1. Paddy | Pests of Field Crops, Stored Grains and their Management (AG-503)

Chapter 1 - Paddy

1. Paddy Bug: Leptocorisa varicornis

(Common name: Rice earhead bug)

1. Scientific Name: Leptocorisa varicornis (Fabricius, 1787)

2. Order: Hemiptera (True bugs)

3. Family: Alydidae (Broad-headed bugs)

4. Host Range:

• Primarily paddy (Oryza sativa)
• Can also attack other grasses such as maize, sorghum, and wild grasses

5. Distribution:

• Widely distributed across Southeast Asia, India, Bangladesh, China, Japan, Philippines, Thailand, and other rice-growing regions of the world.
• Prefers tropical and subtropical regions, but is also found in temperate zones where rice cultivation occurs.

6. Biology and Bionomics:

• Eggs: The female lays greenish or yellowish eggs on the surface of rice leaves in rows or clusters. Eggs hatch in 5–8 days.
• Nymphs: The nymphs pass through 5 instar stages. They are greenish-brown in colour and resemble adults but are smaller and lack fully developed wings. The nymphal period lasts 15–30 days, depending on the temperature and availability of food.
• Adults: Adults are slender, greenish-brown with a long, needle-like proboscis for sucking plant sap. They have a characteristic elongated head and body, reaching about 15–20 mm long. Adult longevity varies, but they can survive for 2-3 weeks.
• Life Cycle: The insect is multivoltine, meaning it has multiple generations per year, particularly in favourable conditions (warm and humid).
• Overwintering: Adults can overwinter in cracks and crevices in rice stubble or in the soil and emerge when conditions improve.

7. Nature of Damage:

• Feeding Behavior: Both nymphs and adults are sap-suckers. They prefer to feed on the rice panicles during the milky stage of the grains, sucking out the sap from developing grains, resulting in unfilled or partially filled grains.
• Symptoms: Infestation causes shrivelled, deformed, or chaffy grains. The grains often remain empty or develop a chalky white appearance.
• Yield Loss: The damage caused by this pest can lead to significant yield loss. Heavy infestations can reduce grain weight and quality, leading to lower market value. In severe cases, yield loss can reach up to 30%.
• Secondary Effects: Damaged grains are more prone to fungal infections, and this pest is known to transmit several bacterial and fungal pathogens.

8. Management:

Cultural Control:

• Synchronized Planting: Synchronizing rice planting across large areas can reduce the availability of host plants for multiple generations.
• Staggered Planting: Avoid staggered planting in an area as it provides continuous food for the pest.
• Water Management: Draining the fields for a few days during the milky grain stage can help reduce pest numbers, as this disrupts the bug's lifecycle.
• Sanitation: Removal and destruction of rice stubble and weeds in and around the field reduce overwintering sites for the adults.

Biological Control:

• Natural Enemies: Various predators (spiders, dragonflies, and ladybird beetles) feed on the nymphs and adults. Egg parasitoids like Telenomus spp. (Hymenoptera: Scelionidae) and Trissolcus spp. help reduce egg populations.
• Predators: Ground beetles (Carabidae), damsel flies, and birds also prey on nymphs and adults.

Chemical Control:

• Insecticides: Insecticides such as carbaryl, acephate, and synthetic pyrethroids (e.g., deltamethrin, cypermethrin) can be used to manage heavy infestations.
• Timing of Application: Insecticide sprays should be timed to coincide with the peak activity of the pest during the milky stage of the rice crop. Repeated applications may be necessary depending on pest pressure.
• Resistance Management: Over-reliance on chemical control should be avoided to prevent resistance. Rotate insecticides from different groups to reduce the risk of resistance development.

Integrated Pest Management (IPM):

• Field Monitoring: Regular field inspections during the milky grain stage can help detect early signs of infestation. Light traps can be used to monitor adult populations.
• Thresholds: Chemical control should be considered if more than 1-2 bugs are observed per panicle or if grain filling is significantly affected.
• Combination Strategies: To ensure sustainable pest management and prevent outbreaks, a combination of biological, cultural, and chemical methods should be integrated.
• Nature of Damage: Mites puncture and suck the sap from leaves, leading to discolouration, speckling, and web formation on the leaves. Severe infestations can cause leaf drop and reduced plant vigour.

2. Grasshoppers: Hieroglyphus spp.

(Common name: Rice grasshopper)

1. Scientific Name:

Hieroglyphus banian (Fabricius, 1798)

Hieroglyphus nigrorepletus (Bolívar, 1902)

2. Order: Orthoptera (Grasshoppers)

3. Family: Acrididae (Short-horned grasshoppers)

4. Host Range:

• Primarily rice (Oryza sativa)
• Also feeds on sugarcane, maize, sorghum, pearl millet, and various other grasses and crops.

5. Distribution:

• Found across South Asia, especially in India, Pakistan, Bangladesh, and Sri Lanka.
• Also distributed in parts of Southeast Asia and Africa. Prefers tropical and subtropical climates.

6. Biology and Bionomics:

• Eggs: Females lay eggs in batches in the soil, usually enclosed in an egg pod containing 30–50 eggs. These eggs are deposited in the moist soil of fields or bunds. Egg hatching occurs after 1–3 weeks, depending on environmental conditions like temperature and moisture.
• Nymphs: Nymphs resemble small adults but without wings. The nymphal period consists of 5–6 instars and lasts for 4–6 weeks, during which they actively feed on plant leaves.
• Adults: Adults are medium to large-sized grasshoppers, green or brown in colour, with a characteristic black stripe on the hind femora. Adults have fully developed wings, and the body length can range from 30–45 mm. Adult longevity varies from 1–2 months.
• Life Cycle: The life cycle involves egg, nymph, and adult stages, and multiple generations (usually 2–3) can occur per year under favourable conditions. The lifecycle may extend or reduce depending on climatic factors, with high humidity and warm temperatures favouring rapid development.
• Overwintering: Eggs typically overwinter in the soil, and nymphs or adults may also overwinter in sheltered areas like crop stubble or weeds.

7. Nature of Damage:

• Feeding Habits: Both nymphs and adults are voracious feeders. They chew on the leaves and stems of rice plants, often cutting them at the base. They feed heavily on the green leaves, causing the plant to lose vigour and reducing its photosynthetic capability.
• Symptoms: Damaged plants show chewed leaves and defoliation, which, in severe cases, can result in stunted growth or lodging. The hopper's feeding can cause "hopper burn," which leads to the plant's death.
• Critical Stages: Damage is most severe during the seedling and early tillering stages of the crop. Heavy infestations can lead to serious yield losses. In severe cases, fields can be completely defoliated.
• Yield Loss: Infestation during the early stages of rice development can lead to delayed maturity and significantly reduce yield, particularly in cases of heavy defoliation.

8. Management:

Cultural Control:

• Timely Sowing: Early planting or synchronized planting across larger areas helps avoid peak periods of grasshopper infestation.
• Field Sanitation: Remove weeds and grasses in and around the field as they act as alternate hosts. Regular removal of crop residues and stubble helps reduce egg-laying sites.
• Deep Plowing: Deep ploughing after harvest helps expose and destroy overwintering eggs laid in the soil.
• Flooding Fields: Flooding rice fields at the early stages of infestation can help reduce the grasshopper population, as it hinders their movement and kills eggs or nymphs in the soil.

Biological Control:

• Natural Predators: Birds, spiders, and predatory insects like beetles feed on grasshopper nymphs and adults.
• Parasitoids: Egg parasitoids like Scelio spp. (Hymenoptera: Scelionidae) attack grasshopper eggs.
• Entomopathogens: Fungal pathogens like Metarhizium anisopliae can be used to control grasshopper populations by causing disease outbreaks in nymphs and adults.
• Predators: Predatory insects, such as mantises, also feed on grasshopper nymphs and adults.

Chemical Control:

• Insecticides: Spraying insecticides like carbaryl, malathion, or synthetic pyrethroids (e.g., lambda-cyhalothrin, deltamethrin) can help manage severe infestations.
• Baiting: In some cases, poisoned bait (insecticide-treated bran mixed with molasses or water) is spread along field borders or on grassy areas to attract and kill nymphs.
• Neem-based Products: Botanical insecticides like neem oil or neem-based insect growth regulators (e.g., azadirachtin) are effective and environmentally friendly for reducing nymphal populations.
• Resistance Management: Overuse of a single type of insecticide should be avoided to prevent the development of resistance in grasshopper populations. Rotate insecticides with different modes of action.

Integrated Pest Management (IPM):

• Field Monitoring: Regular field scouting and population monitoring are critical. Light traps or pheromone traps can be used to monitor adult populations.
• Action Thresholds: Control measures should be implemented when grasshopper populations exceed the economic threshold level (e.g., 2–3 grasshoppers per square meter).
• Biopesticides: The use of biopesticides, including microbial agents and botanical insecticides, can be incorporated into IPM strategies to reduce the chemical load and support sustainable pest management.
• Combination Strategy: A combination of cultural, biological, and chemical control methods should be employed to keep the pest population under control.

3. Brown Planthopper: Nilaparvata lugens

(Common name: Brown planthopper)

1. Scientific Name: Nilaparvata lugens (Stål, 1854)

2. Order: Hemiptera (True bugs)

3. Family: Delphacidae (Planthoppers)

4. Host Range:

• Primarily affects rice (Oryza sativa).
• Occasionally feeds on other grasses such as Leersia, Echinochloa, and Ischaemum.

5. Distribution:

• Widely distributed in rice-growing regions of Asia, including India, China, Japan, the Philippines, Thailand, Vietnam, and other parts of Southeast Asia.
• Also found in some parts of Europe and Africa. Prefers tropical and subtropical regions with high humidity and dense rice cultivation.

6. Biology and Bionomics:

• Eggs: Females lay about 200-300 eggs over their lifespan. Eggs are inserted into the midrib of rice leaves or leaf sheaths, and they hatch in about 5-10 days.
• Nymphs: The nymphs are white or pale brown, wingless, and pass through 5 instars over 15-20 days. Nymphs feed on the phloem sap by inserting their style into the plant tissue.
• Adults: Adults are about 3-4 mm long, light to dark brown. They exist in two forms: macropterous (long-winged) adults that can fly and disperse to new fields and brachypterous (short-winged) adults that remain in the same area to reproduce.
• Life Cycle: The pest completes its life cycle in about 25-30 days. Multiple generations (up to 10-12) can occur in a year under favourable conditions, especially in irrigated rice fields where the crop is grown year-round.
• Overwintering: In temperate regions, the adults may overwinter, but in tropical regions, continuous rice cultivation allows the pest to survive year-round.

7. Nature of Damage:

• Feeding Behavior: Both nymphs and adults suck sap from the base of rice plants, specifically the leaf sheaths. They feed on the plant's phloem sap, causing plant weakening, stunted growth, and a characteristic damage called "hopper burn."
• Symptoms:
• Hopper Burn: Infested plants first show yellowing and then browning of the leaves, eventually drying up. Entire patches of rice fields may appear scorched as the plants die.
• Direct Damage: The planthopper weakens the plants by removing sap, which leads to poor tillering, stunting, and lodging. In extreme cases, fields can experience total crop loss.
• Indirect Damage: The brown planthopper is a vector for viral diseases like rice ragged stunt virus (RRSV) and rice grassy stunt virus (RGSV), both of which cause serious yield losses.
• Critical Stages: Damage is most severe at the tillering and booting stages of the rice crop. Yield loss is particularly high if infestations occur during the reproductive stage.
• Yield Loss: Severe infestations can lead to yield losses of up to 60-70% in heavily infested fields.

8. Management:

Cultural Control:

• Avoid Dense Planting: Dense plantings of rice favour planthopper outbreaks. Proper spacing of plants helps reduce pest populations.
• Water Management: Draining the field temporarily when planthoppers are detected can help reduce their population. Maintaining intermittent flooding can also disrupt their breeding.
• Synchronized Planting: Synchronized planting of rice over large areas can help reduce the planthopper population by removing their continuous source of food.
• Use Resistant Varieties: Growing resistant rice varieties like IR64, IR36, and other region-specific varieties can help reduce the impact of Nilaparvata lugens infestations.
• Field Sanitation: Removal of weeds, stubble, and other alternate hosts helps in reducing overwintering or surviving populations of the pest.

Biological Control:

• Natural Predators: Spiders (Lycosa spp.), dragonflies, and damselflies prey on nymphs and adults of the brown planthopper.
• Parasitoids: Egg parasitoids like Anagrus spp. (Hymenoptera: Mymaridae) and Oligosita spp. (Hymenoptera: Trichogrammatidae) attack planthopper eggs, reducing their populations.
• Fungal Pathogens: Entomopathogenic fungi such as Beauveria bassiana and Metarhizium anisopliae can cause outbreaks of disease in planthopper populations.
• Predators: Predatory insects like Cyrtorhinus lividipennis (a mirid bug) feed on nymphs and adults of the brown planthopper.

Chemical Control:

• Insecticides: In cases of heavy infestations, insecticides such as buprofezin, imidacloprid, and pymetrozine can be used. These chemicals disrupt the feeding and reproduction of planthoppers.
• Timing of Application: Insecticide sprays should be timed to target early-stage nymphs before they cause significant damage.
• Insecticide Resistance: Over-reliance on a single class of insecticides should be avoided to prevent the development of resistance. Rotation of insecticides from different chemical groups is recommended.
• Botanical Insecticides: Neem oil and neem-based insect growth regulators (IGRs) such as azadirachtin are also effective against brown planthoppers.

Integrated Pest Management (IPM):

• Monitoring: Regular field monitoring and the use of light traps to detect early infestations are crucial for effective management. Monitoring economic threshold levels (ETL) helps avoid unnecessary pesticide applications. The ETL is around 1-2 insects per tiller.
• Cultural and Biological Control Integration: Combine resistant varieties, biological control agents, and cultural practices to minimize pesticide use and support long-term control of planthopper populations.
• Threshold-Based Control: Take action when populations exceed ETL to avoid unnecessary damage and overuse of insecticides.

4. Green Leafhopper (Nephotettix spp.)

1. Scientific Name:

• Nephotettix virescens (Distant, 1908)
• Nephotettix nigropictus (Stål, 1855)

2. Order: Hemiptera (True bugs)

3. Family: Cicadellidae (Leafhoppers)

4. Host Range:

• Primarily affects rice (Oryza sativa).
• Also feeds on various other grass species such as Echinochloa, Ischaemum, and Leersia.

5. Distribution:

• Widely distributed across rice-growing regions in Asia including India, Bangladesh, Sri Lanka, Thailand, the Philippines, Indonesia, China, and Japan.
• Also present in parts of Africa and Southeast Asia. Prefers tropical and subtropical regions.

6. Biology and Bionomics:

• Eggs: Females lay eggs in rows inside the leaf veins of rice plants. Each female can lay up to 100-200 eggs, and the eggs hatch in 5-10 days.
• Nymphs: Nymphs pass through 5 instars over 15-20 days. They are pale green and resemble adults but are wingless. Nymphs feed on phloem sap, leading to stunted plant growth.
• Adults: Adults are about 3-4 mm long, pale green with black markings. They have fully developed wings and can fly from plant to plant.
• Life Cycle: The life cycle is completed in 25-30 days under favorable conditions, and several generations (up to 6-8) can occur in a year.
• Overwintering: In temperate regions, the adults or eggs can overwinter, but in tropical regions, year-round rice cultivation allows them to persist continuously.

7. Nature of Damage:

• Feeding Behavior: Both nymphs and adults suck the phloem sap from the leaf blades and leaf sheaths of rice plants, resulting in the depletion of nutrients and stunted growth.
• Symptoms:
• Direct Damage: Feeding causes yellowing of leaves, leaf curling, and overall weakening of the plant. The plant may become stunted and experience poor tillering, leading to reduced yields.
• Indirect Damage: The most significant damage caused by Nephotettix spp. is their role as vectors for transmitting rice tungro virus (RTV) and other viral diseases, such as rice dwarf and rice transitory yellowing viruses. These viruses cause stunting, yellowing of leaves, and significant yield losses in infected plants.
• Critical Stages: Damage is most severe during the seedling and vegetative stages of rice. Virus transmission early in the crop cycle can lead to significant yield losses.

8. Management:

Cultural Control:

• Use of Resistant Varieties: Cultivate resistant rice varieties such as IR36, IR64, and other region-specific varieties that are less susceptible to green leafhopper and tungro virus.
• Crop Rotation: Avoid continuous rice cropping in the same field to disrupt the pest's life cycle.
• Field Sanitation: Remove weeds and alternative host plants that can harbor the leafhoppers and viruses.
• Synchronized Planting: Synchronized planting across large areas helps reduce leafhopper populations by limiting their food source during off-seasons.
• Water Management: Periodically draining the rice fields can disrupt leafhopper breeding.

Biological Control:

• Predators: Predatory spiders, dragonflies, and damselflies feed on the nymphs and adults of Nephotettix.
• Parasitoids: Parasitoids such as Gonatocerus spp. (Hymenoptera: Mymaridae) parasitize the eggs of leafhoppers, helping to control their populations.
• Fungal Pathogens: Entomopathogenic fungi like Beauveria bassiana and Metarhizium anisopliae can infect and kill leafhoppers.

Chemical Control:

• Insecticides: Chemical control can be applied when green leafhopper populations exceed economic threshold levels (ETL). Recommended insecticides include buprofezin, imidacloprid, and thiamethoxam.
• Application Timing: Insecticides should be applied early, targeting nymphs before they can spread viral diseases.
• Botanical Insecticides: Neem-based products such as neem oil or azadirachtin can be effective against Nephotettix spp.

Integrated Pest Management (IPM):

• Monitoring: Regular field scouting is necessary to detect early infestations. Light traps can also be used to monitor adult populations. The ETL for Nephotettix spp. is around 1-2 leafhoppers per hill or 5 per net sweep.
• Biological and Cultural Controls: Integrate the use of resistant varieties, natural enemies, and cultural practices to keep pest populations under control.
• Virus Management: To prevent virus transmission, remove and destroy infected plants. Additionally, controlling leafhopper populations at the seedling stage can significantly reduce virus spread.

5. Armyworm (Mythimna separata)

1. Scientific Name: Mythimna separata (Walker, 1865)

2. Order: Lepidoptera (Moths and Butterflies)

3. Family: Noctuidae (Owlet Moths)

4. Host Range:

• A polyphagous pest, Mythimna separata feeds on a wide variety of crops, including:
• Cereal crops like maize, rice, wheat, barley, sorghum, and millet.
• Grasses such as sugarcane, napier grass, and other wild grasses.
• Sometimes feeds on vegetables and pulses such as beans, peas, and other legumes.
• Its broad host range makes it a major pest in agricultural ecosystems.

5. Distribution:

• Mythimna separata is widely distributed across Asia, including India, China, Japan, Southeast Asia, and parts of Africa.
• It is commonly found in tropical and temperate regions, especially in areas with continuous crop cultivation, which provide abundant food sources.

6. Biology and Bionomics:

• Eggs: Female moths lay around 1000-1500 eggs in clusters on the leaves of host plants. Eggs are spherical and creamy white, hatching in 2-5 days, depending on temperature.
• Larvae: The larval stage is the most destructive. Larvae pass through 6-7 instars over 20-25 days. The young larvae feed gregariously on the leaves, while older larvae become solitary and may feed on stems and grain heads.
• Appearance: Caterpillars are pale green to brown with longitudinal stripes running along their bodies.
• Pupae: Pupation occurs in the soil. The pupal stage lasts for 10-15 days. Pupae are reddish-brown.
• Adults: The adult moth is yellowish-brown with a wingspan of about 40-50 mm. It is nocturnal and migratory, flying long distances in search of food and laying eggs on suitable crops.
• Life Cycle: Mythimna separata completes its life cycle in about 30-40 days, depending on environmental conditions, and can have multiple generations per year, especially in tropical regions where it can persist year-round.
• Migratory Behavior: This pest is known for its long-distance migrations, particularly in areas where host plants are exhausted or during periods of drought.

7. Nature of Damage:

• Feeding Behavior: The larvae feed voraciously on the leaves of cereal crops, stripping them completely. In the early stages, larvae skeletonize leaves, leaving behind only veins. As they grow older, they may also attack the stems, ears, or panicles of cereal crops.
• Symptoms:
• Leaf Stripping: Extensive defoliation occurs, leading to reduced photosynthesis and stunted growth of the plants.
• Head or Ear Damage: In advanced infestations, larvae feed on the developing grains in the panicles, reducing yield directly.
• Marching Behavior: When food is depleted, larvae exhibit "armyworm" behaviour, migrating en masse to nearby fields, causing extensive damage over large areas in a short period.
• Critical Stages: Infestations are most destructive during the late vegetative and reproductive stages of cereal crops.
• Yield Loss: Severe infestations can cause up to 60-70% yield loss in cereals like maize, wheat, and rice.

8. Management:

Cultural Control:

• Timely Sowing: Early sowing of crops can help reduce the risk of infestation, as crops are more likely to escape peak larval periods.
• Field Sanitation: Remove weeds, stubble, and plant debris that may harbour armyworm larvae or pupae. This helps prevent overwintering and early infestation.
• Trap Cropping: Planting trap crops like millet or sorghum along the borders of fields can help attract armyworms away from the main crop.

Biological Control:

• Natural Enemies:
• Predators: Birds, spiders, and predatory beetles feed on armyworm larvae.
• Parasitoids: Parasitic wasps such as Cotesia ruficrus and Tachinid flies parasitize larvae.
• Fungal Pathogens: Entomopathogenic fungi like Metarhizium anisopliae and Beauveria bassiana can infect and kill larvae during humid conditions.
• Biopesticides: The use of Bacillus thuringiensis (Bt) formulations is an effective biological control method, particularly against young larvae.

Chemical Control:

• Insecticides: In cases of severe infestation, insecticides such as chlorantraniliprole, lambda-cyhalothrin, and spinosad can be used to control armyworm populations. Sprays should be targeted at early instar larvae for maximum effectiveness.
• Application Timing: Monitoring is key; insecticide applications should be timed to target early larval stages before significant damage occurs.
• Botanical Insecticides: Neem-based products, such as neem oil or azadirachtin, can also be used to manage armyworms in a more environmentally friendly manner.

Integrated Pest Management (IPM):

• Monitoring: Regular field monitoring is crucial to detect early-stage larvae and prevent large-scale outbreaks. Light traps and pheromone traps can be used to monitor adult moth populations and predict infestations.
• Economic Threshold Levels (ETL): Control measures should be implemented when larvae exceed the ETL, typically around 2-3 larvae per square meter.
• Cultural, Biological, and Chemical Control: An integrated approach combining cultural practices, natural enemies, and judicious use of insecticides should be followed for the sustainable management of Mythimna separata populations.

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