Podcast
Questions and Answers
Infectious ailments are caused by living pathogenic ______.
Infectious ailments are caused by living pathogenic ______.
organisms
Microbial control utilizes microorganisms or their by-products to manage insect ______.
Microbial control utilizes microorganisms or their by-products to manage insect ______.
pest
Inclusion viruses are obligate, intracellular, pathogenic ______.
Inclusion viruses are obligate, intracellular, pathogenic ______.
organisms
Nuclear polyhedrosis viruses (NPV) are encased in a protein crystal called ______.
Nuclear polyhedrosis viruses (NPV) are encased in a protein crystal called ______.
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Symptoms of NPV infection include darkened larval skin with yellow ______.
Symptoms of NPV infection include darkened larval skin with yellow ______.
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Bacteria that are non spore-forming can be potential ______.
Bacteria that are non spore-forming can be potential ______.
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The fat body of lepidopterous larvae is the primary site of infection for the ______ virus.
The fat body of lepidopterous larvae is the primary site of infection for the ______ virus.
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NPV infection causes the infected larva to climb to the highest point and ______.
NPV infection causes the infected larva to climb to the highest point and ______.
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Bacillus thuringiensis is pathogenic to many lepidopterous larvae and immatures of some ______.
Bacillus thuringiensis is pathogenic to many lepidopterous larvae and immatures of some ______.
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When the bacteria sporulates, it forms a toxic ______.
When the bacteria sporulates, it forms a toxic ______.
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The life cycle of Bt includes an endospore in the environment that is ingested by a susceptible ______.
The life cycle of Bt includes an endospore in the environment that is ingested by a susceptible ______.
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Type I reaction to Bt toxins results in general paralysis and death within ______ hours after ingestion.
Type I reaction to Bt toxins results in general paralysis and death within ______ hours after ingestion.
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The cessation of feeding is the first symptom observed after ingestion of ______.
The cessation of feeding is the first symptom observed after ingestion of ______.
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Some fungi cause insect disease and are transmitted from one host to another by a ______.
Some fungi cause insect disease and are transmitted from one host to another by a ______.
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The beta exotoxin produced by Bacillus thuringiensis is known as ______.
The beta exotoxin produced by Bacillus thuringiensis is known as ______.
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Infected insects may show characteristics such as weakness, disorientation, and changes in ______.
Infected insects may show characteristics such as weakness, disorientation, and changes in ______.
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Study Notes
Entomopathogenic Microbials
- Lecture 3-3 covers beneficial microorganisms used to control insect pests
- Microorganisms can be classified as infectious or non-infectious
- Infectious ailments result from living pathogenic organisms, like viruses, bacteria, protozoa, fungi, rickettsia, and nematodes
- Non-infectious ailments, such as those from mechanical injury, chemical agents, or nutritional deficits, are not caused by microorganisms
- Microbial control involves using microorganisms or their by-products to control insect pests
Infectious Pathogens
- Inclusion viruses are submicroscopic, obligate intracellular pathogens
- Nuclear polyhedrosis viruses (NPV) are rod-shaped and encased in an outer envelope, sometimes enclosing multiple virus rods
- Viruses are occluded (encased) in protein crystals called polyhedra
- NPVs are usually transmitted via oral ingestion of polyhedra
Virus Structure
- A typical enveloped virus has a phospholipid envelope, a protein capsid, nucleic acid (genome), and spike projections
- Baculoviruses have a multi-capsid nucleopolyhedrovirus structure with occlusion bodies (enclosed viral particles)
NPV Infection of Insect Hosts
- NPV infection begins with ingestion of polyhedra
- Polyhedra with embedded virions enter the insect's foregut
- NPVs release virions, which break down the peritrophic membrane in the midgut
- Virions multiply in the insect's hemocoel, leading to septicemia
- TIssues are destroyed, and endospores are produced before the insect dies
- Endospores are released when the cadavers disintegrate
NPV Symptoms
- Larval skin darkens, develops yellow patches or appears oily
- Skin becomes fragile, hemolymph becomes turbid
- Infected larvae often climb to the highest point and die
- Integument frequently ruptures after death, releasing polyhedra
- Other viral diseases include granulosis virus (GV) that infects the fat body of lepidopterous larvae, and cytoplasmic polyhedrosis virus (CPV) that infects the midgut epithelium of lepidopterous larvae
Bacteria
- Non-spore-forming bacteria: These bacteria are common in the digestive tracts of insects. Stress, other pathogens, parasites, or poor nutrition can cause them to enter the hemocoel.
- Spore-forming bacteria: Bacillus popillae causes milky disease in white grubs, while Bacillus thuringiensis is very pathogenic to many lepidopterous (butterfly/moth) larvae.
Bacillus thuringiensis (Bt)
- Pathogenic to many lepidopterous and some coleopteran larvae
- Transmitted orally
- When the bacteria sporulates, it forms a toxic crystal (parasporal body)
- Different lepidopteran species respond differently to various crystal and spore combinations
Toxic Products of Bt
- Bt produces alpha exotoxin, phospholipase C, beta exotoxin (thuringiensin), and delta endotoxin
- These toxins are derived from protoxins (crystal proteins)
- Proteolytic enzymes degrade protoxins into smaller toxic peptides
Types of Reactions to Bt Toxins
- Type I: insects exhibit general paralysis and die within 1-7 hours after ingestion
- Type II: insects do not develop general paralysis and die within 2-4 days after ingestion
- Type III: insects are susceptible to a combination of crystals and spores
- Type IV: some lepidopterous larvae are not susceptible to Bt toxins
Life Cycle and Action of Bt
- Bt endospores in the environment are ingested by susceptible insects
- Parasporal crystals activated by alkaline gut fluids and cause leakage into the hemocoel
- Cessation of feeding is the first symptom after ingestion
- Crystal activity depends on pH in the larval foregut and midgut
- Bt multiplies in the insect hemocoel, causing septicemia
- Endospores are produced prior to the insect's death
- Endospores are released upon cadaver disintegration
Fungi
- More than 36 fungi genera cause insect diseases
- Fungi identification can be challenging
- Most fungi transmit from one host to another via spores (often conidia)
Fungi Structure
- Sporangium houses spores
- Sporangiophore is a specialized fungal hypha that may function as a stalk
- Hyphae (long filamentous structures) form a network called mycelium
- Rhizoids anchor fungi to substrates and absorb nutrients
- Conidiophores produce conidia (spores)
- Conidia germinate into new hyphae
Fungi Infection
- Fungi invade insects by contacting the cuticle
- Conidia germinate and form appressoria
- Hyphae penetrate the cuticle
- Mycelium invades the insect
- Insect death occurs following complete invasion
Infected Insect Characteristics
- Infected insects stop feeding, exhibit weaknesses, and disorientation
- Insects may change color, showing dark spots where fungal penetration occurred
- Presence of fungal hyphae (mycelia) is observed in affected areas
How Fungi Kill Hosts
- Asphyxiation or starvation due to fungal blockage or toxins, especially common with Zygomycotina, are a mechanism
- Toxins released by the fungus disrupt insect functions
- Uptake of host nutrients and water desiccation or mummification result
Classes of Fungi
- Ascomycetes (Perfect Fungi): Basidiospores and conidiospores are asexual
- Basidiomycetes (Perfect Fungi): Typicallyseptate hyphae
- Zygomycetes (Perfect Fungi): Zygospores and conidiospores, usually coenocytic hyphae
- Deuteromycetes (Imperfect Fungi): Conidia, septate hyphae
Examples of Entomopathogenic Fungi
- Zygomycotina, Order Entomophthorales: Batkoa, Entomophthora, Entomophaga, Erynia, Neozygites, Zoophthora
- Deuteromycotina, Order Moniliales: Beauveria bassiana (white muscardine), Metarhizium anisopliae (green muscardine), Lecanicillium (Verticillium) lecanii (aphid/scale insect pathogen)
Ascomycota, Class: Sordariomycetes : Order: Hypocreales: Cordyceps
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Description
This quiz covers Lecture 3-3 on entomopathogenic microbials, focusing on beneficial microorganisms for insect pest control. It distinguishes between infectious and non-infectious ailments and explores the role of infectious pathogens, particularly viruses. Test your understanding of microbial control mechanisms and virus structures.
