Trigonorhinus sticticus (Boheman)

Janicki, Julia & Young, Daniel K., 2017, Nemonychidae and Anthribidae of Wisconsin (Coleoptera: Curculionoidea), Insecta Mundi 2017 (579), pp. 1-36 : 21

Trigonorhinus sticticus (Boheman)

(Fig. 31–32)

Brachytarsus sticticus Boheman 1833: 172 .

Anthribus variegatus Say 1826: 251 .

Brachytarsus obsoletus Fahraeus 1839: 167 .

Brachytarsus strictus (Boheman) ; Zimmerman 1936: 191.

Trigonorhinus sticticus (Boheman) ; Valentine 1957: 9.

Description. Length 1.8–3.2mm (head excluded). Integument black and reddish-brown. Vestiture consisting of white, light brown and dark brown setae; pronotum with dark brown setae predominant basally and white or light brown setae predominant apically. Elytra with scattered light brown setae intermixed with white setae, occasionally with scattered spots of dark brown setae surrounded by white setae in an irregular pattern basolaterally, interstriae 1–4 with one large or two connected dark brown spots basally and two dark, medial spots, medial spots sometimes connected by dark setae on interstriae 1–2. Rostrum moderately prolonged, narrowed apically, medial 1/3 prolonged apically; surface finely punctate. Frons weakly convex, transversely impressed below eye level; surface finely punctate. Pronotum slightly wider than long, widest just behind middle, sides distinctly arcuate, converging to narrowly rounded apex; disc evenly convex, with narrow transverse impression just anterad transverse carina, transverse carina basal, weakly arcuate, acutely elevated; surface shining, with obscure shallow punctures interpunctural space minutely punctate or reticulate. Elytral length 1.3X width, sides evenly and slightly arcuate to broadly rounded apex; striae weakly impressed, with large, obscure, more deeply impressed punctures; interstriae 1.0–2.0X strial width, minutely punctate.

Diagnosis. Trigonorhinus sticticus can look similar to T. alternatus in terms of dorsal vestiture, but it can be distinguished by tibial vestiture: not biannulate or with dark spots. It can be distinguished from other species of Trigonorhinus by the conspicuous dorsal setal pattern, consisting of very dark setae in spots that abruptly and distinctly contrast with the light brown or white setae on the surfaces.

Natural history. This species breeds in smut fungi on corn ( Zea mays ), wheat ( Triticum spp. ), wild grasses such as little bluestem ( Schizachyrium scoparium ), or shrubs. It has also been recorded on flowers of buttonbush ( Cephalanthus occidentalis ), and on prairie dropseed ( Sporobolis heterolepis ) and sideoats grama ( Bouteloua curtipendula ).

Phenology. In Wisconsin, adults have been collected from April – August.

Collecting methods. The 52 Wisconsin specimens examined during this study from 21 counties represent a NEW STATE RECORD. Adults are most commonly collected by sweeping grassy fields. They have also been collected in Malaise traps, Lindgren funnel traps, vacuums, and by hand.