Preferred name: Polygraphus proximus
Authority: Blandford
Taxonomic position: Animalia: Arthropoda: Hexapoda: Insecta: Coleoptera: Curculionidae: Scolytinae
Other scientific names: Polygraphus abietis Kurentsov, Polygraphus horyurensis Murayama, Polygraphus laticollis (Wood & Bright) Eggers, Polygraphus magnus Murayama, Polygraphus miser Blandford, Polygraphus nigricans Kurenzov, Polygraphus oblongus Blandford
Common names in English: Japanese silver-fir bark beetle, Sakhalin-fir bark beetle, four-eyed fir bark beetle
view more common names online...
Notes on taxonomy and nomenclature EPPO Categorization: A2 list
EU Categorization: A1 Quarantine pest (Annex II A)
view more categorizations online...
EPPO Code: POLGPR

Polygraphus proximus is a bark beetle primarily attacking firs (Abies spp.) and also infesting a number of other Pinaceae.

In its native range (Far East), P. proximus develops on native fir species: Abies nephrolepis (main host), A. sachalinensis, A. holophylla, A. mariesii, A. firma, A. homolepis (Niisima, 1909, 1910; Kôno & Tamanuki, 1939; Niijima, 1941; Kurentsov, 1941; Krivolutskaya, 1958, 1996; Nobuchi, 1966). In Japan, the beetle causes significant mortality of weakened stands of Abies firma (Tokuda et al., 2008) and notably attacks stands of A. veitchii (Takagi et al., 2018). In its native range, it was occasionally documented on Picea jezoensis, Picea glehnii, Pinus densiflora, Pinus pumila, Pinus parviflora, Larix gmelinii, Larix kaempferi, Tsuga sieboldii (Niijima, 1941; Nobuchi, 1966, 1979). In mixed conifer forests, P. proximus still prefers Abies spp. to other conifers (Niijima, 1941). However, the relationships between P. proximus and its host plants might be more complex than originally thought, as during field studies on the colonization of P. proximus on various Abies species conducted in Japan, a mismatch between host preference and colonization success has been observed. The colonization of A. sachalinensis was high despite the fact that it was the least preferred species, and the colonization of A. firma was low although it was the most highly preferred species (Takagi, 2023).

In its invaded range, in particular in Siberia, P. proximus infests a novel host, A. sibirica (Siberian fir), causing severe damage and tree mortality on a large scale (Kerchev, 2014a). Abies species belonging to the botanical sections Balsamea (which includes A. sibirica and the North American A. balsamea) and Grandis (North American Abies species) are highly preferred hosts, whereas fir species from the section Abies (which includes European fir species, such as A. alba and A. nordmanniana) are the least preferred among Abies species (Kerchev, 2012; Kerchev, 2014a). In indoor experiments, P. proximus showed the ability to develop (i.e. complete one generation and provide fertile offspring) on Picea abies (Norway spruce), Pinus sylvestris (Scots pine), Pinus sibirica (Siberian pine), and Larix sibirica (Siberian larch) (Kerchev, 2012). In Siberia, P. proximus usually does not attack spruce and pine species, although, infestations of wind-broken spruces and pines (P. sylvestris and P. sibirica) have been recorded (Kerchev, 2014a).

In the European part of Russia, the beetle was found in plantings of A. sibirica, A. balsamea and Picea sp. in Moscow Oblast (Chilakhsaeva, 2008), and severe outbreaks have been observed in native stands of A. sibirica in other administrative regions (Dedyukhin & Titova, 2021; Subris, 2003; Semenova, 2023). In a botanical garden in Moscow, the beetle caused significant damage to North American fir species: A. arizonica, A. balsamea, A. fraseri, and the East Asian fir species, A. veitchii (Seraya et al., 2014). In the same botanical garden, lower levels of infestation were recorded on A. lasiocarpa, A. concolor, A. gracilis, A. nephrolepis, A. sachalinensis, A. sachalinensis var. mayriana, whereas, A. alba, A. excelsior, A. holophylla, A. homolepis, A. koreana, A. nordmanniana, and A. semenovii trees were not infested (Seraya et al., 2014).

Host list: Abies balsamea, Abies concolor, Abies firma, Abies fraseri, Abies grandis, Abies holophylla, Abies homolepis, Abies koreana, Abies lasiocarpa, Abies mariesii, Abies nephrolepis, Abies sachalinensis var. mayriana, Abies sachalinensis, Abies sibirica, Abies veitchii, Larix gmelinii var. gmelinii, Larix gmelinii, Larix kaempferi, Picea abies, Picea glehnii, Picea jezoensis, Pinus densiflora, Pinus koraiensis, Pinus parviflora, Pinus pumila, Pinus sibirica, Pinus sylvestris, Tsuga sieboldii

Polygraphus proximus originates from the Far East (China (mostly northeastern part), Japan, Korean Peninsula, and the Russian Far East), where it is one of the most common and widespread bark beetles (Niisima, 1909, 1910; Niijima, 1941; Krivolutskaya, 1958; Knizek, 2011; Park, 2018). Its native range mainly stretches (approximately) between the latitudes 32°54’N and 48°41’N and the longitudes 127°50’E and 148°31’E. As an exception, Yushan (Taiwan) is the most southern record (Nobuchi, 1979).

In the Russian Far East, P. proximus is naturally present in Primorsky and Khbarovskiy Krais, Sakhalin and some of Kuril Islands. Elsewhere in Russia, P. proximus is an invasive species causing significant ecological and economical damage to the forest sector (Kerchev, 2014a), and affecting urban plantings (Seraya et al., 2014). The beetle was first found outside its native range in Western Siberia, Kemerovo Oblast (54°56′N 87°14′E), in 2005 (Baranchikov et al., 2011), where it was first erroneously identified as another bark beetle, Xylechinus pilosus (Baranchikov et al., 2011). In Siberia, P. proximus has been recorded over a huge territory: from at least 51º33′N to 58º22′ N and from west to east from 83º04′E to 94º44′ E (Krivets et al., 2015a, 2015b). During the last two decades, P. proximus was also reported in Eastern Siberia (Bystrov & Antonov, 2019), the Urals, and in a few regions of the European part of Russia (Krivets et al., 2015a; Dedyukhin & Titova, 2021), including Moscow Oblast (55°37′N and 37°44’E) (Chilakhsaeva, 2008). In 2023, the species was detected in Northeastern Kazakhstan (50°45'N 83°01'E, 514 m a.s.l.) causing notable damage to A. sibirica in forest stands (Kirichenko et al., 2023). However, this record was not confirmed by the NPPO of Kazakhstan in 2024.

Polygraphus proximus inhabits both plains and mountains. In Primorsky Krai (Russian Far East), the beetle was found from altitudes ranging from 700 m a.s.l. (Kerchev, 2014a) up to 1300 m a.s.l. (Kurentsov, 1941). In West Siberia (invaded range), it is found in the southern taiga and subtaiga of the West Siberian Plain at an altitude of 100 m a.s.l. The maximal altitudinal record is 1493 m a.s.l. (in Altai Republic), which is the limit of Siberian fir distribution in the mountain-taiga belt (Kerchev, 2014a).

In general, P. proximus lives in cool continental and moderate insular climates (including monsoon climate) and is associated with coniferous forests, mostly dark (fir-spruce) and mixed forests (with inclusion of fir, spruce and pines). In the native range, the beetle distribution coincides with the range of Far Eastern species of firs, in the invaded range (Siberia and the European part of Russia) with that of Siberian fir (A. sibirica).

EPPO Region: Russia (Central Russia, Eastern Siberia, Far East, Western Siberia)
Asia: China (Heilongjiang, Jilin), Japan (Hokkaido, Honshu, Kyushu, Shikoku), Korea Dem. People's Republic, Korea, Republic, Taiwan

Polygraphus proximus habitats include pure fir forests, poly-dominant fir-pine-spruce forests with an admixture of aspen and birch, low-mountain black forests (Krivets et al., 2015a, 2015b). In its native range, beetles choose wind-fallen and wind-broken trees, cut logs as well as living trees weakened by abiotic (fire) and biotic (pathogens, phyllophagous insects) factors (Kurentsov, 1941; Nobuchi, 1966). In its invaded range, in addition to weakened and fallen trees, it attacks live and healthy stands of A. sibirica (Kerchev, 2014a). Outbreaks usually occur in forest monoculture or stands where fir predominates, but the pest can also attack isolated fir trees in mixed forests and urban plantings (Kerchev, 2014a; Seraya et al., 2014).

P. proximus infests both trunk and thick branches (Kurentsov, 1941). It seems to prefer trees with rougher bark (Takei et al., 2021).

In the Russian Far East and Western Siberia, P. proximus has two generations per year, the first developing from mid-May to mid-July, the second in August-September. In some cases, generations overlap (Kurentsov, 1941; Kerchev, 2014b). The adult beetles communicate using an aggregative pheromone, which is mainly produced by males (although females also seem to be able to produce it) (Viklund et al., 2022), and species-specific acoustic signals produced by both sexes (Kerchev, 2020). The beetle is a vector of phytopathogenic fungi, mainly Grosmannia aoshimae, Ophiostoma subalpinum and O. nikkoense (Yamaoka et al., 2004; Pashenova et al., 2018). Fir logs infested by G. aoshimae are more attractive for colonization by P. proximus (Pashenova et al., 2018).

Polygraphus proximus is a monogamous species (Kerchev, 2014b; Köbayashi & Takagi, 2020). The male makes an entry hole and bores a tunnel into the bark. Attracted by the pheromone (Kerchev, 2014b), a female penetrates into the tunnel through the entry hole for mating (Kerchev, 2014a, 2014b). The female lays eggs in distal parts of the galleries, and larvae then make perpendicular galleries. Mature larvae gnaw a pupal chamber in the sapwood (Kerchev, 2014b). After emergence, young beetles remain in the galleries for some time for feeding. During summer, all stages i.e. eggs, larvae, pupae, adults can be found in or under the bark or in the sapwood. After maturing, adult beetles make exit holes and fly to new host trees (Kurentsov, 1941; Kerchev, 2014b). The adult beetles that emerge in autumn overwinter in the galleries under the bark and exit from trees the next season (Kurentsov, 1941). Late instar larvae and pupae can also overwinter; the proportion of overwintering larvae and pupae vs. adult beetles is 1:3 (Kerchev, 2014b).

In galleries, the larvae, pupae and beetles can resist winter air temperatures down to –37.3° C, and even episodic temperature decrease down to –48.7° C (Kerchev, 2014b). In laboratory observations, at constant temperature (+22°C) and humidity (85%), one generation takes about 50 days; the flight peak occurs 5 days after the first beetles emerge (Kerchev, 2014a). Adults fly on sunny and calm (windless) days with air temperature above +15°C. However, windy and cloudy weather, as well as high precipitation can interrupt adult flight and, thus, extend the flight period (Krivolutskaya, 1958). During outbreaks in Western Siberia, 1.5 to 7.5 colonies of P. proximus per dm² were recorded within infested trees (Kerchev, 2014b).

In general, after emergence, adult beetles select trees within a radius of 50 m, although some can cover distances exceeding 100 m, to form new colonization sites (Kerchev & Torchkova, 2018). In Baikal region, over 7 years (from 2014 to 2021), the beetle range had expanded up to 95 km, with an expansion rate of 13-14 km/year (Kerchev et al., 2023).

Symptoms

The external signs indicating the presence of P. proximus in fir stands are as follows: pronounced resin flow on tree trunks of live trees, exit holes (round, about 2 mm in diameter) on trunks and large branches and the presence of fine pinkish-brown sawdust in the lower part of tree trunk and on the grass around the tree (Baranchikov et al., 2011; Krivets et al., 2015a, 2015b). Later on, attacked trees are easily recognized by the presence of red needles on some branches in the lower part of tree crown (or on all branches after 2-4 years of infestation) which may be accompanied by the simultaneous presence of dead trees in forest stand, with no needles and numerous exit holes on tree trunks (Krivets et al., 2015b).

Early internal signs of presence are the attempts to colonize the tree: the entrance holes (approximately 2 mm in diameter) filled with resin; in some cases, bright orange necrotic spots (up to 10 mm in diameter) in phloem tissues caused by phytopathogenic fungi vectored by the beetles, in particular Ophiostoma sp.(Yamaoka et al., 2004;Baranchikov et al., 2011; Krivets et al., 2015a). When colonization is successful, the internal signs of presence are characteristic galleries under the bark (usually double-armed mother galleries under the bark in phloem layer, located transversely on a standing trunk; at high densities, they are arranged randomly) (Kurentsov, 1941; Nobuchi, 1966; Kerchev, 2014a, 2014b). Triple- or four-armed mother galleries may also be found; they have a shape of radially diverging rays or star-like patterns (Kurentsov, 1941; Kerchev, 2014a, 2014b). The mother gallery system is usually 2-3 cm long, exceptionally 5-6 cm (Niijima, 1941).

Other characteristics signs are pupal chambers (oval depressions) in the sapwood, with the simultaneous presence of larvae, pupae and young, light brown small (around 3 mm long) beetles in the galleries under the bark or in the sapwood, or mature (black) beetles preparing to exit the damaged tree (Baranchikov et al., 2011; Kerchev, 2014a).

Morphology

Egg

The eggs are white, broadly oval, and relatively large for bark beetles (about 0.8 mm in length) (Krivets et al. 2015b). In Western Siberia, mean fecundity is 45±15 eggs (Kerchev, 2014b). No specific characters of eggs are known which would allow identification of the species.

Larva

The larva is white, legless, with a well-defined head, slightly bent downwards. Larvae have three instars, which are identified based on the width of the head capsule: larvae of the 1^st instar are 0.38±0.07 mm, 2^nd – 0.53±0.07 mm, 3^rd – 0.68±0.08 mm (Krivets et al., 2015b). No specific characters of larvae are known which would allow identification of the species.

Pupa

The pupa is spindle-shaped. Right after pupation, the pupa is translucent; on the 2^nd–3^rd day, it becomes milky white, on the 4^th day, pupal chitin gets darker, including mandibles and legs. The pupation stage takes about 7 days. A mature pupa is yellowish-whitish with dark brown mandibles and eyes, and the wing primordia are smoky grey (Krivets et al., 2015b). No specific characters of pupae are known allowing identifying the species.

Adult

Adult is up to 2.4–3.2 mm long (Park, 2018). The beetle is black with elytra gradually reddish towards apex; legs are dark red; tarsi and antennae are yellowish-red (Kuznetsov, 1941; Park, 2018). The forehead is flattened ventrally and convex dorsally, rather densely punctured; the male has two blunt, adjacent tubercles (Kurentsov, 1941), and the female has an even brush of reddish hairs. The eyes are divided into two parts (Krivolutskaya, 1996). The antennal flagellum is 6-segmented (if counted with pedicel) and the antennal club is bluntly pointed, large, twice as long as the flagellum. The abdomen is covered with long and dense light hairs directed backwards. The pronotum is wider at the base and tapering towards the anterior margin (Kurentsov, 1941). The elytra are short and wide, two-thirds as wide as long. The punctate grooves of the elytra are shallow and unclear. The entire surface of the elytra is covered with thick, slightly protruding greyish-yellow scales, the thorax and abdomen are covered with adjacent scales and hairs (Stark, 1952). The adult of P. proximus can easily be distinguished from related species living on firs in Europe (P. poligraphus , P. subopacus) by the shape of the antennal club, the 5-segmented antennal funicle (without pedicel) and vestiture on pronotum of fine, sparse hairs and elongate scales and larger body size (Stark, 1952).

Detection and inspection methods

In tree stands, visual inspection of tree trunks, branches, and examination of the bark and phloem tissues underneath the areas near entrance/exit holes are the main detection method (Krivets et al., 2015b). This can be applied to live, dead, fallen trees, logs with bark and pallets (Krivets et al., 2015b).
Aerial methods can be used to detect damaged trees in forest stands (i.e. trees showing certain amount of red needles, dying or dead trees). A new convolutional neural network model has been developed to determine forest spots damaged by P. proximus by using images of fir forests collected by unmanned aerial vehicles (Kerchev et al., 2021).

These external features of adults are sufficient to identify the species without the need to dissect male genitalia (Krivets et al., 2015b). Male genitalia are illustrated and characterized in Kirichenko et al. (2023). DNA barcoding (i.e. sequencing of the DNA barcoding fragment of the mitochondrial cytochrome oxidase subunit 1 (COI) gene of the mitochondrial DNA) can be used to reliably identify the species, especially when immature stages (egg, larva, pupa) are collected, or when adult remnants are found in galleries during the inspection. To-date, 53 specimens of P. proximus (49 from the Russian Far East and Siberia and 4 from Japan) have been sequenced, and their DNA barcodes are publicly available in BOLD System for comparison (Taxonomy browser, 2023). All sequences correspond to one BIN (BOLD:AAN5824), the species code used in BOLD System; the maximal intraspecies genetic divergence reaches 2.03%, which could be used as a threshold to distinguish P. proximus from the related species (Kirichenko N., pers. comm.).

Adult beetles can naturally spread by flight and anemochory (movement with wind currents) (Krivets et al., 2015a; Kerchev et al., 2023).

Over long distances, the main pathway of P. proximus is probably the transportation of timber still carrying its bark of the host plants (Abies, Pinus, Picea, Larix, Tsuga) from countries where the pest is present. Wood may contain all stages (eggs, larvae, pupae and adults) (Kerchev, 2014a). In Russia, long-distance movement of the pest (from the Far East to Siberia and to Moscow region) is suspected to be caused by accidental transportation by trains on the Trans-Siberian Railway (Baranchikov et al., 2011; Krivets et al., 2015a, 2015b; Kononov et al., 2016), as railway carriages transport timber (especially conifer logs with bark) and often have open platforms with side supports made from conifer wood.

Packaging material made with conifer wood is another possible pathway. One interception of P. proximus imported from Japan in a pallet made from Cryptomeria japonica (Cupressaceae) was documented by the quarantine inspection in New Zealand (Brockerhoff et al., 2003). C. japonica is not known to be a host plant of P. proximus (Kerchev, 2014a). This finding may indicate a possible risk of introducing of P. proximus with wood packaging material produced from conifer species, which are currently not known as hosts.

Movements of wood chips, wood particles, and wood waste processed from host trees in countries where P. proximus is present can be also an important pathway, as such materials may contain all stages of the pest (EFSA, 2020).

Considering that P. proximus can colonize trees of any size (Krivets et al., 2015b), the import of conifer plants for planting and bonsais from the regions infested by P. proximus may potentially be a pathway of the pest movement.

Economic impact

In its native range, P. proximus usually attacks weakened trees of Abies spp., but also has the ability to damage and kill visually healthy fir trees (Niijima, 1941; Nobuchi, 1966; Koizumi, 1977). In 2008 in Japan, on the southern island of Kyushu, the beetle caused significant mortality of A. firma stands weakened by the curculionid Parendaeus abietinus (Tokuda et al., 2008). In Hokkaido (Japan), it colonized live trees of A. sachalinensis, causing mass tree decline in forest stands in the 1970s (Koizumi, 1977). During studies conducted in two sites in Honshu and Hokkaido (Takagi et al., 2018),P. proximus caused up to 38 % and 60% mortality in A. veitchii stands, respectively. P. proximus can also influence forest structure. In Japanese subalpine/subarctic territories, its outbreaks result in tree decline predisposing damaged stands to fires and, thus, posing a threat to the regeneration of A. veitchii forests (Takagi et al., 2018). Furthermore, in the Far East, P. proximus is associated with phytopathogenic fungi from the genus Ophiostoma, which can be responsible for tree mortality, thus, accelerating tree decline (Ohtaka et al., 2006).

In its invaded range in Russia, P. proximus causes major tree mortality and attacks healthy A. sibirica trees, a new host that is highly susceptible to the pest (Baranchikov et al., 2011; Krivets et al., 2015a; Astrakhantseva et al., 2023; Semenova, 2023). The pest colonizes A. sibirica trees of any age and attacks fir undergrowth with a diameter of 6 cm, leading to the decline of entire fir stands (Krivets et al., 2015b). Considering that P. proximus is capable of destroying trees before they reach reproduction stage, it could threaten the existence of A. sibirica as a species (Krivets et al., 2015b). In Krasnoyarsk krai (Central Siberia) by 2018, fir mortality associated with P. proximus alone occurred on a territory of 541 400 ha, with significant ecological and economic impacts (Pavlov et al., 2020). In Irkutsk region (Eastern Siberia), where the pest was detected for the first time in 2017 (with an estimated arrival in this region in 2005–2006), the outbreaks covered an area of 1655 hectares by September 2022 (Kobzar et al., 2023).

In the invaded range, P. proximus also acts as a vector of an obligate symbiotic fungus, Grosmannia aoshimae (Ascomycota: Ophiostomataceae). This fungus originates from the Far East and arrived in Siberia with the beetle. The spread of this fungus leads to rapid weakening of A. sibirica trees resulting in unprecedented tree mortality (Pashenova et al., 2012, 2018; Astrakhantseva et al., 2014). In Siberia, massive death of fir trees occurred approximately 3–5 years after the first pest outbreak, followed by the complete collapse of forest stands (Krivets et al., 2015b). Furthermore, fir stands attacked by P. proximus are infected and weakened by phytopathogenic fungi Armillaria mellea s.l. and Heterobasidion annosum s.l., as well as Neonectria fuckeliana, concomitant pathogens occurring in wood lesions after P. proximus attacks (Pavlov et al., 2020).

In Siberia, P. proximus is a major cause of pronounced changes in ecosystem structure (Krivets et al., 2015b; Bisirova & Krivets, 2018). In damaged forests, the microclimate changes dramatically, and as it negatively affects fir reproduction (Shabalina et al., 2017) and results in replacement of taiga by areas overgrown with weeds or by deciduous tree stands (Bisirova & Krivets, 2018). Massive fall of dead trees leads to the accumulation of huge debris stocks and subsequently to a significant misbalance in carbon flux in the ecosystems (Mukhortova et al., 2020).

In its native range, the pest has minor economic importance; however, mass decline of previously healthy trees of the Far Eastern fir species over notable area has been reported in Japan (Koizumi, 1977; Takagi et al., 2018).

In the invaded range in Russia, P. proximus is a major forest pest causing significant economic losses (Mel’nik et al., 2018). Annually, 750 000 m³ of fir forest dies in Russia, with economic losses of at least 150 million rubles per year (Gninenko & Klyukin, 2011). In Tomsk Oblast (Siberia), direct economic losses can amount to a minimum of 24 000 RUB per ha, with additional indirect losses of 25 000 RUB per ha (Mel’nik et al., 2018). Thus, only in one Siberian region (Tomsk), where outbreaks in 2016 were covering a territory of about 1931 ha, the overall costs (i.e. direct and indirect losses) amounted to about 92.14 million RUB (Mel’nik et al., 2018).

Control

Clear-cutting is considered to be effective to eliminate foci and prevent further spread of P. proximus (Koizumi, 1977; Krivets et al., 2015b). Clear-cutting should be carried out when it is confirmed that firs trees are infested and have no chance of surviving, and that the beetles have not yet completed their development within the trees (Krivets et al., 2015b). The threshold for clear-cutting is the presence of around 10% of dying/ dead trees in the tree stands (Krivets et al., 2015b). If clear-cutting is done in summer, trees must be debarked no later than 3–5 days after felling, and the logging residues and bark disposed of (e.g. burned) to prevent any further spread (Krivets et al., 2015b). In infested logs, P. proximus can be killed by submerging debarked logs in water for one month (Krivets et al., 2015b; Efremenko et al., 2020).

Trap trees can be placed in infested forest stands one month before P. proximus adult emergence to allow partial capture and elimination of the pest population (Krivets et al., 2015b). Soon after infestation, trap trees should be debarked, treated with insecticides, or completely destroyed, otherwise they may serve a source of P. proximus and other pests.

Injections with systemic insecticides can be done on individual trees only in small areas, so this is mainly only suitable in urban plantings (Krivets et al., 2015b). A combined approach using systemic insecticides, timely felling and removal of colonized trees was highly efficient to eliminate the outbreak of P. proximus in the N.V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences (Moscow, Russia) (Seraya et al., 2018).

Pheromone monitoring has not been yet developed. Only recently, the specific components of the P. proximus pheromone have been identified. Two male-specific compounds, (Z)‐DMCHE and 3-methyl-2-buten-1-ol were shown to be effective in attracting males and females in the field (Viklund et al., 2022). However, further studies are needed as (Z)‐DMCHE also attracts the adults of Polygraphus subopacus (Viklund et al., 2022).

So far, natural enemies and entomopathogens could not control P. proximus in Siberia (Kerchev, 2014a). Overall, 24 species of predatory insects have been documented in Western Siberia, with Thanasimus femoralis, Nudobius lentus (Coleoptera) and Medetera penicillata (Diptera) being the most abundant larval predators. The latter species moved to Siberia from the Russian Far East together with P. proximus and is currently found in most infested areas (Kerchev & Negrobov, 2012; Kerchev, 2014b). Other dipterans, such as M. signaticornis, Lonchaea bukowskii and Xylophagus sachalinensis may have the potential to decrease pest population densities in Siberia (Krivosheina et al., 2018). The far Eastern fly species, Medetera penicillata (Diptera, Dolichopodidae), which also spread to Siberia with P. proximus, appears to be the most specialized and abundant predator in Siberia (Kerchev & Negrobov, 2012). A highly virulent indigenous strain of Beauveria bassiana, present in Siberia, is a promising biocontrol agent for P. proximus, as in experiments, it could cause 100% insect mortality within 7–11 days at temperatures from 16°C to 24°C (Pavlov et al., 2020).

Phytosanitary risk

In the EPPO region, Abies alba (European fir) and A. nordmanniana (Nordmann fir) are present in native forest stands, but both belong to the botanical section Abies, which is the least preferable host section according to laboratory tests (Kerchev et al., 2014a). Therefore, the risk of their infestation by the pest could be estimated to be low. However, bearing in mind the recently documented mismatch between preference and colonization success in P. proximus observed on Far Eastern firs (Tagaki, 2023), the pest’s behaviour towards its hosts (including those it has not encountered yet in nature) can be unpredictable. Taking in to account that P. proximus is able to successfully develop on other conifers naturally distributed in Europe (spruces, pines, larches), the phytosanitary risk could be significant.

The risk of introducing the pest with imports of fir debarked and treated logs, as well as with sawn fir wood is low, as the insect develops under the bark and in sapwood. Nevertheless, the pest can be accidently transported in conifer wood packing material (e.g. pallets) from Asia, even in those produced from trees not known to be host of P. proximus (e.g. Cryptomeria sp., Cupressaceae) (Brockerhoff et al. 2003), which can increase phytosanitary risk.

In a pest risk analysis (EPPO, 2020), it was concluded that P. proximus could present a serious threat to conifer plantations and forests in all part of the EPPO region where host plants are grown.

In the regions which are at risk ( i.e. areas where conifers from the family Pinaceae are present, efforts should be made to detect the pest as early as possible. Surveys should be conducted in the ports of entry using pheromone traps with newly found pheromone compounds to detect the entry of the pest. Control measures, which are similar to those used for the related bark beetles, can also be applied in adjoining infested areas, especially during outbreaks, to limit the spread of P. proximus.

To prevent the pest introduction, import of plants for planting and bonsais from host plants from infested areas should be strictly regulated; wood, cut branches, chips, pellets and other woody plant material from host plants (Pinaceae) and other conifers (e.g. Cupressaceae) from the infested areas should be appropriately treated (wood should be debarked, fumigated etc.). Alternatively, such commodities should originate from the areas free from the pest. Recommendations on consignment inspections and phytosanitary measures have been provided by EPPO (EPPO, 2019 and 2020).

Astrakhantseva NV, Pashenova NV, Pet’ko VA & Baranchikov YN (2014) [Abies sibirica Lebed. and A. nephrolepis (Trautv. ex Maxim.) Maxim. stem tissue reaction on inoculation by phytopatogenic fungus Grosmannia aoshimae (Ohtaka, Masuya et Yamaoka) Masuya et Yamaoka associated with four-eyed fir bark beetle.] Izvestia Sankt-Peterburgskoj Lesotehniceskoj Akademii 207, 141-157 (in Russian).

Astrakhantseva NV, Seraya LG, Pashenova NV, Kozhenkova AA & Baranchikov YuN (2023) [Anatomical features of the bark as a factor of fir species resistance to infestation by the four-eyed fir bark beetle.] Siberian Forestry Journal 5, 68-81 (in Russian).

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Bisirova EM & Krivets SA (2018) [Dynamics of the state of Siberian fir tree stands damaged by the four-eyed fir bark beetle Polygraphus proximus Blandf. in Tomsk Oblast.] Bulletin of Tomsk State University. Biology 44, 118-140 (in Russian).

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CABI and EFSA resources used when preparing this datasheet

EFSA (European Food Safety Authority), de la Peña E, Kinkar M, Vos S (2020) Pest survey card on Polygraphus proximus. EFSA supporting publication EN-1780, 25 pp. https://doi.org/10.2903/sp.efsa.2020.EN-1780

This datasheet was extensively revised in 2024 by Dr. Natalia Kirichenko (Sukachev Institute of Forest of the Siberian Branch of the Russian Academy of Sciences, Federal Research Center ‘Krasnoyarsk Science Center SB RAS’ and All-Russian Plant Quarantine Center, Krasnoyarsk branch, Krasnoyarsk, Russia and Stanislav Gomboc (Slovenia). Their valuable contribution is gratefully acknowledged.

EPPO (2024) Polygraphus proximus. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-27)

This datasheet was first published online in 2024. It is 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.