Avermectins

Avermectins are a group of macrocyclic lactones derived from bacteria of the genus streptomyces. They exhibit strong insecticidal, acaricidal, and antiparasitic properties and are widely used in agriculture, veterinary medicine, and healthcare. Avermectins are effective against a broad spectrum of pests, including insects, mites, parasitic worms, and other parasites that cause damage to agricultural crops, domestic animals, and humans.

Objectives and significance of use in agriculture and horticulture

The primary objective of using avermectins is to protect agricultural crops from various pests, thereby increasing yield and reducing product losses. In horticulture, avermectins are employed to safeguard ornamental plants, fruit trees, and shrubs from insect and mite infestations, maintaining their health and aesthetic appeal. Due to their high efficacy and broad-spectrum activity, avermectins are an essential tool in integrated pest management (ipm), ensuring sustainable and productive agriculture.

Relevance of the topic

Studying and properly applying avermectins is crucial in modern agriculture and horticulture. With the global population increasing and the demand for food rising, effective pest management becomes critically important. Proper research and application of avermectin insecticides help minimize crop damage, enhance agricultural productivity, and reduce economic losses. However, excessive and uncontrolled use of avermectins can lead to pest resistance and negative environmental impacts, such as the decline of beneficial insect populations and environmental contamination. Therefore, it is vital to understand the mechanisms of action of avermectins, their ecological impact, and to develop sustainable application methods.

History

Avermectins are a group of insecticides and antiparasitic agents derived from compounds isolated from soil actinomycetes. These substances are highly effective against a wide range of pests, as well as various parasites, including nematodes and mites. Avermectins have played a significant role in controlling parasitic diseases and pests in both agriculture and medicine. Their history spans several decades and includes key scientific discoveries.

1. Discovery of avermectin

The history of avermectins began in 1975 when japanese scientist isao yoshida at merck & co. Started investigating soil microorganisms known as actinomycetes. During his experiments, yoshida and his colleagues isolated a new antibiotic that had powerful antiparasitic properties. The probiotic properties, such as its high effectiveness against various parasitic infections, immediately attracted researchers' attention. This antibiotic was named avermectin in 1979.

2. Development and commercial use

After the isolation of avermectin, its molecular structure was studied, and through chemical modifications, new forms were developed. One such modification led to the creation of abamectins — a more stable and potent form. In the early 1980s, it was proven that avermectins had exceptional activity against roundworms, mites, and other parasites, making them ideal for controlling various diseases in both livestock and agriculture.

In 1987, the first commercial avermectin-based insecticide, malathion, was introduced, which quickly became popular due to its high effectiveness against a wide range of insects. It was used in agriculture and to protect public health from insect-borne diseases.

3. Development and usage

Since the early 1950s, avermectin-based insecticides have become widely used in agriculture. They provided higher toxicity to insects compared to many previously used chlorinated compounds, such as ddt. Avermectins became popular in the fight against pests like insects on various crops, including cotton, tobacco, vegetables, and fruits. Some of the most well-known chemicals in this group include parathion, diazinon, and chlorpyrifos.

4. Safety and environmental concerns

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

5. Modern approaches and issues

Today, avermectin-based insecticides remain widely used, but their application is limited due to environmental and safety requirements. Issues related to insect resistance, resistance to avermectin insecticides, and the decreasing effectiveness of these compounds have become major concerns in modern chemical pest control. To prevent the development of resistance, scientists are actively developing new formulations and methods, combining avermectin-based insecticides with biological and mechanical pest control methods.

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

Classification

Avermectins are classified based on various criteria, including chemical composition, mechanism of action, and spectrum of activity. The main groups of avermectins include:

• Ivermectin: one of the most widely used representatives, effective against a broad spectrum of parasites, including mites, worms, and pest insects.
• Abamectin: employed for controlling parasites in livestock and agricultural crops, known for its high stability.
• Epirabamectin: used in veterinary and agricultural settings, effective against various insect and mite species.
• Milbemectin: utilized for plant and animal pest control, characterized by high selectivity and low mammalian toxicity.
• Avermectin b1a: specialized insecticide effective against specific pests such as moths and certain beetle species.

Each of these groups possesses unique properties and mechanisms of action, allowing their use under different conditions and for various crop types.

Mechanism of action

How insecticides affect the nervous system of insects

• Avermectins impact the nervous system of insects by binding to glutamate-gated chloride channels and gaba receptors in nerve cells. This leads to continuous activation of nerve impulses, resulting in paralysis and death of the insects. Unlike organophosphates, which inhibit acetylcholinesterase, avermectins act directly on glutamate and gaba receptors, providing more selective and effective action.

Impact on insect metabolism

• Disruption of nerve signal transmission causes failures in metabolic processes in insects, such as feeding, reproduction, and movement. This results in decreased activity and viability of pests, aiding in effective population control and preventing damage to plants.

Examples of molecular mechanisms of action

• Avermectins like ivermectin bind to glutamate-gated chloride channels, causing continuous nerve excitation. Other avermectins, such as abamectin, may also interact with gaba receptors, blocking their function and producing similar effects. These molecular mechanisms ensure high efficacy of avermectins against various pest insects.

Difference between contact and systemic action

• Avermectins can exhibit both contact and systemic action. Contact avermectins act directly upon contact with insects, penetrating through the cuticle or respiratory pathways, causing paralysis and death on the spot. Systemic avermectins are absorbed into plant tissues and distributed throughout all parts, providing long-lasting protection against pests feeding on different parts of the plant. Systemic action allows for extended pest control over larger areas and longer durations.

Examples of products in this group

Ivermectin
mechanism of action
binds to glutamate and gaba receptors, causing continuous nerve excitation and paralysis of insects.
Examples of products

• Avagil
• Ivermectin-20
• Mirimectilin
  advantages and disadvantages
  advantages: broad spectrum of activity, systemic distribution, low toxicity to mammals.
  Disadvantages: toxicity to beneficial insects, risk of resistance development in pests, environmental hazards.

Abamectin
mechanism of action
binds to glutamate and gaba receptors, causing paralysis and death of parasites.
Examples of products

• Abamet
• Abamectin-10
• Agroabam
  advantages and disadvantages
  advantages: high efficacy, resistance to degradation, systemic action.
  Disadvantages: toxicity to bees and other pollinators, potential soil and water contamination, development of resistance in pests.

Milbemectin
mechanism of action
binds to glutamate receptors, causing continuous nerve excitation and paralysis.
Examples of products

• Milbemectin-2
• Milbegard
• Agromil
  advantages and disadvantages
  advantages: high selectivity, effective against a broad range of pests, low toxicity to mammals.
  Disadvantages: toxicity to beneficial insects, potential environmental accumulation, resistance development in pests.

Avermectin b1a
mechanism of action
binds to glutamate and gaba receptors, causing paralysis and death of insects.
Examples of products

• Avermectin-5
• Agroavermet
• Mirimect
  advantages and disadvantages
  advantages: effective against moths and other pests, systemic distribution, high resistance to degradation.
  Disadvantages: toxicity to bees, potential contamination of water sources, resistance development in pests.

Fenitrazole
mechanism of action
inhibits acetylcholinesterase, disrupting nerve impulse transmission and causing paralysis and death of insects.
Examples of products

• Fenitrazole-150
• Agrofenit
• Fenitrop
  advantages and disadvantages
  advantages: high efficacy against a wide range of pests, low toxicity to mammals.
  Disadvantages: toxicity to aquatic organisms, potential environmental accumulation, resistance development in pests.

Insecticides and their impact on the environment

Impact on beneficial insects

• Avermectins exert toxic effects on beneficial insects, including bees, wasps, and other pollinators, as well as predatory insects that naturally control pest populations. This leads to a decline in biodiversity and disrupts ecosystem balance, negatively affecting the productivity of agricultural crops and biodiversity.

Residual amounts of insecticides in soil, water, and plants

• Avermectins can persist in soil for extended periods, especially under conditions of high humidity and temperature. This results in the contamination of water sources through runoff and infiltration. In plants, avermectins are distributed throughout all parts, including leaves, stems, and roots, providing systemic protection but also leading to the accumulation of insecticides in food products and soil, which can adversely affect human and animal health.

Photostability and degradation of insecticides in nature

• Many avermectins possess high photostability, increasing their environmental persistence. This hinders the rapid degradation of insecticides under sunlight exposure, contributing to their accumulation in soil and aquatic ecosystems. High resistance to degradation complicates the removal of avermectins from the environment and increases the risk of their impact on non-target organisms.

Biomagnification and accumulation in food chains

• Avermectins can accumulate in the tissues of insects and animals, progressing through the food chain and causing biomagnification. This results in higher concentrations of the insecticide at the top levels of the food chain, including predators and humans. Biomagnification of avermectins leads to severe ecological and health-related issues, as accumulated insecticides can cause chronic poisoning and health disturbances in animals and humans.

The problem of pest resistance to insecticides

Causes of resistance development

• The development of resistance in pests to avermectins is driven by genetic mutations and the selection of resistant individuals through repeated use of the insecticide. Frequent and uncontrolled application of avermectins accelerates the spread of resistant genes within pest populations. Insufficient adherence to dosage and application protocols also speeds up the process of resistance development, making the insecticide less effective.

Examples of resistant pests

• Resistance to avermectins has been observed in various pest insect species, including whiteflies, aphids, mites, and certain moth species. These pests exhibit reduced sensitivity to the insecticides, complicating their control and necessitating the use of more expensive and toxic agents or the transition to alternative pest management methods.

Methods to prevent resistance

• To prevent the development of resistance in pests to avermectins, it is essential to rotate insecticides with different mechanisms of action, combine chemical and biological control methods, and implement integrated pest management strategies. It is also crucial to adhere to recommended dosages and application schedules to avoid the selection of resistant individuals and maintain the long-term efficacy of avermectin products.

Rules for the safe application of insecticides

Preparation of solutions and dosages

• Proper preparation of solutions and accurate dosage measurement are critically important for the effective and safe use of avermectins. It is necessary to strictly follow the manufacturer’s instructions for solution preparation and dosage to avoid over-application or inadequate plant treatment. Using precise measuring tools and high-quality water ensures dosage accuracy and treatment effectiveness.

Use of protective equipment when handling insecticides

• When working with avermectins, it is essential to use appropriate protective gear, such as gloves, masks, goggles, and protective clothing, to minimize the risk of insecticide exposure to the human body. Protective equipment helps prevent contact with skin and mucous membranes, as well as inhalation of toxic insecticide vapors.

Recommendations for plant treatment

• Apply avermectins to plants during early morning or late evening hours to avoid affecting pollinators like bees. Avoid application during hot and windy weather, as this can lead to insecticide drift and unintended contact with beneficial plants and organisms. It is also recommended to consider the growth stage of the plants, avoiding application during periods of active flowering and fruiting.

Observance of pre-harvest intervals

• Adhering to the recommended pre-harvest intervals after applying avermectins ensures the safety of consuming the produce and prevents insecticide residues from entering food products. It is important to follow the manufacturer’s guidelines regarding pre-harvest intervals to avoid poisoning risks and ensure product quality.

Alternatives to chemical insecticides

Biological insecticides

• The use of entomophagous organisms, bacterial and fungal formulations offers an environmentally safe alternative to chemical insecticides. Biological insecticides, such as bacillus thuringiensis, effectively combat pest insects without harming beneficial organisms and the environment. These methods support sustainable pest management and preserve biodiversity.

Natural insecticides

• Natural insecticides, such as neem oil, tobacco extracts, and garlic solutions, are safe for plants and the environment and are used to control pests. These substances possess repellent and insecticidal properties, allowing effective management of insect populations without the use of synthetic chemicals. Natural insecticides can be used in combination with other methods to achieve optimal results.

Pheromone traps and other mechanical methods

• Pheromone traps attract and eliminate pest insects, reducing their population and preventing spread. Other mechanical methods, such as sticky traps and barriers, also help control pest populations without the use of chemical agents. These methods are effective and environmentally friendly ways to manage pests.

Examples of the most popular insecticides in this group

Advantages and disadvantages

Advantages

• High efficacy against a broad spectrum of pest insects
• Systemic distribution in plants, providing long-term protection
• Low toxicity to mammals compared to other classes of insecticides
• High photostability, ensuring prolonged action

Disadvantages

• Toxicity to beneficial insects, including bees and wasps
• Potential for resistance development in pest populations
• Possible contamination of soil and water sources
• High cost of some formulations compared to traditional insecticides

Risks and precautions

Impact on human and animal health

• Avermectins can have serious effects on human and animal health if misused. In humans, exposure can cause symptoms of poisoning such as dizziness, nausea, vomiting, headaches, and in severe cases, seizures and loss of consciousness. Animals, especially domestic pets, are also at risk of poisoning if the insecticide comes into contact with their skin or if they ingest treated plants.

Symptoms of insecticide poisoning

• Symptoms of avermectin poisoning include dizziness, headaches, nausea, vomiting, weakness, difficulty breathing, seizures, and loss of consciousness. Contact with eyes or skin can cause irritation, redness, and burning sensations. Ingestion of the insecticide requires immediate medical attention.

First aid for poisoning

• In case of suspected avermectin poisoning, immediately cease contact with the insecticide, rinse affected skin or eyes with plenty of water for at least 15 minutes. If inhaled, move to fresh air and seek medical assistance. If ingested, call emergency services and follow the first aid instructions provided on the product label.

Prevention of pest emergence

Alternative pest control methods

• Using cultural practices such as crop rotation, mulching, removing infested plants, and planting resistant varieties helps prevent pest emergence and reduce the need for insecticide use. These methods create unfavorable conditions for pest insects and strengthen plant health. Biological control methods, including the use of entomophagous predators and other natural enemies of pest insects, are also effective preventive measures.

Creating unfavorable conditions for pests

• Ensuring proper irrigation, removing fallen leaves and plant debris, maintaining cleanliness in gardens and orchards create unfavorable conditions for pest reproduction and spread. Installing physical barriers, such as nets and borders, helps prevent pest access to plants. Regular plant inspections and timely removal of damaged parts reduce the attractiveness of plants to pests.

Conclusion

Rational use of avermectins plays a crucial role in protecting plants and enhancing the yield of agricultural and ornamental crops. However, it is essential to follow safety protocols and consider environmental aspects to minimize negative impacts on the ecosystem and beneficial organisms. An integrated pest management approach, combining chemical, biological, and cultural control methods, promotes sustainable agricultural development and biodiversity conservation. It is also important to continue research on developing new insecticides and control methods aimed at reducing health risks for humans and ecosystems.

Frequently asked questions (FAQ)

1. What are avermectins and what are they used for?
Avermectins are a group of macrocyclic lactones used as insecticides, acaricides, and antiparasitic agents. They are employed to protect agricultural crops, livestock, and humans from various parasites and pests.

2. How do avermectins affect the nervous system of insects?
Avermectins bind to glutamate and gaba receptors in the nerve cells of insects, causing continuous excitation of nerve impulses. This leads to paralysis and death of the insects.

3. Are avermectins harmful to beneficial insects like bees?
Yes, avermectins are toxic to beneficial insects, including bees and wasps. Their application requires strict adherence to regulations to minimize impact on beneficial insects.

4. How to prevent the development of resistance in pests to avermectins?
To prevent resistance, rotate insecticides with different mechanisms of action, combine chemical and biological control methods, and adhere to recommended dosages and application schedules.

5. What environmental problems are associated with the use of avermectins?
Use of avermectins leads to the decline of beneficial insect populations, soil and water contamination, and accumulation of insecticides in food chains, causing serious ecological and health-related issues.

6. Can avermectins be used in organic farming?
No, avermectins do not meet the requirements of organic farming due to their synthetic origin and potential negative impact on the environment and beneficial organisms.

7. How to properly apply avermectins for maximum effectiveness?
Strictly follow the manufacturer’s instructions for dosage and application schedules, treat plants during early morning or late evening hours, avoid application during periods of pollinator activity, and ensure even distribution of the insecticide on plants.

8. Are there alternatives to avermectins for pest control?
Yes, there are biological insecticides, natural substances (neem oil, garlic solutions), pheromone traps, and mechanical control methods that can be used as alternatives to avermectins.

9. How to minimize the impact of avermectins on the environment?
Use insecticides only when necessary, adhere to recommended dosages and application schedules, prevent insecticide runoff into water sources, and implement integrated pest management methods to reduce reliance on chemical agents.

10. Where can avermectins be purchased?
Avermectins are available in specialized agricultural stores, online marketplaces, and from plant protection product suppliers. Before purchasing, ensure the legality and safety of the products being used.