Preferred name: Ips duplicatus
Authority: (Sahlberg)
Taxonomic position: Animalia: Arthropoda: Hexapoda: Insecta: Coleoptera: Curculionidae: Scolytinae
Other scientific names: Bostrichus duplicatus Sahlberg, Bostrichus judeichi Kirsch, Cyrtotomicus rectangulus Ferrari, Tomicus infucatus Eichhoff
Common names in English: northern bark beetle
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EU Categorization: PZ Quarantine pest (Annex III)
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EPPO Code: IPSXDU

The main hosts of I. duplicatus are various species of spruce including Picea abies in Europe, Picea obovata in the European and Siberian parts of Russia, Picea jezoensis on Sakhalin Island (Russia), and Picea koraiensis in China. I. duplicatus may also attack pine (Pinus spp.), less commonly larch (Larix spp.), and in exceptional cases, fir (Abies spp.) Douglas fir (Pseudotsuga menziesii), and juniper (Juniperus spp.) (Izhevskiy et al., 2005; Holuša & Grodzki, 2008; Kašák & Foit, 2015).

Host list: Abies holophylla, Abies sibirica, Juniperus sp., Larix decidua, Larix gmelinii, Larix sibirica, Picea abies, Picea fennica, Picea jezoensis, Picea obovata, Picea omorika, Pinus cembra, Pinus koraiensis, Pinus sibirica, Pinus strobus, Pinus sylvestris, Pseudotsuga menziesii

The northern bark beetle I. duplicatus is a Eurasian species. The pest is widespread in Russia and neighboring Asian countries (Douglas et al., 2019; CABI, 2021). In Europe it was originally restricted to northern countries, however, it has expanded its distribution range to Eastern Europe. In the middle of the last century, I. duplicatus spread to the southeast and has recently been moving west (Wermelinger et al., 2020).

EPPO Region: Austria, Belarus, Czech Republic, Estonia, Finland, Germany, Hungary, Kazakhstan, Latvia, Lithuania, Norway, Poland, Romania, Russia (Central Russia, Eastern Siberia, Far East, Northern Russia, Southern Russia, Western Siberia), Slovakia, Slovenia, Sweden, Switzerland, Türkiye, Ukraine
Asia: China (Heilongjiang, Jilin, Liaoning, Neimenggu, Sichuan, Xinjiang), Japan (Honshu), Kazakhstan, Korea Dem. People's Republic, Korea, Republic, Mongolia, Syria, Taiwan

The northern bark beetle Ips duplicatus is native to Northern Europe, Siberia, and East Asia. It is adapted to low temperatures, short growing seasons, and usually has one generation per year in these areas (Wermelinger еt al., 2020). In the southern regions, where it is spreading as a result of the expansion of its range, it can have two to three generations per year, depending on climatic conditions. I. duplicatus has a very similar biology to the widespread European spruce bark beetle I. typographus. 

I. duplicatus usually overwinters as an adult stage in forest litter, but beetles can also overwinter in the phloem of trees when the last generation has not had time to complete full development. It most often attacks standing trees, 40-70 years old, which have been weakened by drought stress, or by pathogens, but rarely attacks fallen trees or cut logs (Izhevskiy et al., 2005; Holuša & Grodzki, 2008; Holuša et al., 2010; Wermelinger et al., 2020). Usually, I. duplicatus colonizes the upper part of the trunk and large branches unlike Ips typographus which usually infests lower parts. However, under epidemic conditions, the part of the tree infested by I. duplicatus can be much larger and reach the middle and basal parts of the trunks. 

The species is polygamous, and the males initiate gallery construction and produce an aggregation pheromone consisting of ipsdienol (Bakke, 1975) and E-myrcenol (Bakke, 1975; Byers et al., 1990; Ivarsson et al., 1993; Ivarsson & Birgersson, 1995). 

After having excavated a nuptial chamber in the phloem, each male is joined by 1–5 females. The beetle produces a gallery system nearly identical to that of I. typographus but smaller (7-10 cm) and with maternal galleries. One female produces up to 60 offspring. The speed of brood development is similar to that of I. typographus (Schlyter et al., 1987). Development of one generation under Central European climatic conditions usually takes about 6-8 weeks I. duplicatus can co-occur with some other species of bark beetles, mainly I. typographus, I. amitinus and Pityogenes chalcographus, which can be competitors (Holuša et al., 2010).

A general description of the biology of I. duplicatus is provided by Izhevskiy et al., (2005); Holuša & Grodzki (2008), Holuša et al., (2010), CABI (2021), Wermelinger et al., (2020).

Symptoms

Galleries are usually found in standing trees, less often on logs, and in the upper part of trees where the bark is relatively thin. Larger branches can also be used for reproduction. Each gallery has up to five longitudinal female egg galleries. Trees that are infested by I. duplicatus have discoloured crowns. The needles are lighter in colour and often fall to the ground. The frass can be found on the bark, on the basal part of the tree trunk. Woodpeckers, in search of larvae, often break off the bark of infested trees. 

Morphology

Adult

Beetles are 2.6-4.3 mm long, 2.3-2.5 times longer than wide; dark-brown, shiny and hairy, with four spines at each side of the elytral declivity. The second and third spines arise from a tumescence which forms an arcuate ridge between them. This is most distinct in the male where the third spine is the largest and is capitate (Balachowsky, 1949; Grüne, 1979; Douglas et al., 2019; CABI, 2021).

Egg

The eggs are whitish-grey, ovate and small (0.7 mm long). 

Larva

The larvae and adults are similar in size, white, cylindrical and legless. 

Pupa

The pupae have many free segments (pupa libera). They are white and similar in size to the adults.

Detection and inspection methods

The symptoms of early infestations are not very evident. The standing infested trees die during the I. duplicatus colonisation, with an obvious discolouration of their crown, which becomes brown, and then grey after the needles have shed (EFSA, 2017). The frass on the bark surface and around the tree base is easy to find during periods of good weather. However, it disappears after rainfall. Another obvious symptom of infestation is bark that has been broken off by woodpeckers (CABI, 2021; EFSA, 2017).

I. duplicatus mostly attacks individual weakened standing trees in the stands. Attacked trees are often dispersed inside the stands and sometimes on the stand edges.

The nuptial chambers, maternal galleries on the infected dying trees are easy to find under the bark. The galleries of I. duplicatus are however very similar to those of Ips typographus (Balachowsky, 1949). The sapwood shows blue staining due to the fungi that are carried by the beetles. 

Pheromone traps can also be used for detection.

Ips species identification is possible by using the illustrated dichotomous key and interactive LUCID keys developed by Douglas et al. (2019). Both include multiple routes to identification of one or both sexes of Ips species including I. duplicatus. Research is also being carried out on the use of molecular tests for I. duplicatus (Becker et al., 2021).

Studies carried out in laboratory conditions have shown that Ips spp. can fly continuously for several hours, but in nature, the flight distances are usually much shorter. It was found that the flight distance of a related species, Ips sexdentatus, is usually about 5 km, but some individuals can fly up to 45 km (Jactel & Gaillard, 1991). Nilssen (1978) reports that beetles have been found in the stomach of trout in lakes 35 km from the nearest spruce forest, probably carried by the wind. Spread over long distances can occur by transporting the pest under the bark of logs, as well as with plants for planting, isolated bark or wood chips.

Economic impact

Since the end of the last century, this beetle has become an invasive species in European spruce forests (Wermelinger et al., 2020; CABI, 2021). With the expansion of the range of I. duplicatus to the south, under certain conditions when it reaches 3 generations, it can become an economically important pest (Holuša et al., 2010).

In recent years, more frequent and hotter periods of drought have favoured the infestation of spruce trees by bark beetles (Mezei et al., 2017; Knížek & Liška, 2018). A significant increase in the distribution area and population density of I. duplicatus in recent years has been observed in the Czech Republic, Romania, Slovakia and Poland (Holuša et al., 2010; Olenici et al., 2009; Duduman et al., 2011; Knížek & Liška, 2018). In the northeastern part of the Czech Republic, I. duplicatus was involved in up to 80 % of spruce infestations (Holuša et al., 2010). It should be noted that in these countries I. duplicatus often colonizes younger trees with thinner bark, in contrast to I. typographus which usually prefers older trees (Duduman et al., 2011; Wermelinger et al., 2020).

The damage from I. duplicatus is difficult to assess because it is often found together with I. typographus (Grodzki, 2012; Duduman et al., 2011; Wermelinger et al., 2020).

Control

According to Wermelinger et al. (2020), the challenge with northern bark beetle infestations is that its management is more complex than for I. typographus. Firstly, sanitation felling during winter is generally only effective against I. typographus, not against I. duplicatus, because the second generation of I. duplicatus leaves its brood trees in autumn to overwinter in the litter layer. Additionally, I. duplicatus infestations occurring in tree crowns are more difficult to detect. Because of this beetle’s faster larval development, the crowns often turn brown only after the beetles have already left the trees (Holuša et al., 2010; EFSA, 2017).

Control measures for I. duplicatus are similar to those for other bark beetles and include the use of pheromone traps for monitoring and mass trapping of the pest with trap trees.

Phytosanitary risk

I. duplicatus is absent in the islands of Great Britain, Ireland and Greece that are EU Protected Zones, and in these areas, the introduction of conifers (round wood; plants for planting, isolated bark) from countries where this pest is present is banned (EFSA, 2017).

Due to the expansion of the range to the western and southern territories, and also considering that the northern bark beetle can be a primary pest, some countries (Morocco, South Africa, Jordan, Turkey) included I. duplicatus in their quarantine lists (EFSA, 2017; EPPO, 2021a).

If I. duplicatus were always accompanied by I. typographus, it would be irrelevant for trees whether they are infested by I. typographus alone or by both bark beetle species; as they are bound to die in any case (Wermelinger et al., 2020). If, however, the northern bark beetle was able to colonize and eventually kill a substantial number of trees in its own right, this could lead to additional mortality in Norway spruce (Picea abies) or other conifers. Moreover, the northern bark beetle can also carry ophiostomatoid fungi: Ceratocystis polonica; Ophiostoma bicolor; O. penicillatum; O. piceae; O. piceaperdum; Ophiostoma sp.; Pesotum sp. It is considered that C. polonica is a particularly virulent pathogen (Kirisits, 2004).

If it is judged necessary to take phytosanitary measures against I. duplicatus, those taken against I. typographus and other Ips species would be effective (EPPO, 2021b). The following phytosanitary measures recommended by the EPPO Standard PM 8/2 (3) ‘Coniferae’ are considered to be effective against bark beetles. Plants for planting, cut branches (including cut Christmas trees), round wood or other parts of the host plants of I. duplicatus originating from the countries in which I. duplicatus is present should originate from a pest-free area. If not, the following phytosanitary measures are required to import round wood from the area where the pest is present: wood should be bark-free or heat-treated (EPPO, 2009a), or fumigated with appropriate fumigant, or treated with ionizing radiation (EPPO, 2009b). Harvesting wood residues, processing wood residues, hogwood and wood chips of the host should be produced from debarked or heat-treated wood. The heat treatment is also required for import of isolated bark. Wood packaging material should meet requirements of ISPM no. 15 (ISPM, 2018).

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Becker M, König S & Hoppe B (2021) A simple PCR-based approach for rapid detection of Ips typographus and Ips duplicatus in the presence of (associated) symbionts and parasites. Journal of Plant Diseases and Protection 128(2), 527-534.

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CABI (2021) Invasive Species Compendium, online. Datasheet report for Ips duplicatus (double-spined bark beetle). Available online: https://www.cabi.org/isc/datasheet/28823 [Accessed: 11 September 2021] 

Douglas HB, Cognato AI, Grebennikov V & Savard K (2019) Dichotomous and matrix-based keys to the Ips bark beetles of the World (Coleoptera: Curculionidae: Scolytinae). Canadian Journal of Arthropod Identification, 38, 234 pp. https://doi.org/10.3752/cjai.2019.38

Duduman ML, Isaia G & Olenici N (2011) Ips duplicatus (Sahlberg) (Coleoptera: Curculionidae, Scolytinae) distribution in Romania – preliminary results. Bulletin of the Transilvania University of Braşov Series II 4, 19–26. https://www.cabi.org/isc/FullTextPDF/2012/20123387814.pdf

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EPPO (2009a) Standard PM 10/6 Heat treatment of wood to control insects and wood-borne nematodes. EPPO Bulletin 39(1), p 31. https://doi.org/10.1111/j.1365-2338.2009.02227.x

EPPO (2009b) Standard PM 10/8 Disinfestation of wood with ionizing radiation. EPPO Bulletin 39(1), 34-35. https://doi.org/10.1111/j.1365-2338.2009.02229.x

EPPO (2021a) EPPO Global Database (available online). https://gd.eppo.int EPPO (2021b) Ips typographus. EPPO datasheets on pests recommended for regulation. Available online. https://gd.eppo.int

Grodzki W (2012) Two types of Norway spruce Picea abies (L.) H. Karst. infestation by the double spined bark beetle Ips duplicatus C.R. Sahlb. (Coleoptera: Scolytinae) in southern and north-eastern Poland. Folia Forestalia Polonica series A 54, 169–174. https://zenodo.org/record/30734/files/grodzki-12-3-4.pdf

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Holuša J & Grodzki W (2008) Occurrence of Ips duplicatus (Coleoptera: Curculionidae, Scolytinae) on pines (Pinus sp.) in the Czech Republic and southern Poland - Short Communication. Journal of Forest Science 54, 234–236. https://doi.org/10.17221/18/2008-JFS

Holuša J, Lubojacký J & Knížek M (2010) Distribution of the double-spined spruce bark beetle Ips duplicatus in the Czech Republic: spreading in 1997–2009. Phytoparasitica 38, 435–443. https://doi.org/10.1007/s12600-010-0121-9

ISPM (2018) International Standards for Phytosanitary Measures no. 15. Guidelines for Regulating Wood Packaging in International Trade. FAO, Rome (IT).

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Ivarsson P, Schlyter F & Birgersson G (1993) Demonstration of de novo pheromone biosynthesis in Ips duplicatus (Coleoptera: Scolytidae): inhibition of ipsdienol and E-myrcenol production by compaction. Insect Biochemistry and Molecular Biology 6, 655–662.

Izhevskiy SS, Nikitskiy NB, Volkov OG & Dolgin MM (2005) [Illustrated guide to coleopteran – xylophagous pests of forests and timber of Russia]. Tula: Grif and Co. 218 pp (in Russian). 

Jactel H & Gaillard J (1991) A preliminary study of the dispersal potential of Ips sexdentatus with an automatically recording flight mill. Journal of Applied Entomology 112, 138-145.

Kašák J & Foit J (2015) Double-spined bark beetle (Ips duplicatus) (Coleoptera: Curculionidae): a new host – Douglas fir (Pseudotsuga menziesii) – Short Communication. Journal of Forest Science 61(6), 274-276.

Kirisits T (2004) Fungal associates of European bark beetles with special emphasis on the ophiostomatoid fungi. In: Lieutier F, Day KR, Battisti A, Gregoire JC and Evans HF (eds.) Bark and wood boring insects in living trees in Europe, a synthesis. Springer, Netherlands, 181–236.

Knížek M & Liška J (2018) Occurrence of forest damaging agents in 2017 and forecast for 2018. Supplementum, VULHM, Jíloviště, 70 pp (in Czech).

Mezei P, Jakuš R, Pennerstorfer J, Havašová M, Škvarenina J, Ferenčík J, Slivinský J, Bičárová S, Bilčík D, Blaženec M & Netherer S (2017) Storms, temperature maxima and the Eurasian spruce bark beetle Ips typographus – An infernal trio in Norway spruce forests of the Central European High Tatra Mountains. Agricultural and Forest Meteorology 242, 85–95.

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Olenici N, Duduman ML, Tulbure C & Rotariu C (2009) Ips duplicatus (Coleoptera, Curculionidae, Scolytinae) – an important insect pest of Norway spruce planted outside its natural range. Revista Pădurilor 124, 17–24 (in Romanian).

Schlyter F, Byers JA & Löfquist J (1987) Attraction to pheromone sources of different quantity, quality, and spacing: density-regulation mechanisms in bark beetle Ips typographus. Journal of Chemical Ecology 13, 1503-1524.

Wermelinger B, Mathis DS, Knížek M & Forster B (2020) Tracking the spread of the northern bark beetle (Ips duplicatus [Sahlb.]) in Europe and first records from Switzerland and Liechtenstein. Alpine Entomology 4, 179–184. https://doi.org/10.3897/alpento.4.53808

This datasheet was extensively revised in 2021 by Dr Oleg Kulinich (All-Russian Center for Plant Quarantine). His valuable contribution is gratefully acknowledged.

EPPO (2024) Ips duplicatus. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-11-21)

This datasheet was first published in 1997 in the second edition of 'Quarantine Pests for Europe', and revised in 2021. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1997) Quarantine Pests for Europe (2^nd edition). CABI, Wallingford (GB).