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Laboratory studies on the predatory potential of dragon-fly nymphs on mosquito larvae

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Biocontrol potential of dragonfly nymph, Brachythemis contaminata Fabricius against the larvae of Anopheles stephensi, Culex. quinquefasciatus and Aedes aegypti was studied under laboratory conditions. It was found that dragonfly nymph had highest predation efficacy against An. stephensi followed by Cx. quinquefasciatus and Ae. aegypti. Feeding rate increased with decrease in prey size/stage. Analysis of data indicated that dragonfly nymphs have good predatory potential and can be used as a biological control agent for control of mosquito breeding.
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1.
Commull. Dis. 35 (2) 2003:96
Laboratory
Studies on the
Predatory
Potential
of
Dragon-Fly
Nymphs on Mosquito
Larvae
R.K. Singh, *
R.C.
Dhiman*
and
s.F.
Singh*
(Received for publication:Jan 2003)
ABSTRACT
Biocontrol
potential
of
dragonfly
nymph,
Bracllythemis contaminata
Fabricius
against
the
larvae
of
Anopheles
stephensi,
Culex.
quinquefasciatus
and
Aedes aegypti
was
studied
under
laboratory
conditions.
It
was
found
that
dragonfly
nymph
had
highest
predation
efficacy
against
An. stephensi followed
by
Cx.
quinquefasciatus
and
Ae. aegypti.
Feeding
rate
increased
with
decrease
in
prey
size/stage.
Analysis
of
data
indicated
that
dragonfly nymphs have good
predatory
potential
and
can
be
used as a biological
control
agent
for
control
of
mosquito breeding.
Key
Words:-
Bracllythemis contaminata, Anopheles stephensi, Culex
quinquefasciatus, Aedes aegypt;,
bio-control.
INTRODUCTION
Mosquito control in India relies basically
on
the spraying
of
residual insecticides
which has resulted in resistance in vector
mosquitoes, environmental pollution and
other
deleterious effects.
As
a result more
emphasis
is
laid
on
non-insecticidal
methods
of
control and one
of
the methods
receiving
emphasis
is
the
use
of
bio-
control agents.
1-2
Larvivorous fish, bacilli,
nematodes,
fungi,
bugs,
cyclops
have
been tested. Larvivorous fish and bacilli
have been successfully applied on aquatic
stages
of
mosquito in the field
3
-!2
in many
places.
It
is evident from the experiments
that, under the bioenvironmental control
methods
primary importance should be
given to anti-larval operations.
Dragont1y nymphs are
known
as
predators
13-14
(Fig.
I)
but previous workers
have paid little attention to these nymphs
as bio-control agents
of
mosquito larvae.
This paper reports the predatory potential
of
dragonfly
B.
contaminata
nymphs
studied in the laboratory conditions
to
find
out its suitability for biological control
of
mosquitoes.
MATERIAL AND
METHODS
The dragon-fly nymphs,
B.
contaminata
Fabricius
(Odonata
:
Anisoptera)
were
collected
with
the
help
of
dipper
and
strainer from pond
ofBurari
village.north-
east
of
Delhi, and released in
an
aquarium
with dimension
of
60x3Ox38
cm
and
water
was filled up to 10
cm
for maintaining
them
*Malaria Research Centre (ICMR),
11
Sbam Nath Marg, Delhi-1100S4.
97
I,a"or(llor),
Sf/alit's on
tht'
f'rt'dafory
Potentiat
ofl
)ragon-I'
fy
live. This water contained both protozoa
and planktonic algae, which are natural
source
of
food for dragon
tly
nymphs. After
collection
nymphs were identified
by
using key
of
Fraser and Kumar
l5
17
for the
species and measured. Since
it
is
difficult
to
rear
dragonflies
under
laboratory
conditions, nymphs
of
different sizes were
brought from the field and maintained
in
the aquarium. Five stages
of
nymphs
of
different size were used
in
the experiments
during July
1996 to April 1998. All stages
of
mosquito larvae
of
An. stephensi,
Cx.
qUinquefasciatus, Ae. aegypti and pupae
were provided as a supplementary food.
The mosquito larvae
of
An. stephensi,
Cx.
quinquefasciatus and Ae. aegypti used
in
the
experiments,
were
obtained
from
insectories being maintained at the Malaria
Research
Centre.
For
determining
predatory potential
of
dragonfly nymphs,
a series
of
experiments were conducted
in
the laboratory. Plastic bowls
of
SOO
ml
capacity containing 300 ml
of
water with
larval food were used. Observations on
prey mortality were made every
24
hours,
by
counting
and
recording
of
live
mosquito larvae
present
in the plastic
bowls.
The
first set
of
experiment was
done to find out the predatory potential
of
each
nymphal
size
of
dragonfly
by
offering immature stages
of
An. stephens/,
ex.
quinquefasciatus andAe. Aegypti. One
hundred' mosquito larvae
of
a particular
instar
were
provided
to
each
size
of
dragonfly nymph in five replicates. Thus
each
size
of
dragonfly
nymphs
was
, studied with five replicates each separately
for predation against each mosquito stage
and
species.
During
the
experiments
predation
on
Anopheles
larvae
was
apparently found higher then Anopheles
and Culex. As
it
was observed that nymph
of
14
and
16
mm
size consumed more
than
100,
I and
II
instars larvae therefore,
these
experiments
were
repeated
by
offering these nymph
ISO
larvae instead
of
100
mosquito larvae
of
I and
II
instars.
Mean
of
five replicates have been shown
with SO and percentage
in
(Table-I).
The second set
of
experiment was
performed
to
study the comparative prey
preference by nymphs
of
B.
contaminala
on
different
immature
stages
of
mosquitoes,
when
An. stephens;,
ex.
quinquefasciatus and Ae. aegypti were
offered together. One nymph
of
each size
was offered twenty preys
of
each stage i.e.
first
in'll
. larvae to pupae
of
the three
mosquito species.
RESULTS AND DISCUSSION
It was observed that the dragonfly nymphs
captured mosquito larva" dnd engulf with
its mask which
is
thrown forward and
extended with incredible swiftness and the
prey is transfixed
with
the
hooks
and
carried in to the mouth cavity. Results
of
the feeding rate
of
B.
contam/nata on
aquatic
stages
of
An.
stephensi,
ex.
quinquefasciatus and Ae. aegypti indicate
that maximum predation was
of
first instar
larvae
(l27.8±6.96,
12S.3±7.4S
and
112.S±4.54) respectively while minimum
(5.8±1.99, 8.2±2.28 and 6.1±1.37) was
of
pupal stage (Table - 1). The feeding rate
decreased with increase in larval stage
of
mosquito
and
premoulting
time
of
nymphal stage. The predation rate
of
the
nymph was
observed
to
be
increasing
along
with
the
size
of
the
nymph.
U.K.
Sil/gh
£'1
til
Tublc 1 :
Pr~dlltoryp()tcntial
of
dragon-fly nymphs Brac/,ythemis contaminata
Fahricius
on
Anoplrele.'l stepllensi, Clilex l/ub'que/asciatus
and
Aedes
aegypti,
separately
(in 24 hours).
I.
Anopheles stephellsi
Nymphal
size in
mm
Larvae
and
pupae
consumption
in
24
hours
out
of
100 larvae/pupae offered
to
each stage
I
II
III
IV
P
SO
%
SO
%
SO
%
SO
%
SO
%,
4.00 41.3±3.16 41.3 30.2±3.76 30.2
1&.6±2.80
18.6
11.5±2.01
11.5 5.8±1.99
5.8
8.00
74.9±4.72
74.9 67.9±6.76 67.9 43.3±4.64 43.3 33.7±3.71 33.7
\9.6±2.80
19.6
12.00
89.4±7.26 89.4 7
I.
7±3. 77 71.7 68.4±8.64 68.4 46.4±4.05 46.4 24.9±4.61
24.9
14.00*
112.6±7.24 75.6 9K.7±7:33
65.&
SI.I±4.60
81.1
64.6±8.26 64.6 26.7±4.99
26.7
16.00* 127.8±6.96
85.2 I08.9±10.32 72.6
98.6±7.39 98.6 71.3±3.80
71.3
33.3±4.4 t
33.3
Il
Culex quinque/asciatas
Nymphal
size in
mm
Larvae
and
pupae
consumption in 24 hours
out
of
100 larvae/pupae offered to
each
stage
I
If
III
IV
P
SO
%
SO
%
SO
D/O
SO
%
SO
0/
..
4.00 44.0±4.16 44.0
34.2±2.29
34.2 24.0±2.83
24.0
12.2±2.43
12.2 S.2±2.2S
&.2
8.00 60.3±2.83 60.3 53.5±2.33 53.5
47.9±6.65 47.9 27.4±1.65 27.4
18.3±163 IS.3
12.00 83.5±5.11 83.5 62.8±3.35 62.8
51.9±6.74 51.9 37.3±4.24 37.3 19.3±181
19.3
14.00· 97.S±5.38
65.2 82.6±5.42
55.1
68.4±5.54 68.4
56.2±3.79 56.2
23.4±359 23.4
16.00·
125.3±7.45 83.5 1 12.9±8.0\
43.48 99.5±5.50
99.5 87.6±7.1I 87.6
35.\±448
35.1
III
Aedes aegypt;
Nymphal
size in
Larvae
and
pupae
consumption in 24 hours
out
of
100 larvae/pupae offered to
each
stage
I
II
III
N P
mm
SO
%
SD
%
SD
%
SD
"I.
SI)
Ok
4.00 27.7±6.86 27.7 23.3±2.S3 23.3
\8.9±3.41 IS.9
,13.4±1.78
13.4
6.1±1.37
6.1
8.00 63.7±3.86
63.7 46.6±6.68
46.6
44.7±5.12
44.7 24.1±3.74
24.1 17.2±3.19 17.2
12.00 85.2±5.96 85.2 78.1±S.78
78.1
63.7±S.36 63.7
41.6±4.19
41.6 23.6±2.S3
23.6
14.00·
99.8±7.41 66.5
97.6±6,69
65.1
69.6±5.31
69.6 39.2±4.39
39.2
29.2±3.26
29.2
16.00· 112.S±4.54 75.0 9S.8±6.25 63.8
6S.I±6.62
65.1
47.5±3.68
47.5
33.4±2.63
33.4
*150
Larvae
(I
and II), Figures
are
in mean ±
SD
and percentage
99
/,ahora/ofT
S/lIdil'S
oil/ii
..
/'''''''II/orl'
"o/en/ill/
of'
)ragoll-Fly
Table
2 :
Predation
of
dragon-fly
nymphs
Brucl1ytflemi.\' cOl1tumilluta
Fabricius
on
different
mos(luito species
when
offered
together
in 24
hours
Larvae and pupae consumption
in
24
hour
ymphal
size
An.
stl'phl'n.d
Cx.qllillf/llejasciatlls AI'. aeg),pti
in
No.
of
larvae/pupae offered
No.
of
larvae/pupae offered
No.
of
larvae/pupae offered
Grand
mm
I
II
III
IV
P Total
I
II
III
IV
P Total
I
II
III
IV
P Total
Total
20 20 20
20
20 100
20 20
20
20
20
100
20 20
20 20 20
WO
300
4.00
3
2 2 0
0
07
3
2
0
(I
06
2 3 0 0
06
19
8.00
9
8 4
3
25
9 7
3
0
21
6
6 2 2
17
63
12.00
12
12
9
8
42
15
12
8 2
40
13
10
8
5
37
119
14.00
18
14
II
9
3
55
14
16
8 2 2
46
12
11
10
7 2 42
143
16.00
13 15
14
10
3
55
16
15
II
4
3
52
14 12 10
6 3
45
152
184
165
147
496
However, there was
no
marked difference
in
predation by
14
and
16
mOl
nymphal
size.
The
results
of
prey
selection
against different stages
of
An. stephensi.
Cx.
quinquefasciatus andAe. aegyptiwhen
provided together (Table-2) indicated that
B.
contaminata nymphs preferred An.
stephens;
followed
by Cx.
quinquefasciatus
and Ae. aegypti. Since
the dragonfly Naiad is bottom feeder,
logically it
should
feed
more
on
Cx.
quinquefasciatus
andAe. aegypti than An.
stephensi.
As
this
experiment
was
undertaken
in
plastic
bowls
in
the
laboratory with approximately 3.5 cm
depth
of
water, it requires validation in the
field conditions. There was no marked
difference
inpredation by different nymphal
size
of
dragonfly except that predation by
the 4.00
mm
size nymph
was
the least (total
19 larvae
of
all species).
It
was observed
in the experiments that all nymphal stages
I
seemed
to
prefer early larval stage
of
mosquitoes (Tables 1 and 2).
Results
of
this study indicated that
dragonfly nymph
of
B.
contaminata has
good predatory potential against immature
stage
of
Anopheles, Culex and
Aedes
mosquitoes. The size
of
prey
in
relation
to the
predator
is
also
important
in
influencing the predation rate
by
nymph.
The reason
of
decreasing predation with
increase
in
size
of
immature mosquitoes
is
due to increase
in
size
of
prey, which
provides more quantity
of
food intake,
resulting in reduction
in
number
of
prey
to be preyed. However, pupae were least
preferred
by
all nymphal size.
The
laboratory
studies
on
the
predatory potential
of
dragonfly nymphs,
B.
contaminata against different mosquito
species
in
laboratory suggests that these
nymphs have good larvivorous potential.
Therefore, further detailed studies in field
conditions are necessary to evaluate the
efficacy
of
these
nymphs
in
field
conditions.
lOll
/{
J..:
Sil/gh
('I
ill
Fig. 1 Nymphs
of
dragon-fly
Brachytlremis cOlltamilltlta Fabricius
ACKNOWLEDGMENTS
We
are grateful to
Dr.
v.P. Sharma, Former
2.
Director, Malaria Research Centre, for
providing
facilities.
The
authors
are
thankful to Mr. Chand Singh Lohchab for
3.
secretarial assistance and Mr. Veer Pal
Singh. Mr. Rameshwar Gupta
Mr.
Bharat
Singh. Mr. Surendra Kumar and
Mr.
Pan
Singh for their technical assistance in field
and laboratory.
4.
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