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

The Siberian silkworm is widespread in the forest and forest-steppe zones of Siberia - from the Urals to Sakhalin, Kunashir and Iturup inclusive (Kuril Islands). The northern border of distribution - from the White Sea to the Penzhina 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 Western Siberia coincides with southern border 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, 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 mid-mountain taiga of higher mountains located in northern or humid areas - along the slopes of southern points, and in southern or dry areas - along the slopes of other directions. 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 lengthens. An earlier period, beginning earlier in the spring and extending into later autumn, creates conditions favorable to the feeding and faster development of the silkworm. The butterfly's life begins 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 a colder cycle. warm weather- according to the 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 importance 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 those of the pine silkworm, they are deposited in irregular groups from several to 100 pieces and mainly on needles, twigs, twigs, the 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. These races are in progress historical development The species have 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, and 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.

Death of 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 droughts 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, the maximum weight of pupae in the larch race is 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 pests with double generation (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.

Svetlana Lapshina

Unexpectedly, almost all of Siberia was covered by silkworms this year. Siberian pine forests were affected in the Kemerovo region (pests were registered on an area of ​​about 12 hectares), in the Irkutsk region (about 50 thousand hectares), and in the Krasnoyarsk Territory (about 1 million hectares).

– It was the youngest cedar tree. Average age the trees are 100–120 years old,” sighs the district forester of the Bogashevsky forestry, Alexander Boltovsky, pointing towards the field. – This tree was completely eaten by silkworm caterpillars. In 32 years of work, this is the first time I have seen this.

Instead of a gorgeous green crown, there are only bare branches - not a single needle on the tree. And there are dozens of such cedars...

Caterpillars attack

Two areas of plantings in the Luchanovsky pine forest near the village (total area of ​​almost 18 hectares) were destroyed by the Siberian silkworm in three weeks of August. Local boys, climbing cedar trees for cones, told the forester: “There are some worms crawling up there.” But the experienced Boltovsky was already in the know.

“I walked around these fires ten times and calculated the area affected by the silkworm. The most important thing is to prevent the pest from spreading to next year. In the spring, it is imperative to treat these areas and especially those areas that are adjacent to healthy plantings, explains Alexander Boltovsky.

There are about 5 thousand hectares of cedar forests in the Bogashevsky forestry. Problems have arisen so far only in the vicinity of the village of Luchanovo.

Now the pest has left for the winter. We easily found silkworm caterpillars in the forest floor.

“There are so many of them,” Alexander Boltovsky demonstrates a harmful crop in the palm of his hand. – It seems that the caterpillars have died? Nothing like this. Now they are in a state of suspended animation. But this is a cocoon. It will produce an adult Siberian silkworm.

There is a chance that the trees will survive. Because the overeating was one-time and autumn period. And the buds from which the needles grow are still alive.

The silkworm gave the heat

The Siberian silkworm is a common inhabitant of our forests. With low numbers, it does not pose a danger. However, weather conditions favorable to it – last year’s warm winter and long hot summer – provoked uncontrolled population growth. As a result, in the Tomsk region, foci of cedar infestation simultaneously broke out in the Bakcharsky, Verkhneketsky, Pervomaisky, Tomsk, Parabelsky, Kolpashevsky, Chainsky, Molchanovsky and Kozhevnikovsky districts.

Siberian silkworm outbreaks most often occur after two or three dry growing seasons. In such years, the most viable and fertile individuals appear, characterized by particular gluttony.

– The area affected by the pest is at least 424 thousand hectares. None of the specialists expected such a rapid development of events,” explains Anton Balaburkin, chief specialist of the forest protection department of the regional forestry department.

But this is not the final figure yet. Surveys in the region will last until the end of December. They are carried out by forest rangers and forest pathologists from the Forest Protection Center. The main task is to find out the boundaries of the outbreak and the number of the pest. Now experts plan to examine the forest in the Teguldet region.

– This is very hard, but necessary work. It makes it possible to see the whole picture as a whole,” continues Anton Balaburkin.

Experts determine the number of Siberian silkworms by rounding several trees. They count the number of fallen caterpillars and, based on this data, draw conclusions about the threat of overeating. This indicator is necessary for planning actions to eliminate cedar lesions for the next year. If the threat of overeating is 50% or more, special measures must be prescribed. When the silkworm caterpillar stops feeding and goes into the litter, forest pathologists conduct excavations.

– A thousand caterpillars on a tree is not the limit. In some areas of the Bazoi cedar forest of the Kozhevnikovsky district, their number on cedars reached two thousand. And for one hundred percent gorging, even six hundred caterpillars are enough,” comments Anton Balaburkin.

Give for nuts

Almost 450 million rubles are needed to save the cedar forests. It is planned to allocate about 50 million from the regional budget for next year to combat the Siberian silkworm. Therefore, the regional authorities turned to the Federation for support: Governor Sergei Zhvachkin wrote a letter to Rosleskhoz.

– We cannot write off the social significance of cedar forests. Most of them are near villages, that is, they are located close to settlements. And for many local residents, harvesting pine nuts is the main source of income,” emphasized Anton Balaburkin.

The ideal option is to treat the entire affected area. The optimal time for carrying out such work is the first ten days of May. At this time, the caterpillars emerge from the litter, climb into the crown and begin to actively feed. And at this moment it is necessary to strike from the air - to spray special means using air transport.

Siberian silkworms are poisoned using the biological drug “Lepidocid”. It is harmless to people and animals, including bees.

- IN this moment we're trying to get on federal level permission to use chemical control agents. Biological drugs are effective, but they have a very serious limitation - the temperature of use, notes Anton Balaburkin. – “Lepidotsid” acts at an average daily temperature of 18 degrees and above, and here in early May it will be at most plus 10.

The problem is that all Russian chemical products have expired certification periods - they need to be renewed. And this also takes time. IN Soviet years there were more than 20 different products approved for use. Tomsk residents turned to the government with a request to use at least some of them.

The amount of work ahead is very large. But success will be achieved only if everything works out: federal money comes to the region, competitive procedures are successfully completed... At stake is the priceless asset of the region - His Majesty the Siberian cedar.

The Siberian silkworm caterpillar has six instars. Basic nutrition occurs starting from the third age. During the third or fourth period, the caterpillar eats at least 30% of the tree crown, during the fifth or sixth period, everything else. In the Tomsk region there are areas where overeating is 100%.

In our region, there was an outbreak of mass reproduction of the Siberian silkworm in the mid-1950s. Then the silkworm damaged about 1.5 million hectares of taiga. The northeast of the region was especially affected.

The Siberian silkworm feeds on the needles of almost all coniferous species found within its range. It prefers larch, often damages fir and spruce, and to a lesser extent pine trees - Siberian and Scots.

The development cycle of the Siberian silkworm usually lasts two years.

In the second half of July, the butterfly season begins and lasts about a month. Butterflies don't feed.

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, they feed on green needles and in the second or third instar, at the end of September, they go to 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 instar. 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.

Russian ecologists, geneticists and biologists are sounding the alarm: this summer, pine silkworm caterpillars have reached the Curonian Spit in the Kaliningrad region and the forests of the Vyatka region. Together with the Siberian silkworm, they actively destroy coniferous forests, causing irreparable harm.

The Siberian silkworm is one of the most dangerous pests coniferous forests, which are widespread in the Siberian and Ural regions. The butterflies themselves are not dangerous: only silkworm caterpillars cause damage to trees; they feed on pine needles, as well as the bark of thin shoots and cones. Their life cycle extends over 2 years, during which part of the time they actively feed and hibernate for the winter. The silkworm is dangerous because, under favorable conditions for development and reproduction, the caterpillars eat the needles, that is, they weaken the viability of coniferous trees, subsequently the trees are attacked by secondary pests and the forests eventually die. The Siberian silkworm damages about 20 species of coniferous trees: from larch to spruce. Larches that were killed by silkworms are restored no sooner than after 200 years. IN last years this pest appeared in the Perm and Udmurt regions.

Pine silkworms prefer black pine, but if there is none nearby, they will happily feed on any other species. They have impressive claws that allow them to get any pine needles: thick or thin, hard or soft, smooth or rough. Their unpretentiousness in food is their undoubted advantage. When weather conditions change, they settle at a certain height and look for their favorite trees. Caterpillars are not bothered by the cold; they are one of the few insects that can easily survive 3 months of winter. Their winter cocoon is not afraid of bad weather. As insects grow, the cocoon becomes denser and larger. As each caterpillar moves, it wraps a silk thread around it. For 3 winter months chaotic movements, the cocoon noticeably grows. As for the threat of the pine silkworm to humans: the hairs of this insect are extremely dangerous to health: they get on the skin, in the respiratory tract and cause severe attacks of allergies. If help is not provided in time, the person may suffocate. You need to be extremely careful with silkworm caterpillars. The insect's hairs are carried by the wind, they stick to the grass and can be deadly to humans.

Local biologists believe that this is all due to the disruption of the unique ecosystem natural area Curonian Spit. Small settlements of local residents are being crowded out by luxury hotels, and the forest is being cut down. Sewage flows directly into the bay.

To find out whether silkworms have appeared in the forests, Rosselkhoznadzor specialists install pheromone traps. The trap contains a pheromone capsule and an adhesive surface to which the butterfly sticks when it flies to the smell of the pheromone. Butterflies fly from mid-July to August. At this time, traps are set, this makes it possible to determine the presence and number of silkworms in a given area during a given period and take the necessary measures. A preliminary examination of whether an insect is a quarantine pest or just a forest resident is given in the laboratory of the Institute of Plant Quarantine.

Pine silkworm caterpillars began their spread from eastern Spain and northeastern Italy, gradually they reached the northern regions of Europe, and now they are actively devouring forests in Russia and spreading further and further.

The invasion of these caterpillars is worse for the forest than a fire; for humans it is fraught with a threat to health and life.

© Grodnitsky D.L.

Siberian silkworm
and the fate of the fir taiga

D.L. Grodnitsky

Dmitry Lvovich Grodnitsky, Doctor of Biological Sciences,
head department natural disciplines Institute for Advanced Training of Education Workers (Krasnoyarsk).

Who has not heard about the gluttony of locusts, which, when multiplying en masse, unite in swarms of many millions, fly hundreds of kilometers in search of food, and in a matter of hours destroy grain and cotton crops, orchards and vineyards, and eat not only leaves, but also branches, and even bark? from the trees? Many times, locusts doomed hundreds of thousands of people to starvation. Those lucky enough to survive the invasion erected monuments in honor of their salvation. However, locusts rage mainly in the tropics and subtropics, while for Siberian forests a real disaster is the mass reproduction of a lesser-known, but no less voracious insect - the Siberian silkworm ( Dendrolimus sibiricus). It was first described by S.S. Chetverikov more than a hundred years ago. Nowadays, the silkworm has ceased to be exclusively Siberian: the western border of its range has long passed the Urals and continues to slowly advance across the European part of Russia.

An adult Siberian silkworm is a large butterfly up to 10 cm (usually four to seven) in wingspan; males are smaller than females. Butterflies don't eat (they don't even have a proboscis), but caterpillars have an excellent appetite. They eat the crowns of all types of coniferous trees growing in Siberia, but most of all they prefer the needles of larch, fir and cedar, a little less - spruce, and even less pine. At the same time, the caterpillars behave rather strangely: for one to two weeks they actively feed and gain weight, after which an incomprehensible period of rest (diapause) sets in, when they hardly eat. By the way, the caterpillars of another pest (also quite large in size) - the gypsy moth ( Lymantria dispar) - feed continuously and completely complete development within one and a half months, but the life cycle of the Siberian silkworm usually stretches for two years. The biological meaning of short-term diapause in summer, when everything seems to favor the growth and development of the larva, is still unclear.

Ecological catastrophy?

The Siberian silkworm is a common inhabitant of forest ecosystems; in a healthy forest it is constantly found in small numbers (one or two caterpillars per ten trees) and, accordingly, there is little harm from it. Another thing is when a mass reproduction of an insect occurs or, as this population state is also called, an outbreak of numbers. The reasons for this can be very different. For example, drought: after two or three warm, dry seasons, caterpillars manage to develop in a year instead of the usual two years. As a result, butterflies born last year and the year before lay eggs this year. The population density doubles, and natural enemies - entomophagous insects, which usually destroy almost all individuals of the silkworm - manage to infect only half of its egg-laying eggs and caterpillars, while the rest develop unhindered, pupate, turn into butterflies and give birth to offspring. In addition, the increase in silkworm numbers may be associated with spring ground fires. The fact is that the caterpillars spend the winter under the forest floor, from where they emerge with the first thawed patches and rush into the tree crowns. The silkworm's worst enemy, the microscopic egg-eater Telenomus, also overwinters in the litter ( Telenomus). Its females attach to the body of the silkworm (up to 50 telenomus on one butterfly), travel considerable distances to the place where eggs are laid, and then infect them. Since the silkworm lays eggs closer to mid-summer, the egg eaters are in no hurry to emerge from the litter. Even a light fire that passes through dried grass in early spring destroys b O most of the population of these insects, which contributes to the emergence of centers of mass reproduction of silkworms. After two or three years, the caterpillars completely destroy the needles of even the largest tree and then crawl to neighboring areas in search of food.

In Siberia, such centers of mass reproduction (silkworms) are formed in two types of forests: pure (uniform) larch forests (in Yakutia, Khakassia and Tuva) and in dark coniferous taiga (in Altai, Novosibirsk, Kemerovo, Tomsk, Irkutsk regions and Krasnoyarsk Territory). The consequences of outbreaks in these two types of forests are completely different because different types Trees tolerate silkworm infestation differently.

Within a month after damage, larch is capable of forming secondary (compensatory) needles, which are longer, lighter than the original ones and have less photosynthetic activity. Nevertheless, these needles are enough to help the tree survive the loss of the crown. As a rule, larch suffers single and double damage from caterpillars. The exception is areas with unfavorable growing conditions: arid, like Tuva, or permafrost, like Evenkia.

In the dark coniferous Siberian taiga, if there is larch, it is in small quantities; silkworms do not eat aspen and birch foliage, so the fate of the taiga depends on the sustainability of Siberian fir (60-100% of the tree stand), spruce and cedar. Fir and spruce are not capable of forming secondary needles and dry out after being eaten once. Cedar, with the same trunk diameter, has twice the biomass of needles than fir. Accordingly, to destroy the cedar crown, the caterpillars need twice as much time or twice the number. However, this feature of cedar does not change the situation.

It is believed that dark coniferous forests, after death, will sooner or later recover naturally due to succession - sequential shift some biocenoses by others (herbaceous community - deciduous and, finally, coniferous forest). This is true, but not in the case when the death of the taiga is caused by the mass reproduction of silkworms. Unfortunately, not only ordinary people who see no reason to worry are mistaken, but also forestry workers.

In reality, after an outbreak of silkworm numbers, the following happens. All coniferous trees, including the younger generation, die, and the remains of the crowns crumble. The amount of light reaching the ground doubles. As a result, forest grasses, which were previously in a depressed state due to shading, begin to grow, and after a year or two the soil is hidden under a thick grass cover. Reed grass predominates among the herbs ( Calamagrostis) is a grass that causes the rapid formation of turf (a surface layer of soil penetrated by densely intertwined roots and underground shoots). The dead tree stand does not take moisture from the soil, as a result of which a swamp gradually forms under the silkworms. The trunks of dead trees rot and begin to fall five to seven years after the outbreak. Within 10 years, the silkworm breeding area turns into a dump of rotting wood. Such areas are impassable not only for humans, but also for animals.

Change of vegetation in the taiga ecosystem, where the needles were destroyed by the Siberian silkworm.
The numbers indicate the approximate number of years required to complete each stage of succession.

It takes 10-20 years for microorganisms to destroy the remaining wood and gradually make room for young birch trees. However, in most cases, fires prevent the growth of a new generation of trees. It is known that silkworms burn several times, so while flammable residues remain in the former hearth, trees will not grow there. In fact, during the first three decades, silkworms do not produce wood. Only after the fire danger disappears does the birch tree begin to grow.

Another 50 years after the mass reproduction of the silkworm, the former taiga area is covered with dense thickets of birch with a trunk diameter of 2-8 cm. Under the birch there is the same cover of reed grass, under the reed grass there is turf, under the turf there is waterlogged soil (groundwater lies at a depth of just about 20 cm). How long does it take for the original taiga vegetation to be restored in such an area?

To begin with, soil moisture must decrease, since the main species that determines the appearance of dark coniferous forests on the plain is fir, which does not tolerate waterlogging. It can be expected that within several decades the growing birch forest will dry out the soil and it will become suitable for fir seedlings.

But where do the seeds come from in the silkworm? A certain amount of pine nuts may be brought by birds, but their role cannot be overestimated. Spruce seeds sown from cones in winter can be carried by the wind along the crust. However, the most important thing is the natural sowing of fir - the main forest-forming species. Fir cones fall apart in the fall. At the same time, the seeds do not fly far: special measurements show that their distribution range does not exceed 100 m, and the bulk settles 50-60 m from the mother trees. It turns out that silkworms have a chance to be sown sooner or later only if they have a small area.

This is true, but coniferous seedlings, even if they were able to take root in the turf (which is unlikely), do not have the opportunity to compete with reed grass, which grows incomparably faster. This circumstance fully corresponds to the established fact: on the border of the silkworm, all young coniferous trees are concentrated in a hundred-meter strip along the forest edge, which annually produces seeds of fir, spruce and cedar. At the same time, only cedar and spruce are represented in the undergrowth; fir is present only sporadically. Moreover, the density of undergrowth is only 200-300 specimens per hectare, and for forest restoration their number must be at least ten times greater.

So, contrary to popular belief, the natural restoration of dark coniferous forests after their destruction by silkworms is unlikely: rare trees appear only in close proximity to a healthy forest. Let's add to this that an area of ​​20-30 thousand hectares is not the limit for the silkworm. It is clear that the probability of a sufficient number of seeds getting into the silkworm is low, and the successful development of seedlings and the further growth of a new generation of conifers is practically impossible. As a result, after repeated fires, growth and subsequent natural thinning of birch thickets, approximately in the sixth to eighth decade after the mass reproduction of silkworms, a birch woodland appears in place of the dark coniferous taiga.

There is another misconception: outbreaks of silkworms occur every 11-13 years. To doubt this, just look at a simple chronicle of recent events. During the decade from 1992 to 2001, outbreaks of silkworms were noted in the Novosibirsk region. (1995-1999), in Tomsk (1995-1996 and 2000-2001), in Altai and Tuva (1992-2001), in the Kemerovo region. (1998-2000), in Khakassia (1999-2000), in the Krasnoyarsk Territory (1992-1997 and 2000-2001), in the Irkutsk region. (1995-2001), in Buryatia (1992 and 1997-2001), in the Chita region. (1999-2001), in Yakutia (2000-2001). At the same time, outbreaks with a total area of ​​more than 50 thousand hectares were discovered in Altai, Tuva, and Irkutsk region. etc. In the Krasnoyarsk Territory alone, in three years (1992-1995), silkworms killed fir forests on an area of ​​260 thousand hectares; In some areas, almost a fifth of all dark coniferous forests disappeared. Let me note that this is information from official forestry statistics, reporting only on those found, but not on all active outbreaks.

The conclusion is obvious: in Siberia, every year the silkworm damages forests on an average area of ​​about 100 thousand hectares, a significant part of which turns into vast treeless spaces; Accordingly, the activity of the silkworm can hardly be characterized as anything other than an environmental disaster.

Theory and practice

They say that preventing a disease is easier than treating it, and one cannot but agree with this. Outbreaks in the number of phytophages are an obvious pathology of the biocenosis, from which all organisms inhabiting it suffer. The pest itself is no exception: for many years after mass reproduction of silkworms it is difficult to detect in the vicinity of outbreaks.

To establish the beginning of mass reproduction, monitoring is carried out - a set of measures to monitor the number of pests. If the number has exceeded a certain threshold, then treatment (usually from the air) of the emerging foci with chemical or bacterial insecticides is prescribed.

The theory is good, but reality is more complicated. Siberian forests are difficult to access at best, so monitoring can only be carried out in relatively few areas. Even if an increase in numbers is noted in some of them, it is almost impossible to establish the true boundaries of the beginning outbreak. This is exactly what happened in the Krasnoyarsk Territory in 1990-1992, when the impending disaster was anticipated two years in advance and appropriate measures were taken. However, the subsequent mass reproduction led to the formation of foci over an area of ​​250-120 km; It is technically impossible to cover such an area with aerial treatments, not to mention the cost of such measures. It is reasonable to assume that foci of Siberian silkworms will continue to form. What to do?

The resources in the Russian forestry arsenal are few. One of the methods actively discussed these days is the so-called “controlled burning”, a technology imported into Russian forestry practice, as always, from the USA, where burning is used quite often. However, even with American technology and organization, the fire cannot always be kept under control, and then much more burns than was planned. In Russia, under current circumstances, the fire has much more opportunities to escape into the surrounding forests. The consequences of fires in dry forest stands over an area of ​​several thousand hectares are quite obvious. Due to these circumstances, it can hardly be expected that burning silkworms will take any significant place in domestic practice.

Atmospheric explosion of an accumulation of under-oxidized substances,
formed during combustion in conditions of lack of oxygen, -
one of the phenomena accompanying large forest fires.
Photo by V.I. Zabolotsky

All that remains is to cut down the silkworms; Both economic and environmental considerations lead to this conclusion. Otherwise, the silkworm will rot and pose a constant fire hazard. Suffice it to say that the volume of dead wood in the already mentioned Krasnoyarsk silkworms was about 50 million m3. What impact will the astronomical amount of decay and combustion products released into the atmosphere have on climate processes? What will be the geographic scope of this impact? The significance of this aspect of silkworm activity remains to be assessed.

It is obvious that the Siberian silkworm poses a real threat to the very existence of the fir taiga on the plains of Western and Eastern Siberia. Consequently, it is necessary to introduce a specially protected area regime for at least that part of the forests where Siberian fir dominates, if these forests are located in the zone of harmful action of Siberian silkworm populations.

A man-made crisis?

It is assumed that outbreaks in the number of Siberian silkworms are a natural, evolutionarily determined phenomenon. Otherwise, one would have to believe that the ecosystem is capable of self-destruction: after all, the Siberian silkworm is not an alien species, not an invader, but an original taiga inhabitant, i.e. part of the ecosystem. But how, in this case, could the dark coniferous taiga of Siberia - an indigenous forest formation - arise in the conditions of constantly operating large breeding centers of silkworms? Another explanation seems more realistic: outbreaks in the number of this insect arose relatively recently as a result of a disruption in the balanced functioning of taiga ecosystems, which could be caused by human agricultural and logging activities that began in Siberia less than four centuries ago. Fire farming led to the fragmentation of biocenoses and the formation of heated edges. Sudden lightening of the crown has a depressing effect on the fir and suppresses its protective reaction to damage by insects. It is possible that rising temperatures and suppressed host plant immunity once accelerated the development of the Siberian silkworm and allowed it to escape the numerous natural enemies that controlled its numbers. As a result, the system went out of balance - human activity served as a trigger for a process that destroys the natural biocenosis.

This point of view is in good agreement with V.V. Zherikhin’s fundamental idea of ​​the evolution of biological communities, developed on the basis of an in-depth comparative study of the succession of fossil faunas. The development of life on Earth has repeatedly passed through periods of mass extinction of some creatures and the emergence of other creatures. The change in the composition of the fauna occurred against the background (and because of) an ecological crisis caused by depression and the disappearance of dominants (edificators) - plants that determined the appearance and structure of ecosystems in the distant past. In place of extinct communities, new ones arose. In particular, all stable grass communities (steppes, prairies, pampas) historically formed on the site of successional series with forest climaxes due to the loss of the last stages, where trees dominated. The latter is understandable: in any series of changes in communities, the most vulnerable stage is the initial one; if it were stable, there would be no succession at all. Therefore, if the final stages are regularly destroyed by some factor and the succession system returns to its original state, then there is a possibility that the ecological space will be captured by other species that will not allow further changes in cenoses along the established path. “Other species” are not aliens, but inhabitants of local ecosystems, usually in a depressed state, but capable of growing quickly and maintaining territory when suitable conditions arise. In the situation with the taiga and the Siberian silkworm, the role of the invader species is played by the reed grass.

The observed picture is not identical to that known from paleoecology. Fossil forests have disappeared with the active participation of large leaf-eating mammals, while the dark coniferous taiga is being destroyed by insects. And yet the principle is repeated: the consumer of the first order translates forest ecosystem at the initial stage of succession, after which the position of the edifier in the plant community is occupied by one of the common, but previously not dominant species, which modifies the environment in such a way that the path to the former climax ecosystem is closed.

If the noted similarity is not superficial, then the presented example illustrates the process of the anthropogenic biosphere crisis, which V.V. Zherikhin repeatedly spoke about - a radical restructuring of the entire biota caused by human activity. Of course, the crisis did not begin now: locust outbreaks plagued people long before our era. But biocenotic crises do not happen overnight. Abnormal natural phenomena For thousands of years, following the development of civilization, the existing structure of the biosphere is being shaken slowly and little by little, but you still need to think about the consequences.

Literature

1. Kolomiets N.G. Siberian silkworm - a pest of lowland taiga // Tr. according to forest household Novosibirsk, 1957. Issue 3. P.61-76.

2. Kuzmichev V.V., Cherkashin V.P., Korets M.A., Mikhailova I.A.// Forestry. 2001. No. 4. P.8-14

3. Savchenko A.M. On the dispersion distance of Siberian fir seeds in lowland forests // Tr. SibNIILP. 1966. Issue 14. P.3-5.

4. Kondakov Yu.P. Patterns of mass reproduction of the Siberian silkworm // Ecology of populations of forest animals of Siberia. Novosibirsk, 1974. P.206-265.

5. Official data of the Russian Forest Protection Center.

6. Talman P.N. The influence of the environment and the transformative role of humans in connection with the reproduction of the Siberian silkworm // Tr. LTA. 1957. Issue 81. Part 3. P.75-86.

7. Zherikhin V.V. Selected works on paleoecology and phylocenogenetics. M., 2003.

The Siberian silkworm is a large butterfly with a wingspan of up to 80 mm (photo below). Males differ from females in their smaller size and the presence of comb-like antennae. The color is yellowish-brown, brown, gray, black. There are patterns and light spots on the front pair of wings. The hind wings are a single color. A photo of the Siberian silkworm at the adult stage is presented below.

The eggs are spherical, up to 2 mm in size (photo below). Initially, the eggs are bluish-green in color, gradually changing color to brown.

On a note!

The color may vary depending on where the female laid the egg - on the bark of trees, stems, leaves. Siberian silkworm eggs are located in groups or one at a time. The photo can be seen below. One clutch can contain about 200 pieces.

Siberian silkworm caterpillars are born miniature - about 2 mm. They eat well and grow quickly. At the last stage of development, the body length of the larvae is 70 mm. The color is variable - from green to brown and almost black. On the body you can see purple stripes and spots. Caterpillars go through 4 molts and constantly increase in size. Photos of the butterfly's offspring can be seen below.

At the end of development, the Siberian silkworm caterpillar turns into a pupa. The cocoon is formed from a silk thread, which it produces itself. It clings with its paws to the bark of trees, stems, leaves, and freezes. Cocoon size up to 40 mm. Initially, the covers are light, then they acquire a brown tint, black, which is clearly visible in the photo of the Siberian silkworm cocoon.

Features of development

The butterfly flight begins in the second half of July and lasts about a month. Mating occurs on the fly. The male dies soon after fertilization, the female looks for a favorable place to lay eggs. Attaches them to tree bark and leaves using a special sticky substance that is released along with the eggs.

The larvae inside lasts up to 22 days; under favorable conditions, the young offspring of the Siberian silkworm appear already on the 13th day. First instar caterpillars actively feed on needles and grow quickly. During the period from August to September, they increase significantly in size, and the chitinous cover becomes denser. The cycle in the photo. At the end of September, the caterpillars crawl under the bark and forest floor and remain for the winter.

With the onset of warmth - in May, the larvae rise to the crowns, where they live and feed throughout the warm season. The caterpillars undergo the second wintering at the fifth or sixth age. They continue to develop in May and pupate by the end of June. The development of a butterfly in a cocoon lasts about a month. Externally - a motionless creature, inside - the most complex processes of transformation take place. Young butterflies appear in early September. Their task is to find a secluded place for wintering. Below is a photo of the young.

On a note!

Development occurs over 2-3 years, while butterflies at the imago stage live no more than a month and do not feed on anything. Energy reserves are enough to lay about 300 eggs at a time.

Sabotage

It’s not hard to guess why the Siberian silkworm is dangerous. Due to the fact that the development of the larvae stretches over several years, and every spring they rise into the crowns, there is a risk of weakening the tree.

Butterflies disperse their numerous offspring throughout different plants. In July, mass infection covers several million hectares of forest. This causes enormous damage to forestry. Natural enemies Siberian silkworms include borers, bark beetles, and longhorned beetles. The photo can be seen below. Since bark beetles also cause damage to coniferous plantations, the scale of the pest increases several times more. Birds of prey eat insects.

In the mid-90s, the fight against Siberian silkworm larvae lasted 4 years. Then about 600 thousand hectares of forest area suffered from the pest invasion. Cedar trees, which were of great value to local residents, died.

Over the past 100 years, 9 outbreaks of mass pest control of silkworm caterpillars have been observed in Siberia. It was possible to stop the reproduction thanks to the use of modern insecticides. and other plants are taken constantly, if not to destroy caterpillars, then to prevent their appearance. A photo of mass plant damage is presented below.

Interesting!

Sericulture is especially developed in China. Natural silk, which is obtained from threads, is highly valued. Insects are specially bred on mulberries and provide all the necessary living conditions. The cocoons are collected without allowing the butterflies to be born. The length of the threads of one cocoon is about 900 m. Butterflies lead a sedentary lifestyle and practically do not fly. The larvae are not dangerous to surrounding plants.

Fighting methods

Caterpillars damage larch, oak, beech, birch, pine, spruce, aspen, fir, cedar, and maple. prefers deciduous trees, but does not disdain coniferous trees. The first instar larvae feed during the day, and as they grow older they switch to a hidden lifestyle - they crawl out of their shelters at night.

Main control measures:

• Collection and destruction of ovipositions. In small areas, young trees are scraped off by hand, trampled underfoot, or thrown into the fire. Below are photos of infected plants.
• In late autumn or early spring, eggs are destroyed using petroleum products - gasoline, kerosene, motor oil. However, you should always remember that these are flammable substances; if used incorrectly, the risk of a massive fire increases.
• Against the larvae, adhesive rings are used, which are placed at a level of 1.5-2 m above the ground surface, which does not allow pests to reach the crown.
• In small areas, caterpillars are collected by hand and then destroyed in any way.
• Most effective method– insecticidal substances. Spray crowns and tree trunks. Treatment can be carried out in early spring before or after the trees bloom. The effect of the poison lasts for 20-45 days. Repeated processing is carried out as necessary.

Every autumn and spring, you need to carefully inspect the bark of trees for the presence of eggs and larvae, and coat the trunks with a solution of lime and chalk. Life cycle The insect's life spans several years, so there is always a threat of infection. Spread to other trees occurs either in early spring or late autumn. You should carefully examine the pest in the photo so that you can respond to the problem in a timely manner.