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 fumigants 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, Colour: green, oral LD50: >5000
Moderately toxic – Symbol: danger, Colour: blue, oral LD50: 501 – 5000,
Highly toxic – Symbol: poison, Colour: yellow, oral LD50: 51 – 500,
Extremely toxic – Symbol: skull and poison, Colour: red, oral LD50: 1-50
Types of Insecticides
There exist 3 different types of insecticides. They are listed as follows.
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 acts as a poison to any insect that comes to chew the plants.
A few examples of the ingested pesticides type can be given as roaches and rats.
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:
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.
One of the best-known organochlorides 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.
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.
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.
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.