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Data Sheets on Forest Pests

Erannis jacobsoni


Name: Erannis jacobsoni Diakonoff
Synonyms: Hybernia jacobsoni
Taxonomic position: Insecta: Lepidoptera: Geometridae
Common name: Geometrid of Yakobson (English); пяденица Якобсона (Russian).
Bayer computer code:


E. jacobsoni can damage different species of Larix (mainly Larix gmelinii (= Larix dahurica) and Larix sibirica (= Larix sukaczevii)).


EPPO region: Russia (east of Southern Siberia, Transbaïkalia, south of North – Eastern Siberia, Southern Far East).
Asia: Russia (east of Southern Siberia, Transbaïkalia, south of North – Eastern Siberia, Southern Far East), Mongolia.
EU: Absent
Main outbreaks of E. jacobsoni occurs in forests around Baïkal lake (republic of Buryatia, oblast’s of Chita and Irkutsk, northern Mongolia).


Adults of E. jacobsoni in its natural range usually appear in the middle of September and occur till the middle of October with the maximum of activity at the end of September. Females have no wings and do not fly. They have negative geotaxis and move actively on the surface of the soil and up on the trunks of larch trees. They lay eggs under scales of the trunks bark and in cracks of branches bark. Migrative capacities of E. jacobsoni are limited because of non-flying females. At this reason, pest populations develop on the same trees during many consecutive years and may rich the population density till 6000 caterpillars per tree. Eggs overwinter and neonate caterpillars appear at the end of May and in the beginning of June. They feed on needles and the maximum of defoliation is reached in the middle of July. Caterpillars moult 4 times before making cocoons in the soil at the end of July. The full life cycle takes one year (Pleshanov, 1982).

The outbreaks of E. jacobsoni are characterised by cycles of slow build-up of population numbers over several years, reaching a peak ('outbreak') followed by a population collapse. The outbreaks of E. jacobsoni occur with a periodicity of about 6 – 7 years (Amsheev, 1996) and usually last 3 – 4 years (eruption phase of outbreak). Outbreaks are often preceded by periods of droughts and often occurs together with outbreaks of Orgyia antiqua, Dendrolimus sibiricus and/or Lymantria dispar. In general, E. jacobsoni prefers dry conditions and areas with continental climate. A very long eruption phase of E. jacobsoni outbreaks make the pest very dangerous for trees. The full defoliation during several (3 – 4) consecutive years often leads to death of forests. Furthermore, the outbreaks of E. jacobsoni are also very often followed by outbreaks of wood borers (scolytids, cerambycids and others), particularly, I. subelongatus, Tetropium gracilicorne, Melanophila guttulata, Sirex ermak (Epova & Pleshanov, 1995;). These pests are able to kill trees, which are already heavily stressed by E. jacobsoni.

The natural enemies of E. jacobsoni (egg parasitoids Telenomus mayri, pupa parasitoids Cratichneumon pachymerus, Cratichneumon nigritarius, Ceromasia rubrifrons, larva parasitoids Rogos rossicus, Phryxe vulgaris and some other parasitoids, predators and diseases) play the important role in regulation of its populations (Boldaruev, 1972; Kondakov, 1979; Pleshanov, 1982; Amsheev, 1996).



Defoliation of larch is usually very spectacular. The presence of caterpillars is easily detected. The adults and caterpillars have characteristics which permit entomologists to easily distinguish the species from other species of moths.



No information yet.


There exist “normal” and “dark-coloured” caterpillars. The difference between two forms appear since the second instar. Different scientists explain that effect of melanism occurs in cases of food deficit or of high density of pest populations (“group effect”). Dark-coloured caterpillars have a brown-red head with more light spots. Along the dorsal side of the body, there are two brown dotted lines. Lower, there are four similar sub-dorsal lines. Along each lateral side of the body between 1st and 6th segments, there is a yellow stripe, which is broken by stigmal spot. The ventral side of the body is more or less light with four brown dotted lines. Sometimes dark lines join each other and in these cases caterpillars become almost completely dark. There exist many transitional colour variations between “typical” and “dark” forms.

Fig. 1 Larvae of Erannis jacobsoni: a - “dark” and б - “typical” forms


No information yet.


In addition to the “typical” and “dark” forms, there exists a dark form described as E. jacobsoni ab. nigra Pleshanov (the existence of “dark” forms is characteristic to many species of the genus Erannis). Females have no wings. “Dark” females have an abdomen completely covered with dark scales, which form only dark spots on the white abdomen of “typical” females. Front wings of males are uniformly brown with more dark transversal band, which is difficult to distinguish in the case of “dark” form. Back wings are creamy coloured, have not well developed dark transversal band and dark middle spot.

Fig. 2 Adults of Erannis jacobsoni: a - “dark” and б - “typical” forms


E. jacobsoni can not spread much with flights of the adult moths because females have no wings. Eggs may be easily transported on wood containing bark because they are well placed and masked under scales and in cracks of bark and stay there a long period of time (9 months since September to June). All stages of the life cycle can be transported on plants moving in trade particularly plants for planting and cut branches (including Christmas trees). Eggs, larvae and adults may be associated with wood containing bark and may be hitchhikers on other products.


Economic Impact

E. jacobsoni is one of several important defoliators of larch in Russia. It attacks both stressed and healthy trees of different ages (Pleshanov, Vassilieva, 1974; Pleshanov, Issaev, 1981; Pleshanov, 1982). The damage became especially important since the end of 1950th. At the reason of non-flying females, pest populations develop on the same trees during many consecutive years and may rich the population density till 6000 caterpillars per tree. All young trees are killed rather quickly. The pest outbreaks occur throughout large areas (thousands of hectares) and usually cause important decrease of wood and seed production. The outbreaks of E. jacobsoni are characterised by a very long eruption phase (3 – 4 years), which make the pest very dangerous for trees. The 100% defoliation of larch during such a long period often causes the death of forests, either itself or in association with Orgyia antiqua, Dendrolimus sibiricus, Lymantria dispar and/or other defoliators (Boldaruev, 1972; Kondakov, 1979; Pleshanov, 1982; Amsheev, 1996).

Environmental Impact

E. jacobsoni often causes the death of forests, either directly or by leaving the forest susceptible to subsequent attack by other forest pests (scolytids, cerambycids and others), and/or by predisposing the forest to forest fires (Pleshanov, 1982). The reforestation of these areas is often very complicated and takes much time. This results in serious changes of environment over large areas.

Significant control efforts (mainly aviation treatments with chemical and bacterial preparations) against E. jacobsoni are undertaken during years of outbreaks in Russia (Pleshanov, 1982) within the range of the pest.

Phytosanitary risk

E. jacobsoni is not declared a quarantine pest by any regional plant protection organization. It is considered as a serious defoliator of larch forests in eastern Russia (especially in regions around Baïkal lake). It is very likely to be able to establish in most EPPO countries particularly those in the east, north and centre of the European part of the EPPO region where larch species are important forest trees.

To prevent introduction of E. jacobsoni to other countries, the effective measure would be to prohibit import of larch wood with bark and larch plants for planting and cut branches from the infested areas. Inspection of wood with bark can detect eggs of the pest. Inspection of wood products, especially those with bark, can detect hitchhiking larvae and adults.


Amsheev R. M. (1996) Ecology of the most important phytophagous insects in Buryatia and their control. Thesis of doctorate in biological science, Irkutsk, 102 p. (in Russian).

Boldaruev V. O. (1972) Geometrid of Yakobson – Erannis jacobsoni Djak. (Lepidiptera, Geometridae) in forests of Buryatia. In: “Main pests of trees and shrubs of Transbaïkalia”. “Trudy Buryatskogo instituta estestvennykh nauk”, 7, p. 3 – 19 (in Russian).

Boldaruev V. O. (1972) Erannis jacobsoni Djac. (Lepidiptera, Geometridae) – a serious pest of larch in Transbaïkalia. Entomologicheskoe obozrenie, 51, N° 1, p.47 – 58 (in Russian).

Epova V. I., Pleshanov A. S. (1995) The forest regions injured by phyllophagous insects in the Asian Russia. Novosibirsk, "Nauka", Siberian publishing firm RAS, 147 p. (in Russian).

Kondakov Yu. P. (1979) Phyllophagous insects – forest pests of Baïkal lake region. In: “Fauna of forests of Baïkal lake region”. Novossibirsk, "Nauka", Siberian department, p. 5 – 44 (in Russian).

Pavlovskii E. N., Shtakelberg A. A. and all. (1955) Forest pests. Guide. Moscow – Leningrad, Edition of Academy of sciences of the USSR, V. 1, 421 p. (in Russian).

Pleshanov A. S. (1982) Insect defoliators of larch forests of Eastern Siberia. Novossibirsk, "Nauka", Siberian publishing firm RAS, 209 p. (in Russian).

Pleshanov A. S., Vassilieva T. G. (1974) Outbreaks of larch defoliators at Baïkal lake. In: “Transactions of VIII congress of the All-Union Entomological Society", Part II. Leningrad, p. 233 – 234 (in Russian).

Pleshanov A. S., Issaev A. S. (1981) Ecological and physiological aspects of the resistance of larch to insect defoliators. In: “Role of plant-insect interactions in the dynamic of forest pest populations. Abstracts of the Symposium. Irkutsk, p. 40 – 41 and 80 – 81 (in Russian).

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