Scolytus mali (Bechstein, 1805)

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 21

Taxon classification Animalia Coleoptera Curculionidae

Scolytus mali (Bechstein, 1805) Fig. 10

Bostrichus mali Bechstein, 1805: 882.

Scolytus mali (Bechstein, 1805): Eichhoff 1881: 41.

Scolytus sulcatus LeConte, 1868: 167. Brown 1950: 203.

Scolytus mali For complete taxonomic history see Wood and Bright (1992).

Diagnosis.

Both sexes of Scolytus mali are distinguished by having ventrite 2 at an oblique angle to ventrite 1, by the aciculate frons, with most setae found just above the epistoma and on the lateral epistomal margins, by the smooth, shining appearance of the pronotum and elytra, and by the weakly rounded and smooth elytral apex.

Description (male).

3.2-4.1 mm long (mean = 3.7 mm; n = 10); 2.1-2.5 times as long as wide. Head, pronotum and abdominal venter dark red-brown, legs and antennae light brown, elytra brown to red-brown. Pronotum typically darker than elytra.

Head. Epistoma weakly, broadly emarginate; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing convex when viewed laterally, moderately transversely impressed just above epistoma, longitudinally impressed near median line; densely, finely longitudinally aciculate-punctate; aciculations converging at epistoma; punctures small, coarse; sparsely covered by long, fine, erect, yellow hair-like setae, these as long as width of midpoint of eye, more abundant along epistoma. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two arcuate sutures visible.

Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, yellow hair-like setae; base weakly bisinuate.

Elytra with sides sub-parallel on apical half, narrowing to weakly rounded, smooth apex; apex weakly emarginate at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae, bearing sparse, long, semi-erect yellow hair-like setae (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron greater than half-length of metanepisternum.

Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly at an oblique angle to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; surface convex, unarmed; setae erect, short, about half of ventrite 3 length; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 unarmed; length of ventrite 5 equal to combined lengths of ventrites 3 and 4; setal patch absent; median depression present.

Female.

3.0-4.2 mm long (mean = 3.7 mm; n = 10); 2.0-2.5 times as long as wide. Similar to male except epistoma feebly emarginate, frons more strongly convex when viewed laterally, weakly aciculate, setae sparser, shorter, less than width of eye.

Specimens examined.

111.

Type material. Syntypes Bostrichus mali Bechstein (location unknown). Holotype Scolytus sulcatus LeConte: male, labeled "[pink disc = Middle States (Md., Del., N.Y., N.J., Pa., Conn.?, R.I.?)]; type 969" (MCZC).

Non-type material.CANADA:ONTARIO: Hamilton, 14-21.VI.1981, M. Sanborne (CNCI-2), 23.VII.1980, ex. malaise trap (CNCI-1). Owen Sound, 27.V.[19]65, K.E. Stewart, ex. elm [= Ulmus sp.] (CNCI-1). Vineland Station, 8.VI.1949, W.L. Putnam, ex. apple [= Malus sp.] (CNCI-2). QUEBEC: Cantic, 11.VIII.1945, W.J. Brown, ex. apple [= Malus sp.] (CNCI-2). Cap-Saint-Ignace, VII.1970 (CNCI-1). Dunham, 2.IX.1998, Vignoble, L’Orpailleur, ECORC/CRDHAg-Cord (DEBC-1). Napierville, 2 mi N.E., 13.VIII.1945, W.J. Brown (CNCI-1). Noyan, 0.75 mi W., 15.VIII.1945, W.J. Brown (CNCI-1). UNITED STATES:CONNECTICUT: [Fairfield Co.]: Greenwich, 22.VII.1933, F.J. Dillaway, ex. in plum [= Prunus sp.] (USNM-2). New Haven Co.: New Haven, 25.VI.1956, C.W. O’Brien (EMEC-1). MAINE: [Androscoggin Co.]: Livermore Falls, 5.VIII.1975, ex. plum [= Prunus sp.] (USNM-1). MARYLAND:Montgomery Co.: Ashton, 4 mi S.W., 31.V.1986, G.F. & J.F. Hevel, ex. malaise trap (USNM-1). MASSACHUSETTS:Worchester Co.: 16.II.[19]53, ex. indoors (USNM-2). MICHIGAN:Allegan Co.: Fennville area, 30.VI.2003, P. McGhee, ex. apple trees [= Malus sp.] (MSUC-6). Genesee Co.: Richfield County Park, N43°100610, W-83°55810, 16.VI.2008, R. Mech, PI Anthony Cognato (MSUC-1). Ingham Co.: Lansing, 2 mi N., E. State Rd, N42.7842°, W84.5362°, 261 m, 2-18.VI.2007, PI Anthony Cognato, ex. Lindgren trap with ipslure (MSUC-1). Kalamazoo Co.: Gourdneck Lake State Game Area, 16.VII.2011, S.M. Smith, A.I. Cognato, ex. Prunus sp. (MSUC-2). Oakland Co.: Farmington Hills, N42°27.668', W83°25.579', 2.VII.2004, B. Sullivan, ex. Lindgren funnel with multistriatus lure (MSUC-2). Saginaw Co.: St. Charles, 25.VI.1968, J.G. Truchan, ex. rotary trap (MSUC-1), 25.VI.1969 (MSUC-1). Wayne Co.: 20.VI.1960, G. Steyskai (USNM-2). NEW JERSEY: [Essex Co.]: Maplewood, 7.VI.[19]34, D. Fivaz, ex. on elm [= Ulmus sp.] (USNM-12). [Morris Co.]: Chatham, 25.III.[19]34, W.D. Buchanan (USNM-1). NEW YORK:Albany Co.: near Rensselaerville, Huyck Preserve, 3-10.VII.1967, R. & J. Matthews, ex. window pane trap (CNCI-1). [Suffolk Co.]: Cutchogue, [19]45, Tuthill, ex. in apple [= Malus sp.] (USNM-26). [Tompkins Co.]: Groton, 24.V.1942, N.M. Downie (FMNH-1), 23.VI.1946 (FMNH-2). [Westchester Co.]: Armonk, 5.VI.[19]35, H. Dietrich, ex. apple [= Malus sp.] (CNCI-2). OHIO:Medina Co.: 15.VI.[19]62, C.L. Griswold (DEBC-4). PENNSYLVANIA:Luzerne Co.: Nanticoke, 20.IX.[19]60, ex. Malus sp. (CNCI-1). Nuangola, 12.V-23.VIII.1983, S. & J. Peck, ex. forest intercept (CNCI-1). VERMONT:Rutland Co.: Castleon, 18-19.VI.1989, H.V. Weems (FSCA-1). WASHINGTON, D.C.: 5.IV.1983, E.R. Hodges, ex. on sweater of collector (USNM-1). Additional specimens:Czech Republic (MSUC-21) and Italy (MSUC-1).

Distribution.

CANADA: Ontario, Quebec. UNITED STATES: Connecticut, Maine, Maryland, Massachusetts, Michigan, New Jersey, New York, Ohio, Pennsylvania, Vermont, Washington, D.C., Wisconsin (Fig. 11).

Hosts.

Malus spp. (apple), Prunus spp. (cherry), Ulmus spp. (elm), Pyrus spp. (pear) and Sorbus spp. (mountain ash).

Common name.

Large shothole borer.

Biology.

This species colonizes dying and weakened limbs of its host as well as fresh slash. Typical host material is 15.0-38.0 cm in diameter but branches as small as 8.0 cm are colonized ( Pechuman 1938).

Adult galleries are somewhat variable and are either parallel or at a slight oblique angle to the grain of the wood and consisting of a nuptial chamber and a single egg gallery. The adult gallery strongly scores the sapwood and ranges in size from 3.5-6.0 cm in length. Egg niches are constructed along the gallery and score the sapwood. Six to 100 eggs may be laid along the egg galleries with the typical gallery having 40 eggs. Larval mines lightly score the sapwood and radiate perpendicular to the egg gallery. Larval galleries later meander often at an oblique angle to the grain of wood, forming a fan shaped pattern. Pupation occurs within the sapwood and broods overwinter as larvae or adults. The following year, adults emerge and feed at twig crotches before selecting host material ( Pechuman 1938; Balachowsky 1949; Baker 1972; Wood 1982). In New York, Scolytus mali has one generation per year although there are two generations per year in Europe ( Pechuman 1938).

Collection notes.

The senior author collected this species from an 8.0 cm diameter Prunus sp. branch that had broken during a recent windstorm. Females constructed gallery entrances beneath large flakes of bark on the sides and bottom surfaces of the branch. Specimens were infesting the same limbs as Phloeotribus liminaris (Harris, 1852).

Remarks.

This species is native to the Palearctic region and was first detected in New York in 1868 when it was described as Scolytus sulcatus LeConte. LeConte (1868) noted in his description that the species most strongly resembled the Palearctic species Scolytus rugulosus and did not mention the collection date of his specimens. Interestingly, no other specimens were collected until 1933, 65 years after the initial discovery from southeastern New York, northern New Jersey and western Connecticut. It is likely that like LeConte’s Scolytus californicus (= Scolytus scolytus ), Scolytus mali was collected in 1868 but populations never became established. The later collections may be the result of multiple introduction events ( Pechuman 1938).

Brown (1950) recognized that LeConte’s species was morphologically and behaviorally identical to that of Scolytus mali and placed Scolytus sulcatus into synonymy. The native range of Scolytus mali is Europe, Central Asia, Siberia, the Russian Far East, North Africa ( Michalski 1973; Knížek 2011).