Chemistry in Everyday Life

Insecticides

Insecticides are substances that are in use to kill insects. Insecticides include ovicides and larvicides. These are in use against insect eggs and larvae. Insecticides are in use in the field of agriculture, medicine, industry and consumers. Insecticides are the major factor behind the increase in agricultural productivity. Nearly all insecticides have the ability to significantly alter ecosystems. Many of the insecticides are toxic to humans and animals. Some issues become concentrated as they spread along the food chain.

Insecticides

Introduction to Insecticides

Insecticides are divided into two major groups. These groups are systemic insecticides, which have residual or long term activity. Another is contact insecticides; these insecticides have no residual activity.

The mode of action shows how the insecticide kills or inactivates. It gives another way of dividing insecticides. Mode of action looks after whether an insecticide will be toxic to unrelated species, such as fish, birds and mammals.

Insecticides are repellent or non-repellent. Social insects like ants cannot detect non-repellents. Ants readily crawl through insecticides. As ants return to the nest, they take insecticide with them and transfers it to their nestmates. With time, this eliminates all of the ants including the queen and usually completely eradicates the ant colony. Insecticides are distinct from non-insecticidal repellents that are it repel but do not kill.

Types of Insecticides

There are three different types of insecticides as follows:

  1. Systemic insecticide – This type of insecticide is given into the soil for it to get easily absorbed by the plant roots. Once the insecticide enters the roots, it moves to external areas such as leaves, fruits, flowers, twigs, stem and branches. It forms a protecting layer on the plant surface area and acts as a poison to any insect. This surface area protects the plant from the insect that comes to chew the plant.
  2. Ingested insecticide – Some examples of ingested pesticides are rat, roach and many more.
  3. Contact insecticide – These types of insecticides act like bullets. These bullets aim only at a particular target to kill insects by their application. Generally, household insect spray works like contact insecticides as if it directly hits the insect that is in the target.

Classification of Insecticide based on:

  • Chemical composition: This insecticide is classified as organic and inorganic.
  • The mode of entry in the insects: This insecticide is classified as contact poisons, fumigants poisons, stomach poisons, and systemic poisons.
  • The mode of action: This insecticide is classified as physical poisons, nerve poisons, respiratory poisons, protoplasmic poisons, general poisons, and chitin inhibitors.
  • 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
  • The stage of specificity. This insecticide is classified as ovicides, pupicides, larvicides, and adulticides.

FAQs on Insecticides

Question 1: How are insecticides classified based on chemical nature?

Answer: Based on the chemical nature of insecticides, these are classified into four groups as follows:

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

Question 2: What are the disadvantages of insecticides?

Answer: Few disadvantages of insecticides are given below:

  1. Non-target organisms – Insecticides can kill more than targeted organisms. Insecticides are risky to humans and animals. Also, when insecticides are added to water sources through leaching, drift, or runoff, they harm aquatic wildlife. When birds drin9k such contaminated water or even eat affected insects, they die. Some examples of insecticides, like DDT (Dichlorodiphenyltrichloroethane). Dichlorodiphenyltrichloroethane was banned in the US because it affects the reproductive abilities of predatory birds.
  2. Resistance – Insects when again and again exposed to insecticides build up resistance. Because of this, sometimes they have little or no effect at all. The reproduction in insects is so fast that they produce a new generation every three to four weeks. That’s why the resistance builds up rapidly.
  3. Diseases – People who work regularly with insecticides, such as farmers, are at greater risk of cancer. Thousands of non-lethal poisonings and cancer cases each year are due to insecticides and pesticides.
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