# Virulence, Pathogenicity, and Symptoms of Entomopathogenic Pathogens and Nematodes

Ajeet Kumar

► To cite this version:

Ajeet Kumar. Virulence, Pathogenicity, and Symptoms of Entomopathogenic Pathogens and Nematodes. Master. Bio-pesticides and Bio-fertilizers, DR. RAJENDRA PRASAD CENTRAL AGRICULTURAL UNIVERSITY PUSA, SAMASTIPUR-848125, BIHAR, INDIA, India. 2025, pp.1-3. hal-05124491

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https://hal.science/hal-05124491v1

Submitted on 5 Jul 2025

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Dr. Rajendra Prasad Central Agricultural University

Pusa (Samastipur) - 848125, Bihar

A lecture notes

On

Virulence, Pathogenicity, and Symptoms of
Entomopathogenic Pathogens and Nematodes

<figure><img src="image_2.png" /></figure>

COURSE TITLE: Bio-pesticides and Bio-fertilizers

*(Elective course)

COURSE NO.: ASS-307; CREDIT HOUR: 3 (2+1)

YEAR/SEMESTER: 3rd YEAR /6th SEMESTER

Dr. AJEET KUMAR

Assistant Professor-cum-Scientist (Soil Science)

Department of Microbiology

Collage of Basic Sciences and Humanities (CBS&H),

Dr. Rajendra Prasad Central Agricultural University, Pusa (Samastipur)

June 2025
# Virulence, Pathogenicity, and Symptoms of Entomopathogenic Pathogens and Nematodes

Dr. AJEET KUMAR<fnref n="1" />

## 1. Definitions

* **Virulence:** The degree of damage caused by a pathogen to its host. In the context of entomopathogens, it refers to the severity of disease or mortality induced in insects.

* **Pathogenicity:** The ability of a microorganism or nematode to cause disease in an insect host. It is a qualitative trait (presence or absence of pathogenic effect).

## 2. Major Groups of Entomopathogenic Organisms

<table><thead><tr><td>Type</td><td>Examples</td><td>Mode of Action</td></tr></thead><tbody><tr><td>Fungi</td><td>Beauveria bassiana, Metarhizium anisopliae</td><td>Penetrate cuticle, colonize hemocoel</td></tr><tr><td>Bacteria</td><td>Bacillus thuringiensis (Bt), Serratia spp.</td><td>Produce toxins, disrupt midgut epithelium</td></tr><tr><td>Viruses</td><td>Nuclear Polyhedrosis Virus (NPV), Granulosis Virus (GV)</td><td>Replicate inside host cells, lysis</td></tr><tr><td>Nematodes</td><td>Steinernema spp., Heterorhabditis spp.</td><td>Release symbiotic bacteria in hemocoel</td></tr></tbody></table>

## 3. Virulence Mechanisms

### A. Fungi

* Produce cuticle-degrading enzymes (proteases, chitinases).

* Hyphal bodies proliferate in the hemocoel, producing toxins.

* Rapid colonization leads to insect death within 3–7 days.

### B. Bacteria

* Bt produces crystal (Cry) toxins → ingestion by larva → pore formation in midgut → septicemia.

* Other bacteria release endotoxins and hemolysins disrupting tissue integrity.

### C. Viruses

<footnote n="1">¹Assistant Professor-cum-Scientist (Soil Science-Soil Microbiology, Soil fertility, Soil Chemistry), Department of Microbiology, College of Basic Sciences & Humanities (CBS&H), RPCAU, Pusa-848125, Bihar. E-mail: ajeet.sri@rpcau.ac.in</footnote>
* Infect midgut epithelial cells after ingestion.

* Viral replication → cell lysis → systemic spread → death.

## D. Nematodes

* Infective juveniles (IJs) enter insect body via natural openings.

* Release symbiotic bacteria (*Photorhabdus*, *Xenorhabdus*).

* Insect killed within 24–72 hours by toxemia/sepsis.

## 4. Pathogenicity Traits

<table><thead><tr><td>Parameter</td><td>Importance for Pathogenicity</td></tr></thead><tbody><tr><td>Host range</td><td>Determines spectrum of affected insects</td></tr><tr><td>Toxin production</td><td>Key for killing or weakening hosts</td></tr><tr><td>Invasion &amp; replication rate</td><td>Influences speed of mortality</td></tr><tr><td>Immune evasion ability</td><td>Ensures survival within host</td></tr></tbody></table>

## 5. Symptoms in Infected Insects

<table><thead><tr><td>Pathogen Type</td><td>Symptoms</td></tr></thead><tbody><tr><td>Fungi</td><td>White, green or red mold on cadaver, shriveling, mummification</td></tr><tr><td>Bacteria</td><td>Cessation of feeding, flaccid body, liquefied internal tissue</td></tr><tr><td>Viruses</td><td>Milky white hemolymph, body disintegration post-mortem</td></tr><tr><td>Nematodes</td><td>Rigid body, brown/red discoloration, bacterial ooze</td></tr></tbody></table>

## 6. Diagram: Infection Cycle of Entomopathogenic Nematodes

[Infective Juvenile] → [Entry into Insect Host] → [Release of Symbiotic Bacteria] → [Toxin Production & Host Death] → [Nematode Reproduction] → [Emergence of IJs]

## 7. Factors Affecting Virulence and Pathogenicity

* Environmental conditions (temperature, humidity)

* Host species and developmental stage

* Genetic variability among pathogen strains

* Dose and mode of application

## 8. Applications in IPM (Integrated Pest Management)

* Eco-friendly alternatives to chemical pesticides.

* Useful against soil-dwelling and foliage-feeding insect pests.

* Compatible with many biocontrol and cultural practices.