Journal of Insect Science:Vol. 10 | Article 187
Ambrose et al.
Impacts of Synergy-505 on the functional response and
behavior of the reduviid bug, Rhynocoris marginatus
D. P. Ambrosea*, S. J. Rajanb, and J. M. Rajac
Entomology Research Unit, St. Xavier's College (Autonomous), Palayankottai 627 002, India
Abstract
The impact of the insecticide, Synergy-505 (chlorpyrifos 50 % and cypermethrin 5 % E.C), on
the functional response, predatory behavior, and mating behavior of a non-target reduviid,
Rhynocoris marginatus (Fabricius) (Hemiptera: Reduviidae), a potential biological control agent,
were studied. Though both normal and Synergy-505-exposed R. marginatus exhibited Holling’s
type II curvilinear functional response, Synergy-505 caused a less pronounced type II functional
response with reduced numbers of prey killed, attack rate, searching time, and prolonged
handling time in 4th and 5th nymphal instars and adult males and females reflecting reduced
predatory potential. Synergy-505 also delayed the predatory and mating events. The impacts of
Synergy-505 on functional response, predatory behavior, and mating behavior were more evident
at higher concentrations of Synergy-505.
Keywords: biocontrol agent, mating behavior, predatory behavior
Correspondence: a* eruxavier@gmail.com, b sjrajan@ymail.com, c mich02_raja@yahoo.co.in, *Corresponding author
Associate Editor: Megha Parajulee was editor of this paper.
Received: 13 November 2008, Accepted: 13 October 2010
Copyright : This is an open access paper. We use the Creative Commons Attribution 3.0 license that permits
unrestricted use, provided that the paper is properly attributed.
ISSN: 1536-2442 | Vol. 10, Number 187
Cite this paper as:
Ambrose DP, Rajan SJ, Raja JM. 2010. Impacts of Synergy-505 on the functional response and behavior of the reduviid
bug, Rhynocoris marginatus. Journal of Insect Science 10:187 available online: insectscience.org/10.187
Journal of Insect Science | www.insectscience.org
1
Journal of Insect Science:Vol. 10 | Article 187
Ambrose et al.
Introduction
Materials and Methods
Widespread and indiscriminate use of
synthetic insecticides has resulted in
undesirable ecological changes such as
development of resistance in insects,
resurgence of sucking pests, destruction of
residues in or on soil and plant produce, risks
to human beings, and harmful effects to
animal health besides the effects of
environmental pollution (Mahapatro and
Gupta 1998).
Adults of R. marginatus were collected from
Muthurmalai Scrub Jungle (altitude 125.33
MSL, latitude 77º 21' and 8º 7' N), Tirunelveli
district, Tamil Nadu, South India. They were
reared in the laboratory (28 - 34º C; 12:12 ± 1
h L:D; 65-70 RH) in plastic containers (16 x
11.5 x 4 cm) feeding on larvae of the rice
moth Corcyra cephalonica (Stainton)
(Lepidoptera: Pyralidae).
Although the majority of modern synthetic
insecticides are detrimental to beneficial
insects, including natural enemies of crop
pests, the effects vary from one insecticide to
another and among different non-target
beneficials (George and Ambrose 1998).
Thus, screening of insecticides becomes
imperative to safeguard non-target beneficials
from the hazardous effects of insecticides
(Ambrose 2001; Claver et al. 2003).
Rhynocoris
marginatus
(Fabricius)
(Hemiptera: Reduviidae) is one such predator
that voraciously predates on various
economically important insect pests (Ambrose
1999; George and Ambrose 2004). Although,
the insecticidal impacts on biological and
haematological parameters of reduviid
predators have been studied (George and
Ambrose 1999a, b, 2000, 2004), their impact
on functional response, predatory behavior,
and mating behavior have been neglected.
Such an understanding of the sublethal effects
of insecticides would enable selection of soft
insecticides to protect beneficials and thereby
improve the IPM. Such studies are very
limited even in the field of agriculture
(Ambrose 2001).
Journal of Insect Science | www.insectscience.org
Preliminary experiments were carried out to
find the LC50 values, and 0.040 % was found
to be the optimum toxicity level of Synergy505 (chlorpyrifos 50 % and cypermethrin 5 %
E.C). LC50 of 48 h duration was taken as one
toxic unit and 1/10 the value of the 48 h LC50
of insecticide was considered as sublethal
concentration (Croft, 1990). Sublethal
concentration of insecticide was applied with
a micropipette on 1 x 1cm size of absorbent
papers and placed in the rearing containers. 30
laboratory reared fourth nymphal instars were
reared in separate plastic containers (16 x 11.5
x 4.0 cm) with Synergy-505 applied absorbent
papers as test individuals, and another 30
nymphal instars were reared with water
applied absorbent papers as the control. Both
Synergy-505- exposed and control sets of
nymphal instars were allowed to grow up to
adults.
The functional responses of one day-old
control and Synergy-505-exposed 4th and 5th
nymphal instars and adults to the larvae of C.
cephalonica (0.8 to 1.2cm long) were studied
in plastic containers (16 x 11.5 x 4 cm) at
different prey densities (1, 2, 4, 8 and 16). The
prey was first introduced into the
experimental containers and was allowed to
settle. After 30 min, a predator was introduced
into the experimental container. The number
2
Journal of Insect Science:Vol. 10 | Article 187
of prey killed was continuously monitored,
and fresh prey were introduced to replace the
killed prey. After every 24 h, the prey
consumed was counted. Eight replicates were
maintained for each category and observations
were continuously made for 6 days.
Regression analysis (Daniel 1987) was carried
out to determine the relationship between the
prey density and the number of prey
consumed, searching time, attack ratio, and
handling time.
The impact of Synergy-505 on the predatory
and mating behaviors of R. marginatus were
studied by comparing the time durations taken
for predatory events such as arousal,
approach, capturing, paralyzing, and sucking;
and mating events such as arousal, approach,
and copulation in control and Synergy-505exposed test individuals.
Results and Discussion
The 50% lethality concentration (LC50)
values, upper and lower fiducial limits, and
toxicity of Synergy-505 on R. marginatus at
24, 48, 72, and 96 h durations are presented in
Table 1, which shows that as the duration of
Synergy-505 exposure was increased, the
percentage of LC50 values and the upper
fiducial limit decreased. The relative toxicity
increased from 1.0 to 2.13 when exposure
duration was increased from 24 to 96 h.
Similar effects were also reported for a
cypermethrin exposed to a reduviine reduviid,
Acanthaspis pedestris Stål (Claver et al.
2003), and monocrotophos, dimethoate, and
quinalphos (George and Ambrose, 2004), and
Ambrose et al.
for methyl parathion, endosulfan (George and
Ambrose 2006), and cypermethrin exposed-R.
marginatus (Ambrose et al. 2007).
Functional response
Control R. marginatus responded to
increasing prey density by killing a higher
number of prey than were killed at lower prey
densities and thus exhibited Holling’s type II
curvilinear functional response (Holling
1959). The number of prey killed by the
individual predator increased as the prey
density (x) was increased from one prey per
predator to 16 prey per predator. This was
further confirmed by the positive correlations
obtained between the prey density and prey
killed for the 4th and 5th nymphal instars and
adult males and females (y = 1.263 + 0.253x, r
= 0.956; 1.502 + 0.238x, r = 0.928; 1.283 +
0.285x, r = 0.970 and 1.549 + 0.280x, r =
0.922; respectively). A similar functional
response was observed in A. pedestris
(Ambrose and Sahayaraj 1996; Claver et al.
2003), Rhynocoris fuscipes (Fabricius)
(Ambrose and Claver 1995; Claver and
Ambrose 2002), Rhynocoris longifrons Stål
(Claver et al. 2002), Coranus spiniscutis
Reuter (Claver et al. 2004), and Acanthaspis
quinquespinosa (Fabricius) (Ambrose et al.
2008). Though such positive correlations
between the prey density and prey killed were
also obtained for the Synergy-505-exposed 4th
and 5th nymphal instars and adult males and
females (y = 1.101 + 0.122x, r = 0.863; 1.008
+ 0.154x, r = 0.927; 0.785 + 0.165x, r = 0.933
and 0.821 + 0.116x, r = 0.932; respectively),
they exhibited reduced rates of predation
(Tables 2-5 and Figure 1).
Table1. Toxicity of Synergy-505 to Rhynocoris marginatus (n = 30; d.f. = 3).
Fiducial limit
Exposure
duration (h)
X2
Regression
equation Y=a + bX
LC50
(%)
24
48
72
0.37
0.28
1.6
Y = 4.489x - 2.68
Y = 5.844x - 4.29
Y = 9.190x - 8.98
0.051
0.039
0.033
Lower
1.626
1.553
1.487
96
1.38
Y = 8.096x - 6.23
0.024
1.292
Journal of Insect Science | www.insectscience.org
Variance
Relative
toxicity
Upper
1.795
1.626
1.556
0.0019
0.0003
0.0003
1
1.308
1.545
1.482
0.0024
2.125
3
Condition
Normal
Synergy-505
Prey
density
(x)
Prey
attacked
(y)
1
2
4
8
16
1
2
4
8
16
0.93
1.69
2.86
3.64
5.03
0.7
1.25
2.12
2.43
2.79
Maximum'
y (k)
Days/y
b = Tt/k
5.03
1.193
2.79
2.151
Days all
y's (by)
Days searching
Ts = Tt - by
Attack
ratio y/x
Rate of discovery
y/x TS = (a)
1.109
2.016
3.412
4.343
6
1.506
2.689
4.56
5.227
6
4.891
3.984
2.588
1.657
Mean = 2.624
4.494
3.311
1.44
0.773
Mean = 2.003
0.93
0.845
0.715
0.455
0.314
0.7
0.625
0.53
0.303
0.174
0.19
0.212
0.276
0.275
Mean = 0.190
0.156
0.188
0.368
0.392
Mean = 0.220
Discovery equation
y' = a(Tt - by)x
y’ = 0.190
(6 – 1.193y) x
y’ = 0.220
(6 – 2.151y) x
Table 3. Functional response values for control and Synergy-505 exposed fifth nymphal instars of Rhynocoris marginatus to Corcyra cephalonica larvae for 6 days (n=12).
Condition
Normal
Synergy-505
!Table 4.
Prey
density
(x)
Prey
attacked
(y)
1
2
4
8
16
1
2
4
8
16
0.99
1.96
3.06
3.95
4.95
0.69
1.26
2.07
2.56
3.24
Maximum'
y (k)
Days/y
b = Tt/k
4.95
1.212
3.24
1.851
Days all
y's (by)
Days searching
Ts = Tt - by
Attack
ratio y/x
Rate of discovery
y/x TS = (a)
1.199
2.375
3.708
4.787
6
1.277
2.332
3.831
4.738
6
4.801
3.625
2.292
1.213
Mean = 2.386
4.723
3.668
2.169
1.262
Mean = 2.364
0.99
0.98
0.765
0.493
0.309
0.69
0.63
0.518
0.32
0.203
0.206
0.27
0.333
0.406
Mean = 0.243
0.146
0.172
0.239
0.254
Mean = 0.162
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Table 2. Functional response values for control and Synergy-505 exposed fourth nymphal instars of Rhynocoris marginatus to Corcyra cephalonica larvae for 6 days (n=12).
Discovery equation
y' = a(Tt - by)x
y’ = 0.243
(6 – 1.212y) x
y’ = 0.162
(6 – 1.851y) x
Functional response values for control and Synergy-505 exposed adult male Rhynocoris marginatus to Corcyra cephalonica larvae for 6 days (n=12).
Condition
Synergy-505
4
Prey
attacked
(y)
1
2
4
8
16
1
2
4
8
16
0.97
1.92
2.88
3.89
5.6
0.64
0.96
1.62
2.71
3.13
Maximum' y
(k)
Days/y
b=
Tt/k
5.6
1.071
3.13
1.917
Days
all y's
(by)
Days searching
Ts = Tt - by
Attack
ratio y/x
Rate of discovery
y/x TS = (a)
1.039
2.056
3.084
4.166
6
1.227
1.84
3.106
5.195
6
4.961
3.944
2.916
1.834
Mean = 2.731
4.774
4.16
2.894
0.805
Mean = 2.526
0.97
0.96
0.72
0.486
0.35
0.64
0.48
0.405
0.339
0.196
0.196
0.243
0.247
0.265
Mean = 0.190
0.134
0.115
0.139
0.421
Mean = 0.162
Discovery equation
y' = a(Tt - by)x
y’ = 0.190
(6 – 1.071y) x
y’ = 0.162
(6 – 1.917y) x
Ambrose et al.
Normal
Prey
density
(x)
Condition
Normal
Synergy-505
Prey
density
(x)
Prey
attacked
(y)
1
2
4
8
16
1
2
4
8
16
0.99
1.93
3.51
4.43
5.59
0.68
0.94
1.75
2.72
3.19
Maximum' y
(k)
Days/y
b=
Tt/k
5.59
1.073
3.19
1.88
Days
all y's
(by)
Days searching
Ts = Tt - by
Attack
ratio y/x
Rate of discovery
y/x TS = (a)
1.062
2.07
3.766
4.753
6
1.278
1.767
3.29
5.113
6
4.938
3.93
2.234
1.247
Mean = 2.469
4.722
4.233
2.71
0.877
Mean = 2.515
0.99
0.965
0.877
0.553
0.349
0.68
0.47
0.437
0.34
0.199
0.2
0.245
0.392
0.443
Mean = 0.256
0.144
0.111
0.161
0.387
Mean = 0.161
Discovery equation
y' = a(Tt - by)x
y’ = 0.256
(6 – 1.073y) x
y’ = 0.161
(6 – 1.880y) x
!
Ambrose et al.
5
Figure 1. Functional response curves of control (triangle) and Synergy-505 (square) exposed 4th and 5th nymphal instars and adult males and females Rhynocoris marginatus at different
prey densities. High quality figures are available online.
Journal of Insect Science:Vol. 10 | Article 187
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Table 5. Functional response values for control and Synergy-505 exposed adult female Rhynocoris marginatus to Corcyra cephalonica larvae for 6 days (n=12).
Journal of Insect Science:Vol. 10 | Article 187
The searching time decreased as the prey
density was increased in both control and
Synergy-505-exposed R. marginatus as
evidenced by the negative correlations
obtained between prey densities and the
searching time for control (y = 4.493 - 0.302x,
r = - 0.956; 4.179 – 0.289x, r = - 0.928; 4.625
– 0.306x, r = - 0.970 and 4.338 – 0.301x, r = 0.922) and Synergy-505-exposed (3.631 –
0.262x, r = - 0.863; 4.133 – 0.285x, r = 0.926; 4.493 – 0.317x, r = - 0.933 and 4.454 –
0.313x, r = - 0.932) 4th and 5th nymphal instars
and adult males and females, respectively. But
Synergy-505-exposed life stages of R.
marginatus searched their prey quickly, and
this reduction in the searching time was
gradually reduced as the life stages grew
(Tables 2-5). However, the cypermethrinexposed A. pedestris took a longer time to
search its prey due to insecticide repellency in
searching behavior (Claver et al. 2003) as
reported for several other natural enemies
belonging to Aphelinidae, Syrphidae, and
Trichogrammatidae (Ambrose 2001).
The maximum predation represented by k
values was found restricted to high prey
density in both control and Synergy-505exposed life stages of R. marginatus. Prey
density facilitated the predator to spend less
time on its prey, and to utilize all its time
attacking and consuming. The k value for
control 4th and 5th nymphal instars and adult
males and females were 5.03, 4.95, 5.60, and
5.59, respectively. Synergy-505-exposed 4th
and 5th nymphal instars and adult males and
females
exhibited
comparatively
low
predation rates as evidenced by low k values
of 2.79, 3.24, 3.13, and 3.19, respectively
(Tables 2-5). Similar insecticide-affected k
values were observed for many arthropod
beneficials (Croft 1990) and cypermethrinexposed A. pedestris (Claver et al. 2003).
Journal of Insect Science | www.insectscience.org
Ambrose et al.
In both control and Synergy-505-exposed life
stages of R. marginatus the highest attack
ratios were found at 1 and 2 prey per predator
densities and the lowest attack ratio at 16 prey
per predator density and for both control (y =
0.904 – 0.041x, r = - 0.954; 1.000 – 0.047x, r
= - 0.957; 0.962 – 0.042x, r = - 0.936 and
1.026 – 0.045x, r = - 0.973) and Synergy-505exposed (0.682 – 0.035x, r = - 0.959; 0.672 –
0.032x, r = - 0.955; 0.566 – 0.025, r = - 0.921
and 0.588 – 0.026x, r = - 0.904) 4th and 5th
nymphal instars and adult males and females,
respectively (Tables 2-5). It is presumed that
the predator spent less time on searching
activities that might have caused a perceptive
decline in the attack ratio until hunger was
established. Such an indirectly proportional
relationship between the attack ratio and prey
density was earlier reported for several other
reduviids (Ambrose 1999; Ambrose et al.
2000, 2008; Claver et al. 2003). The attack
rate depends upon several component
parameters, such as the rate of prey encounter,
the probability that the prey will be attacked
when encountered, and the probability that an
attack will result in capture (Thompson 1975;
Bailey 1986; Spitze 1985; Getty and Pulliam
1991).
Though the handling time (time taken by the
predator to handle one host) decreased as the
prey density increased in both control and
Synergy-505-exposed R. marginatus, it was
considerably prolonged in 4th and 5th nymphal
instars and adult males and females from
1.193, 1.212, 1.071, and 1.073 min to 2.151,
1.851, 1.917, and 1.880 min, respectively
(Tables 2-5). The present findings are in close
agreement with those of cypermethrinexposed A. pedestris (Claver et al. 2003). The
resting time of the predator in between prey
handling was longer at low prey density than
at higher prey density.
6
Journal of Insect Science:Vol. 10 | Article 187
There was a negative correlation between the
rates of discovery and prey density in control
(y = 0.274 – 0.013x, r = - 0.721; 0.334 –
0.014x, r = - 0.584; 0.277 – 0.014x, r = 0.584; 0.277 – 0.014x, r = - 0.789 and 0.344 0.014x, r = - 0.500) as well as Synergy-505exposed (y = 0.292 – 0.01x, r = - 0.431; 0.226
– 0.010x, r = - 0.627; 0.192 – 0.005x, r = 0.192 and 0.196 – 0.005x, r = - 0.253) 4th and
5th nymphal instars and adult males and
females, respectively. But Synergy-505
reduced the rates of discovery at all prey
densities in 5th nymphal instar and adult males
and females, and only at prey densities of 1
and 2 in 4th nymphal instar (increased at 4 and
8 prey densities) (Tables 2-5). In A. pedestris
cypermethrin rate of discovery decreased only
at a prey density of 4 due to its decreased
feeding rate (Claver et al. 2003).
Predatory behavior
The act of arousal was delayed from 0.28 ±
0.06 to 0.39 ± 0.06, 0.26 ± 0.07 to 0.46 ± 0.13,
and 0.31 ± 0.03 to 0.76 ± 0.26 min in the 4th
and 5th nymphal instars and adults,
respectively due to Synergy-505-exposure
(Table 6).
Synergy-505 also prolonged the act of
approach from 0.04 ± 0.06 to 0.12 ± 0.03,
0.02 ± 0.01 to 0.06 ± 0.02, and 0.16 ± 0.01 to
0.20 ± 0.04 min in 4th and 5th nymphal instars
and adults, respectively. As observed for
arousal and approach, Synergy-505 also
delayed prey capturing in 4th and 5th nymphal
instars and adults from 0.13 ± 0.03 to 0.21 ±
0.09, 0.11 ± 0.02 to 0.14 ± 0.06, and 0.38 ±
0.07 to 0.45 ± 0.15 min suggesting poor
predatory efficiency due to Synergy-505exposure (Ambrose 2001).
Synergy-505 also prolonged paralysing from
0.17 ± 0.06 to 0.31 ± 0.15, 0.15 ± 0.17 to 0.21
± 0.10, and 0.18 ± 0.06 to 0.36 ± 0.07 min in
Journal of Insect Science | www.insectscience.org
Ambrose et al.
4th and 5th nymphal instars and adults,
respectively as observed by Ambrose (1999,
2001).
Synergy-505 further delayed the act of
piercing and sucking from 14.50 ± 2.43 to
22.67 ± 5.37, 13.83 ± 3.89 to 19.17 ± 5.58,
and 16.50 ± 2.98 to 20.67 ± 5.73 min in 4th
and 5th nymphal instars and adults. Such poor
sucking efficiency as a function of insecticide
exposure was reported for other reduviids
(Ambrose 1999, 2001; Claver et al. 2003).
Similar observations of delayed predatory acts
were reported by Claver et al. (2003) in
cypermethrin-treated A. pedestris. Moreover,
Synergy-505-exposed R. marginatus exhibited
reduced food intake and often spitted watery
saliva, as reported by Ambrose and George
(1998) in monocrotophos-treated A. pedestris.
The delayed predatory acts could be attributed
to decreased movements due to malformed
legs as a function of Synergy-505-exposure as
observed by French-Constant and Vickerman
(1985) in cypermethrin- and deltamethrinexposed Forficula auricularia.
Mating behavior
The Synergy-505 prolonged the time taken for
arousal for mating. For instance, control
individuals took 0.082 ± 0.01 min to arouse
whereas Synergy-505-exposed individuals
took 0.315 ± 0.09 min. The act of approach
was also delayed from 0.33 ± 0.05 to 0.58 ±
0.11 min. As observed for arousal and
approach, Synergy-505 also prolonged the
duration of copulation from 33.50 ± 8.94 to
21.67 ± 7.23 min. The total duration of the
mating (34.21 ± 9.00 min) in control
individuals was prolonged to 22.56 ± 7.43 min
in Synergy-505-exposed test individuals
(Table 7).
7
Journal of Insect Science:Vol. 10 | Article 187
Ambrose et al.
Table 6. Chronological analysis of sequential acts of predatory events in normal and Synergy-505 exposed Rhynocoris
marginatus (n = 6, ± SD).
Predatory acts (in min.)
Stage
Treatment
Arousal
Approach Capturing Paralysing
Piercing and sucking
IV-Instar
V-Instar
Adult
Normal
0.28 ± 0.06
0.04 ± 0.06
0.13 ± 0.03
0.17 ± 0.06
14.50 ± 2.43
Synergy-505
0.39 ± 0.06
0.12 ± 0.03
0.21 ± 0.09
0.31 ± 0.15
22.67 ± 5.37
Normal
0.26 ± 0.07
0.02 ± 0.01
0.11 ± 0.02
0.15 ± 0.17
13.83 ± 3.89
Synergy-505
0.46 ± 0.13
0.06 ± 0.02
0.14 ± 0.06
0.21 ± 0.10
19.17 ± 5.58
Normal
0.31 ± 0.03
0.16 ± 0.01
0.38 ± 0.07
0.18 ± 0.06
16.50 ± 2.98
Synergy-505
0.76 ± 0.26
0.20 ± 0.04
0.45 ± 0.15
0.36 ± 0.07
20.67 ± 5.73
Table 7. Chronological analysis of sequential acts of mating events in normal and Synergy-505 exposed Rhynocoris marginatus (n
= 6, ± SD).
Mating acts (in min.)
Treatment
Arousal
Approach
Copulation
Total duration
Normal
0.082 ± 0.01
0.33 ± 0.05
33.50±8.94
34.21±9.00
Synergy-505
0.315 ± 0.09
0.58 ± 0.11
21.67±7.23
22.56±7.43
Synergy-505-exposedmating partners not only
showed significant deviations in terms of
durations for each sequential act of mating
from those of the control R. marginatus, but
also failed to achieve genital connection. Such
behavior was attributed to the inhibitory
effects on various physiological processes
(Ambrose and George 1998; Claver et al.
2003).
Acknowledgements
The authors are grateful to the authorities of
St.
Xavier’s
college
(Autonomous),
Palayankottai, for facilities. DP Ambrose
thanks the Ministry of Environment and
Forest, Government of India (MoEn. No.
23/12/2005RE), for financial assistance.
References
Conclusion
Although the field concentration of (40µl) of
Synergy-505 did not immediately kill nontarget predators like R. marginatus, it affected
their functional response events such as
number of prey attacked, attack ratio and rate
of discovery and prolonged the predatory, and
mating events. Hence, the results of the
present study suggest that the usage of
Synergy-505 is not advisable for a crop
environment where beneficials like R.
marginatus are found or incorporated as a
biocontrol constituent in the integrated pest
management program.
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