Microrhagus subsinuatus LeConte, 1852

Otto, Robert L., 2015, Eucnemid larvae of the Nearctic region. Part V: Fifth instar larval descriptions for eight species of Microrhagus Dejean, 1833 (Coleoptera: Eucnemidae: Melasinae: Dirhagini), with descriptions of four new species and notes on their biology, Insecta Mundi 2015 (421), pp. 1-46 : 7-8

Microrhagus subsinuatus LeConte, 1852

Fifth instar

( Fig. 20–24 )

Diagnosis. Smaller, triangular prothoracic scleromes and larger microtrichial patches will distinguish M. subsinuatus from M. pectinatus .

Specimens Examined. Six larvae collected at USA: WISCONSIN: Oconto County, N. Bayshore County Park, N44° 57.847’, W-87° 47.042’, 13 April 2011, Robert L. Otto, in rotten elm log (2 larvae) ; Dane County, LWRSWA– Mazomanie unit, 16 September 2012, Robert L. Otto, in rotten Betula nigra log (3 larvae) ; Dane County, McDaniel Park , N43° 01.707’, W-89° 18.639’, 22 September 2013, Robert L. Otto, in rotten oak log (1 larva). Larvae are deposited in GERP and WIRC .

Description. Length, 11.5–12.0 mm. Width, 1.0 mm. Orthosomatic, elateriform. Body cylindrical, sides parallel, cream-yellow with head, prothoracic sclerome patches and caudal end of abdominal segment IX dark brown. Setae either indistinct or absent. Legs absent. Dorsal and ventral microtrichial patches slightly darker in color compared to their surrounding areas ( Fig. 20 ).

Head ( Fig. 21 ): Strongly flattened, prognathous and inserted into prothorax. Dorsal cephalic disc sub-circular with a median carina. Venter simple, without any furrows. Ventral lateral sides of head capsule unsclerotized. Anterior portion of head capsule heavily sclerotized. Each lateral side of head capsule consists of five projections. Basal lateral projections enlarged. Second lateral projection blunt, directed anterolaterally. Lateral side of second projections weakly sinuate out and then back towards the tip. Third through fifth lateral projections directed anterolaterally. Antennae minute, arising between the fourth and fifth lateral projections. Scape not visible. Pedicel elongate. Sensorum and flagellum sub-equal in length. Mandibles minute, resting in the mesal acumination of the head capsule. Each mandible heavily sclerotized, oval with two outwardly projecting teeth. Labial and maxillary palpi indistinct. Ligula, mala, lacinia and galea not visible. Hypostomal rods absent.

Prothorax ( Fig. 22–23 ): Sub-equal to subsequent two thoracic segments. Tergum with pair of sub-triangular-shaped scleromes extending from base up three-fourths the length of the segment then diverge towards lateral sides and arches to point of origin. Rectangular-shaped microtrichial patch present between scleromes. Sternum with pair of triangular-shaped scleromes extending from base up three-fourths length of segment then diverge towards lateral sides and converge above point of origin, leaving a short tail at the caudal end of sclerome. Barrel-shaped microtrichial patch present between scleromes. Both surfaces with areoles.

Meso- and metathorax: Terga with oval microtrichial patch. Sterna with broadly oval microtrichial patch. Terga and sterna with longitudinal plicae and carinae between caudal end of microtrichial patch and aerole; areole present near each base. Mesothorax without spiracles.

Abdomen: Segments I–IX sub-equal in length and width. Terga I–VIII with microtrichial patches that successively change from small and oval on segment I to alluvial on segment VIII. Sterna I–VIII with circular microtrichial patch. Terga and sterna with small areole beneath patch, near each base. Tergum IX without microtrichial patch and areole; sternum ( Fig. 24 ) heavily sclerotized at caudal half with prominent, semicircular circumanal asperities. Urogomphi absent on segment IX. Spiracles annular-biforous, with caudally pointed spiracular collar.

Distribution. Microrhagus subsinuatus is known from CANADA: Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Québec; USA: Colorado, Connecticut, District of Columbia, Florida, Illinois, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee (New State Record), Vermont, Virginia, West Virginia, and Wisconsin ( Bousquet 1991; Muona 2000; Majka 2007; Ferro et al. 2012; Webster et al. 2012). All specimens used in this study came from Wisconsin.

Biology. Although M. subsinuatus is a widespread species, very little is known about its biology. Blatchley (1910) obtained one of the specimens on milkweed (Ascelpias sp.; Apocynaceae ) leaves. Knull (1946) reared the species from moist, decayed logs of American beech in Ohio. Muona (1993b, 2000) wrote that M. subsinuatus were taken on Alnus serrata Newberry (not Hortulanorum ex. Lavallée); Betulaceae . However, the information provided may be in reference to smooth alder ( Alnus serrulata (Aiton) Willdenow ) instead. Alnus serrata is an extinct North American alder species once abundant in western United States during the late Pleistocene Epoch ( Peabody Museum of Natural History 2011).

Majka (2007) took one specimen on shoreline vegetation along a pond in Nova Scotia. Webster et al. (2012) collected 23 adults during June, July, and August during their survey work in New Brunswick. One specimen was swept from foliage in a mature hardwood forest. Twenty-two remaining specimens were taken by Lindgren funnel traps placed in various forest systems. They found adults in a mature hardwood forest with American beech, sugar maple ( Acer saccharum Marshall ; Aceraceae ) and ash, old silver maple forest with green ash, red spruce forest with red maple ( Acer rubrum Linnaeus ) and balsam fir ( Abies balsamea (Linnaeus) Miller ; Pinaceae ), an old northern hardwood forest, old-growth white spruce ( Picea glauca (Moench) Voss ; Pinaceae ) and balsam fir forest, and old-growth eastern white cedar ( Thuja occidentalis Linnaeus ; Cupressaceae ) forest. Ferro et al. (2012) reared a number of adults from decay class 3-4 coarse woody materials using emergence chambers. Specimens were reared from materials collected at two locations; both from Sevier County, Tennessee.

Microrhagus subsinuatus was found in a variety of forest systems. In Wisconsin, I collected adults and larvae in northern dry-mesic forest, northern hardwood swamp, northern mesic forest, northern wet forest, northern wet-mesic forest, oak barrens, southern dry-mesic forest, and southern mesic forest. Two adults were reared from a badly decayed elm log in 2010. Several larvae were found less than 1.0 cm beneath the surface of the moist white rotten sapwood of a river birch log ( Betula nigra L.; Betulaceae ) in 2012. Searching in conifers has yielded no larvae, which may indicate the species is a deciduous specialist. Larvae were observed tunneling along the wood grain, leaving no trails behind them. Most larvae were extracted at least 1.0–3.0 cm beneath the surface. Pupation requires about two to three weeks. Many adults in recent history were collected from purple prism traps in northeastern Wisconsin from late June through late August. Collectors in Wisconsin have found M. subsinuatus in Malaise traps, at UV lights, on saplings/herbaceous understory, swept through vegetation, in Lindgren funnel traps, in unbaited Townes Malaise trap, and on girdled ash trees.

Figures

Figures 20–24. Microrhagus subsinuatus, fifth instar. 20) Dorsal habitus. 21) Head, dorsal view. 22) Head and thoracic region, dorsal view. 23) Head and thoracic region, ventral view. 24) Abdominal segments VII-IX, ventral view.