Pesticides can be grouped according to the types of pests which they kill:

  • Insecticides - insects
  • Herbicides - plants
  • Rodenticides - rodents (rats and mice)
  • Bactericides - bacteria
  • Fungicides - fungi
  • Larvicides - larvae
Fig.  5.23: Some well known insecticide containers
Fig. 5.23: Some well known insecticide containers

There are also other ways to group pesticides. For example, they can be grouped according to the chemicals in them or to the method of application.

7.1 How pesticides enter animals and plants

Insecticides

It is important to know the target insect's habits when choosing the insecticide and which form (solid, liquid, granule or aerosol) to use. For example, flying pests such as adult mosquitoes are best attacked by aerosol sprays or fogs (droplets in the air), while crawling insects are best treated with surface powders, sprays or granules for dermal and/or oral entry.

Insecticides kill insects by getting inside their bodies where they then act as poison.

There are three different ways insecticides can get into an insect body.

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These are:
  • Dermal Entry

    The insecticide enters the body through the skin. In insects, the skin is called the cuticle. Insecticides of this kind are called contact poisons.

    Dermal entry can happen when:
    • aerosol spray droplets hit the insect
    • insects walk over and thereby come into contact with powder or granule forms of insecticide
Fig.  5.24: Dermal entry.
Fig. 5.24: Dermal entry.

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  • Oral Entry

    The insecticide enters the body through the mouth when the insect eats it. Insecticides of this type are called ingested poisons. The insecticide may be ingested by the insect:
    • as a poisonous bait ( a food to which insecticide has been added)
    • when it 'grooms' (cleans) itself after the poison comes into contact with its body
Fig.  5.25: Oral entry.
Fig. 5.25: Oral entry.
  • Respiratory EntryT

    The insecticide is breathed in by the insect. These insecticides are called inhaled poisons.

    Insects do not breathe through the mouth as most animals do. They breathe through spiracles (small holes along the side of the abdomen).
Fig.  5.26: Respiratory entry
Fig. 5.26: Respiratory entry.

Herbicides

Herbicides are used to kill plants. This may be by:
  • killing that part of the plant which they touch
  • killing the plant when they are absorbed into it through the leaves, stems or roots

Rodenticides

Rodenticides are used to kill rodents. These poisons are usually put into food to make poisonous baits which rodents eat.