Organophosphorus insecticides

Organophosphorus insecticides (OPIS) are a group of chemical substances containing phosphorus in their molecules, widely used for protecting plants from various pests. These insecticides work by inhibiting essential enzymes in the insect’s body, leading to paralysis and death of the pests. They have had a significant impact on agriculture, providing effective protection against a wide range of insects.

Goals and importance in agriculture and horticulture

The primary goal of using organophosphorus insecticides is to increase agricultural productivity by protecting plants from pests such as insects, mites, and other parasites. In horticulture and gardening, they are used to protect crops such as fruits, vegetables, and ornamental plants. These insecticides significantly reduce damage from insect pests, leading to better quality and larger crop yields.

Relevance of the topic

The study and proper use of organophosphorus insecticides is a relevant topic, as the effective and safe use of these products requires careful attention. Incorrect use or over-application can lead to resistance in insects, as well as negatively impact the environment and human health. Awareness of organophosphorus insecticides is important for minimizing risks and ensuring agricultural sustainability.

The history of organophosphorus insecticides (OPIS)

Organophosphorus insecticides (OPIS) play a key role in pest control and are an important part of agriculture and forestry. Their history began in the first half of the 20th century when scientists started to explore organophosphorus compounds, aiming to create more effective and long-lasting plant protection agents.

1. Early research and discoveries

The first wave of interest in organophosphorus compounds occurred in the 1930s when scientists began to explore phosphorus-containing chemicals as potential means to destroy insect pests. Initial experiments with organophosphorus compounds were focused on developing safer alternatives to organochlorine insecticides, such as ddt. At that time, phosphorus-containing chemicals demonstrated high toxicity to insects, making them potentially effective protection agents.

2. The first commercially successful organophosphorus insecticides

In the 1940s, amid world war ii, organophosphorus compounds attracted the attention of the military as chemical agents for combating pests, including insects. After the war, commercial research based on military developments began, aimed at applying organophosphorus insecticides in agriculture. In 1947, the first commercial organophosphorus insecticide — malathion — appeared, quickly becoming popular due to its high effectiveness against a wide range of insects. It was used in agriculture and to protect human health from insect-borne diseases.

3. Development and use

Since the early 1950s, organophosphorus insecticides became widely used in agriculture. They provided higher toxicity to insects than many previously used organochlorine compounds, such as ddt. Opis became popular in the fight against pests, such as insect pests on various crops, including cotton, tobacco, vegetables, and fruits. Some of the most well-known compounds in this group include parathion, diazinon, and chlorpyrifos.

4. Safety and ecological issues

Although organophosphorus insecticides were effective, their use led to new ecological and toxicological problems. These compounds exhibited high toxicity not only to insects but also to other organisms, including beneficial insects like bees and animals. The high volatility and ability of organophosphorus insecticides to accumulate in ecosystems, polluting soil and water bodies, became significant issues. As a result, many of these compounds were subjected to restrictions and bans in certain countries starting in the late 1970s.

5. Modern approaches and challenges

Today, organophosphorus insecticides remain widely used; however, their application is limited due to environmental and safety concerns. Issues with insect resistance, resistance to organophosphorus insecticides, and their declining effectiveness have become major concerns in modern plant protection. To prevent the development of resistance, scientists are actively developing new compounds and methods, combining organophosphorus insecticides with biological and mechanical pest control methods.

Thus, the history of organophosphorus insecticides is a journey from revolutionary discoveries and successful applications to the recognition of their ecological and toxicological problems, which led to the search for safer and more sustainable methods of plant protection.

Classification

Organophosphorus insecticides are divided into several groups based on chemical structure, mechanism of action, and impact on insects. These include:

1. Organophosphates – the most common group of organophosphorus insecticides, including substances such as malathion, parathion, and diazinon. They work by inhibiting acetylcholinesterase activity, disrupting the transmission of nerve impulses in insects.
2. Phospho-organic esters – chemicals where phosphorus is bonded to carbon via an ester link, such as triexpen and pyraclophene.
3. New classes of organophosphorus compounds – synthetic compounds, such as isopropylamine salts and piperazines, with specific mechanisms of action and high resistance to external conditions.

1. By chemical structure

Organophosphorus insecticides can be classified by the structure of their molecules, which determines their physicochemical properties and activity against different species of insects.

• Aliphatic organophosphorus insecticides: these chemical compounds contain carbon chains in their structure. An example is malathion (one of the first products using organophosphorus compounds to protect plants).
• Aromatic organophosphorus insecticides: these insecticides have an aromatic ring containing phosphorus atoms. An example is trimethaphos.
• Chlorinated organophosphorus insecticides: in these products, phosphorus is connected to chlorine atoms. An example is chlorpyrifos, which is a popular insecticide based on organophosphorus compounds.

2. By mechanism of action

The primary mechanism of action of organophosphorus insecticides involves inhibiting the enzyme acetylcholinesterase, disrupting normal nerve transmission and causing paralysis of insects. Depending on how they affect the nervous system, organophosphorus insecticides can be classified as follows:

• Insecticides that inhibit acetylcholinesterase: these substances block the activity of acetylcholinesterase, leading to the accumulation of acetylcholine in nerve synapses and disruption of nerve impulse transmission. Examples: malathion, metamidophos, chlorpyrifos.
• Insecticides affecting other enzymes: some organophosphorus compounds affect other enzymes involved in nerve transmission. Examples: dimethoate, phosphamidon.

3. By duration of action

Organophosphorus insecticides can vary in their duration of action, which affects the frequency of plant treatments and economic efficiency.

• Long-acting insecticides: these products have a lasting effect and can control pest populations for several weeks or months. Example: chlorpyrifos.
• Short-acting insecticides: these products act quickly, but their effect wears off rapidly, requiring repeated treatments. Example: malathion.

4. By application area

Organophosphorus insecticides can be classified based on their area of application:

• Agricultural insecticides: these products are used to protect agricultural crops from insect pests. Example: chlorpyrifos, malathion.
• Insecticides for public health protection: these products are used to eliminate disease vectors, such as mosquitoes and cockroaches. Example: metamidophos, malathion.
• Household insecticides: these products are used to eliminate household pests. Example: dimethoate.

5. By toxicity

Organophosphorus insecticides can be classified by their toxicity level to humans, animals, and the environment:

• Highly toxic products: these insecticides are highly toxic and can cause poisoning in humans and animals. Examples: metamidophos, parathion.
• Moderately toxic products: these products have moderate toxicity, making them less dangerous but still requiring caution when used. Example: malathion.
• Low-toxicity products: these products have relatively low toxicity for humans and animals, but they are still effective against insects. Example: dimethoate.

6. By type of effect

Organophosphorus insecticides can act either as contact or systemic:

• Contact insecticides: these products act when they come into contact with an insect. They quickly penetrate the insect's body through its outer covering. Example: malathion.
• Systemic insecticides: these products penetrate the plants and spread throughout them, allowing them to affect pests that feed on the plant's sap. Example: phosphamidon.

7. By method of application

Organophosphorus insecticides can be classified by the method of their application:

• Spray products: these insecticides are applied to plants in the form of solutions or emulsions. Example: chlorpyrifos.
• Soil products: these insecticides are applied to the soil before planting or during plant growth. Example: metamidophos.

Mechanism of action

How insecticides affect the insect nervous system

Organophosphorus insecticides block the activity of acetylcholinesterase, an enzyme that normally breaks down the neurotransmitter acetylcholine in synapses of nerve cells. This results in the accumulation of acetylcholine, which causes constant stimulation of nerve cells, leading to paralysis of the insect. In some cases, these insecticides may also affect sodium channels in cells, disrupting normal nerve system functioning.

Effect on insect metabolism

Organophosphorus insecticides can also affect enzymes involved in the metabolism of insects. This includes inhibition of the antioxidant activity system, leading to cell and tissue damage. Disruption of metabolism may cause the insect to die from poisoning by metabolic byproducts.

Examples of molecular mechanisms of action

• Acetylcholinesterase inhibition: most organophosphorus insecticides work by binding to acetylcholinesterase, blocking its activity, and disrupting neuro-transmission.
• Effect on sodium channels: some organophosphorus insecticides act on membrane sodium channels, causing their abnormal activation and resulting in insect paralysis.

Examples of products in this group

Advantages and disadvantages

Products like malathion, parathion, and diazinon are highly effective against a wide range of insects. They quickly kill pests and have a broad spectrum of activity. However, they also have disadvantages, such as high toxicity to beneficial insects (e.g., bees) and animals, as well as high volatility and resistance to degradation in the environment, which can lead to soil and water contamination.

Examples of products

• Malathion: used to protect vegetables, fruits, and crops in horticulture and agriculture. Effective against aphids, thrips, and other pests.
• Parathion: used in agriculture to protect against a wide range of pests such as flies and beetles.
• Diazinon: effective against many soil pests and harmful insects such as larvae, thrips, and others.

Environmental impact

• Impact on beneficial insects

Organophosphorus insecticides can be toxic to beneficial insects such as bees and ladybugs. Bees, which play an important role in pollination, can die upon contact with the insecticide, which disrupts the balance of the ecosystem and reduces crop yields.

• Residual pesticide levels in soil, water, and plants

Some organophosphorus insecticides can remain in soil, water, and plants for long periods. This can lead to environmental contamination and the accumulation of toxic substances in food chains.

• Photostability and degradation of insecticides in nature

Organophosphorus insecticides have varying photostability, which affects their degradation in nature. Some substances break down quickly under sunlight, while others persist in the environment and may contaminate ecosystems.

• Biomagnification and accumulation in food chains

Organophosphorus insecticides can accumulate in the tissues of plants and animals, leading to biomagnification in food chains. This can result in the accumulation of toxic substances in the bodies of humans and animals consuming contaminated products.

The problem of insect resistance to insecticides

Causes of resistance

Insects can develop resistance to organophosphorus insecticides through genetic changes that allow them to survive after exposure to the insecticide. This can result from mutations that increase the insects' ability to metabolize or excrete toxic substances.

Examples of resistant pests

• Colorado potato beetle: with the development of resistance to various insecticides, including organophosphorus products, the colorado potato beetle has become difficult to control in some regions.
• Aphids: in some cases, aphids have developed resistance to organophosphorus insecticides, making them more resistant to treatments.

Methods to prevent resistance

To prevent resistance, it is important to rotate insecticides with different modes of action, use combined treatments, and apply biological and mechanical pest control methods.

Safe use of insecticides

• Preparing solutions and dosages

When using organophosphorus insecticides, it is important to strictly follow the instructions on the packaging regarding dosages. Overuse can lead to environmental contamination and resistance in pests.

• Using protective equipment

Protective equipment such as gloves, masks, and goggles should be worn to prevent contact with the insecticides on the skin and respiratory system.

• Recommendations for plant treatment

Treatment should be done in the early morning or evening to avoid impacting bees and other beneficial insects. Weather conditions such as absence of rain and light winds should be taken into account to improve the effectiveness of the treatment.

• Waiting periods before harvesting

After applying insecticides, it is important to observe waiting periods before harvesting to minimize the risk of pesticide residues in crops.

Alternatives to chemical insecticides

• Biological insecticides

Using natural enemies of pests, such as entomophages (predatory insects), can be an effective alternative to chemical insecticides.

• Natural insecticides

There are many natural insecticides, such as neem oil, garlic infusions, and tobacco solutions, which are eco-friendly and safe for humans.

• Pheromone traps and other mechanical methods

Pheromone traps can attract and capture pests, minimizing the need for chemical treatments.

Examples of the most popular insecticides in this group

Product name	Active ingredient	Mechanism of action	Area of application
Malathion	Malathion	Acetylcholinesterase inhibition	Agriculture, horticulture
Parathion	Parathion	Acetylcholinesterase inhibition	Vegetable crop protection
Diazinon	Diazinon	Acetylcholinesterase inhibition	Agriculture, horticulture

Risks and precautions

• Impact on human and animal health

Organophosphorus insecticides can be toxic to humans and animals, especially with prolonged contact or improper use.

• Symptoms of insecticide poisoning

Poisoning may manifest as headaches, nausea, vomiting, weakness, and in severe cases, seizures and loss of consciousness.

• First aid for poisoning

If poisoning occurs, immediately remove the person or animal from the area, rinse eyes and skin, and seek medical attention.

Conclusion

Organophosphorus insecticides are an effective means of protecting plants from pests. However, their use requires caution and adherence to safety guidelines to minimize negative impacts on human health and the environment.

• Reminder of safety measures

Following instructions, using protective equipment, and observing waiting periods before harvesting are important measures for the safe use of insecticides.

• Call for the use of safer and more eco-friendly pest control methods

It is important to actively seek and implement safer and more eco-friendly pest control methods, such as biological control and the use of natural insecticides.

Frequently asked questions (FAQ)

What are organophosphorus insecticides?
Organophosphorus insecticides are a group of chemical substances containing phosphorus, used to kill insect pests. They work by inhibiting the activity of the enzyme acetylcholinesterase, disrupting the normal transmission of nerve impulses in insects.

How do organophosphorus insecticides affect insects?
Organophosphorus insecticides affect the insect nervous system by inhibiting acetylcholinesterase, the enzyme that breaks down the neurotransmitter acetylcholine. This causes acetylcholine to accumulate in synapses, leading to continuous stimulation of nerve cells, paralysis, and death of the insect.

What insecticides are in the organophosphorus group?
This group includes products such as malathion, parathion, diazinon, and chlorpyrifos. These substances are effective against various pests, including insects, mites, and larvae.

What are the advantages of organophosphorus insecticides?
Organophosphorus insecticides have high toxicity for insects, making them effective against a wide range of pests. They act quickly, allowing for rapid elimination of threats to agricultural crops.

What are the disadvantages of organophosphorus insecticides?
Disadvantages include toxicity to beneficial insects (e.g., bees), animals, and humans if not applied correctly. They may also persist in the environment, contaminating soil and water, which increases ecological risks.

How do organophosphorus insecticides affect the environment?
Organophosphorus insecticides can accumulate in soil and water, leading to ecosystem contamination. They are also toxic to beneficial insects, such as bees and predatory insects, disrupting the ecosystem and reducing biodiversity.

What is biomagnification in the context of organophosphorus insecticides?
Biomagnification is the process of accumulating toxic substances, such as organophosphorus insecticides, in food chains. These substances can accumulate in the tissues of animals and plants, increasing their concentration as they move up the food chain.

How can resistance of insects to organophosphorus insecticides be prevented?
To prevent resistance, it is recommended to rotate products with different modes of action, use combined treatments, and follow recommended dosages and application intervals to avoid creating conditions for the development of resistance in pests.

What safety measures should be followed when using organophosphorus insecticides?
When working with organophosphorus insecticides, protective equipment (gloves, masks, goggles) should be used, dosages should be followed, applications should be made during recommended times, and harvesting intervals should be observed to minimize residue levels in crops.

What are the alternatives to organophosphorus insecticides?
Alternatives include biological insecticides (entomophages, bacteria, and fungi), natural insecticides (e.g., neem oil, garlic infusions), and mechanical methods like pheromone traps and organic pesticides, which are less toxic to the environment and beneficial organisms.