Microrhagus brunneus Otto, 2013

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 : 14-15

Microrhagus brunneus Otto, 2013

Fifth instar

( Fig. 43–47 )

Diagnosis. Rectangular-shaped prothoracic microtrichial patch, shorter basal lateral projection and oval, slightly transverse areoles will distinguish M. brunneus from M. breviangularis .

Specimens Examined. One larva collected at USA: WISCONSIN: Richland County, Lower Wisconsin River State Wildlife Area–Lone Rock, N43° 11.548’, W-90° 13.580’, 20 April 2013, Robert L. Otto, in rotten Quercus log. Larva is deposited in GERP.

Description. Length, 6.0 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 absent or indistinct. Legs reduced to simple setae. Dorsal and ventral microtrichial patches slightly darker in color compared to their surrounding areas ( Fig. 43 ).

Head ( Fig. 44 ): Strongly flattened, prognathous and inserted into prothorax. Dorsal cephalic disc sub-circular. Very weak median carina present on dorsal cephalic disc. Venter unmodified, without furrows or ridges. Base and lateral sides of the head capsule unsclerotized. Anterior portion of head capsule heavily sclerotized. Each lateral side of head capsule consists of four projections. Basal lateral projections short. Lateral sides between basal and second lateral projections weakly sinuate. Second through fourth lateral projections directed anterolaterally. Antennae minute, arising between the third and fourth 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. 45–46 ): Sub-equal to subsequent two thoracic segments. Tergum with pair of triangular-shaped scleromes extending from just above the base up near the cranial end of the segment, extending towards each lateral side and converge to point of origin. All sides of scleromes with well-defined edges. Rectangular-shaped microtrichial patch present between scleromes. Sternum with pair of internally bent sub-rhombus-shaped scleromes. Each sclerome with short, basal extension. Subcircular microtrichial patch present between scleromes. Both surfaces without areoles.

Meso- and metathorax: Terga and sterna with oval-shaped microtrichial patch. Terga and sterna with oval-shaped areole beneath patch, near center of each segment. Metathorax with reduced spiracles.

Abdomen: Segments I–IX sub-equal in length and width. Terga and sterna I–VIII with small, oval to elliptical-shaped microtrichial patch. Terga and sterna I–VIII with oval-shaped areole beneath patch, near base of each segment. Tergum IX without microtrichial patch and areole; sternum ( Fig. 47 ) heavily sclerotized at caudal half with prominent, sub-triangular-shaped circumanal asperities. Urogomphi absent on segment IX. Spiracles annular-biforous, with rounded spiracular collar.

Distribution. Microrhagus brunneus is known from USA: Arkansas, Indiana, Kentucky, Louisiana, North Carolina, Oklahoma, and Wisconsin ( Otto 2013a). A submitted image of a male specimen collected during the annual BugGuide Gathering at VCU Rice Center represents Virginia as a New State Record to the list for the species (Mike Quinn; BugGuide.net 2014). Single specimen used in this study came from Wisconsin.

Biology. Otto (2013a) wrote that M. brunneus were primarily taken by EAB purple prism traps deployed in Wisconsin. The eucnemid species has also been taken from sticky trap on a girdled ash tree, flight intercept traps, Lindgren funnel trap, hanging sugar trap, blacklight, combination mercury vapor and blacklight, Malaise Trap, and U.V. trap. In Wisconsin, during my collections, I found M. brunneus in a variety of forest systems including floodplain forest, northern hardwood swamp, northern mesic forest, northern wet-mesic forest, southern hardwood swamp, and southern mesic forest. A single larval specimen was taken in a rotten Quercus log in a southern mesic forest. The larval type was found within a few millimeters beneath the surface, positioned along the grain, leaving no trail behind it. No additional larval specimens were found in the surrounding section of the log, indicating the single specimen may have arrested its development while the rest completed their development in the previous season.

Figures

Figure 43. Microrhagus brunneus, fifth instar, dorsal habitus. Scale line = 2.0 mm.

Figures 44–47. Microrhagus brunneus, fifth instar. 44) Head, dorsal view. 45) Head and thoracic region, dorsal view. 46) Head and thoracic region, ventral view. 47) Abdominal segments VII–IX, ventral view.