Coleoptera: Anobiidae)
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JOURNAL OF FOREST SCIENCE, 51, 2005 (8): 327–347 Occurrence, development and harmfulness of the bark anobiid Ernobius mollis (L.) (Coleoptera: Anobiidae) J. URBAN Faculty of Forestry and Wood Technology, Mendel University of Agriculture and Forestry Brno, Brno, Czech Republic ABSTRACT: The paper summarizes results of the study of the occurrence, development and harmfulness of Ernobius mollis (Linnaeus, 1758), which occurred plentifully on Pinus nigra Arn. impaired by drought in the CR in 2000. It is based on laboratory rearings in photoeclectors and numerous analyses of branches (stems) of pines from 5 localities in Brno. Partial studies were carried out in 5 other localities in Moravia and Eastern Bohemia. Under laboratory condi- tions, imagoes occurred mainly in June–August, viz at a 1 ♂: 3 ♀♀ ratio. Males and females were on average 4.4 and 4.9 mm long, respectively. In living trees, imagoes of substandard dimensions developed. In dead trees, the average length of males and females gradually decreased with increasing damage in the particular years. Immediately after hatching, gonads of imagoes were mostly only partly developed. Females matured sexually during the first hours (maximally during 2 days) of their life in the open. In their ovaries, some 14 to 136 (on average 42.2) eggs occurred. With the increasing size of females their fecundity increased significantly. The development of larvae progressed through 4 instars. One grown up larva destroyed about 1.8 cm2 cambium. Wood was damaged to a depth of 2 mm and sporadically to a depth of 15 mm. Imagoes left wood through exit holes of a diameter of 1.1 to 2.1 (on average 1.6) mm in bark. Their development was univoltine. The pest damaged the same wood repeatedly for a period of 5 years. Keywords: Anobiidae; Ernobius mollis; Pinus nigra; occurrence; development; harmfulness The bark anobiid Ernobius mollis (L.) is one of the E. mollis (Fig. 1) is the most ordinary representa- most abundant native species of Anobiidae. In the tive of the genus. Linné described the species as fauna of the CR, the family is represented by 63 spe- Dermestes mollis in 1758. Natural variability of ima- cies, 8 of them belong to the genus Ernobius Thoms. goes caused difficulties with the name and systematic (ZAHRADNÍK 1993). Beetles of this taxonomically classification of the species. From the end of the rather difficult and relatively little known genus are 18th century to the beginning of the 19th century, the small, elongated and usually rubiginous or brown. species was usually classified in the genus Anobium They have filamentous 11-segment antennae with F. and described under various (at least 27) scientific 3 enhanced last segments. The scutellum is not tuber- names (CYMOREK 1974; BURAKOWSKI et al. 1986, cled from above but furnished longwise with a sharp etc.). Imagoes were described by RATZEBURG (1839), lateral edge. Wing cases show smooth and finely PERRIS (1854), KLAPÁLEK (1903), KUHNT (1913), scattered spots. Its body is finely monochromatically KEMNER (1915), KOCH (1928), TOOKE (1946), GAR- pubescent, pedal segments are long and slim. Repre- DINER (1953), JOHNSON (1975), ESPANOL and BLAS sentatives of the genus are characterized by sexual (1991), etc. Some authors (e.g. GARDINER 1953) also dimorphism, considerable size variability, formation studied the anatomy of imagoes, namely their diges- of varieties and frequent inversion of genitals. tive and reproductive system. Supported by the Faculty of Forestry and Wood Technology, Mendel University of Agriculture and Forestry Brno, within Re- search Plan MSM No. 6215648902. J. FOR. SCI., 51, 2005 (8): 327–347 327 convex both laterally and from the front to the back and so its rear part heads slightly down. The larva of E. mollis was briefly described by PER- RIS (1854), KEMNER (1915), MUNRO (1915), TOOKE (1946), KELSEY (1946), WEIDNER (1953), DOMINIK and STARZYK (1989), etc. Several authors (e.g. PER- RIS 1854 and TOOKE 1946) also presented a brief description of the pupa. Similarly, a description of the growing larva including diagnostic features distinguishing it from other species was given by PARKIN (1933). The morphology of eggs, larvae of younger instars and pupae including the anatomy of Fig. 1. Ernobius mollis (L.) (female left, male right) the digestive system of full-grown larvae was studied in detail by GARDINER (1953). The digestive system E. mollis differs from the other members of the of full-grown larvae (and particularly histology and genus particularly by the cut-out of the 4th pedal symbiotic organisms of the mid-gut) was studied segment of rear legs reaching about its half. The by HEITZ (1927), BREITSPRECHER (1928), MÜLLER length of the 9th antenna segment is smaller than (1934), etc. the length of previous 4 segments together. Never- The larva is of a white grub type, up to 8(9) mm theless, each of the last 3 segments of antennae long (Fig. 2). It is equipped with well-developed (i.e. 9th to 11th segment) is much longer than any 5-segment thoracic legs and 10-segment abdomen. other segment of antennae. The scutum is slightly According to our observations, its body has long and arched, somewhat uneven, sometimes with a shal- sparse tiny hairs. The fine hairs are grey or red-black low central line before the base. According to our being longest at the rear of the abdomen. Along the extensive measurements, the scutum is on average sides of the last and last but one segments of the 0.1 mm narrower than wing cases in shoulders and abdomen there are numerous tiny dark spines. Erect at the sides, the scutum is round. It connects with and by their point slightly backwards headed spines wing cases along its whole width and rear and front occur also on prenotal folds on the metathorax and edges are markedly round. The top side of beetles on the first 7(8) segments of the abdomen. The more is (except for the yellowish apical drawing on wing intensely sclerotized dark-coloured frontal part of cases) monochromatically rusty or dark brown and the cranium is roughly semicircular its width being slightly bright. The body surface is densely and very nearly a double of its length. finely grainy and densely and tightly pilous. Hairs are rather long being of yellow or grey colour. Only scutellum is frequently more densely pilous and, therefore, of lighter colour. Sexual dimorphism in adults of E. mollis is mani- fested particularly in the body size, length and form of antennae and in the shape of the tergite of the last visible segment of the beetle abdomen. Males are on average smaller than females having longer and slen- der antennae than females. According to GARDINER (1953), the length of the last 3 apical segments of male antennae exceeds the total length of proximal segments. During rest, antennae of males are pulled to the ventral side of the body reaching nearly to the half of the abdomen whereas in females, they do not exceed the thorax. Segments of the antennal club are parallel at the sides in males whereas in females the segments are distally enlarged and somewhat curved at the sides. The tergum of the last visible segment of the abdomen is laterally convex in males and from the front to the back somewhat concave and so its Fig. 2. Larvae of the 1st to the 4th instars and pupae of rear part heads slightly up. In females, the tergum is E. mollis 328 J. FOR. SCI., 51, 2005 (8): 327–347 E. mollis is a Palearctic species with its centre of oc- According to literature it is evident that E. mollis currence in Europe and Siberia. In Fennoscandinavia is the species of dead unbarked coniferous wood. In (particularly in Norway), it reaches far northwards forests, it colonizes particularly recently fallen dead (HELLÉN et al. 1939). E. mollis was introduced to trees (TOOKE 1946; BLETCHLEY 1967), fuelwood North America (CRAIGHEAD 1950; SIMEONE 1962; (CLARKE 1932) or dead standing trees of the stem WHITE 1982; SEYBOLD, TUPY 1993; SEYBOLD 2001, diameter below 20 cm (KELSEY 1946). However, etc.), to N Africa, Near East (e.g. HALPERIN, ESPA- it can also attack physiologically impaired and dy- NOL 1978), Japan and Southern Hemisphere. It oc- ing trees (ROUBAL 1936; DIMINIC et al. 1995) and curs in Australia, New Zealand, New Caledonia and cones (ROQUES 1983; KARANIKOLA, MARKALAS S Africa (CLARKE 1932; KELSEY 1946; TOOKE 1946; 2001). It is abundant not only in the wild but also in CASIMIR 1958; MILLIGAN 1967; NEUMANN 1979; timber-yards and in various wooden constructions, HOCKEY 1987, etc.). furniture, tools, museum exhibits, etc. A number E. mollis develops in phloem (including the inner of entomological and entomological-forest protec- layer of bark), in cambium and in surface parts of the tion papers reported its harmfulness (e.g. NÜSSLIN, wood of dead conifers (more rarely dying conifers) RHUMBLER 1922; ESCHERICH 1923; TRÄGÅRDH and sporadically also in their cones. Hosts are as 1934, 1940, 1947; MADEL 1941; BUTOVITSCH follows: various species of pine (e.g. Pinus sylvestris 1951; HARRIS 1953; SCHMIDT 1954; NUORTEVA, L., P. nigra Arn., P. radiata D. Don., P. pinaster Ait., NUORTEVA 1954; GÄBLER 1955; DOMINIK 1958, P. halepensis Mill., P. taeda L., P. canariensis C. 1967; KUDELA 1970; BECKER 1984; VASILJEV et al. Smith), Norway spruce (Picea abies [L.] Karst.), 1975; HOCKEY 1987, etc.). Protection measures European larch (Larix decidua Mill.), Douglas fir were dealt with for example by TRÄGÅRDH (1949), (Pseudotsuga taxifolia [Poir.] Brit.) and giant sequoia HARRIS (1953), DOMINIK (1958), BAKER (1964) and (Sequoiadendron giganteum [Lindl.] J. Buchh.). On MILLIGAN (1967, 1977). 4–22 October, 2004, its larvae were abundantly found in Brno-Pisárky on dying branches of over- MATERIAL AND METHODS mature trees of blue spruce (Picea pungens Engelm.) which are grown for decorative purposes there.