Semanotus bifasciatus ( Motschulsky, 1875 )

Semanotus bifasciatus ( Motschulsky, 1875) View in CoL

Figs 1–8 View Fig View Figs 2–8

MATERIAL EXAMINED. Russia: Donetsk People's Republic, Mariupol city, Primorsky district, Primorsky park, 47°04'49"N, 37°31'45"E, on Thuja occidentalis L., galleries under the bark, 15.II.2024, leg. E.G. Mulenkova; Donetsk city, Donetsk Botanical Garden, rearing from Thuja occidentalis L. trunk in laboratory, 20.XI.2024 – 03.II.2025, 101♂, 90♀, leg. A.I. Gubin, V. V. Martynov, T. V. Nikulina GoogleMaps .

DIAGNOSIS. (See: Cherepanov, 1988). The examined specimens correspond to the morphological descriptions provided in the literature ( Motschulsky, 1875; Plavilstshikov, 1940; Cherepanov, 1988). However, considerable variation was observed in body size: males exhibited a body length ranging from 8.6 to 15.2 mm and a width of 2.5 to 4.9 mm, females measured between 9.8 and 15.2 mm in length and 3.3 to 5.0 mm in width ( Fig. 1 View Fig ). Semanotus bifasciatus can be readily distinguished from the other two European species of the genus that feed on Cupressaceae by the characteristic light coloration of the apical margin of the elytra. Additionally, it is morphologically distinct from S. russicus due to the presence of two broad black stripes, one in the middle and another in the posterior third of the elytra. It also differs from S. laurasii by its comparatively narrower body, as well as by the glossy elytra, which exhibit finer and more sparsely distributed puncturation, particularly in the anterior third of their length.

DISTRIBUTION. China; Korean Peninsula; Japan; Russia: Primorsky Krai (south), DPR (Azov Lowland) (new record).

BIOLOGY. Oligophagous, feeding on Cupressaceae : Juniperus chinensis L., J. rigida Siebold & Zucc. , Chamaecyparis obtusa (Siebold & Zucc.) Endl. , Thujopsis dolabrata (Thunb. ex L. f.) Siebold & Zucc., Thuja spp. , Cryptomeria japonica (Thunb. ex L. f.) D. Don, Cunninghamia lanceolata (Lamb.) Hook. ( Plavilstshikov, 1940; Cherepanov, 1988; Gao et al., 2007; Iwata et al., 2007). In Cis-Azov region the species has been recorded feeding on Thuja occidentalis L.

The life cycle of the species in Primorsky Krai was comprehensively studied by A.I. Cherepanov ( Cherepanov, 1988), in China, South Korea, and Japan – by several other researchers ( Kim & Park, 1984; Yan, 2003; Li et al., 2003; Gao et al., 2007; Iwata et al., 2007). Generation completed in two years, in southern part of the range – one year. The beetles do not feed, active in spring and summer, exhibit a crepuscular lifestyle, can be found on trunks of windfallen or standing dying trees. In Primorsky Krai, adult flight occurs from June to August, whereas in eastern China, it takes place from late February to early May. The species colonizes trunks and thick branches, oviposit in bark crevices. Larvae feed within the cambial layer, making meandering galleries that are deeply imprinted in the sapwood and filled with fine frass. Mature larvae bore into the sapwood, where they form pupal cells at a depth of approximately 20 mm beneath the cambial layer, oriented longitudinally along trunk axis. Pupation occurs with the head toward inlet plugged with frass. Pupae appear at end of summer, beetles emerge by autumn but remain in pupal cells until the following year. In spring, the beetles break plug around inlet, push back frass, reach bark, nibble oval exit hole and emerge from wood.

The precise timing of S. bifasciatus invasion into the urban plantings of Mariupol remains unknown. Examination of infested trunks revealed that the cambial layer had been completely destroyed due to larval feeding, while the outer sapwood layer exhibited numerous feeding galleries filled with frass ( Fig. 2 View Figs 2–8 ). The maximum recorded width of these galleries was 12 mm. In addition to evidence of larval activity from 2023–2024, remnants of an earlier generation's development were also observed, partially overgrown with secondary xylem. Considering the species’ two-year developmental cycle, these records indicate that a selfsustaining population of S. bifasciatus was already present in Mariupol by 2021.

The emergence of beetles from trunks brought to the laboratory in September 2024 was first recorded on November 20, indicating that exposure to low temperatures is not a prerequisite for initiating imago emergence ( Fig. 3 View Figs 2–8 ). From the trunks brought to the laboratory on December 20, emergence was observed as early as December 24, occurring just four days after placement in laboratory conditions. The emergence period was prolonged, lasting an average of 40 days. Based on these observations, it can be inferred that under the climatic conditions of Cis-Azov region, beetles emergence in natural settings should begin in early to mid-April, with emergence potentially beginning in late March during years with an early spring, and continuing until mid-May. The exit holes were oval in shape, oriented transversely or obliquely relative to the trunk axis ( Fig. 4 View Figs 2–8 ), with widths ranging from 4 to 6 mm. The density of exit holes on the accounting transects averaged 5.38 per dm², with values ranging from 0.7 to 8.5 per dm². The highest population density was recorded in the middle section of the trunk, where the diameter measured 21 cm.

Under regional conditions, S. bifasciatus exhibits a two years generational cycle. Beetles emergence occurred during daylight hours, with mating initiated almost immediately thereafter ( Fig. 6 View Figs 2–8 ). On the second day post-emergence, females were observed probing the surface of the trunk with their ovipositors, suggesting an attempt at oviposition. However, dissections of newly emerged females revealed the absence of mature ovaries, indicating that oviposition was not yet possible. Additionally, the beetles were observed gnawing on fresh Thuja needles placed in the insectarium, calling into question previous assertions regarding their complete aphagia.

A total of 191 beetles emerged in the laboratory between November 20, 2024, and February 3, 2025, after which emergence ceased. However, upon dissection of the trunks on February 3, several adults were found remaining inside their pupal cells, with the entrance holes sealed with frass ( Figs 5, 7–8 View Figs 2–8 ). The beetles were active, running and flying upon removal from the cells. No larvae were found in the pre-pupal stage. The pupal cells were located approximately 20 mm beneath the cambial layer within the sapwood. The emergence passages were oriented upward or downward, parallel to the trunk axis ( Figs 7–8 View Figs 2–8 ). The cells measured an average of 20–25 mm in length and 3.5 mm in height, while the frass plug sealing the entrance ranged from 14 to 25 mm in length.

HARMFUL IMPACT. In East Asia, S. bifasciatus is generally regarded as a secondary pest, primarily damaging weakened or dying trees ( Iwata et al., 2007). However, several studies from China and South Korea suggest that this species can also function be a significant primary pest, infesting healthy and non-stressed mature trees, particularly in urban environments ( Kim & Park, 1984; Yan, 2003; Gao et al., 2007). For example, in 1988, S. bifasciatus infested 67.3% of the surveyed Cupressaceae trees in Dalian, Liaoning Province, China. Between 2002 and 2006, the species was responsible for extensive Cupressaceae mortality in the Linyan Forest, Shandong Province, China. Additionally, in 1979, an outbreak of S. bifasciatus resulted in the infestation of 97% of Cupressaceae trees in Xiangshan Park, Beijing ( Zhang et al., 2019). Given its destructive potential, S. bifasciatus is currently classified as a quarantine species in several Chinese provinces due to the threat it poses to artificial forest ecosystems ( Tian, 1996).

The significant damage caused by S. bifasciatus underscores the need for effective early detection methods and population control strategies, as discussed in the research of Chinese entomologists ( Qiu, 1999; Sun, 2000; Gao et al., 2007; Ma et al., 2010; Wang, 2017; Li et al., 2020; Jiang et al., 2022). To minimize damage and prevent reinfestation, it is recommended that infested trees be promptly removed and utilized upon the first signs of pest activity. Ongoing studies are focused on biological control methods, which include the use of entomopathogenic fungi, nematodes, predatory mites, and parasitic Hymenoptera ( Qiu, 1999; Sun, 2000; Ma et al., 2010; Zeng et al., 2024). Chemical control involves the application of systemic pesticides via trunk spraying, with the timing of treatments being crucial, as pesticides are most effective against the early larval stages of the pest ( Li et al., 2003; Gao et al., 2007).

In Cis-Azov region, S. bifasciatus has proven itself to be a significant pest of Cupressaceae trees in urban areas, causing the mortality of large, mature trees. Further expansion of the species' range presents a substantial threat to urban plantings, where Cupressaceae are extensively utilized in green infrastructure. Additionally, the species poses a risk to natural plant communities, particularly to the mountain forests of Crimea and the Caucasus. It is noteworthy that S. bifasciatus is the third alien invasive specialized woodboring pest of Cupressaceae to penetrate Cis-Azov region in recent years. In 2010, Phloeosinus aubei (Perris, 1855) ( Coleoptera : Curculionidae ) was recorded for the first time in the region ( Nikulina, 2012), followed by Lamprodila festiva (Linnaeus, 1767) ( Coleoptera : Buprestidae ) in 2020 ( Gubin et al., 2020). Both of these species, originating from the European- Mediterranean region, have proven themselves to be dangerous pests in local conditions. The invasion of S. bifasciatus further intensifies the phytopathogenic pressures on artificial coniferous plantations in the area. The continued establishment of a complex of Cupressaceae phytophagous pests raises significant concerns regarding the future use of these trees in green infrastructure projects.