Scolytus schevyrewi Semenov, 1902

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 24-25

Taxon classification Animalia Coleoptera Curculionidae

Scolytus schevyrewi Semenov, 1902 Fig. 16

Scolytus schevyrewi Semenov, 1902: 265.

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

Diagnosis.

The Scolytus schevyrewi male most strongly resembles that of Scolytus piceae because in both species the spine on the second ventrite never attains the apical margin. Both sexes can be distinguished from Scolytus piceae by the subapical carina on ventrite 5 located just before end of segment. Males are further differentiated from those of Scolytus piceae by the laterally compressed spine with a bulbous apex, which frequently has a longitudinal groove and by the banded appearance of the elytra. The female is further differentiated from that of Scolytus piceae by the banded pattern of the elytra and by the low median carina (variable and may be absent) that does not touch either margin on the second ventrite.

Description (male).

2.8-3.5 mm long (mean = 3.2 mm; n = 10); 2.0-2.2 times as long as wide. Color red-brown to dark red brown. Elytra of most specimens appears banded with a characteristic dark brown band on reddish colored elytra, but may also be solely dark brown or red-brown without a band. Antennae yellow-brown. Pronotum typically darker than elytra.

Head. Epistoma weakly, broadly emarginated; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing impressed when viewed laterally; moderately, coarsely reticulate punctate to weakly longitudinally aciculate; punctures dense, small, coarse; moderately covered by long, fine, yellow, erect, hair-like setae, these longer than width midpoint of eye, setae on lateral and dorsal margins longer, thicker, incurved. Antennal scape short, elongate; club flattened, thinner on apical half, irregularly ovoid, setose with partial septum and 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, coarser, deeper 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 basal half, narrowing to moderately rounded, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing small, fine punctures. Scutellar notch densely covered in recumbent white setae (may be abraded). Disc glabrous, smooth, shining; interstriae not impressed, equal in width to striae; interstrial punctures uniseriate, equal in size to those of striae, bearing sparse short, semi-erect yellow hair-like setae; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.

Venter. Apical margin of ventrite 1 flush with base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow; surface convex; densely covered with semi-recumbent, long setae, as long as length of ventrite 3 or less; surface armed with median laterally compressed spine (rarely absent) that has its base close to basal margin but does not touch it; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

2.3-3.6 mm long (mean = 3.2 mm; n = 10); 1.7-2.4 times as long as wide. Similar to male except epistoma feebly emarginated, frons flattened when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed just above epistoma and longitudinally impressed in median area. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Second ventrite armed with low median carina (variable and may be absent) that does not touch either margin.

Specimens examined.

24.

Type material.

Holotype, male (location unknown).

Non-type material.

UNITED STATES:CALIFORNIA:Los Angeles Co.: Whittier, Whittier Fertilizer, 7.IX.2006, A. Sanchez, ex. Lindgren funnel + ETOH & alpha pinene (DEBC-1). COLORADO:Adams Co.: Aurora, wood recycler, N39°807', W104°994', 9.VII.2003, P. McPherren, ex. funnel trap with Ips lure (MSUC-11), 15.IV.2003 (MSUC-1), 26.IV.2003 (MSUC-1), 2.V.2003 (MSUC-1), 29.V.2003 (MSUC-1). MICHIGAN:Ingham Co.: 42.736501 -84.464670, 258 m, 16.IX.2011, S.M. Smith, A.I. Cognato, I.A. Cognato, ex. Ulmus sp. (MSUC-1). Wayne Co.: Trenton-Woodhaven, 26.VII.2004, T. Dutton, ex. Lindgren funnel alpha-pinene Trap WY4 (MSUC-1). UTAH:Weber Co.: Ogden, Ogden Nature Center, 13.VII.2003, ex. funnel trap with alpha pinene & ethanol lure (MSUC-6).

Distribution.

CANADA: Alberta, British Columbia, Manitoba, Ontario, Saskatchewan. UNITED STATES: Arizona, California, Colorado, Connecticut, Delaware, Idaho, Illinois, Indiana, Kansas, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, Ohio, Oklahoma, Oregon, Pennsylvania, South Dakota, Texas, Utah, Virginia, Washington, Wyoming (Fig. 17).

Hosts.

Ulmus spp. including Ulmus americana L. (American elm), Ulmus pumila L. (Siberian elm), Ulmus thomasii Sarg. (rock elm) and Ulmus procera Salisb. (English elm).

Common name.

Banded elm bark beetle.

Biology.

This species prefers to attack drought stressed elms ( Negrón et al. 2005). Scolytus schevyrewi locate a suitable host via host tree volatiles ( Lee et al. 2010).

The adult gallery consists solely of a single egg gallery parallel with grain of the wood; a nuptial chamber is not constructed ( Lee et al. 2006). The adult gallery strongly scores the sapwood. Egg niches are constructed along the gallery and score the sapwood. Twenty to 120 eggs are laid along the egg galleries ( Lee et al. 2010). 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 in the outer bark and broods overwinter as mature larvae or pupae ( Lee et al. 2006). In California, flight occurs from April-September or October. In Nevada, Utah, Wyoming, Colorado, Kansas and Utah, flight occurs from May to September ( Lee et al. 2011). There are two to three generations per year ( Lee et al. 2011). Development from egg to adult takes 30-45 days ( Negrón et al. 2005). Upon emergence, adults feed at twig crotches prior to selecting host material ( Negrón et al. 2005). Scolytus schevyrewi is a less effective vector of the Dutch elm disease fungus Ophiostoma ulmi in North America, especially in Rocky Mountain states ( Jacobi et al. 2013).

Remarks.

This species is native to the Palearctic where it occurs from western Russia and Uzbekistan and east to China, Mongolia and Korea ( Michalski 1973). Scolytus schevyrewi was first detected in North America in 2003. The first specimens were collected in Colorado and Utah. By 2005, it was recorded from 21 states suggesting that it had been present for many years before its initial detection ( Negrón et al. 2005; LaBonte 2010). Subsequent review of bark beetle survey collections revealed the earlier occurrence of this species in Denver, Colorado in 1994 and Clovis, New Mexico in 1998 ( Lee et al. 2006).

In areas where populations of Scolytus schevyrewi and Scolytus multistriatus are both present, the abundance of Scolytus multistriatus is decreasing to the point where this once common species is difficult to find ( Negrón et al. 2005; Lee et al. 2010). This competitive displacement of Scolytus multistriatus by Scolytus schevyrewi is likely the result of differences in fecundity, generation time, and emergence. Scolytus schevyrewi produces larger broods that may overwinter as pupae, have a quicker development period, have an earlier flight, and exhibit rapid, strong aggregation to host kairomones as compared to Scolytus multistriatus ( Lee et al. 2010).

Scolytus schevyrewi is a highly morphologically variable species. LaBonte (2010) provides an excellent discussion regarding intraspecific variation exhibited within Scolytus schevyrewi . There is considerable variation observed in the shape and appearance of spine on the second ventrite. The male second ventrite spine is typically well developed with a blunt apex that is broader than the base and appears triangular when laterally viewed. In females the spine is variously reduced and may even be absent. In most males, the spine is closest to the apical margin of the second ventrite. In some males the base of the spine is closer to basal margin. Most individuals exhibit the characteristic dark brown band on reddish colored elytra, which is the derivative of the species’.

Common name.

Occasionally individuals have been encountered with unicolorous dark brown or reddish elytra. Additional variation was also observed in the coloration of the pronotum. The pronotum can vary from almost entirely dark brown with reddish coloration along the margins (common form) to the entire dorsal surface being reddish with dark brown margins (uncommon form) ( LaBonte 2010).