Dhristi JEE 2022-24

An Introduction to Insecticides

The population of insects is estimated to be a lot more than all the big creatures that we can see easily. They are a very essential creation of nature that can be found in all the habitable regions of earth. Though all of them play a role in the balance of nature as we experience it, from the context of humans they can be either beneficial, harmful, or neutral. Like any other living being they also need food for their survival and are always searching for it. It can be either a herbivore consuming on materials available from plant source or can be a predator hunting down other smaller insects. 


They are also sometimes parasites that stay associated with their hosts for their survival. This is the diversity of nature but as humans what we are worried about is their conflict with us for the  access to natural resources for our survival. Or sometimes they can directly affect the health of our body or the environment surrounding us. Insects are notoriously known to destroy the crops that we create and affect the agricultural and economic system of our society. 


They also affect the livestock of farmers that we raise as a source of food products. Several diseases are also caused due to them which becomes a financial burden. So in order to prevent these mishappenings to occurring, we use various kinds of chemicals. These chemicals can be natural or artificial that can stop the growth of such insects in the crop field, animal houses or even inside our homes. Such types of chemicals are known as insecticide. There are various insecticides and pesticides available in the market under the name of various brands. Some insecticides are banned in different regions of the country after the discovery of harmful effects on our environment.


What are Insecticides?

The substances that can be used to kill insects are referred to as insecticides. Insecticides consist of a wide application in various fields such as agriculture, medicine, and industrials. They also have the potential to alter the components of the ecosystem primarily, and they are toxic to animals and humans as well. As they spread in the food chain, a few insecticides become concentrated.


Classification of Insecticides

Let us look at the classification of insecticide in detail.

  • Depending on the chemical composition, it can be classified into 2 types - organic and inorganic.

  • The mode of action can be classified into various poisons such as nerve poisons, physical poisons, protoplasmic poisons, respiratory poisons, chitin inhibitors, and general poisons.

  • Depending on the mode of entry in insects, it can be classified into fumigant poisons, contact poisons, systemic poisons, and stomach poisons.

  • Depending on the specificity stage, it can be classified as pupicides, ovicides, adulticides, and larvicides.

  • Depending on the toxicity level, it can be classified into 4 types, as listed below:

    • Less toxic – Symbol: caution, Color: green, oral LD50: >5000

    • Moderately toxic – Symbol: danger, Color: blue, oral LD50: 501 – 5000,

    • Highly toxic – Symbol: poison, Color: yellow, oral LD50: 51 – 500,

    • Extremely toxic – Symbol: skull and poison, Color: red, oral LD50: 1-50


Types of Insecticides

There exist 3 different types of insecticides. They are listed as follows.

  • Systemic Insecticides: 

This type of insecticide has been introduced into the soil. Moreover, it is for the soil to get absorbed by the roots of plants. Once the insecticide enters the roots, it moves to the external areas such as fruits, leaves, branches, and twigs. It then forms a layer on the plant surface area and will act as a poison to any insect that comes to chew the plants.

  • Ingested Insecticides: 

A few examples of the ingested pesticides type can be given as roaches and rats.

  • Contact Insecticides: 

These types of insecticides act as bullets that aim only at a specific target to kill the insects with the help of its application. In general, the household insect spray works like a contact insecticide because it must directly hit the insect.


Insecticides Classification based on Their Chemical Nature

Depending on the chemical nature, the insecticides are classified into 4 groups, which are listed below:

  • Organic insecticides

  • Synthetic insecticides

  • Inorganic insecticides

  • Miscellaneous compounds


Synthetic Insecticides and Natural Insecticides

A major organic chemistry's emphasis is given to developing chemical tools to enhance agriculture's productivity. Insecticides can also represent a main area of emphasis. Several major insecticides are inspired by biological analogues, where many others are not found in nature. Some important Synthetic and natural insecticides are listed below. Let us briefly understand these.


Organochlorides

One of the best-known organochlorines is given as DDT, which was created by the Swiss scientist named "Paul Müller." He was awarded the 1948 Nobel Prize for Medicine or Physiology for this discovery, and it was introduced in 1944. It also functions by opening the sodium channels in the nerve cells of the insect. The contemporaneous chemical industry rise, which is facilitated by the large-scale production of DDT and related to the chlorinated hydrocarbons.


Carbamates and Organophosphates

Organophosphates are the other large class of contact insecticide types. These can also target the nervous system of the insects. These interfere with the acetylcholinesterase enzymes and other cholinesterases, disrupting the nerve impulses and disabling or killing the insect. 


Chemical warfare nerve agents such as tabun, sarin, VX, soman, and Organophosphate insecticides work in the same way. These have a cumulative toxic effect on wildlife. Hence, the multiple exposures to the chemicals amplify toxicity. Organophosphate use declined with the rise of substitutes in the US.


Carbamate insecticides contain similar organophosphates, but they have a much shorter action duration and are somewhat less toxic.


Pyrethroids

Pyrethroid pesticide types mimic the natural compound pyrethrum's insecticidal activity, which is the biopesticide found in pyrethrins. These particular compounds are the nonpersistent sodium channel modulators, and they are less toxic compared to carbamates and organophosphates. Compounds present in this group are often applied against household pests.


Disadvantages of Insecticides

Let us look at a few disadvantages of insecticides, as listed below.

  • Resistance: 

When the insects repeatedly exposed to the insecticides build up resistance until finally, they contain either a little or no effect at all. The insect's reproduction is much quicker - they are capable of producing a new generation every 3 to 4 weeks. Thus, the resistance builds up rapidly.

  • Non-target Organisms: 

Here, the insecticides will kill more than the intended organisms, which are risky to humans. Besides, when these insecticides get mixed with water sources through drift, leaching, or runoff, they result in harming the aquatic wildlife. When birds drink this contaminated water and eat the affected insects, they also die. A few examples of insecticides, such as DDT, were banned in the US because it affects the predatory birds' reproductive abilities.

FAQs on Insecticides

1. What are Ryanoids?

Ryanoids are the synthetic analogues with the same mode of action as ryanodine, which is a naturally occurring insecticide extracted from Ryania speciosa (a Salicaceae). They bind to the calcium channels in skeletal and cardiac muscle by blocking the nerve transmission. Rynaxypyr was the first insecticide to be registered from this class, where the generic name is given as chlorantraniliprole.

2. Give the Environmental Effects on Non-target Species?

A few insecticides harm or kill the other creatures in addition to those they are intended to kill. For example, birds can be poisoned when they eat food, which is recently sprayed with insecticides. The birds mistake an insecticide granule on the ground for food and eat it. The sprayed insecticide can drift from the area to which it is applied and into the wildlife areas, especially when sprayed aerially.

3. Explain about a Pesticide?

Any product that kills the pests are called pesticides. In general, this word refers to agricultural chemicals, which can be used to destroy the pests that threaten food crops' mass production. However, they can also be used to describe flea powder, fly spray, or in reality, any pests killer that is regarded as a nuisance to animals we live with or humanity.

4. What is Pesticide Resistance Mean?

When the species of pests become allowed to live in a pesticide-rich environment, the surviving individuals reproduce. Their offspring in turn are more resistant to the pesticide.


Resultantly, farmers and others must use much stronger concentrations of pesticides to achieve similar results. As Sierra mentioned, it is like a forced evolution.

5. What is the difference between selective insecticide and non-selective insecticide?

The artificial and naturally derived chemicals that kill insects are known as insecticides. It can be selective by targeting a particular type or group of insects. But there are also several insecticide chemicals which do not target any specific type or species of insects and can kill all the insects in the area it is applied. Both the types of insecticides are used in agriculture. But  care must be taken while using non- selective chemicals for it can kill beneficial insects present in a crop field.

6. What is the difference between an insecticide and a pesticide?

As we learnt in this chapter, the insecticides are those chemicals that are used for preventing the insects from spreading in the regions of our interest. But there are also some harmful factors or organisms in our crop fields or environment that are not essentially insects. It can be anything among the various categories that we study in the biological taxonomy of animals. It can be a snail or any rodent like rat that destroys the crops too. These animals including insects are termed as pests. So all the chemicals that we use to kill these pest animals as well as insects are together termed as pesticides.

7. What are weedicides?

Mankind has developed agriculture by selecting certain types of fruits and grains that are edible and suitable for our consumption. But there are also other types of plants in the wild that also grow in the field. These wild varieties of plants are usually more adaptable to the natural environment than the domesticated crops. It also competes with the domesticated crops for land, space, water, nutrition, carbon dioxide, light and everything else. This in turn results in the low productivity of the crops and incurs loss for the farmer. So it is essential to remove these plants. It is also done by the application of certain types of chemicals known as Weedicides.

8. Why are there so many insecticides available in the market?

Insecticides are applied in the crop fields and other areas to get rid of the insects which disrupt the peaceful existence of humans. The chemical does this job by getting inside the body of insects and killing it acting like a poison. But in some cases it has been observed that over time insects build resistance against such Insecticides. The chemical formulas no longer remain effective against such insects. So various research units and companies develop new chemical formulas for their control.

9.  What is the use of this article on Insecticides?

The articles on the website of Vedantu are according to various topics taught in the classes of every class. The subject matter available in the course Book is  sometimes not sufficient for the in depth study of the topic. So the subject experts at Vedantu have prepared each topic with precise and accurate facts for the students. Any student can read these articles on various topics for a general understanding. They can also download these articles from the provided link.

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