Feeding Behaviour of the Predatory Reduviid ...

LS - An International Journal of Life Sciences DOI: 10.5958/2319-1198.2014.01087.2

Feeding Behaviour of the Predatory Reduviid, Rhynocoris kumarii (Hemiptera: Reduviidae) Evangelin G1*, Bertrand Horne2, Muthupandi M3 and S John William4 1,2,3

Research Scholar, 4Associate Professor, School of Entomology and Centre for Natural Resources Management (SECNARM), P.G. & Research Department of Advanced Zoology and Biotechnology, Loyola College, Chennai-600034, Tamil Nadu, India Corresponding author email id: *[email protected]; [email protected]; [email protected]; 4 [email protected]

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ABSTRACT The feeding behaviour of the predatory reduviids, which is highly prey specific and replete with evolving prey-capture strategies, is the sole reason for the abundance of these insects in hostile environments. Their search for nutrients can be efficiently put to beneficial use in agriculture. The utilisation of these insects in the biological control of insect pests increases their economic potential; hence, their extensive and varied feeding behaviour needs to be studied carefully in order to make better use of these insects in integrated pest management programmes. Keywords: Rhynocoris kumarii, Feeding behaviour, Biological control, Venomous saliva

1. INTRODUCTION The family reduviidae constitute predatory insects with a profoundly voracious lifestyle that enable them to colonise and successfully perpetuate their progeny in severely hostile environmental conditions. With close to 6,800 described species (Hwang and Weirauch, 2012), they form the largest group of predatory terrestrial bugs. Their uninterrupted streak of success in surviving, occupying and inhabiting extreme conditions is due to a culmination of various factors, including structural, physiological, morphological and behavioural adaptations, constant upgradation of their prey capture strategies and a highly evolved method of feeding, which includes extraoral digestion (EOD) facilitated by their venomous saliva. Their wide representation has been recorded in tropical and subtropical regions, including deserts and rainforests (Ryckman, 1954; Miller, 1959). The other unusual areas of habitation that they seem to thrive include tree barks, foliage of herbs, decomposing logs, mammalian burrows, scrubland, agro-ecosystems, ant hills, termite mounds, cobwebs, bird nests, rat holes and human dwellings Volume 3, Number 2, May-August, 2014, pp. 64-69

(Haridass, 1985; Ambrose, 1999; Readio, 1927; Louis, 1974; Subramanian and Sahayaraj, 2012; Miller, 1953). Due to constant degradation and pollution of the environment on one side caused by chemical pesticides and fertilisers and rapid development of eco-friendly technologies in various fields of food production on the other, the last few decades have witnessed a surge in the study of predatory insects, which could potentially help in curbing the rampant insect pest population that leads to loss of hectares of crops. In such a scenario, reduviidae have occupied the centre stage by proving to be important biological control agents against many economically important crops (Grundy, 2007; George and Ambrose, 2001; Nyiira, 1970; Edwards, 1962; Vennison and Ambrose, 1992; Wignall and Taylor, 2010; Nagarajan and Ambrose, 2013; Claver et al., 2003(a,b); Ambrose and Kumaraswami, 1990). Predatory insects possess the power to regulate the demographic structure and population of a pest species. In some cases, the mortality caused to a pest population by its predator through feeding or natural enemies can be drastic, resulting in the complete extinction of the

Feeding Behaviour of the Predatory Reduviid, Rhynocoris kumarii (Hemiptera: Reduviidae)




pest species. In order to lessen the effect of predators to prevent the extinction of pest species and to control their population in situations where the pest becomes a public menace, the feeding behaviour of the predator must be closely studied. In order to employ reduviids as biological control agents to suppress the pest population, a comprehensive study of its biology, behaviour and functional response in addition to an elaborate observation and record of their feeding mechanism is indispensable. Rhynocoris kumarii is an excellent predator of many harmful insect pests and has been successfully used in biological control (Sahayaraj and Asha, 2010). Ambrose (2000, 2001), Ambrose et al. (2008) and Sahayaraj and Ravi (2007) have recorded the status of R. kumarii as a beneficial insect, the optimum conditions for its mass rearing and its potential deterrents. The ecotypic diversity in R. kumarii was studied by Baskar et al. (2012). Claver and Ambrose (2001b) have investigated the influence of various aspects, such as antennectomy, eye blinding and tibial comb coating, on the behavioural pattern of the predator. Other studies include the nymphal cannibalistic behaviour (George, 2000a), rate of natural increase (George, 2000b) and the effect of insecticides on postembryonic development (George and Ambrose, 1999, 2004) of the predator R. kumarii. Despite the abundance of work on its predatory potential, there is no detailed work on its feeding behaviour. Thus, this study attempts to break down and classify the different stages of feeding behaviour of the predatory reduviid, R. kumarii. 2. METHODOLOGY Adults of the predator R. kumarii were collected from the forest ecosystem in Tirunelveli (8.7300° N, 77.7000° E) and Kanyakumari (8.0780° N, 77.5410° E) districts of Tamil Nadu and were maintained under laboratory conditions (temperature 31-32ºC; RH 75-80%; photoperiod 11-13 h) in a plastic trough (22x10x14 cm3) on Corcyra cephalonica larvae. Certain randomly selected individuals were starved for 24, 48 and 72 h (Figure 1a) and were given the third or fourth instar of the red cotton stainer Dysdercus cingulatus to prey upon. Observations were made directly on their feeding mechanism under laboratory conditions. Volume 3, Number 2, May-August, 2014

3. RESULTS AND DISCUSSION 3.1. Feeding Behaviour Any action that results in the procurement of nutrients can be termed as feeding behaviour. Despite the abundance of literature on the biology and ecology of reduviids, their feeding behaviour has not been thoroughly investigated. While some reduviid bugs prefer a wide array of prey species, others prefer certain taxonomic groups. Haridass et al. (1987) have classified the feeding of reduviids into six main types, namely, sticky trap type, raptorial type, wait and grab type, pin and jab type, chase and pounce type and blood feeding type. The feeding behaviour of R. kumarii, which can be categorised into the wait and grab type, is a highly evolved and sophisticated process in comparison to other predatory insects and can be easily broken down into distinct phases, which at times are seen to blend into and juxtapose over one another. 3.2. Identifying the Prey The predator goes in search of a prey to devour. As stated by Haridass (1985), visual stimuli are seen to play a pivotal role in aiding reduviid bugs in locating and identifying the prey. The well-developed optical system, when fixed on a moving prey, sets into motion a series of successive steps of predator-prey interactions that result in the prey being gorged. When R. kumarii spots a moving prey, it is seen that the predator never turns its gaze away from the prey (Figure 1b). The importance of visual stimuli in the initiation of the feeding process was studied by Haridass and Ananthakrishnan (1980), wherein it was seen that artificial objects simulated in the optical spectrum of the predator were mistaken for prey. The time taken for identification of the prey is less in the case of prey that is wandering, as there is more possibility for both the predator and the prey to collide into each other. In case of a stationary prey, the predator takes longer to ascertain the fact. Moreover, prey movement is a very important factor that helps the predator in detecting the prey. Quick movement of the prey attracted the visual and sensory attention of the prey in comparison with slow moving or unmoving prey. A dead prey, when artificially moved, elicits a quick response from the predator, which immediately tries to attack it. The nervous system of the insect picks up 65

Evangelin G, Bertrand Horne, Muthupandi M and S John William




these stimuli from the surrounding environment and helps the predator to retaliate with proper behavioural responses (Bianco et al., 2011). It is interesting to note the observations made by Claver and Ambrose (2001a), wherein they state that 1-day-starved predator R. kumarii travelled a longer distance searching for prey in comparison to a 4-day-starved prey. The speed of searching, distance travelled, turning time and degree was also greater in the former. This could probably be because a 4-day-starved predator would be left drained and with very little energy to go in search of the prey. A similar observation was made in Rhynocoris marginatus (Claver and Ambrose, 2003). In combination with the visual and sensory cue, the innate prey capture capacity of the predator also helps in the process.

predator takes its time to cautiously move towards the prey. This approach is diligent with the antennae roving in all directions to check for possible distractions. R. kumarii moves towards the prey with slow but definite steps until it reaches a close proximity with the prey. With one swift, gliding motion, the predator captures the prey with its forelegs and pins it down to the ground or to a nearby object (Figure 1c). It pounces on the prey and subdues the prey. It is interesting to notice that the predator almost always grabs the prey from behind or from the sides and very rarely from the front. This results in total entrapment of the prey. In most cases, it grabs the prey with the help of the forelegs and pierces the head or neck region of the prey with its proboscis. The prey then thrashes around for a few minutes and eventually its twitching movements die down. The stylet penetration of the predator is quite powerful, inflicting pain and quickening the process of death of the prey. In

3.3. Capturing the Prey This stage is a rather elaborate process wherein the

(a)

(b)

(c)

(d)

(e)

(f)

Figure 1: Stages in the feeding behaviour of Rhynocoris kum arii (a) A 48-h starved Rhynocoris kumarii; (b) locating the prey by visual stimuli; (c) grabbing the prey and pinning it down with the forelegs; (d) prey trying to break free of the predators grip; (e) injecting venomous saliva through the rostrum in the neck of the prey and sucking out the liquefied contents; and (f) discarding the dead prey.

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LS - An International Journal of Life Sciences

Feeding Behaviour of the Predatory Reduviid, Rhynocoris kumarii (Hemiptera: Reduviidae)

the case of smaller prey, the predator smothers it with the weight of its body by laying on it while enabling stylet penetration. In larger prey, the stylet penetration alone causes the death of the prey. If the prey is of a larger size and manages to break free from the predators grip, an immediate pounce or lunge is needed. While the predator does not hesitate to pounce on a prey much larger than itself, at times, the sheer size of the prey might help it in untangling itself from the predators grip and facilitates its escape. If such an escape occurs after the stylet penetration, the prey invariably dies after a few hours.




3.4. Dragging the Prey After the prey has been subdued and the last of its twitching movements have died down, the predator drags it to a place which is usually a corner or near an immovable object. This could be due to various reasons. Moving the prey to one corner can help the predator keep an eye on other approaching insects from one direction while concentrating fully on feeding. It inserts the stylet into the neck or head of the prey and drags it along as it walks forward or backwards.

predatory techniques as the reduviid bugs can ingest only liquefied food. The rostrum, when inserted into the body of the prey, slowly emits a steady flow of venomous saliva which liquefies the insides of the prey, which are then sucked out (Jacobson, 1911; Edwards, 1960; Sahayaraj, 1994; Haridass and Ananthakrishnan, 1980). The saliva thus emitted contains digestive enzymes which facilitate digestion. This process is referred to as EOD. This process of specialised digestion is ecologically important because it enables comparatively small predators to devour large prey that cannot be taken whole (Cohen, 1990). This characteristic along with their preference for a wide variety of prey make reduviid bugs highly effective in controlling pest population in heavily infested fields. 3.7. Post-Feeding Behaviour After the ingestion of the liquefied contents of the prey, R. kumarii releases its hold on the prey and moves away. It never returns to probe the contents of the now dead prey (Figure 1f). It is found to spend a considerable amount of time cleaning the antennae after a complete session of feeding.

3.5. Injection of Venomous Saliva into the Prey

ACKNOWLEDGEMENT

Once the prey has been pinned down, R. kumarii uses its forelegs to grip the prey and balances itself using the hind legs. It then uses its pointed rostrum to inject its venomous saliva into the body of the prey (Figure 1d and 1e). The site of injection is the neck, antennae or the base of the legs (Haridass, 1985; Haridass and Ananthakrishnan, 1980; Cohen, 1990). After the venomous saliva enters the body of the prey, a gradual and continuous decrease is seen in the twitching movements of the prey. This is followed by general immobilisation, paralysis and eventual death. More often than not, the prey reacts unpleasantly to the venomous saliva. Spodoptera litura when injected emits greenish fluid in self-defense (Sahayaraj, 1994). The capture rate was found to be directly proportional to the size of the prey. Greater prey size resulted in reduced capture success.

The authors would like to thank the authorities of Loyola College, Chennai, Tamil Nadu, for institutional facilities.

3.6. Action of the Venomous Saliva The salivary secretions are the reason for their specialist Volume 3, Number 2, May-August, 2014

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