Siberian silkworm (cocoon moth) – Dendrolimus sibiricus Tschetw

Damages

Silkworm caterpillars in different parts of its wide range they feed on the needles of various coniferous tree species, giving preference to the needles of larch (Daurian, Sakhalin, Siberian, Sukachev), fir (Siberian, Sakhalin and whitebark) and cedar (Siberian and Korean). Less willingly, usually when growing together, the caterpillars feed on the needles of spruce (Siberian and Ayan), Scots pine and dwarf cedar.

Maliciousness

One of the most harmful types of pine-eating pests.

Spreading

Siberian silkworm widespread in the forest and forest-steppe zones of Siberia - from the Urals to Sakhalin, Kunashir and Iturup inclusive ( Kuril Islands). Northern border distribution - from White Sea to Penzhinskaya Bay - coincides with the Arctic Circle, not reaching it in the European part of Russia and east of 145°. The southern limit of distribution in the European part of Russia and in Western Siberia coincides with the southern border of the distribution of Sukachev larch and Siberian larch; further to the east it passes into the northwestern regions of China, Mongolia, the northeastern regions of China and Korea.

Preferred stations

Reservations and primary foci of silkworms are confined to plantings that are more well heated and aerated, with drier growth conditions or with well-drained soils, average density (0.4 - 0.7) or to their outskirts, edges, open spaces, more often to clean plantings , older age classes belonging to groups of drier or fresher forest types (green mosses, forbs, etc.). They are located: in the flat taiga - along the topography, in low mountains (up to 500 m in height) - on plateaus and along slopes, in the lower and middle mountain taiga more high mountains, located in northern or humid areas - along the slopes of southern points, and in southern or dry areas - along the slopes of other points. In plantations disturbed by logging, especially clear-cutting, forced-selective and other unmanaged logging, xerophytization of plantings occurs, which favors the constant nesting of silkworms and the transformation of plantings into primary foci during droughts. The same xerophytization of plantings and destruction of natural biogeocenoses in them occurs, especially with intensive grazing of livestock in them, in the vicinity of large settlements

Generation

Everywhere in the silkworm habitat in our country, a 2-year generation has been registered. Nowhere has the annual generation been established as constant for a given area. However, in warm years, in which the growing season is extended. An earlier period, starting earlier in the spring and extending into later autumn, creates conditions favorable to the feeding and faster development of the silkworm. The life of its butterflies proceeds earlier, the laid eggs develop faster, the emerging caterpillars feed longer, go to winter at an older age, next year they emerge from winter earlier and manage to complete their development completely within a year. Since the development of the outbreak is confined to a period of warmer, sunny and drier years, in these same years a transition in the development of silkworms in Western Siberia from a 2-year to a one-year cycle was noted. It should be emphasized that such a transition was more often observed in the fir race, which is distinguished by its smaller size and fewer instars during the caterpillar stage.

P.P. Okunev (1961) suggests that in areas located north of the July isotherm of +18°, the Siberian silkworm develops on a 2-year cycle. In areas south of the July isotherm of +20°, development proceeds according to an annual cycle. In areas located within the boundaries between the named isotherms, development proceeds according to a variable cycle: in inter-outbreak years, as colder ones, according to a 2-year cycle, and in outbreak years, with warmer weather, according to an annual cycle.

Population structure. With a 2-year generation, two tribes of Siberian silkworms can exist in parallel in the same area, one of which flies in odd years, and the second in even years. The number of these tribes and its ratio may be different, which has great value for surveillance and control.

Diagnostic signs

Siberian silkworm eggs

Siberian silkworm caterpillar

Butterflies

especially during periods of mass reproduction, they are so diverse in color and size that it is difficult to pick a pair of butterflies that are completely similar to each other. Females have short combed antennae and a thick body; their wingspan is from 6 to 10 cm. Males have clearly combed antennae and a more slender body; their wingspan is from 4 to 7.5 cm. The forewings of both sexes are light brown or light gray to almost black. Three jagged stripes run across them; one along the outer edge of the snout, the second near its middle and the third closer to its base. In close proximity to the dark stripes, often along the outer edge of the wing, there are whitish stripes consisting of semilunar spots and strokes. The field between the main and median stripes is often darker in color. Sometimes the main and median stripes are weakly expressed or even completely absent. Near the middle of the main stripe there is a semi-lunar white spot, which is always present in butterflies. The hind wings are light brown without a pattern. Below, both pairs of wings are brown, and there is one wide dark brown curved band running along them. The head and chest are colored similar to the front wings, the abdomen is similar to the hind wings.

Testicles

spherical, 2.0×1.5 mm in size, with a dark dot at the apex. Freshly laid eggs are bluish-green, then turn grey. They are smaller and somewhat lighter than pine silkworm, are deposited in irregular piles from several to 100 pieces and mainly on needles, twigs, twigs, bark of branches and trunks. When the caterpillar emerges from the egg, it eats part of the shell.

Caterpillars

up to 11 cm long, varied in color - from gray to almost black. On the meso- and metanotum there are transverse bands of steel-blue burning hairs that open wide when the caterpillar raises the front part of the body and bends its head (threat pose). On the next seven abdominal tergites there are dark horseshoe-shaped spots. The dorsal side and spots on the sides are covered with silvery-white spear-shaped scales, developed to varying degrees in individuals. On the sides of the body, areas of skin are ocher-yellow, sometimes forming an almost continuous stripe. The body is covered with hairs, the longest and densest on its sides and in front on the prothorax. The head is round, matte, dark brown. Ventral side between legs with yellowish-brown or orange spots, not forming a continuous stripe.

The stool of the caterpillars is cylindrical, with six longitudinal and two transverse grooves, very similar to the stool of the pine silkworm. The pieces of needles in it are hardly noticeable.

doll

up to 5 cm long, pitch-brown to black. Cremaster in the form of a transverse convex plate, densely covered with very small rufous hooked and simple setae. The last segments have short and sparse hairs. The pupa rests in a parchment-like, brownish or dirty-gray cocoon, into which tufts of blue, burning caterpillar hairs are woven, giving the cocoon its burning properties. Cocoons are located on branches, between needles, on trunks.

At the beginning of mass reproduction, dark-colored individuals of butterflies and caterpillars dominate, as in other mass needle- and leaf-eating insects.

Races

The question of the races of the Siberian silkworm remains unresolved. But, apparently, three races can be distinguished: larch, cedar and fir. In the process of the historical development of the species, these races not only adapted to feeding on the needles of the corresponding tree species, but also to the entire complex of forest-ecological conditions created by these species in forest stands. The named races of silkworms differ from each other in different amplitudes of size and weight at different stages of development, the number of caterpillar molts, speed of development and other characteristics. The names of these races are left here for ease of presentation.

Siberian silkworm caterpillars overwintering in the litter

Siberian silkworm cocoons

Complete consumption of Dahurian larch needles by Siberian silkworms

Phenology

First year of development

years of butterflies – June (3), July (1-3), August (1); eggs – June (3), July (1-3), August (1-3); caterpillars – July (2.3), August – March (1-3);

Second year of development

caterpillars – April – March (1-3);

Third year of development

caterpillars April – June (1-3), July (1); pupae – June, July (1-3); years of butterflies - June (3), July (1-3), August (1).

Note: ten days of the month are indicated in brackets

With one-year development, the second year falls out of the scheme, when the silkworm remains in the caterpillar stage throughout the entire growing season. On the contrary, when development is delayed to 3 years, the silkworm remains in the caterpillar stage not only during the second, but also the third growing season and completes development in the first half of the fourth growing season. Caterpillars that produce males molt from four to six times during development, and those that produce females molt from five to seven times; respectively, males have from five to seven, and females from six to eight instars.

Caterpillars developing on fir (S.S. Prozorov, 1952) have the following head width in mm: 1.0; 1.5; 2.0; 2.5; 3.5-4.0; 4.5-5.0, respectively, from the first to the sixth instars.

Caterpillars developing on cedar or larch (V. G. Vasiliev, 1940) have the following head width in mm: 0.9-l.0; 1.4-1.6; 1.8-2.2; 2.5-3.2; 3.5-4.2; 4.5-5.2; 5.5-6.2; 6.5-7.2, respectively, from the first to the eighth ages.

From the above it follows that there is almost no difference in the width of the head of caterpillars fed on different species within individual instars, but the number of instars in caterpillars fed on fir is 6, in caterpillars fed on cedar - 7, fed on larch - 8. When feeding on larch caterpillars reach the largest sizes and produce the most well-fed and fertile individuals (pupae up to 6 grams and butterflies laying up to 826 eggs). However, caterpillars of the larch race, with a lack of food, are able to complete their development at the V (males) and VI (females) instars. But even in this case, they produce heavier pupae and fertile butterflies compared to the cedar and fir races.

During the period of their development, caterpillars of the fir race eat 46.5 g of needles (7185 needles), and 95% of it is consumed in the 5th and 6th instars (S.S. Prozorov, 1952). For other breeds, feed standards remain unstudied.

On the issue of the sum of effective temperatures required for the full development of the silkworm, there are disagreements in the literature: S. S. Prozorov (1952) defines it at 2032 °, P. P. Okunev (1955) - at 1300 - 1500 °, Yu. P. . Kondakov (1957) - at 1200 - 1250°. This issue needs further research.

Siberian silkworm caterpillars are cold-resistant. This gives them the opportunity to leave for the winter late, at temperatures close to zero, and to rise early into the crowns after wintering, following the melting of the snow. However, with sudden and sharp drops in temperature (below -10°), the first instar caterpillars may die en masse. They also die in harsh winters with little snow in their wintering areas. With age, the cold resistance of caterpillars increases, therefore, the chances of their death from frost decrease. In humid wintering conditions and rainy weather, fungal and other diseases spread among the caterpillars, often leading to mass death. This explains the fact that in damp honeydews no centers of mass reproduction of silkworms are created, and the outbreak that has begun subsides under the influence of rainy and cool weather.

Doom is dark coniferous forests from complete devouring by Siberian silkworms

Duration of the outbreak

Conflicting opinions exist in the literature about the duration of outbreaks. The development of an outbreak in the same planting (focus) with a 2-year generation is possible within 14 years, and with a one-year generation - within 7 years. An outbreak that develops with a changing generation duration may have an intermediate duration between these deadlines, i.e., when one part of the generations during the outbreak period develops on a 2-year cycle, and the other on a one-year cycle. In the literature you can find reports of shorter-term outbreaks - within 4 - 6 years.

Reconnaissance surveillance

When organizing surveillance, republics, territories and regions in which outbreaks of mass reproduction of the Siberian silkworm have been observed or may be observed can be divided into two halves by a line running through Sverdlovsk - Tyumen - Kolpashevo - Yeniseisk - Nizhne-Angarsk - Kumora-Bambuika - Sredny Kalar - Stanovoy Ridge to the Sea of ​​Okhotsk. North of this line, outbreaks are possible but have rarely been observed. To the south of it, to the border of distribution of larch, cedar, fir and spruce forests, outbreaks of mass reproduction of the Siberian silkworm were observed most often. The southern half includes forests on the islands of Sakhalin, Kunashir and Iturup. In the forests of the northern half, systematic supervision may not be carried out. When a period of intense drought occurs, which also affects these forests, it is necessary to carry out control aerial surveys in them in the appropriate years with ground verification of the emerging foci.

The forests located in the southern half of the forestry enterprises or timber industry enterprises and their constituent forests can be divided into three groups: those located in high mountains or wetlands, in which outbreaks of mass reproduction of the Siberian silkworm are not observed; located in sparsely populated areas and in mid-mountain zones, in which outbreaks of silkworms are observed sporadically; located in populated areas of the southern part of the taiga zone, forest-steppe and steppe, as well as in the lower mountain zones, in which outbreaks of mass reproduction were observed most often.

carried out on the verge of two generations, i.e. annually in the presence of two generations, a silkworm or a mixed development cycle, or in even or odd years in the presence of one generation with a 2-year development cycle.

Detailed supervision

According to the outbreak phases, the weight of pupae and the fertility of butterflies change within the following limits.

In the first and second phases of the outbreak Weight Limit pupae in the larch race are 5.5 - 6.0 grams, in the cedar and fir races - 3.8 - 4.2 g; The fertility of butterflies in the larch race is 650 - 750 eggs, in the cedar and fir races - 400 - 460 eggs. The average indicators are respectively: 4.0 – 5.0 g; 2.8 – 3.3 g; 440 – 580 pcs.; 250 – 330 pcs.

In the third phase of the outbreak, the average weight of pupae in the larch race is 2.5 - 3.0 grams, in the cedar and fir races - 2.0 - 2.4 g; The fertility of butterflies in the larch race is 220 - 380 eggs, in the cedar and fir races - 150 - 200 eggs.

In the fourth phase of the outbreak, the average values ​​are respectively: 1.4 - 1.8 g, 1.5 - 1.8 g, 70 - 120 pcs., 80 - 120 pcs. The minimum indicators are: 1.0 g, 0.8 g, 25 pcs., 5 pcs.

When the first drought occurs in areas with an annual or variable development cycle of the Siberian silkworm, supervision should be strengthened and expanded to the remaining registered reserves. If there is a repeat drought, a detailed examination of the same reservations, as well as similar plantings, should be carried out. The transition from a 2-year development cycle to a one-year one in areas with a variable development cycle of the Siberian silkworm should itself be perceived as a signal of the need to strengthen and expand supervision. In areas with a 2-year development cycle, surveillance is strengthened and expanded after repeated drought or when ongoing surveillance provides clear evidence of an outbreak.

Repeated drought and indicators obtained during surveillance indicating the beginning of an outbreak should be taken as a signal that it is necessary to conduct control surveys in the above-mentioned second group of forests. Finally, the results of surveillance of other forest pests and even pests should be taken as a signal about the need to strengthen and expand surveillance. agriculture, since droughts initiate the development of outbreaks of many pests. In this regard, for areas with an annual or variable development cycle, supervision of double-generation pests (for example, common and other pine sawflies) is important, since their outbreak occurs 1.5 years earlier than pests with annual generation. In areas with a 2-year development cycle of the Siberian silkworm, mass reproduction of many forest pests with an annual generation, outbreaks of which, generated by the same drought, develop faster, can be perceived as alarms. Such signaling pests include the gypsy moth, ancient, larch and willow moths, larch and pine moths, pine silkworms, larch moths, polyflowers, hawthorn, and in the forest-steppe - locust moths (Siberian moth). Outbreaks of mass reproduction of the gypsy moth and the larch moth do not only occur in tandem. The primary centers of their mass reproduction are formed in similar, and often even in the same larch plantings (Yu. P. Kondakov, 1959).

In plantations affected by ground fires, it is necessary to carry out appropriate methods of supervision over the reproduction of silkworms in the first 3 - 4 years in areas with annual or variable generations, or in the first 6 - 8 years in areas with 2-year generation, even regardless of droughts, since fires can cause local outbreaks that can grow into larger outbreaks during dry periods.

Control measures

Spraying plantings with insecticides in the spring, within 1-2 weeks after the overwintered caterpillars rise into the crowns, or at the end of summer - against young caterpillars.

Egg. The shape is spherical. Diameter - 2.2 mm. The color of the integument is initially light green with a dark brown dot on one side, but as the egg develops it darkens.

Development

Mating period. Mass flight is observed in mid-July and lasts until the first half of August. Immediately after mating, females begin to lay eggs one at a time or in groups on needles, and during periods of increasing numbers - on dry branches, grass, lichens, forest floor. Up to 200 eggs are observed in one clutch. Maximum fertility is up to 800 eggs.

Egg. Embryonic development lasts 13-15, less often 20-22 days.

Older caterpillars are capable of crawling through treeless spaces in search of food plants and migrating over a distance of up to 1.5 km.

Morphologically related species

By appearance(morphology) the pine cocoon moth (silkworm) (Dendrolimus pini) is close to the described species. The butterfly's span is 60-80 mm. The color is variable, most often gray-brown. The front ones have a wide sinuous band, the color of which varies from gray-brown to red-brown. On each forewing there is a small semi-lunar white spot. The rear of the range passes through 40°c. w. According to long-term observations, there is a gradual expansion of the range to the west and partially to the north.

Maliciousness

The Siberian silkworm (cocoon moth) harms more than 20 species of conifers, preferring larch. Caterpillars destroy needles throughout their development, but the greatest damage is caused during the last instars. In a two-year period, this is the time after leaving the second wintering.

In terms of the frequency of outbreaks of mass reproduction and the area of ​​outbreaks, the Siberian silkworm ranks first among the primary pests. Mass reproduction of the Siberian silkworm entails an outbreak of secondary pests (longhorned beetles, bark beetles, golden beetles and others).

The spread of the pest is possible not only naturally(movement of caterpillars and butterflies), but also with the help of transport, by transporting forest products - unbarked logs and other timber, forest litter, seedlings and saplings - eggs and cocoons can spread.

Siberian silkworm – Dendrolimus superans sibiricus Tschtv. (Lepidoptera, Lasiocampidae)

Morphology. Older caterpillars are very large, reaching 11 cm in length, usually black or black-silver with a wide silver stripe along the back and a yellowish stripe on the sides. Behind the head there are two bands of blue, burning hairs, clearly visible in the disturbed caterpillar. The number of instars and the size of the head capsule vary depending on the duration of the caterpillar phase, which can take one, two or three calendar years. Typically, male caterpillars have 5-8 instars, female caterpillars - from 6 to 9 instars.
The color of butterflies is highly variable, from dark brown to light yellow, almost white. Light gray and dark brown coloration with dark, almost black bands and blurred light spots along the edges on the forewings are typical. The hind wings are usually solid brown. The wingspan of males varies from 40 to 83 mm, females - from 60 to 104 mm.
The eggs are oval, yellowish-brown, forming loose clutches or chains on the needles or branches of food plants. The pupa is in a dense cocoon impregnated with blue burning hairs; placed on branches, less often - on the trunk.

Fodder species. The Siberian silkworm feeds on almost all species of the Pine family. Prefers Siberian fir, Siberian larch and Siberian cedar. The white-striped silkworm prefers Sakhalin fir, Ayan spruce and Kuril larch. On the Japanese Islands, silkworms damage several species of fir and Korean pine.

Life cycle. The Siberian silkworm has a typical two-year development cycle, taking three calendar years. Butterflies fly and lay eggs in the last third of June - the first half of July. Average fertility is about 300 eggs. The egg stage lasts 17-19 days. The caterpillar overwinters twice: in the second-third instar and in the fifth-seventh instar. They overwinter under the litter, curled up in a ring. Maximum damage is caused to trees by caterpillars feeding in the spring of the third calendar year. They pupate in late May - early June in the crown. The pupal stage takes about three weeks.
The onset of outbreaks of mass reproduction of the Siberian silkworm is usually associated with the transition of part of the population to a one-year development cycle (taking two calendar years). As a result, butterflies of both generations appear simultaneously, which contributes to a significant increase in population density. At the peak of their numbers, silkworm caterpillars are affected by viral, bacterial and fungal diseases. The decline in numbers is also contributed to by about 40 species of insect parasites of eggs (Telenomus tetratomus Thoms., Ooencyrtus pinicola Mats.), caterpillars (Rogas dendrolimi Mats., etc.) and pupae (Masicera sphingivora R.D., etc.).

Harmfulness assessment. The Siberian silkworm is the main pest of coniferous forests in Asian Russia. Outbreaks of its mass reproduction are especially destructive in the dark coniferous taiga dominated by fir and cedar. Only in the last 100 years in the territory Krasnoyarsk Territory 9 outbreaks of the pest were registered. As a result, forests covering an area of ​​more than 10 million hectares were damaged. The last outbreak of mass reproduction ended here in 1996. More than 140 thousand hectares of forest perished, and about 50 million cubic meters of wood were lost. Five years later, thanks to the attack on weakened trees by a large black longhorned beetle, the area of ​​shrunken forests doubled.

The Siberian silkworm (otherwise known as the hemp moth) is a dangerous insect pest that damages more than 20 species of coniferous trees. The insect is especially destructive for larch, fir, and cedar. Spruce and pine are damaged much less frequently by butterflies.

The Siberian silkworm is a quarantine species. Even if it is absent on the territory of the country, it exists real threat its independent penetration or introduction from the outside, which can lead to massive damage to plants and plant products. That is why it is strongly recommended to carry out phytosanitary measures: when exporting conifers, they must be disinfected or debarked.

An adult Siberian silkworm (photo) reaches 10 cm, females are larger than males. The insect lays about 200 eggs (sometimes up to 800) on tree branches. The butterfly does not feed, but the larva that hatches after 2-3 weeks immediately begins to eat the needles, moving to the very top of the crown. With a lack of nutrition, the Siberian silkworm caterpillar can damage the bark of trees and young cones. In autumn, the caterpillars go to winter. In the spring, their active life activities resume. Pests go through 6–8 instars.

Upon completion of the development cycle, the caterpillars weave a dense cocoon in which pupation occurs. The pupae grow for 3–4 weeks; at the end of June, adults emerge from them and begin mating.

As a rule, the Siberian silkworm is found in healthy forests in small quantity. A population outbreak (mass reproduction of an insect) can lead to an environmental disaster. Drought is one of the main reasons for this phenomenon. During dry seasons, the caterpillar manages to develop not in two, but in one year. The population doubles; the butterfly’s natural enemies do not have time to infect a sufficient number of individuals. Butterflies reproduce unhindered and give birth. Early spring fires are another reason for outbreaks of silkworm numbers. The fact is that silkworm caterpillars overwinter on the forest floor. Telenomus also lives there - the worst enemy that eats silkworm eggs.

And early spring fires destroy most of the Telenomus population, which leads to the emergence of centers of mass distribution of silkworms.

In addition to telenomus, the natural enemy of the silkworm is the cuckoo, as well as fungal infections.

The Siberian silkworm became a real sword of Damocles for coniferous plantations in Siberia and the Far East, where its invasion, comparable to an invasion of locusts, destroyed more than one thousand hectares of coniferous forest, including young spruce and pine seedlings. Huge territories have turned into bare, treeless spaces. According to some scientists, it will take about a hundred years to restore these forest plantations. According to others, restoration of forest plantations after damage by the pest is impossible.

When mass reproduction of the Siberian silkworm occurs, it is very important to treat plants with insecticides. Lepidocide is one of the most effective drugs. To prevent the spread of the butterfly, it is necessary to regularly inspect the plants and treat them with insect repellents.

Siberian silkworm (Dendrolimus superans sibiricus Tschetv.)

Siberian silkworm (Dendrolimus superans sibiricus Tscetv.) in the Asian part of Russia is one of the most dangerous insect 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 tree stands and changes in forest formations.

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

In Russia, a huge contribution to the development and implementation of biological methods for combating foci of mass reproduction of the Siberian silkworm was made by Doctor of Biological Sciences, Prof. Talalaev E.V. In the mid-1990s, vast areas were affected by silkworms. forest plantations in Western and Eastern Siberia, as well as in the Far East. In the Krasnoyarsk Territory alone, over the course of four years, the outbreak covered the territories of 15 forestry enterprises; the area of ​​damaged taiga areas amounted to more than 600 thousand hectares. Destroyed large number valuable cedar plantations. Over the past 100 years, 9 outbreaks of the pest have been registered in the Krasnoyarsk Territory. As a result, forests covering an area of ​​more than 10 million hectares were damaged. The use of modern insecticidal pyrethroid and bacterial preparations has made it possible to partially localize the pest outbreaks 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, silkworms live in reservations - areas with the most favorable development conditions. In the zone of dark coniferous taiga, reservations are located in mature, fairly productive (II-III quality class) stands of forb-green moss forest types with the participation of fir up to six units or more, with a density of 0.3-0.6.

Adult 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 intersected by three darker stripes. There is a large white spot in the middle of each wing; the hind wings are the same color.

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

The eggs are almost spherical in shape, up to 2mm 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.

Siberian silkworm caterpillars 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. In the first instar, the caterpillars eat only the edges of the needles; in the second instar, they eat the entire needle. At the end of September, the caterpillars burrow into the litter, where they overwinter under moss cover.

At the end of April, the caterpillars climb into the tree crowns and begin to feed, eating whole needles, and if there is a lack of food, the bark of thin shoots and young cones. After about a month, the caterpillars molt for the third time, and again in the second half of July. In the fall they leave for the second winter. In May-June of the following year, adult caterpillars feed intensively, causing the greatest harm. During this period, they eat 95% of the food needed for full development. They molt 5-7 times and accordingly go through 6-8 instars.

Caterpillars feed on the needles of almost all coniferous species. But they prefer fir, spruce, and larch. Cedar is damaged to a lesser extent, and pine is even less damaged. In June, the 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. Mass migration of butterflies occurs in the second ten days of July. On the southern slopes of the mountains it occurs 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 there is sometimes a three-year generation. The flight of butterflies begins in the second half of July and lasts about a month. Butterflies don't feed. The wingspan of females ranges from 6 to 10 cm; males - 4-5 cm. Unlike females, males have feathery antennae. The female lays an average of about 300 eggs, placing them one at a time or in groups on the needles in the upper part of the crown. In the second half of August, caterpillars of the first instar emerge from the eggs, feed on green needles, and in the second or third instar, at the end of September, they leave for the winter. Caterpillars overwinter in the litter under a cover of moss and a layer of fallen pine needles. The rise in the crown is observed in May after the snow melts. The caterpillars feed until next autumn and leave for the second wintering at the fifth or sixth age. In the spring, they rise into the crowns again and, after active feeding, in June they weave a dense gray cocoon, inside which they then pupate. The development of the silkworm in the pupa lasts 3-4 weeks.

In the dark coniferous taiga, silkworm outbreaks form after several years of hot, dry weather in the summer. In this case, the caterpillars go to winter later, in the third or fourth instar, and turn into butterflies the following summer, switching to a one-year development cycle. Accelerating the development of caterpillars is a condition for the formation of Siberian silkworm foci.

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

　

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

The count of 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 staking on fabric canopies in early June and late August.

The age of the caterpillars is determined according to the table by measuring the width of the head.

It should be borne in mind that in the conditions of Northern Eurasia, forests destroyed by silkworms are poorly restored. The caterpillars destroy the undergrowth along with the forest stand, and only after a decade is it possible for a small undergrowth of deciduous trees to appear. In old foci, conifers appear only 30-40 years after the tree stands dry out, and not everywhere and not always.

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

This is also facilitated by an increase in soil temperature and humidity, since neither sunlight, and precipitation is no longer retained by tree crowns. In fact, the mass reproduction of silkworms contributes to a more intense flow of the biological cycle as a result of the rapid release of significant amounts of matter and energy contained in the forest floor.

The soil in silkworms becomes more fertile. Light-loving grass cover and undergrowth rapidly develop on it, intensive turfing and often waterlogging occurs. As a result, heavily disturbed plantations are replaced by non-forest ecosystems. Therefore, the restoration of plantings close to the original ones is delayed indefinitely, 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 conditions of global anthropogenic impact remain unstudied.

Outbreaks of mass reproduction of the Siberian silkworm in the larch forests of the Cis-Ural region have been observed since 1900 [Khanislamov, Yafaeva, 1962]. In the dark coniferous lowland forests of the Trans-Ural region in the Sverdlovsk and Tyumen regions, the previous outbreak was observed in 1955-1957, and the next one in 1988-1992 g.g. The first outbreak in the forests of the Sverdlovsk region was discovered in 1955 on the territory of the Tavdinsky and Turinsky forestry enterprises. The total area of ​​the outbreaks was 21,000 hectares and 1,600 hectares, respectively. On the territory of the Tavdinsky forestry enterprise, large outbreaks formed earlier. It is noteworthy that these forestry enterprises have been the site 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 forestry enterprises. In the nai to a greater extent it formed in the forests of the Taborinsky district. The total area of ​​the outbreaks was 862 hectares; individual outbreaks were also observed during aerial surveillance in the Garinsky district.

Research has shown that in 50% of the areas affected by outbreaks in 1988-1992, the main forest-forming species is birch with fir and spruce as part of the undergrowth (Koltunov, 1996, Koltunov et al., 1997). Fir undergrowth is strongly defoliated by the Siberian silkworm and mostly shrunk. As a result, significant damage was caused to the development of coniferous farming in these forestry enterprises. The primary centers of mass reproduction of the Siberian silkworm arose in 1988 in stands 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 areas, spruce was defoliated by the Siberian silkworm, as a result of which it also quickly dried out. As surveys in the foci of this phytophage during the outbreak have shown, the development of the Trans-Ural population occurs mainly in a two-year cycle. In general, studies have shown that the topography of broad silkworm foci in coniferous forests Sverdlovsk region coincides with forest areas disturbed by anthropogenic impact.

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

Over the past 20 years, the most intensive industrial logging has occurred on the territory of the Yuzhno-Kondinskoe private plot. As the results showed, the spatial structure of the foci of mass reproduction of the Siberian silkworm in this forestry enterprise clearly does not coincide with the forests subjected to the most intense anthropogenic impact (primarily deforestation). The largest foci (in the western part of the forestry enterprise) are completely unaffected by anthropogenic impact. There was no logging in the forests before the outbreak. We also did not find any other types of anthropogenic impact. Analysis of forest taxation parameters of tree stands in this group of outbreaks showed that these forests have the usual productivity for this type of forest growth conditions and are not weakened. At the same time, near other, smaller sources, clearings and, in some cases, fires are observed. Some of the areas with severe defoliation of tree stand crowns were previously logging.

As the results showed, anthropogenic impact in the dark coniferous lowland forests of the Trans-Ural region is not a key factor in the formation of foci of mass reproduction of the Siberian silkworm, although its contribution is undoubted. Under conditions of moderate anthropogenic impact, the main factor in organizing the spatial structure of outbreaks is forest conditions in ecotopes and microrelief features. Thus, the largest foci are adjacent to river beds and places with microhighs, which was known earlier [Kolomiets, 1960,1962; Ivliev, 1960]. Especially important fact is that the forests in the hotspot areas 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 shown by geobotanical analysis of the herbaceous layer, the grass cover in these forests has not changed.

Thus, these forests are most affected only by their proximity to clearings (changes in light and wind conditions) and, to a lesser extent, by logging carried out several decades ago in some of them.

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 as a whole that 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 did not find these differences in recent years, and for 50 years or more.

A characteristic feature of the dynamics of defoliation of tree stands during the outbreak period 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 of fir in the main layer, and later of spruce and cedar. The pine was defoliated very weakly. Therefore, no outbreaks formed in pure pine forests. A study of the Trans-Ural population of Siberian silkworms in outbreaks showed that in the eruptive phase and before the outbreak subsided, the imago hatching rate was very low and ranged from 2 to 30%, averaging 9.16%.

Most of the pupal 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%, with an average of 47.7%. Bacterial infections accounted for the main percentage of causes of death from this group of diseases. Viral infections were significantly less common. It should also be noted that microscopic analysis of dead caterpillars in outbreaks both in Sverdlovsk and Khanty-Mansi Autonomous Okrug convincingly showed that the attenuation of outbreaks was not accompanied by a viral epizootic (granulosa 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, dying from infectious diseases.

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

It should be noted that the supply of xylophages in the outbreak areas is sufficient. In addition, at shift sites and in stock warehouses in the Yuzhno-Kondinsky private farm, the canes left untreated are quickly colonized by xylophagous insects. We associate 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 defoliation of the crowns against the background of the cessation of transpiration due to the absence of needles.

Research in the centers of mass reproduction of the Siberian silkworm in the Trans-Urals showed: the last outbreak of this phytophage in the dark coniferous forests of the lowland Trans-Urals was observed 33 years ago. It can be assumed that the cyclical outbreaks of this phytophage on the western border of the range are closely related to the frequency of the most severe droughts in 1955 and 1986. The most severe drought (in 1955) was accompanied by larger area foci of this phytophage in the Trans-Urals.

Previously, there were no outbreaks of Siberian silkworm in the Kondinsky forestry enterprise. Dendrochronological analysis of fir and spruce cores (over the last 100-120 years), carried out by us, showed that forest stands both in the outbreak and beyond its borders had not previously been subject to noticeable defoliation. Based on our results, we can assume that the Siberian silkworm is gradually penetrating to the north and outbreaks of mass reproduction that have not previously been observed there occur in these habitats. This is probably due to gradual climate warming.

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

Based on the results obtained, it was established that under the conditions of anthropogenic transformation of the dark coniferous forests of the Trans-Ural region, the largest foci of the Siberian silkworm can arise both in completely undisturbed forests and in forests exposed to anthropogenic factors.

A comparative analysis of the spatiotemporal structure of the foci during the last two outbreaks shows that the foci of mass reproduction each time are formed in different ecotopes and spatially do not coincide at all. As the research results showed, the first outbreaks in each of the surveyed forestry enterprises arose in 1988 simultaneously with other outbreaks in the more southern regions of the Tyumen region. This excludes the possibility their origin through migration from the southern part of their range. It is likely that the population was in a depression phase in the northern part of the range of this population.

At the western border of the range of this phytophage, outbreaks are fast-moving. This is well explained by the narrow time interval of the climatic optimum during the drought period. Considering this, 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. Maintaining a high outbreak potential is only possible during this narrow period of drought. Therefore, treating lesions during this period will eliminate the likelihood of the formation of large repeated steps.

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

However, it is noteworthy that out of 50 trial plots, only 36% of the plots with a density lower than 0.8 formed foci 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 lower-density forest stands is, on average, 54.5%, while that of high-density forest stands (with a density of 0.8 or more) is 70.1%, but the differences were statistically insignificant. This probably indicates that the level of defoliation is influenced by a complex of other factors that are common to the 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 completeness of forest stands.

Research has shown that this factor is the soil-edaphic conditions in ecotopes. Thus, all the forest stands on the sample plots, which were located on ridges, in drier habitats, were defoliated the most severely, compared to the forest stands on the flat parts of the relief, or microdepressions. Correlation analysis of the degree of defoliation with other forest taxation parameters also did not reveal a statistically significant relationship with the quality class (r = 0.285). However, the average level of defoliation in the lowest quality forest stands (with 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 reliable linear correlation was also probably due to the strong dominance of the factor of soil-edaphic conditions. This is accompanied by severe defoliation of forest stands, which vary 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 we recorded caterpillars in the crown in both groups of forest stands. Consequently, local migration in any case was not the main cause of severe defoliation of low-grade forest stands.

Analysis of the results shows that in the conditions of lowland dark coniferous forests of the Sverdlovsk region. there is a certain tendency towards the predominant formation of foci with the most severe defoliation of crowns in forest stands with more high class bonitet. But there is also no noticeable avoidance of low quality forest stands. Outbreaks with to varying degrees crown defoliation occurs in forest stands with different class bonitet. But the lowest entomoresistance and severe defoliation are characteristic of plantings with the highest quality class. Considering the close relationship between the degree of defoliation and the level of entomoresistance of tree stands at the same initial population density, it can be assumed that in these forest conditions, as a result of exposure to an abiotic stress factor (drought), the entomoresistance of tree stands with a higher quality class decreases more than that of low quality forest stands, which is accompanied by higher crown defoliation high quality forest stands.

Analysis of the characteristics of the composition of forest stands in the foci of mass reproduction of the Siberian silkworm in the Sverdlovsk region made it possible to identify two main types of strategy for the formation of foci in relation to the composition of the forest stands.

1 type of strategy. Outbreaks occur in the main layer of the forest. These tree stands are most often located on higher elevations in drier forest types. Foci with the most significant defoliation of forest stands are formed in spruce-fir and fir-spruce forest 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, severe defoliation is always observed. The lesions are usually of a concentrated type with a well-defined border. Surveys in the outbreaks showed that under these conditions, optimal for the outbreak, the predominant composition of rocks is not critical and can vary within fairly wide limits. However, 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 decline in entomoresistance of both fir and spruce is higher than the level of differences in entomoresistance between these species in less optimal habitats. According to the composition of the forest stand in these centers, there were no plantations with a predominance of fir at all, but there was 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 region there is usually a rapid colonization of dried-out tree stands by xylophagous insects, while in foci of the Siberian silkworm in the forests of the Khanty-Mansiysk Autonomous Okrug, as mentioned above, the colonization of dead tree stands by xylophages almost did not occur.

2 type of strategy. Outbreaks occur not in the main forest type, but in the undergrowth. This is typical for forest areas that have been deforested. In this type of forest, outbreaks occur regardless of the species composition of the main layer. This is due to the fact that in many types of forests that have been heavily deforested, there is abundant fir regrowth, which is completely defoliated and dries out. Often the main layer in these types of tree stands is birch, less often pine and other species. Consequently, these forest types 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 flat elements of the relief, but not excessively moist.

In areas with severe defoliation in the forests of the Sverdlovsk region. Aspen is very rarely found in the main layer, since it is an indicator of moist habitats. However, in some areas with severe defoliation it is still found in small quantities. Usually these are foci formed in the flat part of the relief, with individual depressions. As is known, such tree 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). This was the largest outbreak in Russia over the past 30 years.

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

For the first time, we conducted research into the development of outbreaks of mass reproduction in the forests of the Sverdlovsk region. and Khanty-Mansiysk Autonomous Okrug (KhMAO-YUGRA).

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

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

In the western part of the Siberian silkworm's range, outbreaks are fast-moving. Mostly concentrated foci appear. The nature of the spatial structure of the primary foci suggests that they arose through non-migration and the Siberian silkworm is present in the area of ​​outbreaks and during depression periods. The formation of foci with severe defoliation is observed in forests with a wide range of density and quality classes in the Khanty-Mansi Autonomous Okrug-Yugra - in fir-spruce forests, in the Sverdlovsk region - in derivative birch forests with fir undergrowth and spruce-fir forests.

Dendrochronological analysis of fir and spruce cores (over the last 100-120 years), carried out by us, showed that forest stands both in the outbreak and beyond its borders had not previously been subject to noticeable defoliation. Consequently, previously there were no outbreaks of mass reproduction of the Siberian silkworm in the Kondinsky forestry enterprise of the Khanty-Mansi Autonomous Okrug. Based on our results, we can assume that the Siberian silkworm is gradually penetrating to the north through migration and outbreaks of mass reproduction that have not previously been observed there occur in these habitats. This is probably due to gradual climate warming.

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 reaction to relatively dry growth conditions on ridges and microelevations of the relief, and differences in radial growth persist for many decades .

Despite the obvious increase in the scale and level of anthropogenic impact on the lowland 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 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 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 periodic monitoring of the number of this phytophage in reservations. 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 needs to be significantly strengthened.

It is necessary to analyze the condition and size of the population in other areas of the forest.

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

As a rule, forests are sprayed with insecticides by air. The most promising biological drug to date is lepidocide.