What are insecticides?

Substances which are used to kill insects are called insecticides. Insecticides have a wide application in the field of medicine, agriculture, and industry. They have the potential to alter ecosystem components majorly and are toxic to animals as well as humans. Some insecticides become concentrated as they spread in the food chain.

Table of Contents

Classification of insecticide

        • Based on chemical composition, it is classified as organic and inorganic.
        • Based on the mode of entry in the insects, it is classified as contact poisons, fumigants poisons, stomach poisons, and systemic poisons.
        • Based on the mode of action, it is classified as physical poisons, nerve poisons, respiratory poisons, protoplasmic poisons, general poisons, and chitin inhibitors.
        • Based on toxicity, it is classified into four types:
          1. Extremely toxic – Colour: red, symbol: skull and poison, oral LD50: 1-50
          2. Moderately toxic – Colour: blue, symbol: danger, oral LD50: 501 – 5000
          3. Highly toxic – Colour: yellow, symbol: poison, oral LD50: 51 – 500
          4. Less toxic – Colour: green, symbol: caution, oral LD50: >5000
        • Based on the stage of specificity, it is classified as ovicides, pupicides, larvicides, and adulticides.

Types of insecticides

There are three different types of insecticides. They are

        1. Systemic – This type of insecticide is introduced into the soil for it to get absorbed by the plant roots. Once the insecticide enters the roots, it moves to external areas such as leaves, fruits, twigs, and branches. It forms a layer on the plant surface area and acts as a poison to any insect that comes to chew the plant.
        2. Ingested – Some examples of ingested pesticides are rats and roaches.
        3. Contact – These types of insecticides act like bullets that aim only at a particular target to kill insects by its application. Usually, household insect spray works like contact insecticides as it must directly hit the insect.

Classification of insecticides based on chemical nature

Based on their chemical nature, insecticides are classified into four groups:

        1. Organic insecticides
        2. Synthetic insecticides
        3. Inorganic insecticides
        4. Miscellaneous compounds

Disadvantages of insecticides

        1. Non-target organisms – Insecticides can kill more than intended organisms and are risky to humans. Also, when insecticides mix with water sources through leaching, drift, or run off, they harm aquatic wildlife. When birds drink such contaminated water and eat affected insects, they die. Some examples of insecticides, like DDT, were banned in the US as it affects the reproductive abilities of predatory birds.
        2. Resistance – Insects when repeatedly exposed to insecticides build up resistance until finally, they have little or no effect at all. The reproduction in insects is so quick that they produce a new generation every three to four weeks. Therefore, the resistance builds up rapidly.

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