The digestive system of a pond snail. Garden snail (Cepaea hortensis). Mollusks pond snails taxonomy in Latin

Siberian silkworm - Dendrolimus superans - is a subspecies of the large coniferous silkworm Dendrolimus superans. Wingspan 65-90 mm. Caterpillars feed on almost all conifers.

Since the Siberian silkworm can only be recognized as a subspecies, its ecological and morphological forms should be considered tribes. Siberian silkworm varies greatly in color - from yellowish to brown, sometimes almost black.

There are three such tribes on the territory of Russia: larch, cedar and Ussuri. The first occupies almost the entire range of the subspecies. Cedar and Ussuri have a limited distribution.

Butterflies are especially active during sunset hours. Immediately after mating, females lay their eggs on needles, mainly in the lower part of the crown, and during periods of very large numbers - on dry branches, lichens, grass cover, forest litter. In one clutch, there are usually several dozen eggs (up to 200), and in total the female can lay up to 800 eggs, but most often the fecundity does not exceed 200–300 eggs.

The eggs are almost spherical in shape, up to 2 mm in diameter, at first bluish-green in color with a dark brown dot at one end, then grayish. Egg development lasts 13–15 days, sometimes 20–22 days.

The color of the caterpillars varies from gray-brown to dark brown. The body length of the caterpillar is 55–70 mm, on the 2nd and 3rd body segments they have black transverse stripes with a bluish tint, and on the 4th–120th segments there are black horseshoe-shaped spots.

The first molt occurs after 9-12 days, and after 3-4 - the second. At the first age, the caterpillars eat only the edges of the needles; at the second age, they eat the entire needles. At the end of September, the caterpillars burrow into the soil, where they curl up in a ring and hibernate under a moss cover.

At the end of April, the caterpillars climb into the crowns of trees and begin to feed, eating whole needles, and with a lack of food, the bark of thin shoots and young cones. About a month later, the caterpillars molt for the third time, and in the second half of July - again. In autumn they leave for the second wintering. In May-June of the following year, adult caterpillars feed intensively, causing the greatest harm. During this period, they eat 95% of the food necessary for full development. They molt 5–7 times and go through 6–8 instars accordingly.

Caterpillars feed on the needles of almost all conifers. In June, they pupate; before pupation, the caterpillar weaves a brown-gray oblong cocoon. The pupa, 25–45 mm long, is initially light, brownish-red, then dark brown, almost black. The development of the pupa depends on temperature and lasts about a month. The massive summer of butterflies takes place in the second decade of July. On the southern slopes of the mountains, it passes earlier, on the northern slopes - later.

The development cycle of the Siberian silkworm usually lasts two years, however, in the south of the range, development almost always ends in one year, and in the north and in high mountain forests, sometimes there is a three-year generation. With any phenology, the main periods of the life of the Siberian silkworm (years, development of caterpillars, etc.) are very extended.

Heat plays a decisive role in determining the duration of the development cycle; weather and climate in general, as well as the timely passage of diapause by caterpillars. Characteristically, the transition to a one-year cycle of development in places with a two-year generation is observed most often during an outbreak of mass reproduction. It is also believed that a one-year development cycle occurs if the annual sum of temperatures exceeds 2100 °C. At a sum of temperatures of 1800–1900°C, the generation is two-year, and at 2000°C, it is mixed.

Silkworm years are observed annually, which is explained by the presence of mixed generations. However, with a pronounced two-year development cycle, flying years occur every other year.

The silkworm damages 20 species of tree species. It appears in mass in different years and is characterized by variable forms of the gradation curve. Most often, silkworm outbreaks occur after two or three dry growing seasons and the strong spring and autumn forest fires that accompany them.

In such years, under the influence of a certain way of developing metabolism, the most viable and prolific individuals appear, successfully enduring difficult periods of development (younger ages of caterpillars). Forest fires contribute to the reproduction of the pest, burning the forest floor, in which the entomophages (telenomus) die. In lowland forests, silkworm outbreaks are usually preceded by harsh winters with little snow, leading to the freezing of entomophages, which are less cold-resistant than silkworm caterpillars. Outbreaks occur primarily in forests thinned by cuttings and fires, near raw material bases at a low density of stands of different age and composition. Most often these are overmature and ripe, less often middle-aged pure stands with a sparse undergrowth and a slight admixture of deciduous species.

At the beginning of the outbreak and during periods of depression, the silkworm has a clearly expressed commitment to certain types of forest, landforms, phytoclimate, and other ecological features of plantations. Thus, in the flat part of Western Siberia, the centers of population outbreaks are most often associated with fir, oxalis and green moss. In the zone of coniferous-deciduous forests of the Far East, they are associated with mixed cedar and cedar-fir plantations, and in Eastern Siberia their location is closely related to the relief features of mountain forests and the dominance of larch and cedar.

In terms of nutritional value for caterpillars, larch needles are in first place, then fir needles, cedar needles take only third place. Therefore, in larch forests, the fertility and breeding energy of butterflies is the highest, and in cedar forests - average. Caterpillars are rapidly developing in fir forests according to an annual cycle, but to the detriment of fertility, which falls to average values. When feeding on spruce and pine needles, there is a rapid grinding of individuals, a drop in fertility and survival.

Outbreaks of mass reproduction last 7–10 years, of which 4–5 years the plantations are significantly damaged, the stands bare by caterpillars dry out and are populated by stem pests.

The most unstable species in the taiga is fir (Siberian, white-pored), the most stable is larch (Siberian, Dahurian, Sukacheva).

In the first year of severe caterpillar damage to coniferous trees, the latter are populated by stem pests only when they are completely deneedled. In subsequent years, their number and activity first increase rapidly, and after 2–4 years, a sharp decline begins.

The Siberian silkworm is an enemy of the taiga forests, and the losses it inflicts are comparable to those from forest fires. The distribution area of ​​the silkworm extends from the Urals to Primorye, including Mongolia, Sakhalin, the Kuril Islands, part of China, Japan and North Korea.

The Siberian silkworm is a butterfly of the cocoonworm family. This is a dangerous pest, the object of destructive attention of which are coniferous trees. Most of all, the silkworm harms cedar, fir, larch, less - pine and spruce.

Needles are eaten not by butterflies, but by caterpillars of the Siberian silkworm - they destroy it entirely, and in case of a lack of food, they switch to shoots and young cones.

The development of the silkworm is bisexual; in winter, the caterpillars hide in a layer of fallen leaves and dry grass. The full development cycle of the silkworm lasts 1-2 years in the southern part of its habitat, in other regions - two or three years. For three years, the silkworm develops in the northern and high mountain regions.

As a rule, the periods of life of the Siberian silkworm depend on the ambient temperature and the timing of the caterpillar's passage of the period of physiological inhibition of metabolic processes - diapause.

The Siberian silkworm is a quarantine object - harmful to the plant organism and causing damage to them, with a limited distribution in the country, and requiring special control measures.

Insect structure

The wingspan of the butterfly is 60-95 mm, shortened labial palps, abundantly pubescent. The third segment has a smoothly rounded apex and is 1/3 the length of the second segment. Ocelli hemispherical, glabrous. There are spurs on the middle and hind legs. On the front wings, the edges are even, slightly rounded. There is a basal cell on the hind wing, the shoulder veins are absent.

The color of the wings of the Siberian silkworm butterfly ranges from light gray to dark brown. It also happens to be ocher-brown, dark or light brown. On the front wings there is a white spot and two dark transverse bandages.

Internal ligation is most often incomplete, visible only in the first half of the wings. External - poorly visible from the inside, has teeth on the outside.

Butterflies have differences in wingspan - in males it is 78-96 mm, in females - 60-76 mm.

The eggs are round, 2.2 mm in diameter. The cover of the egg at first is light green with a brown dot on one side. Over time, the egg becomes darker.

The caterpillar has a body without spines and warts. The hairline consists of thick, velvety hairs, and long sparse hairs, which are 10 times longer than short ones. On the second and third segments of the body, the Siberian silkworm caterpillar has black and blue transverse stripes, and on the fourth and twelfth - rounded black spots. The length of the caterpillar is 5-8 cm.

Pupa - at first it is distinguished by light or red-brown covers, then they become dark brown or black.

Stages of development of the Siberian silkworm

Butterflies of the first age appear at the end of June, they become especially active at sunset. "Newborns" do not need additional nutrition, the supply of nutrients in their body has accumulated enough from previous periods of life. Under the influence of wind, young butterflies can fly 13-15 kilometers from the place of birth.

Mass mating begins in mid-July and lasts until early August. After mating, females lay eggs on needles - one at a time or in whole groups. Sometimes dry branches, lichens, grass, forest litter become a place for laying eggs. One clutch can contain up to 200 eggs. The most prolific females can lay up to 300 eggs.

The development of the embryo lasts 13-15 sometimes 22 days.

At an early age, the larva feeds on the tips of the needles, but at the second age it is able to eat the whole needle. Caterpillars are especially fond of soft larch needles, feeding on spruce and pine needles leads to smaller individuals, reduced fertility, and even complete extinction.

At the end of September, the caterpillars leave the trees, burrow into the soil under the moss, and hibernate there, curled up in a ring. As a rule, they spend the winter in the third or second age, depending on the type of forest in which they grew. In total, the Siberian silkworm molts 5-7 times, and experiences 6-8 instars.

In the spring, at the end of April, the caterpillars wake up, climb the trees and begin to feed on needles, shoot bark, and young cones. At the end of May, they begin their third molt, and in July - the fourth. In autumn, the caterpillars again go to wintering, so that with the onset of warm weather, they again begin intensive feeding. It is at this age that they cause more damage to the forest, eating up to 95% of the food they need for final development. Individuals of older ages in search of food can crawl through treeless space for a distance of up to one and a half kilometers.

A full-fledged, developed caterpillar, having survived all the necessary ages, begins to weave a dense gray cocoon, inside which it becomes a chrysalis. The development of the pupa lasts 3-4 weeks.

At the end of June, a sexually mature individual of the Siberian silkworm emerges from the cocoon, ready for mating. And the whole cycle repeats again.

Distribution area of ​​the Siberian silkworm:

The insect is common in Siberia, Eastern Siberia, the Far East and the Urals. The silkworm eats needles and causes damage to coniferous forests over a fairly large area from the Southern Urals to Vladivostok, from Yakutsk to Mongolia and China, where it is also widely distributed.

There is a Siberian silkworm in Kazakhstan, North Korea, the southern border of its distribution is at 40 degrees north latitude. Scientists note the expansion of the range to the north and west.

Silkworm damage and remedies

Most often, in the summer, centers of mass reproduction occur on an area of ​​​​4-7 million hectares, and cause serious damage to forestry. In addition, the mass reproduction of the silkworm leads to an outbreak of secondary pests - bark beetles, borers and barbels.

The Siberian silkworm is also present in a healthy forest, but in limited quantities. An ecological catastrophe can be provoked by the mass reproduction of a pest, and drought is considered one of the reasons for this phenomenon. During drought, the caterpillar is able to develop in a year, and not in two years as usual. Due to the sharp increase in the population, the natural enemies of the silkworm do not have time to destroy them. Early spring fires also contribute to the spread of the pest, because they also destroy the telenomous insect that eats silkworm eggs. The natural enemies of the Siberian silkworm are birds and fungal infections.

The entomological state of the forest is monitored by space satellite instruments, which contribute to the timely detection of breeding centers and allow you to take the necessary measures.

In the mid-1990s, in Eastern and Western Siberia and the Far East, the Siberian silkworm damaged green spaces over a vast area. In the Krasnoyarsk Territory, the outbreak, which lasted four years, caused damage to the forest in 15 forestry enterprises on a total area of ​​600,000 hectares. Then the silkworm caterpillars destroyed the cedar plantations, which are of great value for the national economy.

Over the past hundred years, 9 outbreaks of silkworm distribution have been observed in the Krasnoyarsk Territory. As a result, a forest on an area of ​​ten million hectares was damaged. It was possible to localize the outbreak with the help of modern preparations for the destruction of insects. However, the focus can flare up at any favorable time.

As a rule, the Siberian silkworm waits "in the wings" in places with fairly favorable conditions for development. In the dark coniferous taiga, its reservations are in ripe and productive plantations with a large "forage base".

The pest spreads not only by a natural method, but also by moving to a new place by transport “hare”, hiding under the bark of logs and other timber, as well as in seedlings and seedlings - of course, not adult butterflies, but cocoons and eggs move in this way.

Therefore, bans and restrictions on imported forest products have been introduced in the phytosanitary zone:

Coniferous logs must be debarked and disinfected with pesticides. The absence of silkworms and other pests is confirmed by a special certificate.

Planting material, bonsai, branches of coniferous trees are prohibited from being imported from the phytosanitary zone from May to September without a quarantine certificate. If there is no certificate, all materials must be destroyed within 5 days of discovery.

In the centers of distribution of the silkworm, ground or air treatment of the forest with pyrethroids, neonicotinoids, and organophosphorus compounds is carried out.

In addition, the number of pests is recorded by means of pheromone traps or by counting caterpillars in tree crowns.

Good results are obtained by preventive treatment of the forest with special preparations in the summer.

Siberian silkworm (Dendrolimus superans sibiricus Tschetv.)

Siberian silkworm (Dendrolimus superans sibiricus Tscetv.) in the Asian part of Russia is one of the most dangerous pests of coniferous forests, especially in Siberia and the Far East. Periodic large-scale outbreaks of mass reproduction of this phytophage lead to significant changes in the structure of taiga forests, destruction of forest stands and change of forest formations.

The centers of mass reproduction are observed annually on an area from 4.2 thousand to 6.9 million hectares (0.8 million hectares on average) and cause significant damage to forestry. Therefore, satellite monitoring as a part of entomological monitoring of forests is an important element in monitoring the state of forest cover, which, if properly performed, ensures the preservation of the most important ecological functions of forests.

In Russia, a huge contribution to the development and implementation of biological methods to combat the centers of mass reproduction of the Siberian silkworm was made by Prof. Talalaev E.V. In the mid-1990s, extensive forest plantations in Western and Eastern Siberia, as well as in the Far East, suffered from the silkworm. In the Krasnoyarsk Territory alone, for four years, the outbreak covered the territories of 15 forestries, the area of ​​damaged taiga plots amounted to more than 600 thousand hectares. A large number of valuable cedar plantations have been destroyed. Over the past 100 years, 9 outbreaks of the pest have been registered in the Krasnoyarsk Territory. As a result, over 10 million hectares of forests were damaged. The use of modern insecticidal pyrethroid and bacterial preparations made it possible to partially localize the foci of the pest and stop its further spread.

At the same time, the danger of a new mass reproduction of the Siberian silkworm remains.

In the period between outbreaks, the silkworm lives in reservations - areas with the most favorable development conditions. In the zone of dark coniferous taiga, the reservations are located in mature, quite productive (grade II-III class) stands of forb-green-moss forest types with the participation of fir up to 6 units and more, with a density of 0.3-0.6.

Imago of the Siberian silkworm. Photo: Natalia Kirichenko, Bugwood.org

　

The Siberian silkworm is a large butterfly with a wingspan of 60-80　mm for the female and 40-60　mm for the male. Color varies from light yellowish brown or light gray to almost black. The forewings are crossed by three darker stripes. In the middle of each wing there is a large white spot, the hindwings are the same color.

Females lay eggs on needles, mainly in the lower part of the crown, and during periods of very large numbers - on dry branches, lichens, grass cover, and forest litter. In one clutch, there are usually several dozen eggs (up to 200), and in total the female can lay up to 800 eggs, but most often the fecundity does not exceed 200-300 eggs.

The eggs are almost spherical in shape, up to 2　 mm in diameter, at first bluish-green in color with a dark brown dot at one end, then greyish. Egg development lasts 13-15 days, sometimes 20-22 days.

Caterpillars of the Siberian silkworm have different colors. It varies from gray-brown to dark brown. The body length of the caterpillar is 55-70　 mm, on the 2nd and 3rd body segments they have black transverse stripes with a bluish tint, and on the 4-120th segments there are black horseshoe-shaped spots (Fig.).

The first molt occurs after 9-12 days, the second after 3-4. At the first age, the caterpillars eat only the edges of the needles; at the second age, they eat the entire needles. At the end of September, the caterpillars burrow into the litter, where they hibernate under the moss cover.

At the end of April, the caterpillars rise into the crowns of trees and begin to feed, eating whole needles, and with a lack of food, the bark of thin shoots and young cones. About a month later, the caterpillars molt for the third time, and in the second half of July - again. In autumn they leave for the second wintering. In May-June of the following year, adult caterpillars feed intensively, causing the greatest harm. During this period, they eat 95% of the food necessary for full development. They molt 5-7 times and go through 6-8 instars respectively.

Caterpillars feed on the needles of almost all conifers. But they prefer fir, spruce, larch. Cedar is damaged to a lesser extent, pine is even less damaged. In June, caterpillars pupate; before pupation, the caterpillar weaves a brown-gray oblong cocoon. Pupa, 25-45　 mm long, brownish red, then dark brown, almost black. The development of the pupa depends on temperature and lasts about a month. The massive summer of butterflies takes place in the second decade of July. On the southern slopes of the mountains, it passes earlier, on the northern slopes - later.

The development cycle of the Siberian silkworm usually lasts 2 years. But in the south of the range, development almost always ends in one year, and in the north and in high-mountain forests, sometimes there is a three-year generation. Butterfly flight begins in the second half of July and lasts about a month. Butterflies don't eat. The wingspan of females is from 6 to 10 cm; males are 4-5 cm. Unlike females, males have feathery antennae. The female lays on average about 300 eggs, placing them one by one or in groups on needles in the upper part of the crown. In the second half of August, caterpillars of the first age emerge from the eggs, feed on green needles, and in the second or third age they leave for wintering at the end of September. Caterpillars overwinter in the litter under the cover of moss and a layer of fallen needles. The rise in the crown is noted in May after the snow melts. Caterpillars feed until next autumn and leave for the second wintering at the fifth or sixth age. In spring, they again rise to the crowns and after active feeding in June weave a dense gray cocoon, inside which they then pupate. The development of the silkworm in the chrysalis lasts 3-4 weeks.

In the dark coniferous taiga, silkworm foci form after several years of hot, dry weather in summer. In this case, the caterpillars leave for wintering later, at the third or fourth age, and turn into butterflies the next summer, moving to a one-year development cycle. The acceleration of the development of caterpillars is a condition for the formation of centers of the Siberian silkworm.

Plot of coniferous forest after defoliation by the Siberian silkworm. (Photo by D.L. Grodnitsky).

　

Forest area defoliated by the Siberian silkworm (photo: http://molbiol.ru)

Accounting for wintering caterpillars in the litter is carried out in October or early May. The number of caterpillars in the crown is determined by the method of rounding on cloth canopies in early June and late August.

The age of the caterpillars is set according to the table, measuring the width of the head.

It should be borne in mind that in the conditions of Northern Eurasia, forests that have died from the silkworm are poorly restored. Caterpillars destroy the undergrowth along with the forest stand, and only a decade later, a small undergrowth of deciduous species may appear. In old foci, conifers appear only 30-40 years after the drying of forest stands, and not everywhere and not always.

The main reason for the lack of natural renewal in silkworms is a sharp ecological transformation of plant communities. During the mass reproduction of the silkworm in 3-4 weeks, up to 30 t/ha of eaten fragments of needles, excrement and corpses of caterpillars enter the litter and soil. Literally within one season, all the needles in the plantation are processed by caterpillars and enter the soil. This litter contains a significant amount of organic matter - favorable food for soil bacteria and fungi, the activity of which is significantly activated after the mass reproduction of the silkworm.

This is also facilitated by an increase in soil temperature and moisture, since neither sunlight nor rainfall is trapped by the tree canopy anymore. In fact, the mass reproduction of the silkworm contributes to a more intensive course of the biological cycle as a result of the rapid release of significant the amount of matter and energy contained in the forest floor.

The soil in silkworms becomes more fertile. A light-loving grass cover and undergrowth rapidly develops on it, intensive turfing and often swamping occur. As a result, heavily disturbed stands are replaced by non-forest ecosystems. Therefore, the restoration of plantations close to the original ones is delayed for an indefinite period, but not less than 200 years (Soldatov et al., 2000).

Outbreaks of mass reproduction of the Siberian silkworm in the forests of the Ural Federal District

In general, despite the large number of works on the ecology of the Siberian silkworm in the 50-60s, many features of the ecology of the Trans-Ural population under the conditions of global anthropogenic impact remain unexplored.

Outbreaks of mass reproduction of the Siberian silkworm in the larch forests of the Cis-Urals have been observed since 1900 [Khanislamov, Yafaeva, 1962]. y.y. The first outbreak in the forests of the Sverdlovsk region was discovered in 1955 on the territory of the Tavdinsky and Turinsky forestries. The total area of ​​outbreaks was 21,000 ha and 1,600 ha, respectively. On the territory of the Tavdinsky forestry large foci were formed earlier. It is noteworthy that these forestry enterprises have been the place of intensive timber harvesting for many decades. Therefore, coniferous forests have undergone anthropogenic transformation and currently have an admixture of secondary birch forest with pine, spruce and fir in the undergrowth. It should be noted that a new outbreak (1988-1992) in the Sverdlovsk region was registered in other forestries. To the greatest extent, it was formed in the forests of the Taborinsky district. The total area of ​​the outbreaks was 862 ha, some outbreaks were also observed during aerial surveillance in the Garinsky district.

Studies have shown that on 50% of the areas affected by outbreaks in 1988-1992, the main forest-forming species is birch with fir and spruce in the undergrowth (Koltunov, 1996, Koltunov et al., 1997). Fir undergrowth strongly defoliated by the Siberian silkworm and mostly shrunken. As a result, significant damage was caused to the development of coniferous economy in these forestries. The primary centers of mass reproduction of the Siberian silkworm appeared in 1988 in plantations with fir undergrowth. In 1993, the outbreak completely died out. On the territory of KHMAO-YUGRA, the outbreak of mass reproduction died out in 1992. In some quarters, defoliation by the Siberian silkworm of spruce was observed, as a result of which it also quickly dried out. As studies in the foci of this phytophage during the outbreak showed, the development of the Trans-Ural population occurs mainly according to a two-year cycle. In general, studies have shown that the topography of broad silkworm foci in coniferous forests of the Sverdlovsk region coincides with forest areas disturbed by anthropogenic impact.

On the territory of the Khanty-Mansiysk Autonomous Okrug, an outbreak of mass reproduction of the Siberian silkworm was found in the territories of the Mezhdurechensky, Uraisky, Tobolsky, Vagaysky and Dubrovinsky forestry enterprises. The total area of ​​outbreaks was 53,000 ha. We carried out the most detailed studies in the centers of mass reproduction of the Siberian silkworm in the Mezhdurechensk forestry.

Over the past 20 years, the most intensive industrial logging has taken place on the territory of Yuzhno-Kondinsky LPH. As the results showed, the spatial structure of the centers of mass reproduction of the Siberian silkworm in this forestry clearly does not coincide with the forests subjected to the most intense anthropogenic impact (first of all, cutting down). The largest outbreaks (in the western part of the forestry enterprise) are completely unaffected by anthropogenic impact. Felling in the forests before the outbreak was not carried out. We also did not find any other types of anthropogenic impact. An analysis of the forest inventory parameters of forest stands in this group of foci showed that these forests have the usual productivity for this type of forest growth conditions and are not weakened. At the same time, cuttings are observed next to other, smaller foci, and in some cases, fires. Some of the centers with a strong defoliation of crowns of forest stands were previously cut down.

As the results showed, the anthropogenic impact in the dark coniferous lowland forests of the Trans-Urals is not a key factor in the formation of centers of mass reproduction of the Siberian silkworm, although its contribution is undoubted. Under conditions of moderate anthropogenic impact, the main factor in the organization of the spatial structure of foci is forest conditions in ecotopes and microrelief features. Thus, the largest foci adjoin river beds and places with microelevations, which is known earlier [Kolomiets, 1960, 1962; Ivliev, 1960]. A particularly important fact is that the forests in the areas of outbreaks were not noticeably weakened under the influence of anthropogenic factors. The level of anthropogenic transformation of these forests was extremely insignificant, no higher than stage 1 in some ecotopes (5-10% of forests). As the geobotanical analysis of the grass layer showed, the grass cover in these forests is not changed.

Thus, to the greatest extent these forests are affected only by the proximity to clearcuts (changes in light and wind conditions) and, to a lesser extent, by fellings carried out several decades ago in some of them.

An analysis of the radial growth of trees in the foci and beyond their boundaries confirms our conclusion about the preservation of the stability of forests in general, which have undergone defoliation. We associate the reduced radial growth of trees in the foci with the adaptive response of forest stands to forest vegetation | conditions, but not with their weakening, since we have found these differences not in recent years, but for 50 years or more.

A characteristic feature of the dynamics of stand defoliation during the outbreak in the lowland forests of the Trans-Urals was a clear preference for defoliation of fir in the undergrowth at the beginning of the outbreak, then fir in the main layer, and later spruce and stone pine. Pine defoliated very weakly. Therefore, no foci were formed in pure pine forests. A study of the Trans-Ural population of the Siberian silkworm in the outbreaks showed that in the eruptive phase and before the outbreak faded, the imago hatching rate was very low and ranged from 2 to 30%, averaging 9.16%.

Most of the pupae population dies. The most significant percentage of the population dies from infectious diseases (bacteriosis and granulosa virus). Death from these causes ranges from 29.0 to 64.0%, on average, 47.7%. Bacterial infections accounted for the main percentage of the causes of death from this group of diseases. Viral infections were much less common. It should also be noted that the microscopic analysis of the dead caterpillars in the outbreaks both in Sverdlovsk and Khanty-Mansiysk Autonomous Okrugs convincingly showed that the attenuation of outbreaks was not accompanied by a viral epizootic (granulosis virus).

Our results are in good agreement with the data of other researchers on other populations of the Siberian silkworm [Khanislamov, Yafaeva, 1958; Boldaruev, 1960, 1968; Ivliev, 1960; Rozhkov, 1965].

During the period of attenuation of the outbreak of mass reproduction of the Siberian silkworm in the forests of the Khanty-Mansi Autonomous Okrug, up to 30 caterpillars per 1 m 2 were found in the litter, which died from infectious diseases.

As the results showed, an interesting feature of the stands that dried out after defoliation by the Siberian silkworm in the flat dark coniferous forests of the Khanty-Mansi Autonomous Okrug was the almost complete absence of their colonization by xylophagous insects within 1-2 years after drying, although in the forests undamaged by the Siberian silkworm, colonization by xylophages is observed. drying stands and individual trees.

At the same time, it should be noted that the supply of xylophages in the areas of outbreaks is sufficient. In addition, at the shift plots and at the stock depots in Yuzhno-Kondinsky LPH, the whips left without treatment are quickly populated by xylophagous insects. We attribute the slowdown in the colonization of shrunken forest stands by xylophages after their defoliation by the Siberian silkworm to a greater extent with the increased moisture content of the wood. This, in our opinion, was due to the active transport of water by the root system of trees after crown defoliation against the background of the cessation of transpiration due to the absence of needles.

Studies in the centers of mass reproduction of the Siberian silkworm in the Trans-Urals showed that the last outbreak of this phytophage in the dark coniferous forests of the plain Trans-Urals was observed 33 years ago. It can be assumed that the cyclicity of outbreaks of this phytophage at the western border of the range is closely related to the periodicity of the most severe droughts in 1955 and 1986. The most severe drought (in 1955) was also accompanied by a larger area of ​​foci of this phytophage in the Trans-Urals.

Previously, there were no outbreaks of the Siberian silkworm in the Kondinsky forestry enterprise. The dendrochronological analysis of fir and spruce cores (for the last 100-120 years), carried out by us, showed that forest stands, both in the outbreak and outside it, had not previously been subjected to noticeable defoliation. On the basis of our results, we can assume that there is a gradual penetration of the Siberian silkworm to the north and the emergence of outbreaks of mass reproduction in these habitats, which were not previously observed there. This is probably due to the gradual warming of the climate.

The relationship between the spatial structure of foci and anthropogenic impact on forest biogeocenoses is not convincingly traced. Foci were identified both in forest areas where active logging was carried out, and in forests completely unaffected by logging, which are significantly removed from roads, winter roads and settlements.

On the basis of the results obtained, it was established that under the conditions of anthropogenic transformation of the dark coniferous forests of the Trans-Urals, the largest centers of the Siberian silkworm can appear both in completely undisturbed forests and in forests exposed to anthropogenic factors.

A comparative analysis of the spatio-temporal structure of the foci during the last two outbreaks shows that the foci of mass reproduction each time are formed in different ecotopes and do not coincide spatially at all. As the results of the research showed, the first outbreaks in each of the surveyed forestries appeared in 1988 simultaneously with other outbreaks in the more southern regions of the Tyumen region. This excludes the possibility their emergence by migration from the southern part of the range. Probably, the population in the phase of depression was also in the northern part of the range of this population.

On the western border of the range of this phytophage, outbreaks are of a fast-moving character. This is well explained by the narrowness of the time interval of the climatic optimum during the drought period. Taking this into account, as well as the presence of a two-year cycle in Siberian silkworm caterpillars, this gives good prospects for reducing the economic damage from outbreaks through the use of active measures in the period immediately before the eruptive phase of the outbreak. Sustaining a high outbreak potential is possible only during this narrow period of drought. Therefore, the treatment of foci during this period will eliminate the likelihood of the formation of large repeated steps.

As shown by the results of a comparative analysis of the forest taxation parameters of 50 sample plots laid in the centers of mass reproduction of the Trans-Ural population of the Siberian silkworm in the Taborinsky forestry enterprise of the Sverdlovsk region, the centers were formed in forest stands with different density: from 0.5 to 1.0, on average - 0, 8 (Tables 3.1,3.2). Correlation analysis showed that the areas of the foci positively correlated with the quality class (R=0.541) (with the worst growth conditions), average height (R=0.54) and negatively correlated with fullness (R=-0.54).

However, he draws attention to the fact that out of 50 trial plots, only 36% of the plots with a density lower than 0.8 formed centers of mass reproduction of the Trans-Ural population of the Siberian silkworm, while in the vast majority of trial plots the density was 0.8 and higher. The average level of defoliation of more low-density forest stands is, on average, 54.5%, while for high-density stands (with a density equal to 0.8 or more) - 70.1%, but the differences were not statistically significant. This probably indicates that the level of defoliation is influenced by a complex of other factors, which is common for a group of forest stands. The contribution of this group of factors to the level of entomoresistance of forest stands was significantly higher than the influence of the density of forest stands.

Studies have shown that this factor is the soil-edaphic conditions in ecotopes. Thus, all the stands on the test plots, which were located on ridges, in drier habitats, were defoliated most strongly, compared with the stands on the flat parts of the relief, or microdepressions. Correlation analysis of the degree of defoliation with other forest inventory parameters also did not reveal a statistically worthy of its relationship with the quality class (r = 0.285). However, the average level of defoliation in the lowest quality forest stands (with a quality class: 4-5 A) was 45.55%, while in the highest quality stands it was 68.33%. The differences are statistically significant (at P=0.01). The absence of a significant linear correlation was also probably due to the strong dominance of the factor of soil and edaphic conditions. This is accompanied by a strong defoliation of forest stands, which differ significantly in quality class. It is also impossible to exclude the possible influence of the factor of local migration of caterpillars from completely defoliated high quality forest stands to nearby low quality stands. Although it should be noted that caterpillars in the crown were recorded by us in both groups of forest stands. Therefore, local migration in any case was not the main reason for the strong defoliation of low quality forest stands.

Analysis of the results shows that in the conditions of flat dark coniferous forests of the Sverdlovsk region. there is a certain tendency to the predominant formation of foci with the strongest crown defoliation in stands with a higher quality class. But there is also no noticeable avoidance of low quality forest stands. Foci with varying degrees of crown defoliation occur in forest stands with different quality classes. But the lowest insect resistance and strong defoliation are characteristic of plantations with the highest quality class. Taking into account the close relationship between the degree of defoliation and the level of resistance of forest stands at the same initial population density, it can be assumed that under these forest conditions, as a result of the impact of the abiotic stress factor (drought), the resistance of forest stands with a higher quality class decreases more than low-quality forest stands, which is accompanied by higher crown defoliation. high quality forest stands.

An analysis of the features of the composition of forest stands in the centers of mass reproduction of the Siberian silkworm in the Sverdlovsk region made it possible to identify two main types of strategies for the formation of centers in relation to the composition of forest stands.

1 type of strategy. Foci occur in the main layer of the forest. These forest stands are most often located on the manes of elevated parts of the relief in drier types of forest. The centers with the most significant defoliation of forest stands are formed in spruce-fir and fir-spruce stands with an admixture of birch (6P2E2B, 5E2P2B). The undergrowth contains fir, which is the first to undergo severe defoliation. In foci of this type, strong defoliation is always observed. The foci, as a rule, are of a concentrated type with a well-defined border. Surveys in the foci have shown that under these conditions, which are optimal for an outbreak, the predominant rock composition is not critical and can vary within fairly wide limits. Nevertheless, in forests with a predominance of fir in the main layer and undergrowth, the formation of foci with severe defoliation is most likely. It can be assumed that under optimal soil-edaphic conditions, the overall level of the drop in resistance to fir and spruce is higher than the level of differences in resistance between these species in less optimal habitats. According to the composition of the forest stand in these foci, there were no plantations with a predominance of fir at all, but there is a spruce forest with fir and a birch forest with fir undergrowth.

It should be noted that, in foci of this type in the Sverdlovsk oblast, there is usually a rapid colonization of dried forest stands by xylophagous insects, while in the foci of the Siberian silkworm in the forests of the Khanty-Mansiysk Autonomous Okrug, as mentioned above, the colonization of dead stands by xylophagous insects almost did not occur.

2 type of strategy. The foci do not appear in the main type of forest, but in the undergrowth. This is typical for areas of forest that have been cut down. In this type of forest, the occurrence of foci occurs regardless of the species composition of the main layer. This is due to the fact that in many types of forest that have undergone heavy felling, there is an abundant undergrowth of fir, which is completely defoliated and dries out. Often the main layer in these types of forest stands is birch, less often pine and other species. Consequently, these types of forests are intermediate in the dynamics of succession, when the change of species occurs most often through birch (Kolesnikov, 1961, 1973).

As studies have shown, in these types of forests, foci are formed under a wider range of forest-vegetation and soil-edaphic conditions. Foci of this type are often found not on elevated, but on plain elements of the relief, but not excessively moistened.

In foci with severe defoliation in the forests of the Sverdlovsk region. aspen is very rare in the composition of the main layer, as it is an indicator of wet habitats. However, in individual foci with severe defoliation, it is still found in small quantities. Usually these are foci formed in the flat part of the relief, with separate depressions. As is known, such forest stands begin to be damaged by the Siberian silkworm after a long drought, which reduces soil moisture (Kolomiets, 1958, 1962).

The last outbreak of mass reproduction of the Siberian silkworm occurred in 1999 and continued until 2007 (Fig. 3.3). It was the largest outbreak in Russia in the last 30 years.

The main area was made up of centers of mass reproduction in Siberia and the Far East. In the Trans-Urals, it was, on the contrary, very weak. In the forests of the Chelyabinsk region. areas of outbreaks in 2006 and 2007 amounted to 116 and 115 ha, respectively, in the forests of the Tyumen region. in 2005 their total area was 200 ha, in the next 2 years they were not recorded. In the forests of the Sverdlovsk region. she was absent.

For the first time, we have studied the features of the development of outbreaks of mass reproduction in the forests of the Sverdlovsk region. and the Khanty-Mansiysk Autonomous Okrug (KhMAO-UGRA).

In general, the results showed a very close similarity of the forest conditions of the preferred ecotopes in the Trans-Urals and West Siberian populations of the Siberian silkworm. This is due to the close similarity of the habitat conditions of these populations in swampy lowland dark coniferous forests.

It has been established that under the conditions of anthropogenic transformation of the dark coniferous forests of the Trans-Urals, the Siberian silkworm can form large foci both in forests disturbed by anthropogenic factors and in completely undisturbed forests. Studies have shown that a moderate level of anthropogenic transformation of the lowland dark coniferous forests of the Trans-Urals is not the dominant factor in the occurrence of foci. The rank of this factor is approximately similar to other natural preference factors, the main of which is the microrelief and relatively dry habitats.

In the western part of the range of the Siberian silkworm, outbreaks are of a fast-moving character. There are predominantly concentrated foci. The nature of the spatial structure of the primary foci suggests that they arose in a non-migratory way and the Siberian silkworm is found in the area of ​​outbreaks and during the period of depression. The formation of foci with strong defoliation is observed in forests with a wide range of density and quality classes in KhMAO-Yugra - in fir-spruce forests, in the Sverdlovsk region - in derived birch forests with fir undergrowth and spruce-fir forests.

The dendrochronological analysis of fir and spruce cores (for the last 100-120 years), carried out by us, showed that forest stands, both in the outbreak and outside it, had not previously been subjected to noticeable defoliation. Consequently, earlier there were no outbreaks of mass reproduction of the Siberian silkworm in the Kondinsky forestry of the Khanty-Mansiysk Autonomous Okrug. On the basis of our results, we can assume that there is a gradual penetration of the Siberian silkworm to the north by migration and the emergence of outbreaks of mass reproduction in these habitats, which were not previously observed there. This is probably due to the gradual warming of the climate.

It has been established that the reduced average annual radial growth of spruce and fir in the centers of mass reproduction of the Siberian silkworm is not a consequence of the weakening of forests in recent years, but represents the norm of the reaction to relatively dry growth conditions on ridges and microelevations of the relief, and the difference in radial growth persists for many decades. .

Despite the obvious increase in the scale and level of anthropogenic impact on the plain dark coniferous forests of the Trans-Urals and Khanty-Mansi Autonomous Okrug-Yugra, the frequency of outbreaks of mass reproduction of the Siberian silkworm has not changed.

The Siberian silkworm in the Trans-Urals and the Western part of Western Siberia is still a very dangerous pest, causing significant environmental and economic damage to the forestry of the region. Therefore, we consider it necessary to strengthen the monitoring of the Trans-Ural population of the Siberian silkworm.

It is quite obvious that the basis for successful control of the Siberian silkworm is the periodic monitoring of the abundance of this phytophage in the reserves. Due to the fact that the occurrence of outbreaks of mass reproduction of the Siberian silkworm is closely synchronized with spring-summer droughts, surveillance during this period must be significantly strengthened.

It is necessary to analyze the state and size of the population in other parts of the forest.

Control measures should be planned for the start of an outbreak when more than 30% defoliation in fir and spruce, cedar pine, or severe (70%) larch defoliation is predicted.

As a rule, aerial treatment of forests with insecticides is carried out. The most promising biological drug to date is lepidocid.