburg’s (1968) contention that the parasitic flies insert their eggs
into the body of the second-stage larvae. Development of the parasitic maggot
continues until the stainer reaches adulthood when, after the death of the bug,
the fully developed maggot emerges and burrows into the soil to pupate.
Attempts were made to determine the incidence of parasitization in
Dysdercus colonies from both forest and savanna zones. Parasitization was
extremely low in the wild (see Table 6). Parasitlzation was 4% in a forest
colony (Koforidua-see Table 6) where D. melanoderes was dominant. This
proved to be the highest rate of parasitization in the forest zone. In the savanna
zone, the highest rate of parasitization (3.3%) was recorded in a Sterculia
foetida (wild host plant) colony. Orher savanna colonies had either 0% or under
1.0%parasitization.
Table 6. Incidence of parasitization by Dipterous parasite (Alophora nasalis) of
Dysdercus species from southern Ghana
Species of
Colony
Host plant
1
Sterculia foetida
Dy sdercus
%
Locality
Sample size
parasitization
D. fasciatus
D. voelkeri
D. fasciatus
D. voelkeri
Legon
(savanna)
zone
Legon
(savanna)
zone
1 2 0 (50%D. fasciatus
1 2 0 (50%D. fasciatus
50% D. voelkeri)
3.3
0.0
50%D. voelkeri)
2
Sterculia foetida
3
Ceiba pentandra
D. voelkeri
Legon
(savanna)
zone
120
0.8
4
Ceiba pentandra
D. melanoderes
Koforidua
(forest)
120
4.0
5
Ceiba pentandra
D. voelkeri
D. melanoderes
Tafo
(forest)
1 2 0 (50%D. voelkeri,
50%D. melano-
1.7
deres)
6
Ceiba pentandra
D. voelkeri
7
Ceiba pentandra
D. voelkeri
D. melanoderes
Aburi
(forest)
120
0.0
Krobo Hills
120 (50%D. voelkeri,
(wooded savanna)
50%D. melano-
deres)
0.0
ECOLOGY O F COTTON STAINERS
139
High rates of tachinid parasitization (40-100 %) have been recorded in
Uganda on wild host plants and a rate of 25 % has been recorded on a wild
population of D. superstitiosus (probably in fact D. voelkeri) in West Africa
(Pearson, 1958). With very low rates of parasitization in Ghana, it is doubtful
whether such parasites can exert any significant degree of control over the
stainers.
Small reddish ectoparasitic mites were observed on D. melanoderes,
D. voelkeri and D. fasciatus. In the wild host colonies as many as nine mites
were found on one adult D. melanoderes, but they did not seem to have any
serious effect on the bug.
Predators
The predators of Dysdercus range from insects such as reduviids to mammals
such as the mongoose.
Invertebrate predators
Assassin bugs which are known to be predators of these stainers include
species of Rhinocoris and Phonoctonus. Phonoctonus appears to be the most
important so far as predation on Dysdercus is concerned. The Phonoctonus
species live in close mimetic association with members of the Pyrrhocoridae
(see Table 7). In the present study, three species of Phonoctonus were
encountered. These are P. fasciatus Beauvois, P. lutescens Guerin & Percheron
and P. subimpictus Stol. P. fasciatus was found to be most abundant in colonies
dominated by D. voelkeri and D. jasciatus. the two species of Dysdercus it
most closely resembles. P. subimpictus was observed to be most abundant in
colonies of D. melanoderes, the species of Dysdercus it most closely resembles.
P. lutescens was not particularly associated with any particular species of
Table 7. Species of Phonoctonus showing the Dysdercus species they
are associated with
Phonoctonus mimic
-.
Dysdercus species it
closely resembles
--__________---~
__
All Dysdercus species found
Colony
with it
60% D. melanoderes, less than
40%D. voelkeri
.-
P. subimpictus
D. melanoderes
Forest
colony
P. fascintus
D. fasciatus
D. voelkeri
D. superstitiosus
Savanna
colony 1 70%D. voelkeri, 20%D. fasci atus, 0%D. superstitiosus
2 70% D. voelkeri, 20%
D. fasciatus, under 0.5% D.
superstitiosus
3 80% D. voelkeri. 20% D.
fasiatus, 0%D. superstitiosus
4 80% D. voelkeri, 20% D.
f;wcc.intus.0%D. superstitiosus
5 70% D. voelkeri, 30% D.
P. lutescens
(resembles Odontopus
sexpunctatus)
fasciatus, 0% D. superstitiosus
Krobo Hills Over 60%D. melanoderes less
than 40%D. voelkeri (Less
than 2% 0. sexpunctatus)
B. A. FUSEINI AND R. KUMAR
140
Dysdercus though it was first found in a colony of D. melanoderes. P. lutescens
rather closely resembles Odontopus sexpunctutus, also a pyrrhocorid. However,
as Stride (1956) observed, in the field specimens of Phonoctonus were quite
often seen in association with Dysdercus species to which they bore no mimetic
resemblance. Mimetic resemblance is therefore not a sine qua non m predation.
However, “it seems reasonable to suppose that, in general, a species of
Phonoctonus would be more closely associated with the pyrrhocorid species
that it mimics than with any others” (Stride, 1956).
Feeding preferences of Phonoctonus species. An investigation was carried
out to find out whether the three Phonoctonus species have any preference for
feeding on the Dysdercus species they most closely resembled. The results of
the above mentioned investigation are given Tables 8 to 10.
Chi-squares for the results of predation by the three predators were worked
out to test the agreement between the null hypothesis and the observed results.
The null hypothesis in this investigation is that choice of prey by the reduviids
is per chance.
I t is important to mention that each of the reduviids feeds on one stainer a
day. However, there were days during the investigation when some of the
predators fed on two stainers (e.g. P. subimpictus and D. fasciatusl
D. melanoderes, see Table 8).
As explained in the section under methods, four stainers were presented to
each predator, two of each species of the stainers. Stainers eaten up were
Table 8. Numbers of Dysdercus species eaten by
Phonoctonus subimpictus in a food preference test. The
investigation was carried out over a period of 21 days
Species of Dysdercus presented
as food
No. presented
No. eaten
x’, = 2.924
P > 0.10 > 0.05
D. fasciatus
D. melanoderes
42
42
D. voelkeri
D. superstitiosus
D. melanoderes
D. voelkeri
42
42
12 Not significant by
10 inspection
42
42
12 Not significant by
9 inspection
D. fasciatus
D. voelkeri
42
42
10 Not significant by
16
10
not significant
11 inspection
replaced the next day to keep the number of stainers presented constant. Table
8 shows the results for predation of P. subimpictus on all four species of
Dysdercus. P. subimpictus very closely resembles D. melanoderes.
From Tables 8 to 10 it is clear that Phonoctonus species have no particular
preference for any species of Dysdercus though in some cases (see Table 9) the
results are nearly significant. It can therefore be said that given all species of
Dysdercus, a particular species of Phonoctonus will not necessarily show
preference for feeding on the Dysdercus species it most closely resembles.
However, when all species of Phonoctonus were starved and each presented
with the four species of Dysdercus the following were their first victims (see
ECOLOGY O F COTTON STAINERS
141
Table 9 . Numbers of Dysdercus species eaten by
Phonoctonus fasciatus in a food preference test.
Excepting the investigation on D. superstitiosus which
lasted for 14 days, rest of the work was carried out over
a period of 21 days
~~
Species of Dysdercus presented
as food
No. presented
N o . eaten
D. fasciatus
D. melanoderes
42
42
D. voelkeri
D. superstitiosus
D. fasciatus
D. voelkeri
D. melanoderes
D. voelkeri
28
28
6 Not significant by
7 inspection
42
42
11 Not significant by
10 inspection
42
42
12 inspection
14 x’, = 3.074
6 P > 0.05 > 0.02
Not significant
9 Not significant by
Table 11). One of each of the four species of Dysdercus was kept in a llb
Kilner jar, i.e. there was a total of four individuals of Dysdercus in one Kilner
jar. Three such Kilner jars contained the four species of Dysdercus. To each of
these jars was introduced one of the starved species of Phonoctonus used in the
experiment. Table 11 shows the first stainers attacked by the predators. The
result shows that the reduviids attacked the stainers they most closely
resembled.
Table 10. Numbers of Dysdercus species eaten by
Phonoctonus lutescens in a food preference test. The
investigation was carried out over a period of 21 days
Species o f Dysdercus presented
as food
No. presented
No. eaten
D. melanoderes
D. voelkeri
42
42
8 x*, = 1.190
1 3 P > 0.50 > 0.20
Not significant
D. fasciatus
D. voelkeri
D. superstitiosus
D. voelkeri
D. fasciatus
D. melanoderes
42
42
11 Not significant by
10 inspection
28
28
7 Not significant by
7 inspection
38
38
7 x 2 , = 2.50
14 P
> 0.10 > 0.05
Not significant
Both the adults and larvae of Phonoctonus prey on adults and larvae of the
pyrrhocorids. From field observations, it is clear that although the Phonoctonus species mix with the stainers in the same colony, very often the
reduviids collect or rest a little distance away from the main colony. From here
they then make excursions to the main colony to feed. Phonoctonus lays its
eggs in batches on the weeds or grasses on which they rest.
B. A. FUSEIN1 AND R. KUMAR
142
From laboratory and held observations it would appear that Phonoctonus is
not a serious predator. In a day of normal feeding an individual Phonoctonus
feeds on only one stainer. But when starved, it can consume two stainers in a
day. The question of starvation does not, however, arise when Phonoctonus is
living within a colony of Dysdercus. Therefore, it can be assumed that in a
colony of Dysdercus and Phonoctonus, one stainer is consumed by an
individual reduviid per day. In colony three (host plant-Sterculiu foetidu) in
the last week of May 1972, the total number of adult stainers was 82 and the
numbers of larvae was 3800. The total number of larvae and adults of
Phonoctonus for the same period in that colony was 110. Phonoctonus feeds
on both the larvae and adults. Sometimes larvae of Phonoctonus were observed
feeding on adult stainers. I t can be worked out that a combined adult and larval
attack by the predator on both the adults and larvae of the stainers will wipe
out the Dysdercus population in thirty five days, assuming that no new
Dysdercus enter the population.
During the period of study, populations of Phonoctonus were very low in
most of the colonies. Their effect will, however, be very much felt when
Dysdercus numbers are reducing as a result of lack of food for the stainers. I t is
very likely that when the population of Dysdercus is low, predation by
Phonoctonus on Dysdercus will have a significant effect on the stainers.
Table 1 1. Species of Dysdercus attacked first by
starved Phonoctonus species
First stainer victim
Species of Phonoctonus
_____
-._
-~
_______
-- . -- - .-. -
f.subimpictus
P. fasciatus
P. lutescens
D. melanoderes
D. superstitiosus
D. superstitiosus
Oecophylh longinoda. These red ants are vicious biters. They often make their
nests on trees colonized by Dysdercus They were observed in Dysdercus
colonies carrying away larvae of the stainers. Occasionally, adults were also
attacked by the ants and sometimes overpowered and carried away to their
nests. Though these ants were living within the same colony with the stainers,
predation of the ants on the stainers was not frequently seen. This indicates
that even though Dysdercus does not appear distasteful t o Oecophylla, they are
not regular prey for the ants.
Spiders. In both field and the laboratory it was observed that spiders,
belonging to the families Uloboridae and Araneidae trapped these bugs in their
webs and fed on them. In the laboratory the uloborid spider webs were woven
below and above the stock culture cages. Wandering larvae and adults were
caught in the webs and eaten. All the four species of Dysdercus studied were
readily eaten by the spiders which were in the laboratory, but it is doubtful if
spiders are serious predators in the field.
Vertebrate predators
Vertebrates also do not appear to be persistent predators of the stainers,
though quite a wide variety have been observed feeding on them.
ECOLOGY OF COTTON STAINERS
143
Examination of faecal pellets of Agumu ugumu lizards living amongst a
colony of Dysdercus voelkeri revealed some undigested parts of adult
Dysdercus. I t was not possible to estimate numbers of the stainers consumed,
but out of a total of 120 faecal pellets examined 56 contained some parts of
the stainers. A lizard (Aguma agama) which was living free in a little hedge of
shrubs within the court yard of the laboratory was given both larvae and adults
of all four species of Dysdercus studied. On the first occasion it ate all the three
adults given. Subsequently, more were given on different days and the lizard
ate them up with no visible signs of distaste. So it appears that the observations
of Myers (1927) that “Lizards may eat an occasional nymph but for the most
part ignore them”, are not correct. Dysdercus may not form a regular meal for
lizards but they are edible and are often eaten when available.
Doesburg ( 1968) cites records of previous observations of bird predation on
some American species of Dysdercus. But throughout the course of this study,
only two birds, both cattle egrets, were seen eating D. voelkeri (both larvae and
adults).
Mammalian predation of Dysdercus has been less often observed. Stride
(1956) observed that Mona Monkeys, Putty-nosed Monkeys and Green
Monkeys all found the Dysdercus species given to them distasteful. However, in
this investigation when a mongoose (Grossarchus obscurus) was given both
larvae and adults of the Dysdercus species, it ate them. This mammal normally
ate the bugs one after the other. From the mongoose’s behaviour it appeared
obvious that while the basic taste was good, there was also an unpalatable
component present, though not in a sufficient quantity to prevent eating. This
experiment with the mongoose was repeated, this time using Zonocerus
vuriegutus and Dysdercus superstitiosus. I t ate all the bugs given to it but
rejected the Zonocems after two attempts to eat it. Since the mongoose did
not refuse the bugs in the second experiment, but rather rejected only
Zonocems, it can be assumed that the bugs were palatable to it.
From the above account, it is obvious that the Dysdercus species studied in
this project are not distasteful to predators. The question now to be asked is, if
they are palatable, does their colour pattern play a role in protecting them
against predators? Four of the five Ghanaian species are reddish with striking
red and white markings and black spots or bands. This colouration is
conspicuous when compared to some blackish species or even D. melanoderes
which has cryptic colouration. The protective value of their colour pattern is
little known to workers in this field. Doesburg (1968) is of the opinion that
“these bugs have a bad taste or possess some other unpleasant attribute,
because only such attributes will make it understandable that they are avoided
by the majority of predators”. But Brindley (1930) reported that the bugs “do
not produce any of the disagreeable aromatic scents characteristic of many
other bugs, even though they possess a well developed metasternal scent
apparatus”. This observation by Brindley seems to run counter to the work of
Youdeowei & Calam (1969) in which it is reported that secretions from the
third abdominal gland of the fifth instar larva as well as some secretions from
the adult gland perform defensive functions. The analysis of the secretions
from the glands by Youdeowei & Calam (1969) of both larvae and adults shows
that n-tetradecane is the major hydrocarbon in the secretions. This component
of the secretion, according to Youdeowei & Calam (1969) is found in defensive
144
B. A. FUSEINI A N D R. KUMAR
secretions of bugs of several species and is usually found in association with
aldehydes including hex-2en-1-al. The function of n-tetra-decane is “believed to
be two-fold: to prolong the action of the active repellants by retarding their
rate of evaporation, and to aid penetration of these substances into the
predator’s cuticle”. The hex-2en-I-a1 present in the secretion of the third scent
gland also repels other individuals of the same species (Youdeowei & Calam,
1969).
Discussion
From the above account on the natural enemies of Dysdercus in Ghana, it is
clear that it has few parasites and predators. Egg parasites have not been found
in Ghana. Parasitization of larvae and adults was found to be low in Ghana as
compared to East Africa where the rate is as high as 40-100% (Pearson, 1958).
From the biological control point of view, parasites of the Ghanaian stainers
can play no significant role in the control of the bugs.
Few predators have been found and the most consistent of them is the
reduviid Phonoctonus which lives in close mimetic association with the bugs in
the same colony. These reduviid predators are therefore of some economic
interest to cotton entomologists. Though these predators show very close
mimetic resemblance to some of the stainers, specimens of Phonoctonus were
frequently found feeding or associated with the pyrrhocorid species to which
they bore no mimetic resemblance. Stride (1956)carried out an experiment on
the food preference of P. lutescens “to ascertain whether some species of
pyrrhocorids attracted a species of Phonoctonus more strongly than did
others”. In this experiment, Stride attempted to find out whether P. Zutescens
would show a food preference when given the choice between udontopus
sexpunctutus (which the reduviid most closely resembles) and Dysdercus
voelkeri (incorrectly called D.superstitiosus by Stride). He found that
P. lutescens showed a significant preference for feeding on Odontopus than on
Uysdercus. Although the results of the present project indicate that generally,
there is no definite preference by Phonoctonus for any species of Dysdercus,
we, however, think that more detailed investigation in the relationship between
Phonoctonus and Dysdercus must.be done.
Various workers have discussed the significance of the resemblance between
certain species of Phonoctonus and the Pyrrhocoridae. Schouteden (1916)
stated that the mimicry deceived, not the pyrrhocorids, but some other insects
found in company with the pyrrhocorids, on which the Phonoctonus preyed.
However this does not explain the significance of the mimicry, but raises the
question of whether the Phonoctonus species are deriving some sort of
protection as a result of this mimicry. Also, as Stride (1956)observed, there is
no evidence to show that Phonoctonus preys to any significant extent on
insects other than the pyrrhocorids.
From the consideration of Phonoctonus b d Dysdercus association in South
Africa, Marshall & Poulton (1902)were of the view that the association was an
example of Batesian mimicry. Other workers think that mimetic resemblance in
Hemiptera is likely to be of Mullerian nature. But according to Stride (1956),
“the information obtained at Achimota suggested that all species of Phonoctonus and Pyrrhocoridae concerned were somewhat distasteful to possible
predators, implying a Mullerian basis to the mimetism”. But the results of the
ECOLOGY O F COTTON STAINERS
145
present work show that the stainers are not altogether distasteful. They are not
distasteful to lizards, and birds also eat them. Though they produce some
unpleasant secretions, which, coupled with their colouration, makes them
somewhat aposematic, this attribute may be directed towards birds only since
mammalian predators are nocturnal. But if their conspicuousness -and the
secretion of unpleasant material affect only some birds, what attribute of the
stainers is responsible for the lack of serious natural enemies which are capable
of inflicting devastating damage t o the bug? This problem is beyond the scope
of the present pioject, but it is hoped that workers in this field will be
stimulated to investigate it further.
The larvae are even more conspicuous than the adults. In aggregations they
resemble flowers (Myers, 1927). In our experience, these brightly coloured
larvae, when in large aggregations on leaves can completely deceive predators,
which take them for flowers or fruits. This protective device is strengthened by
the fact that the larvae are not easily alarmed. The conspicuous colouration of
both adults and larvae contrasted against the lack of predators probably led
Doesburg (1968) t o state that “in all probability these insects are not palatable
and as a rule this is accompanied by a corresponding warning colouration”. The
writers, from the above account on natural enemies, are convinced, that
Doesburg is incorrect in his conclusion. The bugs are not distasteful t o all
predators. To clarify the situation, more work will have to be done to
determine the palatability of the stainers and a detailed investigation conducted
into the reasons for the lack of many predators.
SUMMARY
In southern Ghana, Dysdercus species colonize a succession of host plants
throughout the year. In the Savanna zone, in November, the stainers leave
Hibiscus micranthus completely, moving on to tree hosts such as Sterculia
foetida and Bombax sessilis as these come into fruiting. In January-February
they move on to Ceibu penfundru. When none of these tree hosts is in fruit, the
stainers return to H. micranthus which flowers and fruits all the year round.
This plant was found to act as a reservoir, migration from which could quickly
build up large populations of Dysdercus when a suitable tree host came into
fruiting. In the forest zone, Sidu acufa acted as the reservoir for
D. melanoderes.
Preference tests showed that C. pentandra is the most preferred host plant
for all the four species of Dysdercus examined, followed by S. foetida,
B. sessilis and H. micranthus.
In the savanna zone, colonies of D. voelkeri, D. fmciatus and rarely
D. melanoderes were found to coexist, forming aggregations in which the
individuals of different species were often to be seen feeding together on one
seed. In the forest zone, colonies of D. melanoderes were frequently found to
exist in sympatric association with pyrrhocorids other than Dysdercus.
In all colonies, adult numbers declined before any noticeable fall in larval
numbers. This was observed to be linked with migratory activities. Migration
from the colonies of all the larval and adult stages (excepting gravid females) of
stainers was observed and resulted from lack of food or in search of preferred
hosts.
B. A. FUSElNl AND R. KUMAR
146
The mimetic resemblances of a resident reduviid predator, Phonoctonus sp.
to a particular species of Dysdercus was under normal conditions, found
unrelated to its feeding preferences. The Dysdercus species were not distasteful
to mammalian predators though they produced a disagreeable aromatic
substance when attacked.
ACKNOWLEDGEMENTS
We would like to thank Dr M. Edmunds and Dr D. Duviard for valuable
discussions. We are indebted to Dr R. F. Ewer for feeding our bugs to her
mongoose and helping us with observations on his feeding behaviour.
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