Cryphalus asperatus (Gyllenhal, 1813)

Justesen, Mathias Just, Hansen, Aslak Kappel, Knizek, Milos, Lindelow, Ake, Solodovnikov, Alexey & Ravn, Hans Peter, 2023, Taxonomic reappraisal of the European fauna of the bark beetle genus Cryphalus (Coleoptera, Curculionidae, Scolytinae), ZooKeys 1179, pp. 63-105 : 63

Cryphalus asperatus (Gyllenhal, 1813)

Bostrichus asperatus (Gyllenhal, 1813: 368); designated by Wood 1972: 41.

Bostrichus abietis (Ratzeburg, 1837: 161) (syn: Wood 1972).

Type material.

Destroyed during the Second World War together with C. piceae type material (see C. piceae ).

Neotype designation.

We designate a neotype of Cryphalus asperatus with the express purpose of clarifying the taxonomic status. In the original description, the distribution of C. asperatus is mentioned from Upper Silesia (Poland), East Prussia (Poland/Russia), Thuringian Forest (Germany) and Harzen (Germany) and the species is mentioned from Picea Mill. (Ratzeburg, 1837). A neotype of Cryphalus asperatus (Gyllenhal, 1813) is designated (Fig. 15 ). It is a male collected on 18/05-2023 from a Picea abies branch collected in Czechia (Silensia) (48°58'20.9"N, 19°35'16.2"E) not far from Upper Silesia. The specimen will be stored at NHMD in the entomological collections.

Material examined.

599 specimens from 8 countries in Europe (Table 1 ) were examined. Morphological measurements were done on 38 specimens from Romania (7), Czechia (12), Slovakia (6), Netherlands (6), and Belgium (7). The results are presented in Fig. 2 .

Diagnosis.

This species can be diagnosed from similar Cryphalus in Europe by the combination of body size usually <1.75 mm (average 1.61 mm), setae on lateral margin of pronotum clearly shorter between apex and summit compared to setae in line with summit (character 3, Fig. 1 ), randomly distributed asperities on pronotal declivity (<50), interstrial setae on the elytral declivity shorter than width of second interstria, often clear elytral striation. For confident identification, extraction of male genitalia is recommended. Penis body when seen dorsally is, aside from the apex, equally broad and is almost bilateral in symmetry. The entire aedeagus ~ 0.5 mm in length (Fig. 16B-E ).

Description.

Length 1.38-1.90 mm, average 1.61 mm. Proportions : 2.3 × as long as wide, elytra 1.5 × as long as wide, elytra 1.95 × longer than pronotum. Antennae: club with three procurved sutures marked by long setae. Funiculus with four antennomeres (including pedicel). Pronotum: dark brown to black on both slope and disc. Profile anterior to summit triangular to rounded, slightly wider in line with summit. Anterior margin with 2-7 asperities, the outer pair usually smaller, and with erect setae in line with the summit and near apex, usually short or upwards facing in-between. Anterior slope with <50 asperities, including the ones on the anterior margin. Disc between 1/4-1/5 the length of entire pronotum, gently sloped, weakly tuberculate surface texture with a small hair-like setae in each tubercule. Vestiture on declivity and disc hair-like. Suture between pronotum and elytra weakly sinuate. Scutellum: completely covered with trifurcate hair-like setae (Fig. 16D ). Elytra: usually black or dark brown but occasionally light brown, margins parallel and straight. The curvature on the declivity regularly rounded. Surface smooth. Striae often visible as rows of punctures with a short hair-like seta arising from each puncture. Interstrial setae short (0.05-0.08 mm) and erect. Interstrial ground vestiture is serrated, ~ 2-3 × as long as wide and translucent brown with a weak iridescence (Fig. 16B, D, E ). Proventriculus: sutural teeth of irregular size, confused, in two or more longitudinal rows. Apical teeth extend laterally to <2/3 of the plate. Masticatory brush slightly <1/2 of the proventricular length (Fig. 7 ).

Sexual dimorphism. Males and females can be separated using the last ventrite (Fig. 11 ), as suggested by ( Johnson et al. 2020a). Wood (1982) also suggests that the sexes of several scolytines including Cryphalus , can be separated by males having a clearly visible 8th tergite and the females a highly reduced or absent 8th tergite. This character was not examined. No obvious differences in tubercles or carina on the frons was noticed.

Male. The aedeagus is ~ 0.5 mm long when measured vertically (i.e., from the two points furthest away from each other). The penis body when seen from above is at the side of the apex, equally broad, and almost bilaterally symmetrical and <0.4 mm. Aedeagus apodemes makes up ~ 35% of the entire aedeagus length when measured vertically and are more or less straight and bending downwards. The tegmen is sclerotised and completes a ring around the penis body. It is thin and has two ventral apodemes, which are ~ 1/2 the length of the distance between them. The dorsal part of the tegmen ring is narrowest in the middle (Figs 5 , 16C ).

Larvae. For a description of larvae see the work by Ritchie (1918) or Lekander (1968).

Host plants.

This species is mentioned in the literature from several conifer genera, but primarily from different Picea species ( Escherich 1923; Hansen 1956; Lekander et al. 1977; Grüne 1979; Wood 1992b). In a study designed to test the specificity of bark beetles to different conifer hosts, C. asperatus was found to prefer Abies and Picea over Pinus and Cupressus ( Chararas et al. 1982). Ritchie (1918) found Abies as a preferred host plant of C. asperatus . We collected C. asperatus in large numbers from monocultural Abies procera Rehder plantations in Denmark, which seem to support these data ( Justesen et al. 2017; pers. obs. MJJ).

Distribution.

According to the Palearctic catalogue ( Knížek 2011; Alonso-Zarazaga et al. 2023), C. asperatus is found in Europe: Austria, Belgium, Bosnia-Herzegovina, Bulgaria, Belarus, Czechia, Croatia, Denmark, Estonia, Finland, France, Great Britain, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxemburg, Macedonia, Montenegro, Netherlands, Norway, Poland, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Russia: Central European Territory, North European Territory, South European Territory; North Africa: Algeria, Morocco; Asia: Japan, North Korea, Turkey, Russia: East Siberia, Far East.

The catalogue reported C. asperatus in all European countries except Portugal, Ukraine, Moldova, Albania, and Serbia. Nikulina et al. (2015) collected C. asperatus in Ukraine and Marković (2013) in Serbia. Considering the natural distribution of Picea and Abies in Albania, it is unlikely that C. asperatus is not present here as well. Studies from Finland ( Voolma et al. 2004) and distribution maps from Sweden ( Artportalen 2023) and Norway ( Artsdatabanken 2023), show that C. asperatus is not adapted to the Arctic region. The fact that the catalogue mentions C. asperatus from Japan, North Korea, and Eastern Russia needs confirmation. Distribution records from these areas could be erroneous because of similar looking species, e.g., Cryphalus sichotensis Kurenzov, 1941, C. saltuarius or others. More comparative work on the eastern species, similar to that of Johnson et al. (2020b), is necessary to figure out the easternmost extent of C. asperatus . Our distribution map follows the note by Mandelshtam (2002) stating that C. asperatus is not found east of Altai ( Mandelshtam 2002). Records of C. asperatus in Morocco and Algeria also need confirmation, especially considering the one specimen (1.28: Georgia, Tlughi) from Georgia, which is 5.6% different from the European populations (Fig. 8 ). A larger sampling in and around Georgia, including in-depth morphological study are needed to elucidate the relationship and establish if these specimens represent a separate species or just intraspecific variation. See distribution illustrated in Fig. 16A .

Bionomics.

During winter C. asperatus can hibernate as adults, larvae, pupae and more rarely as eggs ( Ritchie 1918; Pfeffer 1955). It hibernates underneath the bark of infested material ( Ritchie 1918; pers. obs. MJJ). Flight activity can start already in March ( Ritchie 1918; data from Wermelinger et al. (2002); pers. obs. MJJ). Comparable unpublished data from Denmark showed that C. asperatus became active a few weeks earlier than C. piceae . During the period from March to May C. asperatus aggregates on suitable material and mates. The males will try to mate with as many females as possible, and after mating the males will excavate a nuptial chamber. Males of C. asperatus display a very distinct preference for branch nodes, and often you find branches where only nodes are inhabited ( Ritchie 1918; Justesen et al. 2017). This preference is so evident that it was mentioned in the original description by Ratzeburg (1837). The preferred material seems to be moist and shaded branches, compared to sun exposed dry branches ( Ritchie 1918; pers. obs. MJJ). Compared to the other European Cryphalus species, C. asperatus can target relatively old/decomposed material but can also be found in recently fallen branches. Once the males complete their nuptial chamber, the female will lay 14-24 eggs ( Ritchie 1918). The development from egg to adult is variable depending on temperature, type of material, the position of the material (sun-exposed) and the time of egg-laying ( Ritchie 1918). According to Ritchie (1918) two generations per year is unlikely, but he mentions the possibility of a sister generation. Grüne (1979) and Pfeffer (1955) suggested two generations per year. In an unpublished study from Denmark, 90 Abies procera branches were cut and placed as bait in an A. procera plantation in the spring. Six branches were then collected every second week and evaluated for the presence of various life stages of C. asperatus . These results suggested one generation. Based on the above information, C. asperatus most likely has two generations under ideal conditions and only one in colder climates.

Economic significance.

In older literature C. asperatus is described as a possible harmful pest ( Eichhoff 1881; Nüßlin 1905; Bodenheimer 1958). However, as already mentioned by Ritchie (1918) and Hansen (1956), these reports seem unlikely. A recent study looking at Norway spruce seedlings weakened by transport, found C. asperatus as a potential problem ( Fiala and Holuša 2021). Our observations of C. asperatus support that this species is a harmless species not able to kill or weaken trees.

Remarks.

Differences between C. asperatus and C. saltuarius .

The shape and size of the aedeagus is the best character to separate the two species. The penis body when seen dorsally is equally broad in C. asperatus , but broadest one quarter down from the apex and then becomes increasingly narrow towards the base in C. saltuarius . The entire aedeagus is longer (~ 0.7 mm) in C. saltuarius compared to C. asperatus (~ 0.5 mm).The size difference between C. asperatus and C. saltuarius is commonly highlighted and the following lengths were reported for C. asperatus : 1.75 mm average ( Ritchie 1918), 1.2-1.7 mm ( Grüne 1979; Pfeffer 1995; Noblecourt and Schott 2004), 1.2-1.8 mm ( Hansen 1956), and 1.3-1.8 mm ( Spessivtseff 1922). We measured 38 C. asperatus specimens and found a range of 1.38-1.90 mm but, besides one noticeably larger specimen, the remaining 37 specimens were all <1.75 mm. The following lengths were reported for C. saltuarius : 1.5-2 mm ( Spessivtseff 1922; Hansen 1956; Grüne 1979; Pfeffer 1995) and 1.5-2.2 mm ( Noblecourt and Schott 2004). We measured 25 specimens of C. saltuarius to 1.73-1.98 mm, with eight specimens lying between 1.73-1.75 mm. These measurements confirm that body size often is a reliable character, but also highlights that overlap occurs.

We found that C. saltuarius specimens usually had longer and perpendicularly erect setae along the margins of pronotum (Figs 1 , 17B, E ), whereas most C. asperatus only had erect setae in line with the summit and near apex, and then short and sometimes upwards facing setae in-between apex and summit (Fig. 16B, E ). It should be mentioned that authors have observed old C. saltuarius museum specimens lacking these setae. The scutellum of C. asperatus is covered in trifurcate hair-like setae, whereas C. saltuarius only has these hairs along the elytral margin of scutellum (Figs 16D , 17D ); however, this character requires high magnification and was therefore not included in the key.

Several keys mention that the striae in C. asperatus are clearer (Fig. 16B, D, E ) compared to more indistinct striae in C. saltuarius (Fig. 17B, D, E ) ( Ritchie 1918; Spessivtseff 1922; Hansen 1956; Grüne 1979; Pfeffer 1995; Noblecourt and Schott 2004). Generally, we could confirm this tendency (Fig. 4 ), but nine of the 25 C. saltuarius specimens had clearer striation, which could be confused with C. asperatus specimens with less distinct striation.

Noblecourt and Schott (2004) used the shape of the elytral declivity to separate C. asperatus (regular curvature) from C. saltuarius (flattened on the declivity). Our studies also found this tendency, but with a slight overlap (Fig. 4 ).

Most keys include proportional differences as a good character to separate the species. Noblecourt and Schott (2004) found C. asperatus was 2.3 × longer than wide and C. saltuarius 2 × longer than wide. Our results (Fig. 2 ) showed a slight tendency of C. asperatus being comparably longer than wide, but with a very high degree of overlap between the species. Grüne (1979) and Pfeffer (1995) found that the elytra of C. asperatus was 1.5-1.57 × as long as wide, whereas C. saltuarius was 1.6-1.67 × as long as wide. Our measurements had a large overlap in the proportional difference of elytra. Therefore, we did not find proportions as a good character. It should be noted that we measured elytral width as in Fig. 1 , across the scutellum. Measurements 1/3 down from the basal border of elytra could slightly increase the width measurements, resulting in less similar proportions.

Figures

Figure 1. Morphological measurements and magnification at which they were measured.

Figure 2. The variation of measured characters in five European Cryphalus species. Pronotal lateral setae, mid (mm), refers to the length of the lateral setae on pronotum between the summit and the apex.

Figure 4. The variation of measured characters in five European Cryphalus species.

Figure 5. Lateral and dorsal illustration of male genitalia of five European Cryphalus species.

Figure 7. Proventricules of the five native Cryphalus species currently recognised in Europe.

Figure 8. Species tree based on COI barcodes. Support values are given as posterior probability for Bayesian analysis and ultrafast bootstrap and SH-aLRT values for maximum likelihood analysis. Nodes coloured green for PP ≥ 0.90, UFB ≥ 80 and SH-aLRT ≥ 95, yellow for either PP ≥ 0.90, UFB ≥ 80 or SH-aLRT ≥ 95, and red for PP <0.90, UFB <80 and SH-aLRT <95.

Figure 11. Sexual dimorphism of ventrite in Cryphalus spp.

Figure 15. Neotype of Cryphalus asperatus. Stored at NHMD in the entomological collections.

Figure 16. Cryphalus asperatus A distribution B lateral and dorsal view C aedeagus D SEM, specimen from Calibaba, Romania E SEM (43 x magnification), specimen from Calibaba, Romania.

Figure 17. Cryphalus saltuarius A distribution B lateral and dorsal view C aedeagus D SEM, specimen from Ostby, Norway E SEM (43 x magnification), specimen from Ostby, Norway.