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A pest is an organism which harbors disease organism(s) or causes damage to other organism(s). There are crop and livestock (animals) pests.


Crop pests include insects such as grasshoppers, mealy bugs, myriads, beetles, birds and mammals (such as rodents) while livestock pests are ectoparasites such as ticks, mites and endoparasites such as liver flukes, round worms and tapeworms. They can also be plant pests known as weeds or animal pests such as insects, birds, rodents, monkeys, man or nematodes.



Insects pest: These are arthropods that carry diseases or cause damage to plant and animals. Examples include: tick, lice, grasshoppers, cotton stainer etc.

Non insect pest: These are vertebrates and molluscs that common cause disease to plants and animals or destroy crops. E.g rodents, worms, nematodes, monkeys etc.



Stem Borers: Stem borers of cereal crops like maize are the larvae of certain moths. They lay eggs at the junctions of leaf sheaths and stem of a maize plant which hatches after a week and weakens the stem causing the maize plant to break even in slight wind.


Fruit and Seed Feeders: These include fruit-piercing moths, fruit flies, cotton strainers and certain beetles. Examples are red boil-worm and the cotton stainer. Their host plant includes tomato, millet, maize and okra.


Root Feeders: They may be insect larvae or adults. An example is the yam beetle which lives mainly in the soil. They burrow into the ground and feed on yam tubers.


Leaf Feeders: Leaves of crops are eaten by snails, leaf-feeding beetles, caterpillars of various moths and butterflies, grasshoppers and locusts.


Young Shoot Feeders: Insects like aphids and mealy bug pierce and suck juices from young shoots of crop plants. They first settle on the apex and feed on the young tissue. Many sucking pests also transmit disease-causing fungi, bacteria, and virus to the plants e.g. cassava mosaic transmitted by white flies.


Life Cycle of Some Selected Pest

Grasshopper( Zonocerus variegates)

History: Male and female mate and eggs are then fertilized internally. The female then digs a hole with her ovipositor in the soil usually near the roots of plants and lays about 40 to 100 eggs the hole. A protective material is produced to cover the eggs. After about 3 days, the eggs hatch into nymphs. A nymph resembles the adult in all respect except it is sexually immature and wingless. The nymph moults several times and hops about feeding on the shoots of plants


nearby. They begin to migrate into areas where there are cassava farms and start feeding on the cassava leaves until an adult stage is attained.



life cycle of grassshopper

Effects of Grasshoppers on Cassava

Nymphs and adults feed on the leaves, shoots and barks of cassava thereby reducing cassava yield drastically as photosynthesis is seriously impaired.

Control: Spray with gammalin 20.


Cassava mealy bug (Phenacoccusmanlhot)

The female insect lays eggs without fertilization by the male. This type of reproduction is called parthenogenesis. The unfertilized eggs hatch into larvae which are wind borne or carried with cassava stem cuttings during planting because they hide in the buds of the stem. The larvae undergo three moulting stages before adult stage. One generation is completed in about twenty-two days and the adult has life span of about one hundred and forty-five days.



  1. They suck the sap of cassava leading to the stunted growth of shoot.
  2. The shoots develop bunchy tops.
  3. The leaves of the shoot die and drop.
  4. Mealybug infestation impairs photosynthesis


Control: Dip cassava cutting in 0.1% ultracide solution for one minute before planting tuber


  1. Describe the life cycle of a grasshopper.
  2. What is parthenogenesis?


The Life Cycle of Cassava Mealy bug

Life Cycle of Cassava Mealy bug

Life History of Bean Weevil

Male and female adults mate and fertilized eggs are then laid in the ripening pods in the farm. The eggs hatch into larvae which enter into the bean seeds before harvesting. In the store, the larvae feed on the cotyledons of the beans. The larvae develop into pupae in the store. The pupae later develop into adults which fly away to mate again in the farm.



The larvae feed on the seed thereby reducing the quality and value of the beans.


Fumigate the store in which beans are stored with fumigants such as methyl bromide.

Cocoa Myriads (Capsid)

These are piercing and sucking insects. They attach the young shoot of cocoa, introducing toxic saliva into the sap which may kill the plant. It can also introduce viral diseases into the plant.



Cocoa myriads cause die back disease which reduces the growth of cocoa plant. Fruit yield is reduced.


Spray the cocoa farm with kokotine or gammalin 20


Yam Beetle (Heteroligusmeles)

Life History

The mating of the female and the male yam beetles takes place between November and December in riverine areas and fertilized eggs are laid. Between December and February, eggs hatch into larvae that feed on the decayed organic substances. The larvae melt thrice before developing into pupae. In March, the pupae develop into adults after moulting.


The adults then fly to areas where yams are planted between April and June. They dig into the soil to search for yam tubers. When they eventually come in contact with tubers, they feed on them and seriously damage the tubers. Between October and November, the adult yam beetles undergo breeding migration to the riverine areas again for mating.



Adult beetles feed on yam tubers causing serious damage to the tubers and render the tubers valueless. If the tubers are attacked at early stage, the yield becomes poor.


Dust yam or yam sets with Aldrin before planting.



  1. Describe cocoa myriads as a pest.
  2. Suggest a way of controlling yam beetle.


Examples of Pests of Crops, their Effects and Control  (Summary)

1.      Grasshopper Nymphs and adults feed on leaves and shoots thereby reducing yield. Spray with gammalin 20
2.      Yam beetle Adults feed on yam tubers rendering the tubers valueless or causing poor yield Dust yam or yam sets with aldrin before planting.
3.      Cocoa myriads (capsids) Piercing and sucking insects that attack young shoots of cocoa introducing toxic saliva and viral diseases into the plants. This may kill the plants, reduces the growth and fruit yield. Spray cocoa farm with kokotine or gammalin 20.
4.      Mealy bug They suck sap of cassava which makes the shoots to develop bunchy tops; the leaves die and drop resulting in low root tubers. Dig cassava cuttings in 0.1% rogor before planting.
5.      Beans weevils Field to store pests. Larvae feeds on bean seed bore holes into them thereby reducing the quantity and quality of the grains. Fumigating the store with insecticides and early harvesting.
6.      Cotton strainers Feeds on cotton seeds and stains lint. Spray suitable insecticides
7.      Mammals (monkeys, grass cutter, squirrel) Destroy tubers, fruits and shoots of crops by feeding on them. Trapping, shooting and clearing their hide out by proper weeding.
8.      Birds Feed on grains, plantains and other crops Chasing away



  1. Discuss four insect pests of crops under the following sub headings: pests and effects.
  2. Suggest ways of controlling the mentioned pests in question 1.


Pests and Parasites of Livestock and their Effects

A parasite is an organism living in or on another organism called host having a harmful effect on the host as a result of the association.  Parasite which lives inside its host is called endoparasite e.g. tapeworm, roundworm, liver fluke.  Parasite which lives on or outside the host is called ectoparasite e.g. ticks, lice and mite.


Examples of Animal Pests, their Effects and Control

1.        Ticks Cattle, goats, sheep Suck blood which result in anaemia, restlessness, sores on the skin of animals and loss of weight. They also transmit viruses and protozoa that cause diseases Spray animal houses with insecticides, remove the ticks from the body of the animals
2.       Liver fluke (Fasciola hepatica) Cysts are picked up when animals drink water and feed on grasses. The cyst develops into a young fluke which burrows through the wall of the small intestine and liver. This affects digestion; result in liver rot, leading to drowsiness and death. Destroy water snail, an intermediate host, treat pools with copper sulphate.
3.       Round worm (Ascarissuum) Cattle, pigs Feeds on digested food from the host which results in slow growth, indigestion and constipation, loss of appetite, weakness & death.


Deworm animals regularly, good sanitary measure


4.       Lice Birds Suck blood of their hosts resulting in great irritation, restlessness, loss of weight and low productivity. They also transmit disease pathogens.


Prevent over crowding, good sanitary measures and use of insecticide (DDT)
5.       Tse-tse fly Cattle Suck blood and transmits trypanosome (a protozoan parasite) which causes sleeping sickness anaemia and loss of weight. Clearing bushes around a farmland, use of insecticide


Economic Importance of Pests

  • Reduction in yield and productivity of crops and plants.
  • Reduction in quality of farm produce.
  • Increase in cost of production in the course of controlling.
  • Reduction in income of farmers.
  • They render farm produce unattractive and unmarketable.
  • They cause malformation in plants and animals.
  • They cause death of plants and animals.



  1. Discuss the life cycle of the following animal parasites (a) Round worm (b) liver fluke
  2. What are parasites?



A disease is a change of the plant or animal from the normal state of health, presenting marked symptom or outward visible signs in the organism. Disease pathogens are disease causing organisms, which include bacteria, viruses, fungi, nematodes and protozoan.


Diseases of Crops, Effects and Control

1.   Maize rust Fungus Cob and grains covered with black spores, premature death. Apply fungicides before planting.
2.   Groundnut rosette Virus Leaves curl and turn yellow, show mottling and wrinkles, leads to death. Uproot and burn infected plants. Plant resistant varieties
3.   Rice blasts Fungus Brown spots on leaves, leaves dry up. Use resistant variety, apply fungicide.


4.   Cassava mosaic Virus Distorted leaves, yellow patches on leaves, stunted growth Plant resistant varieties
5.   Cocoa black pod Fungus (Phytophytorapalmivora Brown spots on pods. The pods turn black and dry up Apply fungicides. Remove and burn all infected pods
6.   Cassava wilt Bacterium Leaves wilt and fall off Early planting, crop rotation
7.   Cocoa swollen shoot Virus Stems and roots become swollen, leave chlorolysis Burn infected plants, use resistant varieties



  1. Discuss one disease of cassava, cocoa and maize under the following sub headings causative organism     b. mode of transmission     c. symptoms     d. control
  2. Mention the groups of disease pathogens.


Livestock Diseases, Effect and Control

1.      New castle disease (poultry) Virus Neck twisting, paralysis of legs, respiratory and nervous disorder, low productivity and death Sanitation, vaccination
2.      Rinder pest (cattle) Virus High fever  and diarrhea Isolation of infected animal, vaccination
3.      Anthrax (cattle, goat, sheep) Bacteria Swellings in the neck, and lower abdomen, fever, blood stained discharge from the nostrils Immunizatio, sanitation
4.      Coccidiosis  (poultry) Protozoan Blood stool, affects intestines Sanitation
5.      Trypanosomiasis (cattle) Protozoan (trypanosome) Intermittent fever, general body weakness Spray tse-tse fly with insecticide, rear resistant breed




  1. What is a disease?
  2. Describe the disease pathogens, effects and control of diseases of poultry and cattle.


General Effects of Pests & Diseases

  1. Reduction in yield and productivity of crops and plants
  2. Reduction in quality of farm produces
  3. Increase in cost of production in the course of controlling them
  4. Reduction in income of farmers
  5. They render farm produce unattractive and un marketable
  6. They cause malformation in plants and animals.
  7. They cause death of plants and animals.


General Control of Pests & Diseases

  1. Cultural control – use of farm practice to prevent or control pests and diseases e.g crop rotation, regular weeding, early harvesting, and use of resistant varieties.
  2. Biological control – The introduction of natural enemies of pests to control the pests.
  3. Physical control – Physical removal of pest by hand – picking, setting traps, shooting or fencing a farm with wire nets.
  4. Chemical control – Use of chemicals called pesticides to control pests.


General Evaluation

  1. List five general effects of pests and diseases on plant and animals.
  2. State four ways of controlling pests and diseases.
  3. Mention five examples of fungal disease.
  4. Differentiate between a pest and a pathogen.
  5. State five economic importance of pests



  1. Which of these is not a pest of crop? (a) Insect (b) Birds (c) Ticks (d) None of the above
  2. The following are viral diseases except (a) under pest   (b) coccidiosis   (c) new castle     (d) none of the above
  3. The following except one are cultural ways of controlling pests (a) Regular weeding (b) early planting    (c) crop rotation    (d) use of lethal chemicals
  4. Which of these is not an endoparasite? (a) Round worm     (b) Louse     (c) Liver fluke     (d) Tape worm
  5. Neck twisting, paralysis and nervous disorder are marked symptoms of (a) rinder pest     (b) coccidiosis      (c) new castle     (d) ringworm



  1. Define the following terms (a) pest     (b) parasite     (c) diseases    (d) resistant varieties
  2. Discuss one plant and one animal disease each caused by (a) virus (b) bacteria     (c) protozoan


See also






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