Pests are defined as any organism capable of reducing the crop quality and quantity leading to huge economic damage. Pest invasion is a very huge threat in agriculture, either crop production or animal production, though very common in crop production.
Pests are capable of causing tremendous economic damage in a commercial farm.

Not only their attack is fatal but they are also vectors or carriers of destructive diseases like mosaic in cassava, tomato and yam caused by white flies, thrip and aphids on the course of their feeding. Insect pests are the most successful class in animal kingdom, more than 70% of animals are of the class, insecta. Insects are widespread with notable features such as:
  • Possession of compound eyes.
  • They have six feet.
  • They are divided into 3 cavities namely the head; thorax and abdomen.
  • They breath with spiracles.
  • They have exoskeleton or chitin, which protects the body cavity from being killed easily.
  • They have haemocheal which is the fluid flowing in their body.
Reproduction of insect has to be mentioned because each stage has a major role it plays in the act of causing damage. Insects have two main forms of reproduction namely:
1. Complete metamorphosis
2. Incomplete metamorphosis.
Insects that possess complete metamorphosis have four stages of reproduction which are from the eggs to larvae to pupa and finally to adult, insects belonging to this category are butterflies, beetle etc. The ones with the incomplete form of reproduction have just three stages of reproduction which are from the eggs to the nymph and finally the adult, examples of insects with this form are grasshoppers, aphids etc.
The fascinating thing is that some insects are destructive at their larvae stage but beneficial at their adult stage examples are the butterfly and moth. Also, some are destructive at both their larvae and adult stage example is the beetle. The larvae also known as grub has the same destructive effective as the adult beetle that feeds on leaves and also bore holes.
Another consideration to take note about insects to know the exact insect causing a damage is the modification of their mouth. This is how their mouth is designed by nature, it is worth considering because their mouth is their main instrument.
The modifications of insect mouth are:
1. Biting and chewing.
2. Piercing and Sucking.
3. Boring.
Insects with biting and chewing mouth are the ones that often feed on the plant leaves. They are defoliators. They defoliate the plant leaves by biting and chewing the leaves, exposing the plant to fungi attack. A good example is the larvae of butterfly, also know as caterpillar, is a leaf eater and can be as voracious as the adult grasshopper. Also, the elegant grasshopper(Zonocerus variegatus) is a leaf defoliator, they are sometimes voracious that they can eat up the shoot portion of the plant. Examples of insects in this category are the leave beetle, grasshopper, leaf skeletonizer, leaf worm etc.
Piercing and sucking insects are the type of insects which pierce the succulent part of the plant and suck the sap juice of the plant thereby reducing the plants vigour. Aphids (Aphids crassivora) are most popular insect of this category, after sucking the sap juice they also transmit viral disease called mosaic in tomato, cassava and yam. Also thrip and cotton strainer belong to this category.
The boring insects are the type of insects that bore into the plant system or the soil before carrying out their nefarious activities. The maize stem borer (Busseola fusca) and sugar cane stalk borer (Eldana saccharina) are larva of moth. The larva bore through the stem of the crops causing lodging of the plant. Adult moth is a harmless insect that is only active in the night.
Harmful effects of insects.
After knowing the metamorphosis and mouth modifications of insects, it will be easier to identify the type of insect disturbing the farm. This will aid good decision making on the type of control measure to be adopted. These are some of the destructive activities of insects, once you observe any of these in your farm; you can easily identify the real insect doing it.
  • Sucking of the sap juice of the plant, thereby reducing the plant vigour: This is done chiefly by Aphids and thrips.
  • Defoliation of plant leaves: This is done by grasshopper, leaf beetles, leaf worm.
  • Feeding on underground root system: this is done by termites.
  • Feeding on the stem trunk of plant causing lodging: This is done by stem borers.
  • Reducing photosynthetic late by forming wooly substance: this is done by mealy bugs.
  • Contamination of stored products: this is done by weevils.
  • Discoloration of the leaves: this is done by mealy bugs.
  • Destruction of plant flowers: This is done by cotton strainer and thrips.
  • Eating parts of the leaves through the lamina: This is done by caterpillars.
  • Reduction of quality of fruits: This is done by Fruit flies, fruit worms.
  • Reduction of quantity and quality of stored products: This is done by weevils.
  • Damage of planting materials: This is done by weevils.
Control of insect pests.
These pests can be controlled using different methods, some of which are:
  • Use of insecticides, this may be organic or synthesized or inorganic insecticides. Learn how to make organic insecticide HERE.
  • Proper tillage of soil: this is the adoption of conventional tillage practise, the soil are greatly pulverized. The insects eggs would be exposed to undesirable weather conditions leading to their death.
  • Use of resistant variety.
  • Pruning and thinning of plant: infected plants should be pruned or thinned to avoid further infection to healthy crops.

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