Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Pests of Crops
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Pests of Crops
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Subject: Agricultural Science
Class: Senior Secondary 2
Term: 3rd Term
Week: 2
Theme: Crop Production
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i. state the meaning of pests.ii. Classify pests in to in sects and non-in sects pests.iii. classify in sects pests based on the ir mode of mouth parts.iv. discuss the important in sects pests of major crops.v. recognize and name the important storage in sects pests of farm producevi. describe the nature of damage of crops.vii. describe the biology of some of the selected crops.viii.state and discuss the general control and preventive measures. ix.State and discuss the possible side effects of the various preventive and control methods on man and the environment.x.State general effects/economic importance of pests.
("bunchy top").
Variegated Grasshopper: (Zonocerus variegatus) Feeds on leaves, causing defoliation, especially in young plants.
Whiteflies: (Bemisia tabaci) Vector for Cassava Mosaic Disease and Cassava Brown Streak Disease.
Yam: Yam Beetle: (Heteroligus meles) Adults bore into yam tubers in the soil, creating tunnels and wounds, leading to rot.
Yam Tuber Moth: Larvae damage stored yam tubers.
Scale Insects: Suck sap from yam vines and stored tubers.
Cowpea: Cowpea Pod Borer: (Maruca vitrata) Larvae bore into flowers and pods, feeding on developing seeds.
Aphids: (Aphis craccivora) Suck sap from young shoots, leaves, and pods, causing deformation and transmitting viruses.
Cowpea Seed Weevil (Bruchids): (Callosobruchus maculatus) (Storage pest, but can infest maturing pods in the field) Damages seeds.
Flower Thrips: (Megalurothrips sjostedti) Feed on flowers, causing flower abortion.
Oil Palm: Oil Palm Weevil: (Rhynchophorus phoenicis) Larvae bore into stems and growing points, causing decay.
Termites: Attack young seedlings and older palms.
Cocoa: Cocoa Mirids (Capsids): (Sahlbergella singularis, Distantiella theobroma) Suck sap from young shoots and pods, causing "cherelle wilt" and "dieback." Pod Borers: Larvae bore into cocoa pods.
Tomato: Tomato Fruit Worm/American Bollworm: (Helicoverpa armigera) Larvae bore into fruits. Whiteflies, Aphids, Thrips: Suck sap, transmit viruses. 2.
5. Important Storage Insect Pests of Farm Produce (PO v) Storage pests cause significant post-harvest losses, crucial for food security.
Maize/Cereal Grains: Maize Weevil: (Sitophilus zeamais) The most common and destructive pest of stored maize, rice, wheat. Both larvae and adults feed inside grains.
Lesser Grain Borer: (Rhyzopertha dominica) Bores into whole grains.
Angoumois Grain Moth: (Sitotroga cerealella) Larvae feed inside grains, emerging as moths.
Rust-Red Flour Beetle: (Tribolium castaneum) Primarily feeds on broken grains and flour. Legumes (Cowpea, Groundnut, Soybean): Cowpea Seed Weevil (Bruchid): (Callosobruchus maculatus) Lays eggs on cowpea seeds; larvae bore in and develop, emerging as adults.
Groundnut Borer: Damages stored groundnuts.
Yam: Yam Tuber Moth: Larvae tunnel into tubers. Termites, Rodents: Also cause significant damage to stored yams. 2.
6. Nature of Damage of Crops (PO vi) Pests cause damage in various ways, often characteristic of their feeding habits: Defoliation: Chewing pests (grasshoppers, caterpillars) eat leaves, reducing photosynthetic capacity.
Stunted Growth: Sap-sucking pests (aphids, mealybugs) remove nutrients, leading to reduced plant vigour.
Wilting/Drying: Stem borers (maize stem borer) damage vascular tissues, disrupting water and nutrient transport. Root feeders (nematodes) also cause wilting.
Galls and Deformities: Some insects induce abnormal growths (galls) or distorted plant parts.
Boring into Stems/Fruits/Tubers: Pests like stem borers, yam beetles, fruit borers tunnel into plant parts, making them unmarketable or leading to rot.
Sooty Mould: Sap-sucking insects excrete honeydew, which promotes the growth of black sooty mould, reducing photosynthesis and market value.
Transmission of Diseases: Many piercing-sucking insects (aphids, whiteflies, leafhoppers) act as vectors for plant viruses and other pathogens.
Reduced Yield and Quality: Direct feeding on reproductive parts (flowers, fruits, grains) or general plant debilitation leads to lower quantity and poorer quality of harvest.
Contamination of Stored Produce: Pests in stored products not only consume grains but also contaminate them with faeces, webbing, and insect parts, making them unfit for consumption. Increased Susceptibility to Secondary Infections: Pest wounds provide entry points for fungal and bacterial pathogens. 2.
7. Biology of Some Selected Insect Pests (PO vii) Understanding the life cycle (biology) of pests is crucial for effective control, as different stages may be vulnerable to different interventions. Complete Metamorphosis (Holometabolous) -
Example: Maize Weevil (Sitophilus zeamais)
Stages: Egg -> Larva (grub) -> Pupa -> Adult.
Description: The female weevil drills a small hole in a grain kernel, lays a single egg, and seals the hole. The egg hatches into a legless larva that tunnels and feeds within the grain. After several instars, it pupates inside the grain. The adult weevil emerges from the grain, mates, and repeats the cycle. The entire development occurs inside the grain, making early detection difficult.
Control Relevance: Targeting adults (traps, insecticides) or preventing egg-laying is important. Infested grains require fumigation. emphasizes monitoring, prevention, and judicious use of pesticides. 2.
9. Side Effects of Control Methods (PO ix) While essential, pest control methods, particularly chemical, can have adverse effects.
On Man: Pesticide Poisoning: Direct exposure during application or handling, leading to acute (nausea, dizziness, skin irritation) or chronic (cancers, neurological damage, reproductive issues) health problems for farmers and consumers.
Residues in Food: Pesticide residues on crops can be ingested by consumers, posing long-term health risks.
On the Environment: Water and Soil Pollution: Runoff from sprayed fields contaminates rivers, streams, and groundwater, harming aquatic life and making water unsafe. Pesticides can accumulate in soil, affecting soil microorganisms and fertility.
Air Pollution: Pesticide drift during spraying can contaminate nearby areas, affecting non-target organisms and human populations.
Destruction of Beneficial Organisms: Pesticides are often non-selective, killing natural enemies (predators, parasitoids, pollinators like bees) along with pests, disrupting ecological balance.
Pest Resistance: Repeated use of the same pesticide can lead to pests developing resistance, rendering the chemical ineffective over time.
Biodiversity Loss: Reduction in populations of non-target insects, birds, and other wildlife. 2.
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0. General Effects/Economic Importance of Pests (PO x) Pests have significant negative economic and social impacts.
Reduced Crop Yield and Quality: Direct feeding damage, disease transmission, and plant debilitation lead to lower harvests and inferior produce, impacting farmer income.
Increased Production Costs: Farmers spend money on pesticides, labour for application, and other control measures, increasing the cost of production.
Post-Harvest Losses: Storage pests can destroy a significant portion of harvested crops, especially grains, leading to food scarcity and economic losses.
Food Insecurity: Large-scale pest outbreaks can lead to widespread crop failure, threatening national food security and potentially causing famine.
Economic Disruption: Reduced agricultural output affects agricultural value chains, food processing industries, and export earnings.
Market Restrictions: Damaged or pesticide-contaminated produce may not meet market standards, leading to rejection and loss of income.
Health Implications: Contaminated food from pest infestation (e.g., fungal toxins produced in damaged grains) or pesticide residues can pose health risks to consumers. * Loss of Investment: Farmers lose the money, time, and effort invested in cultivating crops if they are destroyed by pests.
Stages: Egg -> Larva (grub) -> Pupa -> Adult.
Description: The female weevil drills a small hole in a grain kernel, lays a single egg, and seals the hole. The egg hatches into a legless larva that tunnels and feeds within the grain. After several instars, it pupates inside the grain. The adult weevil emerges from the grain, mates, and repeats the cycle. The entire development occurs inside the grain, making early detection difficult.
Control Relevance: Targeting adults (traps, insecticides) or preventing egg-laying is important. Infested grains require fumigation. Incomplete Metamorphosis (Hemimetabolous) -
Example: Variegated Grasshopper (Zonocerus variegatus)
Stages: Egg -> Nymph (immature form resembling adult but without wings) -> Adult.
Description: Eggs are laid in masses in the soil. They hatch into nymphs, which are wingless but otherwise resemble small adults. Nymphs moult several times, growing larger and developing wing pads, until they reach the adult stage with fully developed wings and reproductive organs.
Control Relevance: Nymphs and adults are both destructive. Control measures (e.g., direct spraying, hand-picking) can target both stages. Egg destruction can prevent outbreaks. 2.
8. General Control and Preventive Measures (PO viii) Integrated Pest Management (IPM) is the most sustainable approach, combining various methods.
Cultural Control: Crop Rotation: Breaking the life cycle of soil-borne pests and those specific to certain crops (e.g., rotating maize with legumes to reduce maize stem borers).
Timely Planting and Harvesting: Planting early or harvesting early can help escape peak pest populations (e.g., early maize planting to avoid severe stem borer damage).
Sanitation/Field Hygiene: Removing crop residues, volunteer plants, and weeds (alternate hosts) reduces pest harborage (e.g., burying or burning old cassava stems to kill mealybug eggs).
Resistant Varieties: Planting crop varieties bred to be resistant or tolerant to specific pests (e.g., maize varieties resistant to stem borers, cowpea varieties resistant to bruchids).
Trap Cropping: Planting a small area of a preferred host crop to attract pests away from the main crop, then destroying the trap crop with accumulated pests.
Proper Fertilization and Irrigation: Maintaining vigorous plant growth allows plants to better withstand pest damage.
Biological Control: Natural Enemies: Using beneficial organisms (predators, parasitoids, pathogens) to control pest populations.
Predators: Ladybird beetles feed on aphids; praying mantises feed on various insects.
Parasitoids: Tiny wasps (e.g., Anagyrus lopezi for cassava mealybug) lay eggs inside or on pests, killing them.
Pathogens: Fungi, bacteria, viruses that infect and kill pests (e.g., Bacillus thuringiensis (Bt) for caterpillars).
Chemical Control: Pesticides (Insecticides): Application of chemical compounds to kill pests.
Types: Contact (kills on contact), stomach (kills when ingested), systemic (absorbed by plant, kills feeding pests).
Application Methods: Spraying, dusting, seed treatment, fumigation (for stored products).
Considerations: Use as a last resort, follow manufacturer's instructions, observe pre-harvest intervals.
Physical/Mechanical Control: Hand Picking: Manually removing and destroying large pests (e.g., variegated grasshoppers, yam beetles, caterpillars) or infested plant parts.
Trapping: Using physical traps to catch pests (e.g., light traps for moths, pheromone traps for specific insect species, sticky traps for flying insects, rat traps).
Barriers: Physical barriers to prevent pest access (e.g., netting, trenches).
Heat Treatment: For stored produce (e.g., sun-drying grains to reduce moisture content and kill some pests).
Hermetic Storage: Storing grains in airtight containers to deplete oxygen and kill pests (e.g., PICS bags, metal silos).
Integrated Pest Management (IPM): A holistic approach that combines various control methods to keep pest populations below economically damaging levels, while minimizing risks to human health and the environment. It emphasizes monitoring, prevention, and judicious use of pesticides. 2.
9. Side Effects of Control Methods (PO ix) While essential, pest control methods, particularly chemical, can have adverse effects.
On Man: Pesticide Poisoning: Direct exposure during application or handling, leading to acute (nausea, dizziness, skin irritation) or chronic (cancers, neurological damage, reproductive issues) health problems for farmers and consumers.
Residues in Food: Pesticide residues on crops can be ingested by consumers, posing long-term health risks.
On the Environment: Water and Soil Pollution: Runoff from sprayed fields contaminates rivers, streams, This section provides the comprehensive content for the teacher to deliver effectively. 2.
1. Definition of Pests (PO i) A pest is any organism that causes economic damage to crops, livestock, or humans. In an agricultural context, pests are organisms that interfere with the production of crops, reducing yield, quality, or increasing production costs. This includes insects, mites, nematodes, rodents, birds, and even some weeds. 2.
2. Classification of Pests (PO ii) Pests can be broadly classified into two main categories: Insect Pests: These are arthropods belonging to the class Insecta, characterized by a segmented body (head, thorax, abdomen), three pairs of legs, and often one or two pairs of wings. They are the most significant group of agricultural pests.
Examples: Grasshoppers, stem borers, aphids, weevils, armyworms, beetles.
Non-Insect Pests: This category includes other organisms that cause damage to crops.
Mites: (e.g., spider mites) Tiny arthropods, related to spiders, that suck plant sap.
Nematodes: (e.g., root-knot nematodes) Microscopic roundworms that live in soil and attack plant roots.
Rodents: (e.g., rats, mice) Mammals that feed on crops in the field and in storage.
Birds: (e.g., weaver birds, sparrows) Feed on grains, fruits, and young seedlings.
Molluscs: (e.g., snails, slugs) Feed on leaves and young plant parts.
Vertebrates: Other mammals like monkeys, antelopes, etc., that raid farms. 2.
3. Classification of Insect Pests Based on Mouthparts (PO iii) Insect mouthparts are adapted to their feeding habits, which directly relate to the type of damage they inflict.
Chewing Mouthparts (Mandibulate): Structure: Strong, toothed mandibles for biting and chewing solid food, maxillae for manipulating food, and a labium.
Damage: Characterized by holes, torn or ragged leaves, defoliation, cutting of stems, boring into fruits/stems.
Examples: Grasshoppers, caterpillars (larvae of moths and butterflies), beetles (e.g., yam beetle, variegated grasshopper, maize stem borer, locusts). Piercing and Sucking Mouthparts (Haustellate): Structure: Stylets (needle-like structures) enclosed in a proboscis (beak). They pierce plant tissues and suck up plant sap.
Damage: Wilting, curling, distortion of leaves, stunted growth, yellowing (chlorosis), transmission of plant viruses, honeydew excretion leading to sooty mould.
Examples: Aphids, whiteflies, mealybugs, leafhoppers, stink bugs, scale insects, cassava mealybug, cocoa mirids.
Sponging Mouthparts: Structure: A fleshy proboscis with sponge-like lobes (labella) at the tip, used to soak up liquid food.
Damage: Indirectly cause damage by spreading diseases or contaminating produce. They cannot pierce plant tissues.
Examples: Houseflies, fruit flies (some fruit flies like Bactrocera dorsalis have piercing components to lay eggs in fruits, but adults mainly sponge liquids). For crops, they are less direct pests, but can spread pathogens.
Siphoning Mouthparts: Structure: A long, coiled proboscis (like a coiled spring) that uncoils to suck up nectar or other liquids from flowers.
Damage: Primarily observed in butterflies and moths (adults) which are generally not considered direct crop pests (larvae are the pests). They cause no direct damage to crops in this stage but feed on nectar.
Examples: Adult butterflies and moths. 2.
4. Important Insect Pests of Major Crops (PO iv) This list focuses on common crops in Nigeria and their significant insect pests: Maize: Maize Stem Borers: (Busseola fusca, Sesamia calamistis, Eldana saccharina) Larvae bore into stems, causing dead hearts and lodging.
Armyworms: (Spodoptera frugiperda) Larvae feed on leaves, often in large numbers, causing defoliation.
Maize Weevil: (Sitophilus zeamais) (Storage pest, but can infest field maize) Damages grains.
Aphids: Suck sap from leaves and young cobs.
Cassava: Cassava Mealybug: (Phenacoccus manihoti) Sucks sap from growing tips, causing stunted, distorted growth ("bunchy top").
Variegated Grasshopper: (Zonocerus variegatus) Feeds on leaves, causing defoliation, especially in young plants.
Whiteflies: (Bemisia tabaci) Vector for Cassava Mosaic Disease and Cassava Brown Streak Disease.
Yam: Yam Beetle: (Heteroligus meles) Adults bore into yam tubers in the soil, creating tunnels and wounds, leading to rot.
Yam Tuber Moth: Larvae damage stored yam tubers.
Scale Insects: Suck sap from yam vines and stored tubers.
Cowpea: Cowpea Pod Borer: (Maruca vitrata) Larvae bore into flowers and pods, feeding on developing seeds.
Aphids:*
Food Security and Post-harvest Losses: Students can relate the knowledge of storage pests (e.g., maize weevil, cowpea bruchid) to the significant post-harvest losses experienced by Nigerian farmers. This understanding can inspire them to promote better storage practices like hermetic storage (e.g., PICS bags) or improved cribs in their local communities to reduce food waste and enhance food availability. This directly links to national food security efforts. Farmer Decision-Making and Sustainable Agriculture: The discussion on different control methods (cultural, biological, chemical) and their side effects allows students to understand the complex decisions farmers face. They can apply the principles of Integrated Pest Management (IPM) to suggest sustainable farming practices to local farmers, promoting reduced reliance on harmful chemicals and fostering environmentally friendly approaches that protect human health and biodiversity. This integrates into discussions on sustainable development goals. Community Health and Environmental Stewardship: The awareness of pesticide poisoning and environmental pollution connects agricultural practices to public health and environmental protection. Students can become advocates for safe pesticide handling, proper disposal of chemical containers, and the promotion of organic farming practices in their communities, contributing to a healthier environment and safer food supply.