Review Article

Distribution, Biology and Management Strategies about a Less Studied Insect Pest (Trilocha varians) of Ficus: A Review

Muhammad Ramzan1*, Unsar Naeem-Ullah2, Muhammad Umair Sial2, Naeem Iqbal2 and Shafqat Saeed2

1State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China; 2Institute of Plant Protection, Muhammad Nawaz Shareef University of Agriculture, Multan Punjab Pakistan.

Received | January 03, 2021; Accepted | July 12, 2021; Published | July 31, 2021

*Correspondence | Muhammad Ramzan, State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China; Email: ramzan.mnsua@gmail.com

Citation | Ramzan, M., U.N. Ullah, M.U. Sial, N. Iqbal and S. Saeed. 2021. Distribution, biology and management strategies about a less studied insect pest (Trilocha varians) of Ficus: A review. Pakistan Journal of Agricultural Research, 34(3): 638-642.

DOI | https://dx.doi.org/10.17582/journal.pjar/2021/34.3.638.642

Keywords | Enicospilus spp., Ficus spp., Goryphus spp. Leaf eating caterpillar, Trilocha varians, Telenomus spp.

Introduction

Ficus is a large group of plants species which exceeds more than 800 species of trees, shrubs and vines. Some of them like F. benjamina, commonly known as weeping fig are planted to increase aesthetic value in landscape in various states of the world including Pakistan due to their easy adaptability and hardy nature against odd environmental conditions (Arya, 2020). Ficus species can grow well in every environmental condition such as at high as well as low temperature. These are mostly native to tropical and sub-tropical regions of the globe. Some of these have well recorded medicinal value such as anti-fungal and anti-tumor characters that used for the treatment of various diseases (Sirisha et al., 2010; Lansky et al., 2008; Mousa et al., 1994) such as ulcers. The plants are also used as bio-indicator for very toxic chemicals or gases such as formaldehyde and CO (Kim et al., 2008) in the environment and can act as purifier of the surroundings.

Ficus plants are attacked by several sucking (thrips, whiteflies and mealy bugs) and chewing insect pests including lepidopteran pests in the world. Trilocha (=Ocinara) varians (Walker, 1855) (Lepidoptera: Bombycidae) moth is one of the major pest that causes huge (100%) damages to the ornamental Ficus species. The severe attack of these insect pests can damage the plants to the tune of complete defoliation (Navasero and Navasero, 2014).

There is need to control this notorious insect pest by using management strategies like chemical and biological. Much less work regarding biology, distribution and management of this notorious pest of precious plants has been presented in literature and an effort to compile published work on above mentioned aspects has been summarized in below paragraphs for ready reference for futuristic workers.

Geographical distribution

T. varians is distributed in various countries such as Pakistan (Ramzan et al., 2019a), Malaysia (Basari et al., 2019); China (Wang et al., 2015; Chu and Wang, 1993), India (Rajavel and Shanthi, 2007; Singh and Brar, 2017), Vietnam (Zolotuhin and Witt, 2009), Sri Lanka, the Philippines (Navasero and Navasero, 2014), Indonesia, Sulawesi, Hong Kong, Java, Borneo (Gurule, 2013), Thailand (Chuenban et al., 2017), Japan (Kishida, 2002).

Hosts of Trilocha varians

This insect belongs to Subfamily Bombycinae of Family Bombycidae in Order Lepidoptera. It is closely related with domesticated silkworm moth, Bombyx mori. The larvae of T. varians are oligophagous that feed on different closely related moraceous plants (Ramzan et al., 2019b) while larvae of B. mori are monophagous and only feed on mulberry (Morus alba) leaves (Chuenban et al., 2017). Several plants species belonging to Family Moraceae and Poaceae have been reported to serve as hosts of T. varians (Table 1).

Biology of Trilocha varians

A single female of T. varians can lay about 215 ±33.85 eggs in rowson lower surface of the F. benjamina leaves. The newly laid eggs were yellow in colour and round flat in shape (Daimon et al., 2012). The incubation period was 3-8 days (5.8±0.48). The yellow colour of eggs was changed into black colour before hatching (Kedar et al., 2014; Ramzan et al., 2019a).

There were five larval instars of T. varians (Ramzan et al., 2020) and duration of first instar was 2-3 days. The colour of neonate larvae was brown and changed with stage (age). Duration of 2nd, 3rd, 4th and 5th instarsis 3.36±0.16, 3.18±0.13, 4.45±0.17 and 7.09±0.26 days, respectively. The colour of later instar was similar to the colour of branches and difficult to locate. A fleshy and long horn was present on the eighth abdominal segment (Ramzan et al., 2019a; Daimon et al., 2012) of each larval instar.

 

Table 1: Comprehensive summary of host diversity forT. varians.

Sr. No.	Host Plants		Family	Author
	Scientific name	Common name
1	F. benjamina	Weeping fig	Moraceae	Naeem-Ullah et al. (2020); Basari et al. (2019); Ramzan et al. (2019a, b); Kedar et al. (2014), Navasero and Navasero (2014).
2	F. religiosa	Pipal	Moraceae	Ramzan et al. (2019a, b); Kedar et al. (2014); Rajavel and Shanthi (2007)
3	F. elastic	Rubber plant	Moraceae	Chu and Wang (1993); Kedar et al. (2014)
6	F. mclelandi	Popular	Moraceae	Navasero et al. (2013)
7	F. infectoria	White fig	Moraceae	Kedar et al. (2014)
8	F. caraica	Common fig	Moraceae	Chu and Wang (1993)
9	F. benghalensis	Banyan fig	Moraceae	Kedar et al. (2014)
10	F. septic	Hauili	Moraceae	Navasero et al. (2013)
11	A. heterpphyllus	Jackfruit	Moraceae	Navasero et al. (2013); Huang et al. (2002); Udayagiri (1988); Hutson (1930)
12	A. communis	Marang	Moraceae	Navasero et al. (2013)
13	A. kamansi	Kamansi	Moraceae	Navasero et al. (2013)
14	F. nitida	Blue fountain bamboo	Poaceae	Navasero et al. (2013); Navasero and Navasero (2014)

 

Pupation was occurred in whitish yellow silken cocoons (Rajavel and Shanthi, 2007) and started from tail to head (Ramzan et al. 2019b). The pupal period had reported 5-6 days. The type of pupa was obtect (Ramzan et al., 2019a, b).

Adult male was short lived than females. The longevity of male and female was 5.5 ±0.37 days and 10.3 ± 0.53 days, respectively. Mated female was short lived as compared to unmated female. The abdomen, thorax and head of the insect are dark reddish brown in colour. The forewings and hindwings were pale reddish brown and grayish with reddish brown outer margins (Jia and Jinxin, 1997).

Economic importance and damage pattern of T. varians

Larvae of T. varians attack on the new leaves of plants and feed on dorsal side. The white papery patches appeared on dorsal side of plant leaves (Singh and Brar, 2016) which are major symptom of infestation. The early instars (1st-2nd) of T. varians can consume only the fresh green twigs of plant (Navasero et al., 2013; Navasero and Navasero, 2014) while later instar (3rd-5th) found most destructive and consume the all types of leaves like soft or rough.

The later instars are spread on the whole canopy of plant and difficult to locate due to resemblance of larvae colour with plant branches (Ramzan et al., 2019b). After consumed by the larvae of pest, the plants lack their leaves resultantly loosing health and start to die (Chuenban et al., 2017). Some studies depict that larvae consume 80-100% foliage (Ramzan et al., 2019a; Singh and Brar, 2016; Zolotuhin and Witt, 2009) and even cause death of whole plant.

Management strategies

Different control measures have been adopted by farmers and scientists at national and international level to control insect pests like cultural, physical, mechanical, botanical, biological and chemicals etc. Among these, chemical management is widely and excessively used but has some negative impact on environment and causes insecticides resistance to insect pests.By integrating of all possible management strategies from above mentioned, pest species can be controlled in efficient and ecofriendly way and this is now widely accepted tool for controlling harmful insect species throughout the globe. Here are given only two widely used methods for management of the pest under consideration, i.e. Biological and Chemical method.

Biological control

Biological agents such as predators and parasitoids are the best method to maintain pest population below economic threshold level in an ecofriendly way. Some studies narrated about eggs, larval and pupal parasitoids of T. varians. A couple of workers reported unidentified species of parasitic wasps as natural enemies of this pest (Navasero and Navasero, 2014).Eggs of T. varians have been reported to be parasitized by Ichneumonid like Telenomus spp., Trichogramma dendrolimi and T. euproctidis (Udayagiri, 1988) and T. pretiosum (Hai-Ying et al., 2006). Whereas, Enicospilus spp. (Ichneumonid: Hymenoptera) have been reported as parasitoid of larvae of T. varians (Kedar et al., 2014). Some pupal parasitoids have also been documented in the literature for this lepidopteran pest like Listrognathus spinifrons and Goryphus spp. (Ichneumonid: Hymenoptera) (Kedar et al., 2014). The life histories of natural enemies of T. varians have also been studied earlier (Udayagiri, 1988). Egg parasitoids had been proved best control against this pest in the world. The natural enemies of T. varians have not been reported from Pakistan till now.

Chemical control

Synthetic insecticides have although exert hazardous effect on environment, ecosystems and non-target species but it is a highly efficient way to control insect pests and have knock-down effect, so widely accepted and used in the world. Same is true for the pest species under consideration and a few studies in this regard have been narrated here. In Malaysia, two insecticides malathion (57% active ingredient) and fipronil (5% active ingredient) were tested against T. varians larvae under laboratory conditions, and LT50 and LT95 were evaluated. The study reported that fipronil had lower LT50 and LT95 than malathion (Basari et al., 2019).

In Pakistan, only one study of toxicity of four insecticides such as chlorantraniliprole, deltamethrin, emamectin benzoate and fipronil was evaluated against third instar larvae of T. varians. Among tested insecticides, deltamethrin was reported more toxic followed by emamectin benzoate, chlorantraniliprole and fipronil against 3rd larval instar under laboratory conditions (Naeem-Ullah et al., 2020).

Future prospectus

There is a great need to control this pest by using integrated pest management (IPM) approaches including botanical, biological (predators, parasitoids and entomopathogenic fungi) and chemical. The biological fauna (parasitoids and predators) should be identified and tested against this pest. Survey to check the pest distribution from areas or countries should also be proposed to identify its complete rangealong with the list of alternative hosts. The genome sequence of T. varians is suggested as bioinformaticstool and systematic aspects.

Acknowledgements

Authors are highly thankful to the Institute of Plant Protection, MNS-University of Agriculture Multan, Pakistan for providing necessary facilities.

Novelty Statement

Trilocha variansi, the greenish silk-moth is emerging pest of ornamental plants especially weeping fig (Ficus benjamina) in various countries including Pakistan. The current study provides basic informations about it and prove fruitful in managing this pest in Pakistan.

Author’s Contribution

Muhammad Ramzan: Conceived the idea and wrote the manuscript.

Unsar Naeem-Ullah: Helped in write up and Technical Input at every step.

Muhammad Umair Sial, Naeem Iqbal and Shafqat Saeed: Critically reviewed the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

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