Pyrethroids

Pyrethroids are a group of synthetic insecticides that mimic the action of pyrethrins, naturally occurring substances extracted from chrysanthemum flowers. These insecticides are actively used to control various pest insects in agriculture, horticulture, and in households. Pyrethroids are highly toxic to insects, blocking their nervous system and causing paralysis, which leads to their death. Unlike pyrethrins, synthetic pyrethroids are more stable to degradation by sunlight, making them more effective and long-lasting.

Objectives and importance in agriculture and horticulture

The primary goal of using pyrethroids is to protect plants from pests. These insecticides are applied to protect a wide range of agricultural crops, from vegetables and fruits to cereals and ornamental plants. Pyrethroids help reduce the population of insects that can cause significant damage in the agricultural sector, reducing both the quality and quantity of harvests. In horticulture, pyrethroids effectively combat pests such as aphids, whiteflies, and mites, protecting ornamental plants and improving their health. Proper use of these products contributes to increased yield and minimizes damage from pest insects.

Relevance of the topic

The study of pyrethroids is extremely important, as improper use of these insecticides can lead to the development of resistance in insects and negatively affect the environment. It is crucial to learn how to select insecticides properly, adhering to dosages and application rules, in order to minimize risks to beneficial insects and ecosystems as a whole. Furthermore, increasing awareness of pyrethroids will help in the fight against insect resistance to insecticides, which is one of the current issues in agriculture and horticulture.

History of pyrethroids

Pyrethroids are synthetic insecticides that mimic the action of natural pyrethrins found in the flowers of certain species of chrysanthemum. Since their discovery and creation in the 1970s, pyrethroids have been widely used in agriculture and gardening due to their high effectiveness, low toxicity to mammals, and rapid breakdown in the environment. The history of pyrethroids began with the study of natural substances and the development of their synthetic analogs for safer and more effective pest control.

1. Early discovery and study of pyrethrins

Natural pyrethrins were first isolated in the 19th century from chrysanthemums. By the 1940s, it was discovered that pyrethrins have insecticidal activity and can effectively kill insects. These substances break down quickly and have minimal impact on mammals, making them attractive as insecticides. However, natural pyrethrins had limitations in stability and effectiveness, which led to the search for synthetic analogs.

2. Development of synthetic pyrethroids

In the 1970s, scientists began developing synthetic analogs of pyrethrins—pyrethroids. Pyrethroids were created to improve stability and increase their duration of action, as well as to provide higher toxicity to insects and lower toxicity to humans and animals. These synthetic compounds mimicked the mechanisms of natural pyrethrins, blocking nerve impulses in insects, leading to paralysis and death.

Example:

• permethrin – the first synthetic pyrethroid developed in the 1970s, which gained widespread recognition for its high effectiveness and resistance to degradation. Permethrin became one of the most popular insecticides for controlling pests in agriculture and also in households for protection against mites and mosquitoes.

3. Widespread use of pyrethroids in the 1980s and 1990s

Since the 1980s, pyrethroids have been used in various fields, including agriculture, household pest control, and veterinary medicine. With the increase in the use of pyrethroids, the development of new formulations with improved characteristics, such as increased effectiveness, environmental stability, and reduced toxicity to non-target organisms, began.
Example:

• cypermethrin – a synthetic pyrethroid developed in the 1980s that quickly became one of the most popular insecticides. It is used to control a wide range of pests in agriculture and also for controlling disease vectors, such as mosquitoes that transmit viruses.
• deltamethrin – another pyrethroid that became widely used in the 1990s. It was known for its high effectiveness against various insects such as cockroaches, mosquitoes, and flies and was also used to protect agricultural crops from pests.

4. Modern applications and improvements

With the advancement of technology in the 2000s and 2010s, pyrethroids continued to improve, becoming safer and more effective. The new generation of insecticides features improved stability, high activity against a wide range of pests, and reduced risks to the environment and human health. Pyrethroids continue to play an important role in integrated pest management systems, combining chemical, biological, and mechanical control methods.

Example:

• lambda-cyhalothrin – one of the modern pyrethroids that is highly active against a wide range of pests, including insects resistant to older insecticides. This product is used in agriculture and planting for protection against pests such as the colorado potato beetle and various moth species.

5. Problems and prospects

Despite the success of pyrethroids, their use is not without problems. One of the most significant issues is the development of resistance in insects, leading to reduced effectiveness of the products. In response to this issue, scientists continue to develop new pyrethroid formulations, as well as combination products, to overcome resistance and provide effective protection against pests.

Modern trends in the use of pyrethroids

Today, pyrethroids remain important insecticides in the fight against pests, but their use is significantly limited due to insect resistance problems and environmental risks. Modern research focuses on developing pyrethroids with improved characteristics that will be more effective against resistant pests, as well as reducing their impact on beneficial insects. As an alternative and supplement to pyrethroids, biological plant protection methods, including natural insect enemies and the use of microorganisms, are being developed.

Thus, the history of pyrethroids includes their establishment as effective and relatively safe insecticides, as well as the development of the issue of pest resistance and environmental impact. Understanding this history helps in the search for new and safer methods of pest control.

Classification

Pyrethroids are a large group of insecticides primarily used to control pest insects. They synthetically mimic pyrethrins—natural insecticides found in chrysanthemum flowers. Depending on their chemical structure, activity, and application, pyrethroids can be classified according to various characteristics.

1. By chemical structure:

Pyrethroids can be classified based on their chemical structure, which is determined by the presence of certain functional groups. The most common classes are:

• type i pyrethroids (class i): this class includes pyrethroids that do not contain an additional atomic group, making them more toxic to insects. An example is permethrin, which has good activity and a fast effect.
• type ii pyrethroids (class ii): these pyrethroids contain an additional atomic group, which significantly increases their stability and reduces toxicity to animals. Cypermethrin is one of the most popular examples of type ii. It is used in agriculture to control pest insects and in the fight against disease vectors.

2. By speed of action:

Pyrethroids differ in how quickly they affect insects. Depending on how fast they induce paralysis and death in the insect, they can be classified as follows:

• fast-acting pyrethroids: these insecticides rapidly paralyze insects and begin working within minutes of contact. Permethrin is an example of a fast-acting pyrethroid.
• slow-acting pyrethroids: these products work more slowly, with their effects becoming noticeable only after several hours. Deltamethrin is an example of such pyrethroids.

3. By application form:

Pyrethroids can be classified depending on the form in which they are applied:

• systemic pyrethroids: these insecticides penetrate into the plant and spread throughout its tissues, making them effective against insects that feed on plant tissues. An example of such a pyrethroid is landamethrin.
• contact pyrethroids: these substances act directly upon contact with the insect, causing paralysis and death. Cypermethrin is an example of a contact pyrethroid that acts on the external parts of the plant or on the insects themselves.

4. By application area:

Pyrethroids can be classified based on their application area:

• for agriculture: this is the most common application area for pyrethroids, as they are actively used to protect agricultural crops from various pest insects. An example is chlorpyrifos, which is widely used on vegetables, cereals, and fruit crops.
• for household use: pyrethroids are also used in households, for example, to protect against indoor pests such as cockroaches, flies, mosquitoes, and other insects. Deltamethrin and permethrin are frequently used in household insecticidal sprays.
• for veterinary use: pyrethroids can be used in veterinary medicine to protect pets from parasites such as fleas and ticks. An example is fenvalerate, which is used in anti-flea treatments for dogs and cats.

5. By stability:

The classification of pyrethroids by stability is based on their ability to maintain activity under different environmental conditions:

• photostable pyrethroids: these insecticides do not degrade quickly under sunlight, making them effective for long-term use in open spaces. Cypermethrin and deltamethrin are examples of such photostable pyrethroids.
• photounstable pyrethroids: these substances lose their activity under sunlight, which limits their use in open agricultural conditions. However, they can be used in enclosed spaces or in combination with other products that enhance stability.

6. By toxicity:

Pyrethroids differ in their toxicity to humans, animals, and insects. Toxicity depends on the molecular composition and its interaction with the insect nervous system.

• highly toxic pyrethroids: products that are highly toxic to insects and are used against a wide range of pests. An example is permethrin.
• moderately toxic pyrethroids: these insecticides have moderate toxicity and are often used to protect more sensitive plants. An example is fenvalerate.

Mechanism of action

• How insecticides affect the insect nervous system:

Pyrethroids block nerve impulse transmission in the insect body by affecting sodium channels in their nervous system. These channels regulate the flow of sodium ions into nerve cells, which is a key process for normal nervous system functioning. When pyrethroids are applied, these channels become hyperactive, leading to the disruption of normal nerve impulse transmission. This results in paralysis and eventually the death of the insect.

• Impact on insect metabolism:

In addition to direct effects on the nervous system, pyrethroids can alter the metabolism of insects. For example, some pyrethroids interfere with the normal function of cells, which can affect energy metabolism, slowing down growth and development processes. These changes can weaken pests' ability to reproduce and increase their sensitivity to other stress factors.

• Examples of molecular mechanisms of action:

1. Action on acetylcholinesterase: pyrethroids can inhibit the activity of acetylcholinesterase, leading to an accumulation of acetylcholine in nerve synapses, thereby disrupting normal nerve impulse transmission.
2. Action on sodium channels: pyrethroids affect sodium channels, causing their continuous opening, which leads to uncontrolled ion flow and excitation of nerve cells.

Difference between contact and systemic action:

• contact pyrethroids act directly upon contact with the surface of the insect's body. They quickly penetrate the organism through the outer shell and rapidly cause paralysis.
• systemic pyrethroids can penetrate plants and spread through them, affecting pests not only through contact with their bodies but also through feeding when insects consume treated plants.

Examples of products

Advantages:

• Fast action: pyrethroids start working within minutes after contact, providing rapid control of pest populations.
• Wide range of action: these insecticides are effective against various types of pests, including aphids, flies, mites, and other insects.
• Low toxicity to mammals: pyrethroids have lower toxicity to humans and animals compared to other insecticides.

Disadvantages:

• Impact on beneficial insects: pyrethroids can be toxic to bees and other beneficial insects, which reduces pollination and disrupts ecological balance.
• Resistance in pests: insects can develop resistance to pyrethroids, requiring the rotation of products or the use of combined control methods.

Examples of products:

• Deltamethrin: effective against aphids, whiteflies, and other pests. A highly active pyrethroid with a fast effect.
• Cypermethrin: widely used in agriculture to protect vegetables and fruit crops from various insects.

Environmental impact

• Impact on beneficial insects (bees, predatory insects):

Pyrethroids can be dangerous for beneficial insects, such as bees and ladybugs. Bees, which play an important role in plant pollination, may die upon contact with pyrethroids. This reduces biodiversity and affects the ecosystem.

• Residual amounts of insecticides in soil, water, and plants:

After pyrethroids are applied, residual amounts of the substance may remain in the soil, water, and plants. This creates a risk of contamination of ecosystems, especially water bodies, which can affect living organisms like fish and aquatic plants.

• Photostability and degradation of insecticides in nature:

Pyrethroids have good photostability, meaning they resist breakdown by sunlight. This increases their activity and duration of action but also contributes to the accumulation of chemicals in the environment.

• Biomagnification and accumulation in food chains:

Insecticides can accumulate in animal bodies, leading to biomagnification—increased concentrations of chemicals at each level of the food chain. This can have harmful effects on animals and humans who consume products containing residual insecticides.

Problem of resistance in insects to insecticides

• Causes of resistance:

Resistance in insects arises due to natural selection: individuals that have mutations allowing them to survive insecticide exposure pass these traits on to their offspring. Over time, such insects become resistant to the products, reducing their effectiveness.

• Examples of resistant pests:

The colorado potato beetle, aphids, and other insects have become resistant to pyrethroids after repeated use of these products in the same area.

• Methods to prevent resistance:

To prevent resistance, it is recommended to rotate insecticides with different mechanisms of action, use combined products, and practice integrated pest control methods such as biological control and the use of natural enemies.

Safety guidelines for insecticide use

• Solution preparation and dosages:

Strictly follow the specified dosages, as an excess of insecticide can harm plants and the environment. Before application, it is important to properly dilute the insecticide in water and mix it thoroughly.

• Use of protective equipment when handling insecticides:

When using pyrethroids, protective equipment such as gloves, masks, and goggles should be worn. This protects against chemical contact with the skin and respiratory system.

• Recommendations for plant treatment:

Treat plants in the evening or early morning when temperatures are lower, and insects are more active. Avoid application during rainy weather or strong winds to prevent the insecticide from washing off or spreading to other areas.

• Compliance with waiting periods before harvesting:

It is important to adhere to the waiting periods specified on the packaging to prevent residual chemicals from entering the food.

Alternatives to chemical insecticides

• Biological insecticides:

The use of entomophages, such as predatory mites, as well as bacterial products like bacillus thuringiensis, represents an effective way to control pests without using chemicals.

• Natural insecticides:

Neem oil, garlic solutions, and tobacco infusions are natural methods that can effectively repel insects without harming plants and the environment.

• Pheromone traps and other mechanical methods:

Pheromones and traps for insects help reduce pest populations without using chemicals.

Examples of popular products from this group

Product name	Active ingredient	Mechanism of action	Application area
Bi-58	Deltamethrin	Disrupts sodium channel activity	Agriculture, horticulture
Aktara	Thiamethoxam	Affects nicotinic receptors	Protection against sucking pests

Risks and precautions

• Impact on human and animal health:

Pyrethroids can be toxic to humans and animals if misused. Caution should be exercised when using them.

• Symptoms of insecticide poisoning:

Poisoning by pyrethroids manifests as headaches, nausea, vomiting, and dizziness. In case of poisoning, immediate medical help should be sought.

• First aid for poisoning:

Rinse the mouth and eyes, call for medical help, and take activated charcoal to accelerate the removal of toxins from the body.

Conclusion

rational use of pyrethroids helps control pests effectively but requires careful attention to safety. Following dosage and application recommendations minimizes risks and achieves maximum effectiveness.

Frequently asked questions (FAQ)

• What are pyrethroids?

Pyrethroids are synthetic chemical insecticides developed from pyrethrin, a natural compound extracted from chrysanthemum flowers. These insecticides are actively used to combat a wide range of pest insects due to their high toxicity to insects and relatively low toxicity to mammals.

• How do pyrethroids work?

Pyrethroids affect the nervous system of insects by disrupting the normal functioning of neurons. They block sodium channels on cell membranes, causing continuous activation of nerve cells, leading to paralysis and insect death. This leads to rapid and effective pest elimination.

• How do pyrethroids differ from other insecticides?

Pyrethroids are highly effective against insects with relatively low toxicity to mammals, including humans. They act quickly and have a relatively short duration of action, which reduces the risk of residue accumulation in the environment. However, pyrethroids can be toxic to aquatic organisms and some beneficial insects.

• What are the advantages of pyrethroids?

Pyrethroids have several advantages: they act quickly, are effective against many insect species, have low toxicity to humans and animals when used properly, and break down relatively quickly in the environment. This makes them popular for use in agriculture and horticulture.

• What are the disadvantages of pyrethroids?

The main disadvantage of pyrethroids is that they can cause resistance in insects when used repeatedly or continuously. They can also be toxic to beneficial insects, such as bees and other pollinators, as well as to aquatic ecosystems. Pyrethroids are highly toxic to fish and other aquatic organisms, which requires caution when used near water bodies.

• How do pyrethroids affect the ecosystem?

Pyrethroids can affect beneficial insects, such as bees, ladybugs, and entomophages (natural enemies of pests), disrupting the ecosystem. They can also enter water bodies and harm aquatic ecosystems by killing fish and other aquatic organisms. To minimize environmental impact, it is important to follow usage guidelines for pyrethroids.

• What insects are most vulnerable to pyrethroids?

Pyrethroids are effective against many insect species, including mealybugs, aphids, mites, ants, and agricultural pests such as the colorado potato beetle. They are used for pest control in both agriculture and domestic settings.

• How can resistance to pyrethroids be prevented?

To prevent resistance, it is important to rotate insecticides with different modes of action, use them in combination with other control methods (e.g., biological insecticides or mechanical methods), and follow dosage and application frequency recommendations. Rotating products and proper use reduces the likelihood of resistant pest populations.

• How should pyrethroids be used safely?

When using pyrethroids, it is important to follow the packaging recommendations and wear protective clothing (gloves, goggles, mask) to avoid contact with skin and respiratory pathways. Also, avoid applying them in strong winds and rain, and comply with waiting periods before harvesting to minimize the risk of pesticide residues in products.

• Are there alternatives to pyrethroids?

Yes, alternatives to pyrethroids exist, such as organic insecticides (neem oil, garlic infusion), biological pest control methods (entomophages, bacteria, and viruses), and mechanical methods like traps and physical removal of pests. These methods can be safer for the environment and human health but may require more effort and time to achieve similar effectiveness.