Microrhagus audax Horn, 1886

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 : 9

Microrhagus audax Horn, 1886

Fifth instar

( Fig. 25–29)

Specimens Examined. Two 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. Larvae are deposited in GERP.

Description. Length, 8.0–9.0 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 distinct. Legs absent. Dorsal and ventral microtrichial patches slightly darker in color compared to their surrounding areas ( Fig. 25).

Head ( Fig. 26 ): Strongly flattened, prognathous and inserted into prothorax. Dorsal cephalic disc sub-circular with a median carina. Venter with two shallow furrows diverging from anterior portion of the head capsule below the mandibles. Center of the ventral disc with single shallow furrow. 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 enlarged. Lateral sides between basal and second lateral projections strongly sinuate. Second through fourth lateral projections directed laterally. 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. 27–28 ): 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 diverges towards lateral sides and converges to point of origin; caudal and lateral sides with undefined edges. Rectangular microtrichial patch present between scleromes. Sternum with pair of internally bent sub-triangular shaped scleromes present converging towards median of segment. Sub-triangularshaped microtrichial patch present between scleromes. Both surfaces without areoles.

Meso- and metathorax: Terga with alluvial-shaped microtrichial patch. Sterna with kidneyshaped microtrichial patch. Terga and sterna with small circular areole beneath patch, near middle of each segment. Mesothorax without spiracles.

Abdomen: Segments I–IX sub-equal in length and width. Terga and sterna I–VIII with relatively narrowed, oblonged transverse microtrichial patch near anterior. Small circular areole present beneath patch, near middle of each segment. Tergum IX without microtrichial patch and areole; sternum ( Fig. 29 ) heavily sclerotized at caudal half with prominent, campaniform circumanal asperities. Urogomphi absent on segment IX. Spiracles annular-biforous, with rounded spiracular collar.

Distribution. Microrhagus audax is known from USA: Alabama, District of Columbia, Georgia, Illinois, Indiana, Iowa, Maryland, Michigan, Missouri, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, Texas, Virginia, West Virginia, and Wisconsin ( Muona 2000). Both specimens used in this study came from Wisconsin.

Biology. Microrhagus audax is an uncommon species most frequently collected in southeastern areas of the United States, yet little is still known about its biology. Muona (2000) wrote M. audax were taken at UVCC-light and window traps. In Wisconsin, I found M. audax in two different forest systems including northern mesic forest and a degraded southern hardwood swamp. All encountered adult specimens were taken from purple prism traps placed in ash trees. Collectors in Wisconsin have found M. audax in Malaise traps, on a log, and swept from grass.

Figures

Figures 26–29. Microrhagus audax, fifth instar. 26) Head, dorsal view. 27) Head and thoracic region, dorsal view. 28) Head and thoracic region, ventral view. 29) Abdominal segments VII–IX, ventral view.