Insecticides: Definition, Types, Classification and Disadvantages
Namrata Das
Exams Prep Master
Insecticides are chemicals that are used to control insects by killing or preventing
them from engaging in undesirable or destructive behaviours. Insecticides are
classified based on their structure and mode of action. There are many insecticides
that act upon the insect’s nervous system, while others act as growth regulators
or endotoxins. Such substances are generally used in order to control pests that
infest cultivated plants or to reduce disease-carrying insects in specific areas. Let’s
learn more about the topic and discuss some important questions.
Table of Content
1. What are Insecticides?
2. Classification of Insecticide
3. Types of Insecticide
4. Classification of Insecticide based on Chemical Nature
5. Disadvantages of Insecticide
6. Things to Remember
7. Sample Questions
Keyterms: Insecticides, Indsects, Nervous system, Endotoxins, Plants, Growth
regulator, Agriculture, Medicine, Industry, Food chain
Read More: Maltose
What are Insecticides?
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The substances that are used to kill insects are called insecticides. They have a
wide application in the field of agriculture, medicine, and industry and have the
potential to alter ecosystem components primarily and are toxic to animals and
humans as well. Few of the insecticides become concentrated as they spread in
the food chain.
Insecticides
Read More: Polyamides
Classification of Insecticide
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Insecticides are classified as organic and inorganic depending on the
chemical composition.
They are classified as stomach poisons, contact poisons, fumigant poisons,
and systemic poisons based on the mode of entry in the insects.
Insecticides are classified as physical poisons, nerve poisons, respiratory
poisons, protoplasmic poisons, general poisons, and chitin inhibitors based on
the mode of action.
Depending on toxicity, they are classified into four types:
1. Extremely toxic – Colour: red, oral LD50: 1-50, symbol: skull and
poison
2. Moderately toxic – Colour: blue, oral LD50: 501 – 5000, symbol:
danger
3. Highly toxic – Colour: yellow, oral LD50: 51 – 500, symbol: poison
4. Less toxic – Colour: green, oral LD50: >5000,symbol: caution
They are classified as ovicides, pesticides, larvicides, and adulticides based
on the stage of specificity.
Classification of Insecticide
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Types of Insecticide
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Below mentioned are the three different types of insecticides.
1. Systemic – Systemic insecticides are the type of insecticide that is
introduced into the soil to get absorbed by the plant roots and once the
insecticide enters the roots, it moves to external areas such as fruits, twigs,
leaves and branches. It acts as a poison to any insect that comes to chew the
plant and forms a layer on the plant surface area.
2. Ingested – Few of the examples of ingested pesticides are roaches and rats.
3. Contact – Contact insecticides are the type of insecticides that act like
bullets as they aim only at a particular target to kill insects by its application
and usually, household insect spray works like contact insecticides as it is
directly hit at the insect.
Types of Insecticide
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Classification of Insecticides based on Chemical Nature
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Insecticides are classified into four groups based on their chemical nature.
1. Organic insecticides
2. Synthetic insecticides
3. Inorganic insecticides
4. Miscellaneous compounds
Synthetic Insecticides and Natural Insecticides
A major organic chemistry's emphasis is given to developing chemical tools to
enhance agriculture's productivity and insecticides can also represent a
main area of emphasis. Along with this, various major insecticides are inspired by
biological analogues, where many others are not found in nature.
Below listed are some important Synthetic and natural insecticides. 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" and for this, he was awarded the 1948 Nobel
Prize for Medicine or Physiology, and it was introduced in 1944. Organochlorides
also function by opening the sodium channels in the nerve cells of the insect and
the contemporaneous chemical industry rise, which is facilitated by the large-scale
production of DDT and related to the chlorinated hydrocarbons.
Organochlorides
Read More: Copolymers
Carbamates and Organophosphates
Organophosphates are the other large class of contact insecticide types and they
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.
Carbamates and Organophosphates
Read More: Synthetic Polymers
Chemical Warfare
Nerve agents such as tabun, sarin, soman, VX and Organophosphate insecticides
work in the same way and they have a cumulative toxic effect on wildlife. Hence,
the multiple exposures to the chemicals amplify toxicity and Organophosphate use
declined with the rise of substitutes in the US.
Carbamate Insecticides
Such have a much shorter action duration and are somewhat less toxic and contain
similar organophosphates.
Pyrethroids
Pyrethroid pesticide types mimic the natural compound pyrethrum's insecticidal
activity, which is the biopesticide found in pyrethrins and are less toxic compared to
carbamates and organophosphates. Along with this, these compounds are the
nonpersistent sodium channel modulators, Compounds present in this group are
often applied against household pests.
Pyrethroids
Read More: Sulphonation
Disadvantages of Insecticides
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1. Non-target organisms – Insecticides can kill more than intended organisms
and are risky to humans and when these insecticides mix with water sources
through drift, leaching, or runoff, they harm aquatic wildlife. Birds when
drinking such contaminated water and eating affected insects then they die.
Few examples of insecticides such as 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 and
the reproduction in insects is so quick that they produce a new generation
every three to four weeks and because of this, the resistance builds up
rapidly.
Read More: Diazotisation
Things to Remember
The substances that are used to kill insects are called insecticides. They have
a wide application in the field of agriculture, medicine, and industry and
have the potential to alter ecosystem components primarily and are toxic to
animals and humans as well.
Systemic insecticides are the type of insecticide that is introduced into the
soil to get absorbed by the plant roots and once the insecticide enters the
roots, it moves to external areas such as fruits, twigs, leaves and branches.
Contact insecticides are the type of insecticides that act like bullets as they
aim only at a particular target to kill insects by its application and usually,
household insect spray works like contact insecticides as it is directly hit at
the insect.
One of the best-known organochlorines is given as DDT, which was created
by the Swiss scientist named "Paul Müller" and for this, he was awarded the
1948 Nobel Prize for Medicine or Physiology, and it was introduced in 1944.
