Microrhagus pectinatus LeConte, 1866

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 : 5-6

Microrhagus pectinatus LeConte, 1866

Fifth instar

( Fig. 15–19 )

Diagnosis. Larger, triangular prothoracic scleromes and narrowed microtrichial patches will distinguish M. pectinatus from M. subsinuatus .

Specimens Examined. Forty-nine larvae collected at USA: WISCONSIN: Dane County, Festge Park , 1 October 1994, in soft, moderate wet white rotten deciduous wood, Robert L. Otto (4 larvae) ; Shawano County, Navarino State Wildlife Area , N44° 38.9’, W-88° 37.4’, 14 April 2009, Robert L. Otto, in white rotten northern pin oak log (4 larvae) ; Forest County, along State Highway 55, N45° 49.360’, W-88° 49.247’, 12 April 2010, Robert L. Otto, in rotten maple log (4 larvae) ; Dane County, Picnic Point , 13 March 2012, Robert L. Otto, in rotten oak log (1 larva) ; Fond du Lac County, Northwoods Park , 3.2 km N. Rosendale, 13 March 2012, Robert L. Otto, in rotten oak log (3 larvae) ; Dane County, LWRSWA– Mazomanie unit, 19 March 2012, Robert L. Otto, in rotten maple stump (1 larva) ; Dane County, Turville Point Preserve , 3 October 2012, 7 October 2012, 16 October 2012, 25 October 2012, Robert L. Otto, in rotten Quercus and basswood logs (30 larvae) ; Dane County, McDaniel Park , N43° 01.676’, W-89° 18.600’ 27 September 2013, in rotten Acer log (2 larvae). Larvae are deposited in GERP and WIRC .

Description. Length 9.0–13.0 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. 15 ).

Head ( Fig. 16 ): Strongly flattened, prognathous and inserted into prothorax. Dorsal cephalic disc sub-circular with a median carina. Venter simple. 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. Lateral side of second projections weakly sinuate out and then back towards the tip. Second through fifth lateral projections directed anterolaterally. Antennae minute, arising between fourth and fifth lateral projections. Scape not visible. Pedicel elongate. Sensorum and flagellum sub-equal in length. Sensory papillae indistinct. 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. 17–18 ): Sub-equal to subsequent two thoracic segments. Tergum with pair of triangular-shaped scleromes extending from base up three-fourths the length of the segment then divergent toward lateral sides and arching to point of origin. Oblong trapezoidal-shaped microtrichial patch present between scleromes. Sternum with pair of internally bent sub-triangular-shaped scleromes extending from base up three-fourths the length of segment then divergent towards lateral sides and converge above point of origin, leaving a short tail at the caudal end of sclerome. Circular-shaped microtrichial patch present between ventral scleromes. Both surfaces with areoles.

Meso- and metathorax: Terga and sterna with oval microtrichial patch; oblonged areole present near each base. Posterior end of each microtrichial patch tricarinate. Sterna with longitudinal plicae and carinae between caudal end of microtrichial patch and aerole. 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 circular on segment VIII. Sterna I–VIII with oval microtrichial patch. Terga and sterna I–VIII with small areole beneath patch near each base. Segment IX laterally constricted caudally. Tergum IX without microtrichial patch and areole; sternum ( Fig. 19 ) heavily sclerotized at caudal half with prominent, wide, semicircular circumanal asperities. Mediocaudal end of segment IX cleft. Urogomphi absent on segment IX. Spiracles annular-biforous, with caudally pointed spiracular collar.

Distribution. Microrhagus pectinatus is known from CANADA: British Columbia, New Brunswick, Nova Scotia, Ontario, Québec; USA: Georgia, Illinois, Indiana, Iowa, Kansas, Maine, Maryland, Michigan, Missouri, New Hampshire, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Tennessee, Texas, Virginia, West Virginia, and Wisconsin ( Muona 2000; Majka 2007). All specimens used in this study came from Wisconsin.

Biology. Microrhagus pectinatus is a widespread, although uncommonly collected species. Some biological information is available. Dury (1888) collected the species on dead beech ( Fagus grandifolia Ehrhart ; Fagaceae ). Blatchley (1910) observed adults occurred in partially rotten elm ( Ulmus sp. ; Ulmaceae ) and other logs. Knull (1947) reared adults from a badly decayed beech log. Muona (1993b) wrote that M. pectinatus was reared from sycamore ( Platanus sp. ; Platanaceae ) in Maryland. Muona (1996) also wrote the hosts for the species were beech and elm. Majka (2007) collected several specimens by a flight intercept trap placed in an old red spruce ( Picea rubens Sargent ; Pinaceae ) forest in Nova Scotia.

Microrhagus pectinatus were found in a variety of forest systems. In Wisconsin, I collected adults and larvae in floodplain forests, northern dry-mesic forest, northern hardwood swamp, northern mesic forest, northern wet forest, northern wet-mesic forest, oak barrens, oak woodlands, southern hardwood swamp, and southern mesic forest. I found one adult in 1995 by sweeping through maple foliage in southern Wisconsin. Twenty adults were reared from a white rotten northern pin oak ( Quercus ellipsoidalis Hill ; Fagaceae ) log on 30 April 2009. I extracted five larvae from a rotten maple stump and rotten oak logs during 2012. Many larvae were also extracted from white rotten, moist maple, oak and basswood logs during 2009 through 2012 .

Several species of Eucnemidae were observed tunneling in the same area of the Quercus log. Isarthrus rufipes (Melsheimer) and M. pectinatus were both tunneling in moist, softer, separate sections of the log closest to the soil. A third species, Dirrhagofarsus ernae Otto, Muona and McClarin was burrowing in moist, firmer section of the same log. 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. Many larvae were extracted at least 2.5–3.0 cm beneath the surface. Like many other observed species ( Otto 2012a, 2012b), M. pectinatus larvae construct a pupal chamber near the surface and assume a U-shaped position. Larvae overwinter in their pupal chamber and continue their development in the following spring. Pupation requires about two to three weeks. Many adults in recent history were collected from purple prism traps (Synegy Semiochemicals Company, British Columbia) while monitoring for the adventive Emerald Ash Borer (EAB) ( Agrilus planipennis Fairmaire ; Buprestidae ) in northeastern Wisconsin during late June through late August.

Collectors in Wisconsin have found M. pectinatus in Malaise traps, sweeping through grass, in moderately wet, white rotten deciduous wood, at mercury vapor light trap, collected on girdled ash trees, and in wood crevices. As previously observed, adults are capable of snapping into the air when placed on their backs. Adults were also observed to quiver their extended antennae while in captivity.

Figures

Figures 15–19. Microrhagus pectinatus, fifth instar. 15) Dorsal habitus. 16) Head, dorsal view. 17) Head and thoracic region, dorsal view. 18) Head and thoracic region, ventral view. 19) Abdominal segments VII–IX, ventral view.