Bioefficacy of Sycanus reclinatus Stal Dohrn, (Hemiptera: Reduviidae) on the Euproctis fraterna Moore (Lepidoptera:Lymantriidae)

doi:10.21203/rs.3.rs-4944183/v1

Sycanus reclinatus Dohrn, (Hemiptera: Reduviidae) is a reduviid predator of many agricultural crop pests. A laboratory experiment was conducted to evaluate the bio efficacy of this predator using functional response as a tool. Sycanus reclinatus Dohrn third, fourth, and fifth instar nymphs and adults on Euproctis fraterna Moore were evaluated. The predatory rate gradually increased from the third instar nymph to adults. S. reclinatus killed and consumed more prey in high densities (4.5, 4.6, 6.0 and 4.5 prey/ predator). The rate of discovery gradually increased when the predator grew older. Handling time also increased when the predator grew older. S. reclinatus showed an exponential (Type II) functional response when E. fraterna was exposed to it. Type II functional response is more pronounced in pests. Such different patterns show that the predator needs to adapt distinct strategies according to the kind of prey available in the field. The biological control potential of S. reclinatus concerning the pest E. fraterna shows that the, searching time, handling time, and number of prey killed depended upon the prey densities and predator life stages. Hence, the predator S. reclinatus can be utilized to control and manage the selected lepidopteran pest.

Euproctis fraterna

Functional response

Sycanus reclinatus

Bio efficacy

Reduviid predators are potential biocontrol agents against many insect pests and hence, they have the potential for an even greater role in Integrated Pest Management (Ambrose, 2000; Grundy and Maelzer 2000, Anonymous, 2018, Arshad et.al. 2021; Laura et.al. 2021). In biological control program, the reduviid predator has been widely used worldwide under laboratory and field conditions. Reduviids have been recorded as important natural enemies in suppressing several pests especially orthopteran, hemipteran, and lepidopteran insects (Sahayaraj 2006, Grundy, 2007, Assefa, 2019; Sahayaraj et al., 2020, Besmer et.al., 2021; China Chenchaiah, 2020). Reduviid predators are frequently recorded as effective regulators of insect populations (Ambrose et al., 2009; Ambrose and Claver, 2009; Chandral et al., 2009). Sycanus reclinatus (Hemiptera: Reduviidae) is a multivoltine, voracious harpactorine reduviid predator (Ambrose et al., 2003). It has been recorded as an efficient predator of pests of the cotton. Presently, biological control is considered advantageous for pest management through integrated approaches and also helps to avoid insecticidal application and its ill effects in different crop ecosystem.

The hairy caterpillar Euproctis fraterna (Lepidoptera:Lymantriidae) is an important forest pest which feeds on the foliage of many dicotyledonous tree species(Ambrose, 2008). Larvae of E. fraterna were found defoliating one of the important forest trees Terminalia arjuna in Mysore (Karnataka). Suresh Chand and Sanjayan (2010) have reported the feeding efficiency of the caterpillar E. fraterna. The following two species of hymenopteran parasitoids, viz. Apanteles prodiniae [A. prodeniae] (Braconidae) and Euplectrus sp. (Eulophidae) were recorded.

To understand predator – prey interaction has been the purpose of numerous studies, especially for predator use in biological control in agro-ecosystems(Gurjar et al.2023). Furthermore, the feeding rate of an individual predator as a function of prey density is termed as functional response (Holling, 1959). The knowledge of functional response is a pre-requisite for understanding the predator – prey interaction and to evolve strategies for mass rearing, large scale release and utilization in biological control programs.

Insect collection and maintenance

The reduviid predator and the pests were collected from cotton agro ecosystems in and around Tirunelveli and Kanyakumari districts, Tamil Nadu, India. The collected insects were maintained under the laboratory conditions (31 ± 1^o C, 75 ± 5% RH and 11–13 hours (L: D) in plastic containers of 20 cm diameter). They were initially fed with C. cephalonica larvae.

Bioefficacy of reduviid on cotton pests

Stage preference

Stage preference study of the third, fourth, fifth nymphal instars and adult of S. reclinatus on E. fraterna were performed under laboratory condition by providing all the life stages except first instars of E. fraterna. Preys were introduced into the Petri dish along with cotton leaves and were left undisturbed for 10 minutes. Each nymphal instar and adult of the predator was introduced into the Petri dishes separately and successful killing of the prey by the predator and percentage of consumption were recorded.

Functional response

To evaluate the functional response, 10 newly emerged (24 h starved) third instar nymphs of S. reclinatus were used in each one of the densities (1, 2, 4, 8, 10) of preferred life stages of E. fraterna (1, 2, 4, 8, 16). After 15 minutes, the predators were individually released into the Petri dish (9cm diameter). To mimic the natural condition, a cotton leaf was placed inside the experimental setup. Predatory behavior such as approaching time and handling time were recorded for 3 hours continuously by visual observation. The numbers of ingested or killed and remaining preys were recorded after 24 h (T). The predator search efficacy was calculated from the number of dead and offered prey. The linear regression graphs were plotted for the feeding efficacy of the predator.

Stage preference

The third instars of E. fraterna were preferred by III and IV instars of the predator. The V instars of the predator fed maximum on the fourth instars of the pest and adults of the predator preferred fifth instars of E. fraterna. These results show that life stages of S. reclinatus preferred different stages of the tested pest. The results also suggest that both fifth instar and adult predators were more successful in encountering the large sized E. fraterna (Figure. 1).

Functional response

It is a density dependent function of the tested predators response to the increasing prey density by killing more number of prey than it killed at lower prey densities i.e., its predatory rate was increased with increase in prey density. The functional response of third, fourth, fifth and adult of S. reclinatus was recorded, and the results revealed that the attack ratio decreased with increase in prey density. Handling time seemed to decrease with increasing prey density in both fifth nymphal instars and adults, but this relation was not defined in the third and fourth nymphal instars of S. reclinatus while provided with E. fraterna. The predators exhibited a typical functional response and thus established the applicability of the second model of Holling’s ‘disc’ equation (Table .1) (Fig. 1).). The third, fourth and fifth nymphal instars and adult of S. reclinatus on E. fraterna showed maximum Na values (4.5, 4.6, 46.0 and 4.5) at 10 prey densities respectively (y = 1.24 + 0.22x, r = 0.921; y = 0.89 + 0.32x; r = 0.99; y = 0.96 + 0.34x; r = 0.98; y = 0.92 + 0.36x; r = 0.98).

The effectiveness of the predator under controlled condition depends upon the type and number of prey consumed. Moreover, before utilizing a natural enemy for biological control, it is important to asses its ability to capture and consume relevant stages of the targeted insect pests. The biocontrol potential of S. reclinatus on E. fraterna was recorded in this study. The result revealed that particular stages of the predator preferred certain specific stages of the pests. Moreover, younger reduviids preferred younger prey and vice versa. Stage preference exhibited by the life stages of S. reclinatus could be attributed to the dynamics of prey – predator interaction which is governed by the size of both predator and prey (Sahayaraj and Ambrose, 1994; Sarkar et.al., 2019). The potentiality of S. reclinatus was previously analyzed on Riptortus clavatus (Ambrose and Claver 1995), Spodoptera litura (Ambrose and Claver 1997; Ambrose and Maran 2000). The feeding efficacy of the predators increased while the prey density increased. This exhibits a typical type II model holling’s disc equation. The feeding efficacy was positively correlated with prey density but the attack ratio was higher in low prey densities (Rahate 2023). This experiment clearly revealed that different stages of the predator can be utilized in pest management program. However, before recommending this reduviid for biological control programs, it is essential to evaluate its potentiality at augmentation level.

Author Contribution

M contribute to the research and curation Manimaran is the supervisor MS contribute review and coreection

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Table 1.Biological control potential evaluation of Sycanus reclinatus against Euproctis fraterna using functional response as tool

Life stages	Prey density (x)	No. of prey consumed (y)	Consumed ratio (y/x)	Handling (by)	Days searching (Ts=1-by)	Pre. y’ y’=a(1-by)	Predicted attack (y’/x)	Max(y)	B=by/y	Rate of discover (a=y/x/Ts)
III	2	1.13	0.57	0.004	0.996	1.13	0.57		0.0035	0.565
	4	2.0	0.50	0.006	0.994	2.0	0.50		0.003	0.503
	6	3.13	0.52	0.005	0.995	3.12	0.52		0.002	0.523
	8	4.13	0.52	0.003	0.997	4.16	0.52		0.0007	0.522
	10	4.5	0.45	0.004	0.996	4.56	0.45	4.5	0.0009	0.452
IV	2	1.0	0.50	0.001	0.999	1.00	0.50		0.001	0.501
	4	2.0	0.50	0.002	0.998	2.00	0.50		0.001	0.501
	6	2.8	0.47	0.002	0.998	2.82	0.47		0.0007	0.471
	8	3.8	0.48	0.001	0.999	3.84	0.48		0.0003	0.480
	10	4.6	0.46	0.003	0.997	4.6	0.46	4.6	0.0007	0.461
V	2	1.8	0.90	0.002	0.998	1.8	0.90		0.001	0.901
	4	2.8	0.70	0.002	0.998	2.79	0.70		0.0007	0.701
	6	3.4	0.56	0.002	0.998	3.36	0.56		0.0006	0.561
	8	4.6	0.56	0.003	0.997	4.48	0.56		0.0007	0.562
	10	6.0	0.60	0.002	0.998	6.0	0.60	6.0	0.0005	0.601
Adult	2	1.13	0.57	0.004	0.996	1.15	0.57		0.004	0.572
	4	2.0	0.50	0.004	0.996	2.0	0.50		0.002	0.502
	6	3.13	0.52	0.003	0.997	3.12	0.52		0.001	0.522
	8	4.13	0.52	0.002	0.998	4.15	0.52		0.0005	0.521
	10	4.5	0.45	0.005	0.995	4.5	0.45	4.5	0.001	0.452

No competing interests reported.

Bioefficacy of Sycanus reclinatus Stal Dohrn, (Hemiptera: Reduviidae) on the Euproctis fraterna Moore (Lepidoptera:Lymantriidae)

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

Insect collection and maintenance

Bioefficacy of reduviid on cotton pests

Stage preference

Functional response

Results

Stage preference

Functional response

Discussion

Declarations

Author Contribution

References

Table 1

Additional Declarations

Status:

Version 1