Unit 2(b) - Silkworm Pests, Management, Lac Insect Biology, and More | Management of Beneficial Insects

Contents Pest and diseases of silkworm, management, rearing appliances of mulberry silkworm and methods of disinfection. Species of lac insect, morphology, biology, host plant. Click here to open Previous Part

Pests and Diseases of silkworm

Pests

Silkworms, which are the larvae of the silk-producing moth Bombyx mori, are susceptible to various pests that can negatively impact their growth and silk production. Here's a detailed overview of some common pests that affect silkworms:

1. Spindle Caterpillar (Achaea janata): Spindle caterpillars are known to feed voraciously on mulberry leaves, which are the primary food source for silkworms. They can cause substantial defoliation, leading to a shortage of food for the silkworm larvae. Regular scouting and manual removal of spindle caterpillars from the rearing environment are essential to prevent their spread.
2. Armyworms: Armyworms are another group of pests that can cause significant damage to mulberry leaves. They can quickly devour leaves, leading to decreased food availability for the silkworms. Proper sanitation and regular inspection of the mulberry plantation can help identify and manage armyworm infestations.
3. Cutworms: Cutworms are nocturnal pests that feed on young silkworm larvae. They can cut through the silkworm larvae, causing injury and mortality. Maintaining a clean rearing environment, proper mulberry cultivation practices, and ensuring proper sanitation can help prevent cutworm infestations.
4. Leafroller Caterpillars: These caterpillars roll and feed on mulberry leaves, causing damage and reducing the available leaf surface for silkworm larvae. Regular pruning of affected leaves and adopting appropriate pest management practices can help control leaf roller caterpillar populations.
5. Grasshoppers and Crickets: Grasshoppers and crickets can also feed on mulberry leaves, causing leaf damage and reduced food availability for silkworms. Implementing physical barriers or using natural predators can help manage grasshopper and cricket populations.
6. Ants: Ants can disrupt the rearing process by carrying away eggs and larvae.
7. Predatory Insects: Some predatory insects, such as wasps, can attack and feed on silkworm larvae.
8. Rodents: Rodents, such as rats and mice, can also pose a threat to silkworm rearing by damaging rearing equipment, eggs, and larvae.

Diseases

Silkworms are susceptible to various diseases that can significantly affect their growth and silk production. Here's a detailed overview of some common diseases that affect silkworms:

1. Pebrine (Nosema bombycis): Pebrine is a serious protozoan disease caused by the microsporidian parasite Nosema bombycis. Infected silkworms show symptoms such as dark spots on the body, larval mortality, and reduced silk production. Pebrine-infected silkworm eggs also exhibit irregularities. The disease is spread through infected eggs and contaminated rearing equipment. Preventive measures include using disease-free eggs, proper sanitation, and disinfection of rearing equipment.
2. Flacherie: Flacherie is a bacterial disease caused by the pathogen Bacillus bombysepticus. Infected silkworms become flaccid and exhibit a watery appearance. The larvae stop feeding, and mortality rates increase. Flacherie is often associated with poor hygiene and unsanitary rearing conditions. Maintaining a clean rearing environment, providing proper nutrition, and preventing overcrowding can help control the disease.
3. Muscardine Disease (Beauveria bassiana): Muscardine disease is caused by the fungus Beauveria bassiana. Infected silkworms show symptoms such as a white powdery coating on the body, sluggish movement, and eventual death. The disease is transmitted through contact with infected larvae or contaminated rearing environments. Proper ventilation, maintaining optimal humidity levels, and regular cleaning of rearing facilities can help prevent muscardine disease.
4. Grasserie: Grasserie is a viral disease caused by the nuclear polyhedrosis virus (NPV). Infected silkworms display symptoms like darkening of the body, sluggish movement, and eventually hanging upside down. The virus spreads through contact with infected larvae and rearing equipment. Implementing strict hygiene practices, disinfecting rearing equipment, and using disease-free eggs can help manage grasserie.
5. White Muscardine Disease (Nomuraea rileyi): White muscardine disease is caused by the fungus Nomuraea rileyi. Infected silkworms exhibit symptoms such as white powdery spots on the body, sluggishness, and death. The disease is more prevalent during humid conditions. Proper ventilation, maintaining optimal humidity levels, and practicing proper sanitation can help prevent white muscardine disease.
6. Slow Growth Syndrome: Slow growth syndrome is a complex condition that can result from various factors, including improper nutrition, poor rearing conditions, and the presence of other stressors. Infected silkworms show stunted growth, reduced feeding activity, and increased susceptibility to other diseases. Providing proper nutrition, maintaining optimal rearing conditions, and preventing stressors can help prevent slow growth syndrome.

Effective disease management in silkworm rearing involves a combination of preventive measures, early detection, and prompt intervention. Integrated disease management strategies that focus on maintaining clean rearing conditions, practicing proper hygiene, and using disease-free eggs are essential for successful silkworm rearing and silk production. Regular monitoring, maintaining a healthy rearing environment, and adopting appropriate disease control measures are crucial for minimizing disease-related losses and ensuring healthy silkworm growth.

Management of Pests and Diseases in Silkworm Rearing

Effective management of pests and diseases is essential for maintaining healthy silkworm populations and ensuring quality silk production. Here's a comprehensive guide on managing pests and diseases in silkworm rearing:

Pest Management:

1. Sanitation: Maintain a clean and hygienic rearing environment. Regularly clean rearing trays, shelves, and equipment to prevent pest buildup.
2. Isolation: Isolate infected or sick silkworms to prevent the spread of pests. Remove and destroy any infected larvae.
3. Cultural Practices: Practice proper hygiene, such as removing dead larvae and waste materials promptly. Avoid overcrowding rearing trays to minimize stress and disease spread.
4. Biological Control: Introduce natural enemies of pests, such as predatory mites and parasitic wasps, to control pest populations. These beneficial organisms can help reduce pest infestations.
5. Chemical Control: In severe cases, chemical pesticides may be used as a last resort. However, exercise caution and use only approved pesticides, following recommended dosage and safety guidelines.

Disease Management:

1. Disease-free Eggs: Start with disease-free eggs obtained from reliable sources to prevent introducing diseases into the rearing process.
2. Hygiene Practices: Maintain a clean and sanitized rearing environment. Regularly clean and disinfect rearing trays, shelves, and equipment.
3. Proper Ventilation: Ensure proper ventilation to prevent humidity buildup, which can lead to disease development.
4. Nutrition: Provide a balanced and nutritious diet to silkworms. Proper nutrition boosts their immune system and helps them resist diseases.
5. Quarantine: Isolate and treat infected silkworms to prevent disease spread. Quarantine new silkworm batches before introducing them to the main rearing area.
6. Biopesticides: Use biopesticides containing beneficial microorganisms to suppress disease-causing pathogens. These can be applied to rearing trays or added to silkworm food.
7. Fungicides and Antibiotics: In some cases, fungicides and antibiotics may be used to control disease outbreaks. However, these should be used judiciously and as a last resort.
8. Avoid Stress: Minimize stress factors such as overcrowding, poor nutrition, and handling. Stressed silkworms are more susceptible to diseases.
9. Regular Monitoring: Monitor silkworms regularly for signs of diseases. Early detection allows for timely intervention.
10. Temperature and Humidity Control: Maintain appropriate temperature and humidity levels according to the silkworm growth stage. Extremes in temperature and humidity can predispose silkworms to diseases.
11. Disease-Free Rearing House: Implement strict hygiene and management practices in the rearing house to prevent disease outbreaks.
12. Seed Production: Properly manage and maintain the seed production area to ensure disease-free eggs for subsequent generations.

Integrated pest and disease management involves a holistic approach that combines preventive measures, cultural practices, biological controls, and judicious use of chemicals. It's essential to follow recommended practices, stay updated on the latest management techniques, and work closely with experts or agricultural extension personnel to effectively manage pests and diseases in silkworm rearing.

Rearing Appliances in Mulberry Silkworm Rearing

Efficient rearing appliances play a crucial role in the successful rearing of mulberry silkworms (Bombyx mori). These appliances help create a controlled and conducive environment for silkworm growth and cocoon formation. Here's an overview of the key rearing appliances used in mulberry silkworm rearing:

1. Rearing Trays: Rearing trays are shallow, rectangular containers made of plastic or bamboo. They are used to hold silkworms during their growth and development stages. The trays are designed to accommodate silkworms' feeding and movement, and they have holes for ventilation and waste removal.

2. Bamboo Shelving: Bamboo shelves are used to stack rearing trays in a vertical arrangement. They allow for efficient use of space and proper air circulation within the rearing house.

3. Rearing House: The rearing house is a dedicated structure or room where silkworms are reared. It provides a controlled environment with regulated temperature, humidity, and ventilation. The rearing house is equipped with rearing trays, shelving, and other necessary equipment.

4. Heating Devices: In cooler climates or during the winter season, heating devices such as electric heaters or temperature-controlled systems may be used to maintain the optimal temperature for silkworm growth and development.

5. Cooling Systems: Cooling systems, such as fans and evaporative cooling pads, help regulate the temperature and humidity inside the rearing house, especially in hot and humid climates.

6. Ventilation System: Adequate ventilation is essential to ensure proper air exchange and prevent the buildup of moisture and carbon dioxide inside the rearing house. Ventilation fans or natural airflow mechanisms are used for this purpose.

7. Lighting: Adequate lighting is required for silkworms to feed and move properly. Natural light or artificial lighting sources can be used to maintain a suitable photoperiod for silkworms.

8. Feeding Trays: Feeding trays are used to provide mulberry leaves to the silkworms. These trays are placed inside the rearing trays and hold freshly harvested mulberry leaves for consumption.

9. Waste Removal System: Rearing trays are equipped with a waste removal system that allows frass (silkworm excreta) to drop through holes in the trays. This prevents the accumulation of waste, which can be a breeding ground for pests and diseases.

10. Hygrometers and Thermometers: These instruments are used to monitor and regulate humidity and temperature levels inside the rearing house. Maintaining optimal conditions is crucial for silkworm health and growth.

11. Monitoring Tools: Magnifying glasses and microscopes are used to closely observe the development and health of silkworms. They help identify any issues early on and facilitate timely intervention.

12. Hand Gloves and Aprons: Rearing personnel use gloves and aprons to prevent contamination and to ensure hygiene during the handling of silkworms, trays, and leaves.

13. Silkworm Breeding Equipment: For seed production, specific equipment is used for mating and egg laying. These may include mating cages, oviposition trays, and egg storage containers.

14. Humidifiers and Dehumidifiers: These devices help control humidity levels within the rearing house, ensuring that silkworms do not experience stress due to extreme humidity conditions.

Effective use of rearing appliances ensures a conducive environment for mulberry silkworms to complete their life cycle successfully. Rearing conditions must be meticulously managed to prevent stress, disease, and other issues that can affect silkworm growth, cocoon quality, and silk production.

Methods of Disinfection in Mulberry Silkworm Rearing:

Disinfection is a critical aspect of maintaining a healthy and disease-free environment for mulberry silkworms (Bombyx mori) during their rearing process. Proper disinfection practices help prevent the spread of pathogens and ensure the overall well-being of silkworms. Here are some methods of disinfection commonly used in mulberry silkworm rearing:

1. Cleaning and Sanitization:
• Regular cleaning of rearing trays, shelving, and rearing house is essential to remove debris, frass (silkworm excreta), and any organic matter that can serve as breeding grounds for pathogens.
• Scrubbing trays and equipment with mild disinfectants and soap helps eliminate contaminants.

2. Fumigation:
• Fumigation involves exposing the rearing house, equipment, and trays to gaseous disinfectants or fumigants that kill or suppress pathogens.
• Common fumigants include formaldehyde, potassium permanganate, and sulfur dioxide. These substances are released in controlled amounts to disinfect the environment.

3. Heat Treatment:
• Rearing trays, equipment, and rearing house can be subjected to heat treatment to kill pathogens and pests.
• This method involves raising the temperature to a certain level for a specified period to achieve effective disinfection.

4. UV Radiation:
• Ultraviolet (UV) radiation is an effective method to sterilize the rearing environment.
• UV lamps are used to expose surfaces, trays, and equipment to UV rays, which can destroy bacteria, viruses, and other microorganisms.

5. Chemical Disinfectants:
• Chemical disinfectants are commonly used to sanitize rearing trays, equipment, and surfaces.
• Disinfectants like quaternary ammonium compounds, chlorine-based solutions, and hydrogen peroxide can be diluted according to recommended concentrations and applied to surfaces.

6. Footbath Disinfection:
• Footbaths containing disinfectant solutions are placed at entry points to prevent the introduction of pathogens by rearing personnel.
• Anyone entering the rearing area should dip their footwear in the footbath to reduce the risk of contamination.

7. Use of Clean Water and Mulberry Leaves:
• Providing clean water and fresh, uncontaminated mulberry leaves to silkworms is a preventive measure to avoid introducing pathogens into the rearing environment.

8. Isolation and Quarantine:
• Sick or infected silkworms should be isolated immediately to prevent the spread of diseases to healthy individuals.
• Quarantining newly introduced silkworms before introducing them to the main rearing area can prevent the introduction of potential pathogens.

9. Proper Waste Disposal:
• Effective disposal of waste, including dead silkworms and waste material, is important to prevent contamination and the spread of diseases.

10. Regular Monitoring:
• Regular monitoring of silkworms for signs of disease or stress allows for timely intervention and management.

11. Personal Hygiene:
• Rearing personnel should practice good personal hygiene, including washing hands thoroughly before handling silkworms and using appropriate protective gear.

12. Use of Disease-Resistant Strains:
• Using disease-resistant silkworm strains can reduce the risk of disease outbreaks and the need for excessive disinfection.

Species of lac insects

The primary species of lac insect is Kerria lacca. This species is the most economically significant and widely cultivated for the production of lac resin, which has various industrial applications. While Kerria lacca is the dominant species, there are other species within the same family (Kerriidae) that also contribute to lac production, but to a lesser extent.

Some of these include Tachardia lacca, Tachardia albizziae, and Paratachardina lobata. However, Kerria lacca remains the primary focus due to its importance in the lac industry.

Morphology of lac insect

The morphology of the lac insect (Kerria lacca) goes through various stages as it progresses through its life cycle. Here is an overview of the key morphological characteristics of different stages:

1. Egg: The eggs of the lac insect are tiny, oval-shaped, and usually laid in clusters on the twigs of host trees. They are initially pale yellow but turn darker as they mature.
2. Crawler (First Instar Larva): After hatching, the insect is in its crawler stage. Crawlers are very small, mobile, and have six legs. They are pale yellow with a dark head and body.
3. Settled Larva (Second Instar Larva): The crawler molts into the settled larva stage. These larvae are larger and are often described as grub-like. They have a waxy covering that helps them adhere to the host plant. The waxy covering is secreted from specialized structures called dermal glands.
4. Pupa: The settled larva undergoes metamorphosis to become a pupa. The pupa is immobile and covered with a hard, reddish-brown shell. Inside the shell, the insect undergoes transformation into its adult form.
5. Adult Female: The adult female lac insect is wingless and remains immobile throughout its life. It is pear-shaped and has a hard, shell-like covering. The covering is made up of layers of lac resin secreted by the insect. The female produces and lays eggs, completing the life cycle.
6. Adult Male: The adult male lac insect is rarely seen and is short-lived. It is small and winged, and its primary purpose is to mate with the females. The males do not feed and die shortly after mating.

Throughout its life stages, the lac insect undergoes physiological and morphological changes. Its ability to produce lac resin, which contributes to its protective covering, is a unique characteristic that plays a vital role in the production of valuable lac products.

Biology of the lac insect

The biology of the lac insect (Kerria lacca) encompasses its life cycle, behavior, and interactions with its environment. Here is an overview of the key aspects of the biology of lac insects:

Life Cycle: The life cycle of the lac insect involves several distinct stages:

1. Egg Stage: The female lac insect lays eggs on the host plant. The eggs are deposited in clusters and are covered with a waxy substance for protection.
2. Crawler Stage: After hatching, the newly emerged larvae, known as crawlers, are very small and mobile. They move to settle on the host plant, where they begin to feed.
3. Settled Larva Stage: The crawlers molt and become settled larvae. These larvae secrete a waxy covering that adheres them to the host plant. They continue to feed and grow in size.
4. Pupa Stage: The settled larva undergoes metamorphosis and transforms into a pupa. The pupa is encased in a hard, reddish-brown shell formed from layers of lac resin. Inside the pupal shell, the transformation from larva to adult takes place.
5. Adult Stage: The female adult lac insect is wingless and remains attached to the host plant. She produces and lays eggs, completing the life cycle. The male adult lac insect is winged and has a short lifespan, primarily dedicated to mating.

Behavior: Lac insects are sedentary creatures, with adult females remaining immobile on the host plant once they reach maturity. They feed on plant sap using specialized mouthparts called stylets. The immobile nature of the females is a unique feature, as they become encased in the resinous secretion, forming a protective covering.

Host Plant: The primary host plant for the lac insect is the Laccifer lacca tree, commonly known as the lac host tree or the host plant. The insect feeds on the sap of this tree and forms a symbiotic relationship with it. The host plant provides nutrition for the insect, while the insect produces valuable lac resin that benefits both parties.

Reproduction: Lac insects reproduce through sexual reproduction. The females lay eggs, which hatch into crawlers. Mating occurs when adult males mate with adult females. After mating, the females lay eggs, and the cycle continues.

Lac Resin Formation: One of the most distinctive aspects of lac insects' biology is their ability to produce lac resin. The insects secrete this resinous substance, which forms their protective covering in the pupal stage. The layers of resin contribute to the formation of the shell-like covering that encases the pupa.

Understanding the biology of lac insects is crucial for their sustainable management, as well as for optimizing the production of lac resin and its various valuable products.

Host plant of the lac insect

The primary host plant of the lac insect is commonly known as the "lac host tree." The scientific name of this tree is Ficus religiosa, also referred to as the sacred fig or peepal tree. This tree belongs to the Moraceae family and is native to the Indian subcontinent.

Characteristics of the Host Plant:
• Botanical Features: The lac host tree is a deciduous tree that can grow to a significant size, reaching heights of up to 30 meters. It has heart-shaped leaves with a distinct leaf base that resembles a drip tip. The leaves have prominent veins and a smooth texture.
• Habitat: The lac host tree is well-adapted to a variety of environments, including tropical and subtropical regions. It is often found growing in open spaces, near temples, roadsides, and rural areas.
• Sap and Nutrition: The sap of the lac host tree serves as the primary source of nutrition for the lac insects. The insects use their specialized mouthparts to pierce the tree's vascular tissues and feed on the sap. The nutrients obtained from the sap contribute to the insects' growth, development, and production of lac resin.

Symbiotic Relationship: The relationship between the lac insect and the host tree is a unique example of mutualism. The insect benefits from the nutrients in the tree's sap, while the tree benefits from the protection provided by the insect's resinous covering. The tree's sap serves as nourishment for the insect, and in return, the insect produces lac resin that covers its body and protects it from external elements.

Economic Significance: The cultivation and management of lac host trees play a crucial role in the production of lac resin, which has various industrial and commercial uses. The collection and processing of lac resin contribute to rural livelihoods and income generation, particularly in regions where lac cultivation is practiced.

Lac Cultivation: Lac cultivation involves establishing and maintaining lac host trees to support the growth and development of lac insects. The trees are cultivated and managed in lac plantations to ensure a sustainable supply of lac resin.

Overall, the lac host tree is a central element in the lifecycle of the lac insect and is intrinsically linked to the production of valuable lac resin. Understanding the biology and cultivation of the host plant is essential for the successful management and utilization of lac insects for resin production.

Note: Summarized key points for easy exam review.

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