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www.agrilscience.com Article No.-05

Role of Entomopathogenic in IPM

P. Bharadwaz*

Post-Graduation Student, Department of Plant Pathology, Assam Agricultural University Jorhat, Assam – 785013 *Corresponding author. Email id: [email protected]

Abstract

Entomopathogenic group of microorganisms are proved to be very beneficial in controlling of devastating pests of several essential crops which are of economic importance. These group includes mostly fungi , bacteria , , nematodes etc . The viruses are sub- microscopic entities consisting of a protein coat and nucleic acid (either RNA or DNA). These viruses can be of great importance in Integrated Pest Management(IPM)strategies. Several research has been going on to use entomopathogenic viruses for controlling the pests naturally without applying hazardous chemical pesticides. Agricultural pest reduces the yield and quality of the produce by feeding on the crops thus transmitting diseases. So there is an urgent need of alternative methods for reducing the impact of the pests and preventing the crop damage caused due to pests or by application of entomopathogens (with special reference to viruses)

Key words: Entomopathogen, Hazardous, Chemical, Pesticides, Virus, Alternative method

Introduction

Entomopathogenic viruses can infect and kill pest insects. In nature there are entomopathogenic fungi, nematodes, bacteria and viruses everywhere. They contribute to the natural regulation of many populations of pest insects.

Insect viruses are classified into 12 viral families. Viruses from families like (Baculovirus), (Ascovirus), (Iridovirus), Polydnaviridae (), (Cypovirus), (Entomopoxvirus) etc have been found to be entomopathogenic in nature. Insect viruses are highy diverse and highly host specific and only a few groups are frequently found in insects and show potential to be used as biocontrol agents.

Typically, insect viruses are ingested with food material, enter the host tissues via the gut epithelium and replicate in this tissue and in some cases in other tissues as well. Baculovirus replication ultimately leads to the death of the host insect followed by lysis of the cadaver and release of virus into the environment. Other viruses have more subtle effects on the host by reducing longevity and fecundity, with both release of virions from infected individuals and vertical transmission playing important roles in virus dissemination. In all cases, the virus has to negotiate a series of barriers for successful infection: (1) the pH

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www.agrilscience.com Article No.-05 and contents of the gut, (2) penetration of the peritrophic membrane (PM) if present, (3) entry into and infection of gut epithelial cells, (4) sub-cellular immune mechanisms (apoptosis and RNA interference in particular), (5) navigation of the basement membrane (BM) overlying the gut epithelium, (6) cellular immune responses, (7) humoral immunity, and (8) developmental resistance

SOME MOST IMPORTANT VIRAL GROUPS USED AS ENTOMOPATHOGENS ARE:

1.Baculovirus:

They belong to the family baculoviridae and are grouped under two main genera -

a. Nucleopolyhedrosisvirus or NPVs b. Granulosis virus or GVs. • Both are dsDNA virus and rod shaped. Difference lies in shape of their occlusion body, one is polyhedral while the other is granular. • NPVs are again classified into – • Multiple nucleopolyhedrosis virus or MNPVs (several virions per envelope) • Single nucleopolyhedrosis virus or SNPVs (single virion per envelope). • GV virions are always single within the envelope • 90% of baculoviruses have lepidoteran hosts • This insect infecting viral group is the most extensively studied and used one.

NPV INFECTED LARVAE GV INFECTED LARVAE

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Insects infected with baculoviruses have a characteristics shiny-oily appearance and are seen hanging limply from vegetation • They are extremely fragile to touch • The infected insect dies and melts or falls apart on foliage , releasing more viruses

2. Entomopoxvirus:

• It belongs to the family poxviridae • Poxviridae family has two sub family - chordopoxvirinae and entomopoxvirinae ( causes insect disease). • Entomopoxvirinae cause diseases to orthopteran, lepidopteran, dipteran and coleopteran insects. • They are brick-shaped ds-DNA virus occluded with ovoid OBs (occlusion bodies). • It produces whitish appearance in the infected larvae • The infected larvae is under-developed

3. Cypovirus:

• These viruses belong to the family reoviridae which have both mammal and inset infecting viruses. The inset infecting viruses from this family is called as Cytoplasmic Polyhedrosis Viruses or Cypoviruses • These are linear dsRNA and have a icosahedral shape • These mainly infect lepidopteran larvae • It leads to a retarded development and reduce feeding in the infected larvae • Longevity and breeding performance of infected adults decreases • The CPV infection is restricted to the gut which may become white or yellow

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4. Iridovirus:

• It belongs to the family iridoviridae • These viruses have been found infecting insects belonging to order diptera, hymenoptera, hemiptera, lepidoptera and coleoptera • These have linear dsDNA as genetic material and have a icosahedral shape • The most distinctive feature caused by the infection from these viruses is the iridescence of the infected tissues • Reduction of fecundity , longevity and body size of Infected insects • All host species of iridovirus is associated with aquatic environment, probably for viral transmission.

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5. Ascovirus:

• It belongs to the family ascoviridae • These are dsDNA viruses occluded within a vesicle-like OBs (occlussion bodies) that infect only the lepidopteran insects. • It causes a chronic infection taking between 2-6 weeks to kill the respective insect host • Infected larvae show a milky white appearance, which is a major characteristic of infection caused by this virus.

Mode of action:

• Entomopathogenic viruses need to be ingested by the insect host and therefore are ideal for controlling pests that have chewing mouthparts. And hence, lepidopteran pests are important hosts of these viruses.

• These viruses have different types of inclusion bodies in which the virions are embedded. Virus particles invade the nucleus of the midgut, fat body or other tissue cells, compromising the integrity of the tissues and liquefying the cadavers.

• Before death, infected larvae climb higher in the plant canopy, which aids in the dissemination of virus particles from the cadavers to the lower parts of the

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•

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VIRUS REPLICATION

When insects inadvertently consume OB-contaminated food, the infection cycle of a virus starts. Virus gains entry into a permissive host cell, using a variety of infective mechanisms: endocytosis, phagocytosis, pinocytosis, membrane fusion, etc. Subsequently, the viral genome is dissociated from the and released into the host cell in a great variety of mechanisms. Once in the cell (either in the nucleus or in the cytoplasm) the viral genome replicates itself, frequently using the host cell’s enzymatic machinery, creating a great number of identical copies. Also, structural, functional, and auxiliary viral genes are transcribed and translated into proteins, which will be used to assemble, part by part, new viral particles. The new copies of the viral genome are packed within the new and the new viral progeny is released by a variety of procedures, which are distinctive of each viral group. Some viruses are released by inverted pinocytosis, which engulfs the viral particle within a membranevesicle, creating what is known as “enveloped viruses”.

MULATIONS:

Fig : Viruses registered for commercial application

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FORMULATIONS:

VIRUS TRADE NAME TO BE USED AGAINST REGISTRANT YEAR

NPV ELCAR Bollworm and Tobacco bud Sandoz 1973 worm on cotton

NPV BIOCONTROL Fir tussock moth USDA 1973

NPV GYPCHECK Gypsy moth on forest and USDA 1976 ornamental tress

NPV NEOCHECK Pine saw fly USDA 1978

CPV MATSUKEMIN Japanese pine moth - 1974

Advantages and disadvantages of using viruses as entomopathogens

Advantages :

1. Most insect viruses are host-specific so the risk of non-targeted effects on beneficial insects is very low

2. Insect viruses are unable to infect mammals, including humans which makes them very safe to handle

3. Many viruses occur naturally and may already be present in the environment so there is no need of applying them again externally .

Disadvantages :

1. Most insect viruses take several days to kill their host insect during which the pest still continue to cause damage to the crop plants

2. Viruses are only effective against early larval life stages because with the insect age they become less susceptible to virus infections

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3. Exposed virus particles available on plant surface are quickly inactivated by direct sunlight or high temperatures, which can limit their persistence within a given season. Also some agricultural practices like – tillage can burry the exposed virus particles in the soil.

References

Entomopathogenic viruses – Researchgate.net.

Entomopathogenic microorganism; mode of action and their role in IPM https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24119#:~:text=Examples%20of%2 0some%20commercially%20available,Cydia%20pomonella%20granulovirus%20(CpGV)

Entomopathogenic viruses – reasearch gate https://www.researchgate.net/publication/263765284_Entomopathogenic_Viruses

Virus Entomopathogens https://slideplayer.com/slide/14848032/

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