Classification and Disadvantages of 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 in Chemistry: Types, Uses, and Regulations
1. What is an insecticide, and how does it differ from a pesticide?
An insecticide is a chemical substance specifically formulated to kill, harm, repel, or mitigate one or more species of insects. A pesticide is a broader term for any substance used to control pests, which includes not only insects but also weeds (herbicides), fungi (fungicides), and rodents (rodenticides). Therefore, all insecticides are pesticides, but not all pesticides are insecticides. For example, Malathion is an insecticide, whereas glyphosate is a herbicide, but both are considered pesticides.
2. How are insecticides classified based on their chemical structure? Please provide examples.
Insecticides are most commonly classified by their chemical nature, which determines their properties and mode of action. The major classes include:
- Organochlorines: These are chlorinated hydrocarbons that are highly stable and persistent in the environment. Examples include DDT (Dichlorodiphenyltrichloroethane) and BHC (Benzene hexachloride).
- Organophosphates: These are esters of phosphoric acid and are generally more toxic but less persistent than organochlorines. Examples include Malathion and Parathion.
- Carbamates: These are derivatives of carbamic acid that function similarly to organophosphates but are generally less toxic to mammals. An example is Carbaryl.
- Pyrethroids: These are synthetic analogues of pyrethrins, which are naturally found in chrysanthemum flowers. They are potent and fast-acting. An example is Allethrin.
3. What is the difference between selective and non-selective insecticides?
The primary difference between selective and non-selective insecticides lies in their target range. A selective insecticide is toxic to a very specific or narrow range of insect species, posing minimal risk to non-target organisms like beneficial insects (e.g., bees, ladybugs) or other animals. In contrast, a non-selective (or broad-spectrum) insecticide is effective against a wide variety of insect species, which can be detrimental to the local ecosystem by eliminating both pest and beneficial populations.
4. What are the main uses of insecticides in agriculture and public health?
Insecticides serve critical functions in two major sectors:
- Agriculture: Their primary use is to protect crops from insect pests that can significantly reduce yield, damage produce, and transmit plant diseases. This ensures food security and maintains the economic viability of farming.
- Public Health: They are essential for controlling insect vectors that transmit diseases to humans. For instance, insecticides are used to kill mosquitoes carrying malaria, dengue, and Zika virus, and fleas that can transmit the plague.
5. How does a common class of insecticides, like organophosphates, actually work to kill an insect?
Organophosphates function as potent nerve poisons by irreversibly inhibiting an essential enzyme in the nervous system called acetylcholinesterase (AChE). Normally, the neurotransmitter acetylcholine transmits a nerve impulse across a synapse and is then immediately broken down by AChE to terminate the signal. By blocking AChE, organophosphates cause a toxic accumulation of acetylcholine. This leads to continuous and uncontrolled nerve firing, resulting in tremors, convulsions, paralysis, and ultimately, the death of the insect due to respiratory failure.
6. What is the significance of distinguishing between biodegradable and non-biodegradable insecticides?
This distinction is critical for understanding an insecticide's environmental impact.
- Non-biodegradable insecticides, such as the organochlorine DDT, are resistant to breakdown by natural processes. They persist in the environment for years, accumulating in soil and water. This leads to biomagnification, where their concentration increases up the food chain, causing long-term harm to wildlife and humans.
- Biodegradable insecticides, like organophosphates and carbamates, are broken down relatively quickly by microorganisms and other environmental factors into less harmful substances. Using them helps minimise long-term ecological damage, which is why they are generally preferred in modern agriculture and pest control.
7. What is insecticide resistance, and how does this phenomenon occur?
Insecticide resistance is the evolved ability of a pest population to survive exposure to a dose of insecticide that was previously lethal. It is a classic example of natural selection in action. When an insecticide is first applied, it kills most of the susceptible insects. However, a few individuals with random genetic mutations may be naturally less affected. These survivors reproduce, passing their resistant genes to their offspring. With each subsequent application of the same chemical, the proportion of resistant individuals in the population grows, until the insecticide becomes largely ineffective.
8. What are the key regulations governing the manufacturing and use of insecticides in India?
In India, the entire lifecycle of insecticides—from import and manufacture to sale and use—is regulated by the Insecticides Act of 1968 and the supporting Insecticides Rules of 1971. The primary regulatory body established under this act is the Central Insecticides Board and Registration Committee (CIBRC). According to these regulations, no insecticide can be legally sold or used in the country without first being registered with the CIBRC, which assesses its efficacy and safety for humans, animals, and the environment as per the 2025-26 guidelines.
9. Why is it so important to regulate insecticides, even though they are beneficial for crop protection?
Regulation is crucial because insecticides are, by design, toxic substances. While they provide immense benefits, their misuse or overuse can lead to severe negative consequences. Proper regulation helps to:
- Prevent Human Health Risks: Protects farmers from occupational exposure and consumers from harmful pesticide residues in food.
- Safeguard the Environment: Minimises harm to non-target species, including essential pollinators like bees, birds, and aquatic life.
- Manage Resistance: Slows the development of insecticide-resistant pests by promoting responsible usage patterns.
- Avoid Food Chain Contamination: Restricts the use of persistent chemicals that can accumulate in the food chain.
10. Besides the intended effect on pests, what are some major unintended environmental impacts of insecticides?
The use of insecticides can trigger a cascade of unintended environmental effects. Key impacts include:
- Harm to Pollinators: Broad-spectrum insecticides can decimate populations of bees, butterflies, and other pollinators, threatening both natural ecosystems and the yield of many agricultural crops.
- Water and Soil Contamination: Runoff from treated fields can carry insecticides into rivers, lakes, and groundwater, harming aquatic organisms and killing beneficial soil microbes essential for fertility.
- Secondary Pest Outbreaks: By killing the natural predators of pest insects, insecticides can sometimes lead to a resurgence of the target pest or an outbreak of a different, secondary pest.
- Biomagnification: Persistent chemicals can build up in the fatty tissues of organisms, becoming more concentrated at higher trophic levels and causing reproductive failure or death in top predators like birds of prey.
