Biology, behaviour and functional response
of Cydnocoris gilvus Brum.(Heteroptera: Reduviidae: Harpactorinae) a predator of Tea Mosquito Bug (Helopeltis
antonii Sign.) on cashew in India
K.K. Srikumar 1, P.S. Bhat 2, T.N. Raviprasad3 & K. Vanitha 4
1,2,3,4 Department
of Entomology, Directorate of Cashew Research, Puttur, Dakshina Kannada,
Karnataka 574202, India
1 sreeku08@gmail.com
(corresponding author), 2 pshivarama59@gmail.com,3 tnrprasaad@gmail.com, 4 vanis102@gmail.com
Abstract: Helopeltisspp. (Hemiptera: Miridae) are major sucking pests of
cashew (Anacardium occidentale L.) in India. Cydnocoris gilvus Brum.
(Heteroptera: Reduviidae: Harpactorinae) is recorded as a potential predator ofHelopeltis spp. Biology,
mating behaviour and functional response of C. gilvus were studied by
rearing in the laboratory (temperature 26–28 0C; relative
humidity 89–94 %) with wax moth, Galleria mellonella, larvae. Based on
laboratory rearing, the fecundity was 56.33 eggs in 8.67 batches per
female. The average stadial period
was 37.3 days, with a maximum of 11 days for V instar and a minimum of 4.5 days
for III instars. C. gilvus took 45.5 days to complete a generation. The innate capacity of natural increase
was 0.07 with a gross reproduction of 67.8 females per female. The adult exhibited a pin and jab mode
of predation in a sequence of actions. The sequential action of mating comprised arousal (1.32 min), approach
(12.30 min), riding over (140.48 min) and copulation (85.40 min). The predator responded to
increasing prey density by killing more prey than at lower prey densities
Keywords: Anacardium occidentale, developmentalstages, Galleria mellonella, Helopeltis antonii, predator.
doi: http://dx.doi.org/10.11609/JoTT.o3815.5864-70 | ZooBank:urn:lsid:zoobank.org:pub:46BCC1B1-91E6-4EA5-82F6-A16426C2CFDE
Editor: Renkang
Peng, Charles Darwin University, Darwin, Australia Dateof publication: 26 June 2014 (online & print)
Manuscript details: Ms #
o3815 | Received 15 October 2013 | Final received 23 May 2014 | Finally
accepted 02 June 2014
Citation: Srikumar, K.K., P.S. Bhat, T.N. Raviprasad & K.
Vanitha (2014).Biology, behaviour
and functional response of Cydnocoris gilvus Brum. (Heteroptera: Reduviidae: Harpactorinae) a predator of Tea Mosquito Bug (Helopeltis antonii Sign.) on
cashew in India. Journal
of Threatened Taxa 6(6): 5864–5870; http://dx.doi.org/10.11609/JoTT.o3815.5864-70
Copyright: © Srikumar et al. 2014. Creative
Commons Attribution 4.0 International License. JoTT allows unrestricted
use of this article in any medium, reproduction and distribution by providing
adequate credit to the authors and the source of publication.
Funding: Supported by ICAR network
project ‘ORP on management of
sucking pests of horticultural crops’ through IIHR (Indian Institute of
Horticultural Research)
Competing Interest: The
authors declare no competing interests.
Acknowledgements:We are
very thankful to Indian Council of Agricultural Research, Govt. of India, for
financial assistance (OPR on management of sucking pest of horticultural
crops). The authors are grateful to the Director, Directorate of Cashew
Research for institutional facilities. Our thanks are also due to Dr. Dunston
P. Ambrose, Entomology Research Unit, St. Xavier’s College, Palayamkottai, for
morphologically identifying C. gilvus.
For figures, images, tables -- click here
Cashew (Anacardium occidentale L.) is a native of Brazil, and it
was introduced into the western coast of India by Portuguese travelers during
the 16th century. India’s share in world cashew area is 22.50% and
the share in world cashew production is 20.74% (DCR 2011). Cashew is presently grown in an area of
0.982 million hectares with an annual production of about 0.728 million tonnes
of raw cashewnuts in the country (DCCD 2013). Infestation by insects has been
identified as a major factor responsible for low productivity in cashew
(Sundararaju 1993). The main insect affecting cashew is the Tea Mosquito Bug (TMB), Helopeltis
antonii Signoret (Hemiptera: Miridae). Both nymphs and adults damage tender shoots, inflorescence, immature
nuts and apples at various stages of development, resulting in a yield loss of
30–50% (Devasahayam & Nair 1986).
Reduviids (Hemiptera: Reduviidae) are recorded as potential natural
predators of Helopeltis spp. on cashew (Devasahayam & Nair 1986;
Stonedahl 1991; Sundararaju 1996). Five species of reduviids, viz., Sycanus collaris Fab., Sphedanolestes signatus Dist., Endochus
inornatus Stal, Irantha armipes Stal and Occamus typicusDist., were reported as predators of Helopeltis antonii on cashew in
India (Sundararaju 1984). E. inornatus was reported to feed on 20 individuals of H.
antonii per day in cashew plantations (Sundararaju 1984; Devasahayam &
Nair 1986). Vennison & Ambrose
(1990) accounted for the significance of S. signatus in controlling Helopeltisspp. The biological control
programme against Helopeltis spp. using reduviids has been reported from
Southeast Asia and Pacific region (Rao et al. 1971).
Reduviids can be successfully used as effective biological control
agents of important agricultural pests (Ambrose 2003; Sahayaraj et al.
2006). Biological parameters were
reported for Rhynocoris kumarii Ambrose and Livingstone (Ambrose 2000), Sphedanolestes minusculus Berg. (Ambrose et al. 2006), Endochus migratorius Dist. (Ambrose et al.2007), S. himalayensis Dist., S. signatus Dist. (Vennison
& Ambrose 1990) and S. variabilis Dist. (Ambrose et al. 2009). Although the biologies of a few species
of Oriental reduviids are known, there are still plenty of other species to be
explored (Sahayaraj 2012).
During the survey for natural predators of Helopeltis spp. in
cashew plantations we recorded Cydnocoris gilvus Burmeister
(Heteroptera: Reduviidae: Harpactorinae). Earlier, the prey mediated feeding response of C. gilvus was
reported and it is described in the checklist of Indian assassin bugs
(Venkatesan et al. 1997). The
knowledge on bioecology, behaviour, and pest suppression efficacy of any
organism is a prerequisite for its utilization as a biological control agent. Hence, we reared C. gilvus in the
laboratory using wax moth, Galleria mellonella L. (Lepidoptera: Pyralidae),
larvae as prey, and examined its biology, behaviour and the functional response
towards its natural prey, Helopeltis antonii.
Material and Methods
Laboratory culture of C. gilvus: The nymphs of C. gilvus were
collected from cashew plantations of Directorate of Cashew Research (DCR),
Puttur (12.450N & 75.40E; elevation 90m) in Karnataka
State, southern India. They were
reared in glass rearing bottles (500ml capacity) using larvae of wax moth,
under laboratory conditions (temperature 26–28 0C; relative
humidity 89–94 %). The virgin
males and females that emerged in the laboratory were allowed to mate in glass
rearing bottles. Only adults reared
in the laboratory were used in the experimental studies.
The containers were carefully examined at regular intervals to record
the number of eggs laid. Ejection
of spermatophore capsules by mated females confirmed successful copulation. The eggs laid were allowed as such to
hatch in the same bottles, which were kept over wet cotton swabs for
maintaining optimum humidity (85%). The cotton swabs were changed periodically in order to prevent fungal
attack. Mated females were maintained
individually in order to record the number of batches of eggs and the number of
eggs in each batch. Twenty-five newly hatched nymphs were separated soon after
eclosion and reared individually with first and second instar (5–6 mm)
larvae of wax moth. As the nymphal
development advanced the fourth and fifth instar larvae (10–15 mm) of the
wax moth were supplied.
We observed eclosion, fecundity, hatchability, ecdysis, nymphal
mortality, adult emergence, sex ratio and adult longevity from the adults that
emerged in the laboratory for two generations. The life table parameters were obtained
according to the methods of Atwal & Bains (1974). Observations from hatching of eggs till
the emergence and death of adults were made daily, which provided the values
for a life table (lx).
Predatory behaviour of C. gilvus: Predatory behaviour of C. gilvus towards wax moth larvae and H.
antonii adults was observed in a span of 24 hours. The extent of juvenile cannibalism in C.
gilvus was also recorded.
Mating behaviour of C. gilvus: The mating behaviour of sex
starved C. gilvus was studied in laboratory conditions. The time taken for the sequential acts
was observed.
Laboratory mass culture of H. antonii: The H. antonii gravid females were collected from the
cashew plantations of DCR. They
were allowed to lay eggs in the laboratory on potted cashew seedlings, which
were confined in perforated tubular cages (30×7.5 cm) made from
transparent polyester film (thickness 175 micron). The respiratory processes of eggs
projecting from the surface of the bark were indicative of the presence of
eggs. Immediately after hatching, the nymphs were transferred into nymphal
rearing cages (size: 15×15×20 cm and thickness: 18 gauge) developed
by Sundararaju & John (1992). Nymphal rearing cages consisted of four glass vials of 5ml capacity
fixed on a small aluminum stand with a handle of 15cm height fixed at the
centre. A tender cashew shoot was
kept erect inside each vial filled with water and the opening of the vial was
closed with wet absorbent cotton. Every third day another aluminum stand along with four fresh tender
shoots was placed adjacent to the already existing aluminum stand without
transferring/disturbing the nymphs feeding on the shoots kept on the previous
day. In the rearing cage, two side
provisions were fixed with cloth sleeve in order to facilitate the removal of
adults after final moulting
Functional response: Laboratory raised and
starved for 24 h adults of C. gilvus were used in this experiment. The functional response was assessed
separately at four different prey densities viz., 1,2,4 and 8 prey/predator of
its natural prey, H. antonii for five days in rearing glass bottles
(500ml). Six replicates were made
for each category. At 24 hr
interval the number of prey killed was recorded and the prey number was
maintained constant by the introduction of fresh prey throughout the
experiment. “Disc” equation of
Holling (1959) Y′=
α Tt-by X was used to describe
the functional response of C. gilvus to H. antonii.
Where
X = Prey density
Y = Total number of prey killed in given period of time (Tt)
Tt = Total time in days for
which prey was exposed to the predator
b = Handing time in days
α = Rate of discovery per unit of searching time (y/x / Ts)
x/y = Attack ratio
Ts = Searching time in days
Linear regression analysis was used to explore the relationship between
the prey density and number of prey attacked, searching time and attack ratio.
Results
Biology: Cydnocoris gilvus laid broadly oval, orange yellow coloured eggs in batches on the bottom
of the rearing bottles, each egg vertically glued to the substratum (Image
1). Females laid 8.67±0.67 batches
of eggs with a total number of 56.33±7.88 eggs. The batch size varied from the mean
minimum of 3.33±0.33 per batch to the mean maximum of 11.33±1.45 per
batch. The fertilized eggs turn
into dark reddish chorion with eyespots prior to hatching whereas unfertilized
eggs become shrunken after a few days. The eggs hatched after 8.17±0.31 d. The pre-oviposition period of C. gilvus was 11.00±0.37 d and
females lived only 3.83±0.17 d (post-oviposition period) after laying its last
batch of eggs (Table 1). The
oviposition index value observed was 67.07%.
The newly hatched nymphs were fragile and they became tanned in
3–4 hr after emergence and thereafter start feeding, showing preference
to small and sluggish larvae. The
developmental duration of I, II, III, IV and V instars were 9.50±1.45,
6.33±0.33, 4.50±0.62, 6.00±0.68 and 11.00±1.88 d, respectively (Table 2). Survival percentage of first instar was
comparatively lower than other instars.
The developmental period of females was faster (36.67 ± 2.96 d) than
males (38.00±3.00 d) (Fig. 1). C.gilvus took 45.5±0.92 days to complete a
generation.
The innate capacity of natural increase (rc) was 0.07 with a gross
reproduction (mx) of 67.80 females per female. Mean length of generation (Tc) was 52.26
days (Table 3).
Predatory behaviour: C. gilvus exhibited a pin and jab mode of predation in a sequence of acts. The sequential action of predatory
behaviour was observed in a span of 24 hr as follows: arousal - approach -
capturing - rostral probing - paralysing - sucking - postpredatory
behaviour. The nymphs showed no
cannibalistic behaviour when they were mass reared (Image 2).
Mating behaviour: The sequential act of mating behaviour
observed in C. gilvus as follows:
Arousal - approach - riding over - copulation - post copulatory acts: The matured C. gilvus adults (4–5 days old)
were aroused immediately by the sight of the opposite sex in 1.32±0.29 min. The aroused male chased the females
within a span of 12.3±1.34 min with extended antenna movement. Sometimes the females escaped from the
approaching male. The male placed
its legs on the female after approaching. Males rode over the females with extended rostrum for 140.48±5.48 min. Riding over was seen longer than all
other mating behaviors (Image 3c). Copulation was 85.40±2.99 min in duration. It remained motionless during
copulation and exhibited pterothorax rostral pinning. Drooping down of antennae by both the
sexes was observed at the termination of copulation and thereafter separation
of mating partners. After
separation both male and female moved away from the place of copulation (Image
3d). The post copulatory acts such
as genitalia brushing, antennal grooming, cleaning the legs, and wing beating
were observed in both sex partners. Post copulatory acts lasted for 5.70±0.37 min. Successful completion of copulation was
evidenced by the ejection of spermatophore capsule by female after termination
of copulation.
Functional response: C. gilvus responded to increasing prey density by
killing more prey than at lower prey densities (Table 4). The number of prey killed (y) by the
individual predator increased as the prey density (x) increased from one prey/predator
to eight prey /predator. This was
further confirmed by the positive correlation (r=0.63) obtained between prey
density and prey killed. The
maximum predation was represented by ‘k’ value (2.60). The highest attack ratio was observed at
the density of two prey/predator and the lowest attack ratio was found at the
density of eight prey /predator. Hence, the attack ratio decreased as the prey density increased
(r=-0.63). A negative correlation
was obtained between prey density and searching time (r=- 0.35) of the predator
at all prey densities.
Discussion
Biological studies on reduviids and their utilization in biological
control of insect pests have been gaining momentum in India and other countries
in recent years (Sahayaraj 2007; Schaefer 2010).
The laboratory culture technique standardized using wax moth larva as
prey was found to be similar to the other reduviid rearing techniques (Vennison
& Ambrose 1990; Ambrose 1999; Ambrose 2000; Sahayaraj 2012).
C. gilvus laid eggs on the bottom and sides of the rearing bottles and muslin
cloth as reported in Edocla slateri Distant (Vennison & Ambrose
1986), Coranus soosaii Ambrose & Vennison (Vennison 1989) and C.
spiniscutis Reuter (Claver & Reegan 2010). The fecundity of C. gilvus was
higher than Sphedanolestes spp. (15.33±6.41 eggs) (Vennison &
Ambrose 1990) while lower than that of Rhynocoris marginatus Fab.
(208.3±3.9 eggs) (Sahayaraj & Sathiamoorthi 2002) and C.
spiniscutis (173.72±11.67 eggs) (Claver & Reegan 2010).
The egg incubation period was shorter than other harpactorines
like R. kumarii (10 d), Sycanus collaris Fab. (15 d) and Panthous bimaculatus Dist. (21 d) (Sahayaraj
2012) and higher than R. marginatus (6-7 d) (Sahayaraj &
Sathiamoorthy 2002) and S. variabilis (6.92±0.29 d) (Ambrose et al.
2009). The longest stadium
was the fifth instar and the shortest was the third instar. Harpactorines generally have the
shortest stadial period for II and III instars (Das 1996).
The total nymphal developmental period of C. gilvus was closer toS. variabilis (37.33±4.40 d) (Ambrose et al. 2009) and shorter than that
of S. collaris (75.67±9.06), R. kumarii (88.30±3.60) and P.
bimaculatus (101.12±2.30) (Sahayaraj 2012). The higher mortality of first instar
nymphs might be owing to a higher susceptibility to mechanical injuries and
temperature variations.
The male biased sex ratio was observed in harpactorines as well as
nonharpactorine reduviids (Ambrose 1999; Ambrose et al. 2007).
The sequential pattern of pin and jab mode of predation observed in C.
gilvus was similar to that of several other harpactorine reduviids (Ambrose
1999). Congregational feeding and cannibalism observed in many reduviids (Das
& Ambrose 2008) were not observed in C. gilvus when they were mass
reared. Though cannibalism is
common among adults and nymphs, the degree of intensity of such behaviour vary
considerably among different subfamilies and species (Ambrose 1999).
Mating behaviour was reported in Ectomocoris tibialis Dist. and Acanthespis
pedestris Stal (Ambrose & Livingstone 1978), Rhynocoris
kumarii (Ambrose & Livingstone 1987a) and Coranus vitellinus Dist. (Ambrose & Livingstone 1987b). The duration of riding over was significantly longer than arousal,
approach and copulation. C. gilvus mated in dorsoventral position as reported in Sycanus
reclinatus Doh. and Coranus soosaii Ambrose
& Vennison (Vennison 1989) and in several other harpactorine reduviids
(Ambrose 1999).
The number of prey killed (y) by the individual predator increased as
the prey density (x) increased, thus exhibiting the typical functional response
of the second model of Holling’s ‘disc’ equation (1959). The type II functional response is
typical for most heteropteran predators (Cohen & Byrne 1992). Awadallah et al. (1984)
working on Allaeocranum biannulipes Montr. of a stored product pest, Ambrose et al. (2000) on R.marginatus of a pest of pigeon peas and Claver et al. (2004) on C.
spiniscutis Reut. Spodoptera litura Fab. and Helicoverpa armigera Hub. (Noctuidae:
Lepidoptera) observed a similar response. An indirectly proportional relationship was found between the attack
ratio and the prey density which is similar to the
results obtained by Ambrose et al. (2009) in S. variabilis. It is assumed that when the prey density
increases, predator took less time on nonsearching activities, resulting in
discerning decline in attack rate until the hunger is established (Claver et
al. 2004). A negative correlation
was also obtained between prey density and searching time as the results of
Ambrose et al. (2009).
In conclusion the study suggested that C. gilvus can be multiplied within 50 days for a generation in the
laboratory. Cannibalistic behaviour
was not observed, which is ideal for the mass culture of this predator. The present study on the functional
response suggested that C. gilvus is capable of reducing pest numbers
(Image 4). However, the efficacy ofC. gilvus in biocontrol of Helopeltis spp. needs further
investigation.
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