The United Nations declared 2020 as the International Year of Plant Health. Humans care about plant health primarily because we obtain food, raw materials, and building materials from plants, and we want to maximize the quantity and quality of these products rather than share them with insects, snails, and fungi. To protect future harvests, people mainly use chemical pesticides, which not only kill harmful organisms but also harm other ecosystem components and human health. One alternative to chemical plant protection is the biological method.

Humans are peculiar creatures. We want to eat vegetables and fruits without pesticide residues, which forces producers to synthesize substances that quickly decompose in the soil. But when we want to prevent beetles from damaging forest plantations, we're dissatisfied that all approved pesticides stop working on their larvae after 3-4 months. Therefore, we have to apply additional insecticides to unclosed plantations where the density of beetle larvae exceeds 2-3 specimens per square meter.

Protecting nursery stock and young plantations requires resources, though less than replanting or writing off damaged areas. Therefore, seedlings in greenhouses and nurseries, as well as unclosed forest plantations, must be protected, primarily using chemical insecticides. If we want to obtain acorns from seed plantations, we must spray the crowns with pesticides before weevils lay eggs in the ovaries. Since beetle activity is prolonged, we must be prepared to spray these plantations two or three times.

Similarly, if timber is harvested in summer but not immediately removed and debarked, within days it becomes infested with stem borers that introduce spores of wood-staining and wood-destroying fungi under the bark. When it's time to transport this timber, its quality, grade, and value will differ from what was expected. Sometimes such protection is also needed at lower warehouses.

The last case where chemical insecticides might be justified in forests is during mass outbreaks of particularly dangerous needle-eating insects. In Ukraine, these are primarily the pine moth, occasionally the pine processionary, and in some cases the pine looper and common pine sawfly, especially if they completely defoliate trees in August-September after the trees were already damaged in May by the pine beauty moth and in June by the spring generation of common pine sawfly. Such mass outbreaks recur in certain stands every 10-12 years and, with timely forest protection measures, last no more than 2-3 years.

The biological method of forest protection involves using natural enemies to regulate pest populations. These natural enemies of tree-damaging insects include parasitoids, predators, and pathogens (disease-causing agents). Insect parasitoids and predators are called entomophages.

Parasitoids spend much of their life on or inside a single host, gradually killing it. This distinguishes them from parasites, which don't kill their hosts (like worms or lice). Many parasitoids are so-called "riders," named because the female mounts the victim like a rider on a horse and lays one or several eggs on or under the host's body covering. The victim becomes a living carrier of fresh food reserves for the parasitoid's larvae that hatch from the eggs.

About 10% of insect species are parasitoids - more than all mammal, bird, reptile, amphibian, and fish species combined. These parasitoids have long been used to protect plants from harmful insects. The insect in which a parasitoid lays eggs is called a "host" in English or "живитель" (nourisher) in Ukrainian, as it provides nourishment for the parasitoid.

Hosts have developed defense measures against parasitoids through behavior and physical and chemical adaptations during long evolutionary periods. Just as lymphocytes surround splinters in our fingers, special blood cells in insect hosts surround parasitoid eggs to prevent their development. To overcome host resistance, parasitoids introduce chemical substances and even viruses that affect the host's immune system.

Predators are organisms that feed on other living organisms or their parts. In natural selection, prey evolution aims to avoid becoming predators' meals. Prey may escape, hide, camouflage, or gather in large groups. Since prey resists, predators hunt old, young, or sick individuals whose removal doesn't significantly impact prey population dynamics.

The third group of biological control agents are insect pathogens - viruses, bacteria, fungi, microsporidia, and nematodes that penetrate and multiply in insect tissues. Pathological changes appear after an incubation period depending on pathogen and insect species, development stage, and ecological conditions, primarily temperature.

Biological control is applied through three main approaches:

1. Conservation biological control - preserving effective natural enemies in ecosystems by ensuring nectar plants for entomophage nutrition, maintaining entomophage habitats after clear-cutting, and reducing insecticide impacts. Back in 1957, UkrNDILGA developed "Instructional Guidelines for Preserving Entomophages During Pest Control Measures."

2. Augmentation biological control - increasing natural enemy populations by mass-rearing them in specialized facilities and repeatedly releasing them into pest outbreaks. This approach is similar to pesticide application. Carl Linnaeus in the 18th century relocated ground beetles to protect orchards. In the 19th century, France introduced collected Calosoma beetles into gypsy moth outbreaks. In the 1930s, Chernihiv laboratory reared and released Trichogramma wasps against pine moth.

3. Classical biological control - introducing natural enemies from other regions or countries. In early 20th century, about 600 species of parasitoids and predators were introduced from Europe to the US against over 90 pest species, with about 100 species establishing. Similarly, Canada introduced 220 entomophage species, with 50 establishing. As a result, the gypsy moth rarely appears as a pest in America.

A striking example of biological control success was using the viral preparation VIRIN-ENSH against gypsy moth in several Ukrainian regions during 1975-1984, after which outbreaks of this pest were practically absent for many years. This preparation was created by E.V. Orlovska, who enhanced virus virulence through multiple caterpillar infections and developed production technology. Unlike spraying, which requires at least half of leaf surface development and egg hatching, Orlovska's ground outbreak method involves treating egg clusters with viral suspension before larvae hatch.

After successful VIRIN-ENSH applications, Ukrlisozakhyst (now Kharkivlisozakhyst) initiated production of viral preparations VIRIN-NSH (gypsy moth), VIRIN-RSP (red pine sawfly), and VIRIN-ZSP (common pine sawfly). However, production of these forest protection viral preparations in Ukraine has stopped due to lack of funds for registration renewal in the State Chemical Commission, just as gypsy moth outbreaks began recurring.