Importance of integrated pest management
The independence established in the Central Asian countries in 1991 opened up the opportunities for many residents to work on the land and become farmers. Often, the new farmers were interested in greater yields, in food security of their families, or higher profits. Targeting at higher yields, they have not paid much attention to the rational use of resources, the land in particular. Until now the land users apply different pesticides, fungicides and herbicides to combat pests and diseases. This resulted in high resistance of pests to pesticides, and in the vast habitats of pests that dominate the beneficial species. As a consequence, growers had to apply more chemicals, and therefore spend more.
The use of insecticides and the crop management practices lead to almost complete destruction of pest populations. However, the few surviving individuals are able to restore the population again and pass their descendants the ability to resist poisoning and death. Other important changes occur in populations when they merge with the other ones, or when the new species – workers – enter the population. Many insects behave as dangerous pests of agricultural crops since there are no former predators and parasites at the new location. At the same time, in nature, there are certain relationships between living organisms, so as the insects cannot propagate out of control and cause therefore damage to crops. Pests are destroyed by a large number of predators.
The development of
environmentally friendly methods of plant protection, the biological control in particular, is nowadays given special attention. In Central Asian countries the biological method is used to protect field and greenhouse crops. In all provinces of Uzbekistan the biolaboratories under the plant protection stations provide farmers with pure cultures of microorganisms and natural enemies, as well as provide methodological guidance on the use of biological control methods.
However, until now the share of environmentally friendly methods applied in the fields and gardens of Central Asia is not significant. This gap can be improved by introducing the experiences from the developed countries and especially the United States and Canada.
Presently, biological control in plant protection has to be enriched by new non-chemical methods of suppressing the pest population, whilst the role of biological control among various methods of pest control has to be enhanced as well.
People have attempted to use certain organisms to fight the other ones for a long time. Ants were used to combat the pests of citrus plants; similarly the bird myna imported from India was used to combat red locusts on the island of Mauritius. People repeatedly used to spread the predatory beetles in different countries.
The first scientific experiments on biological control methods have been conducted in the late seventies - early eighties XIX century. Ilya Mechnikov, famous Russian zoologist, discovered the pathogens of fungal and bacterial diseases of grain beetle, and conducted a series of experiments on the use of agents of green muscardine and founded the prospects for the practical use of pathogens.
Since the 1970s the Soviet scientists have carried out the reproduction of three types and 15 interspecific forms of trichogramme at 16 industrial biocontrol laboratories of the Ministry of Agriculture. The different forms of Trichogramma evanescens have been used against winter, cabbage and other types of noctuids of winter cereals, sugar beet, cabbage and potatoes. This progressive method was largely applied in Uzbekistan in more than 3 million ha. A large group of scientists and agricultural experts of that time was awarded the prizes for the development and implementation of biological control in the country.
Uzbekistan has developed and is currently implementing measures to introduce an integrated system of plant protection with pesticides safe for humans and animals. A network of biological laboratories and biofactories (total 809) with improved entomological services has been established in provinces throughout the country.
In the United States, Japan and in Europe there are large firms in the sphere of “biological control” - Valent Bioscience, Certis, Koppert Biological Systems, Biobest and many smaller companies. Jointly they produce about 90 agents of biological protection of more than $ 100 million dollars a year.
Today, the biological method is considered as part of an integrated pest management system (IPM), which is used together with the other measures to combat pests. The biological control products are produced out of beneficial microorganisms and their metabolic products that cause disease and mortality of pests.
Biological control method in plant protection
The biological method of pest management (biological control) is based on the use of parasitic and predatory insects (entomophages), as well pathogens to suppress, restrict or prevent mass reproduction of harmful species.
Initially, parasitic and predatory insects, entomophages, have been used, which were then followed by pathogens (bacteria, fungi, viruses) – the causative agents for plants.
Crop protection from pests, diseases and weeds has to combine a variety of agronomic, chemical and biological methods. However, the crop management and biological control methods shall have a priority and thus gradually replace the chemical measures.
Biological control may include a number of techniques to reduce the number of unwanted organisms with the help of other species (animal predators specialized herbivorous species or parasites), by sterilizing male pest species that displace males capable of reproduction (genetic method). Close to the biological control are the agronomic and microbiological methods, the former utilizes crop management practices, the latter uses microorganisms to combat pests.
Biological pest control means balancing the pest populations by means of natural factors and human intervention. The method should imply knowledge of the environment and functioning of ecological systems. It is important to understand that the biological agents are not designed for the complete extermination of pest population, but only to control its density and reduce the damage to an acceptable level.
Natural enemies in biological control method
The fauna of pests (insects and mites) threatening agricultural crops in Central Asia - is rich and diverse. The largest number of pests belongs to the order of mites, beetles and lepidopterous insects.
Natural enemies of insect pests are divided into several groups: predators, parasites, pathogens and nematodes.
Well-known predators - spiders, ladybugs, ground beetles, dragonflies, lacewings and hoverflies - hunt or set traps to catch their prey. They feed on a variety of insects. Both the adult insects and larvae may be predators. Predator population corresponds to the population of pests. They lay more eggs when prey is abundant.
Parasites are those organisms that live and develop inside other insects. Parasites of tomato are Trichogramma, braconides (Braconidae), ichneumon wasps (Ichneumonidae) and flies. The parasites attack only one type of insect or their close relatives. Larvae only are parasites. One or more parasitic larvae develop on or inside the host. Parasites are often smaller than their hosts. Some parasites (e.g. Trichogramma), lay their eggs in pest eggs, others lay their eggs in the body of caterpillars or larvae as most of the ichneumon –gold wasps and tachina flies - do. Caterpillar continues to live and eat, together with the egg and later larvae, which ripen it.
Pathogens are fungi, bacteria or viruses that infect and kill the insect. For breeding, they require special conditions (such as high humidity, some sunlight). Most pathogens are specific for certain groups of insects, or even for a particular life stage of the insect. The most well-known pathogens are Bacillus thuringiensis (Bt) and virus NPV.
Nematodes are very small worms. Some types attack plants like root nematodes. Others, so-called entomopathogenic nematodes attack and kill insects. Entomopathogenic nematodes are usually effective against pests living in the soil or in wet conditions. The nematodes like Steinernem are also useful in pest control.
The most famous entomophages are ichneumon wasps, lacewing flies (Chrysopidae), tachina flies, earwigs, snakeflies, assassin bugs, and ground beetles.
Role of entomophages in nature can be enhanced by use of plant resources. Plants serve as a shelter and a source of additional food for insects like flower pollen and nectar, which are absent in monoculture systems (cotton, wheat, rice, etc.).
For successful wintering of entomophages the presence of certain trees is of particular importance. A cracked bark of mature trees like mulberry, plane trees, apricot, is a place where insects gather for wintering. Feeding on nectariferous plants increases the life expectancy and fertility of many entomophages.
Insects are closely related to forage crops: it is both a habitat and a food source for them. Therefore, through plants it is possible to change the relationship with the different types of entomophages and thus enhance the effectiveness of the biological plant protection.
The natural enemies, besides food, need in sun-protected, shady, wet habitats and plants, suitable for egg laying.
In future, biological control takes an important place in the integrated pest management system. As compared with the chemical method, it has a number of advantages:
The ecological foundations of biological control are poorly studied. The studies of the biogeocenosis are difficult, time-consuming, costly, and require the precision instruments. Relationships in ecosystems are very complex and multifaceted. Thus, there are still many unsolved problems in this area of science. Currently the biological control research focuses on conditions that determine the effectiveness of natural enemies of pests and methods that regulate relations between them.
Pesticides destroy a life cycle chain and create favorable conditions for uncontrolled reproduction of pests. The natural enemies-predators are killed at first: they live openly and do not hide as pests do. When applying pesticides, farmers kill their own allies and then face the problem of protecting their gardens and fields.
The live fences, plantings around the canal, and tree plantations are the habitat for a large variety of pests and natural enemies, where they live in equilibrium. Natural enemies kill the pests, thus preventing them to multiply out of control, but at the same time, they never kill them completely, maintaining its own population at a high level.
If pests become suddenly abundant in the garden, entomophages are ready to move to the crop plants and help the farmer to cope with this disaster. First, the number of pests increases, and only 2-3 weeks after, the number of predators and parasites grows in response to an increased amount of food, i.e. pests have 2-3 weeks for uncontrolled reproduction.
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