Trigonorhinus tomentosus (Say)

Janicki, Julia & Young, Daniel K., 2017, Nemonychidae and Anthribidae of Wisconsin (Coleoptera: Curculionoidea), Insecta Mundi 2017 (579), pp. 1-36 : 22

Trigonorhinus tomentosus (Say)

(Fig. 33–34)

Anthribus tomentosus Say 1826: 251 .

Brachytarsus brevis Fahraeus 1839: 168 .

Brachytarsus paululus Casey 1884: 194 .

Brachytarsus beyeri Schaeffer 1906: 277 .

Brachytarsus tomentosus (Say) ; Blatchley and Leng 1916: 40.

Brachytarsoides tomentosus (Say) ; Pierce 1930: 31.

Brachytarsus franseria Barrett 1931: 188 .

Brachytarsoides irregularis Tanner 1934: 285

Trigonorhinus tomentosus (Say) ; Valentine 1957: 9.

Description. Length 1.3–2.1mm (head excluded). Body short and ovate. Integument light to dark reddish-brown to black. Vestiture consisting of grey and brown setae that are randomly mixed; brown elytral setae sometimes forming large and diffuse basal-median spots. Rostrum separated from frons by weak transverse impression just below level of eyes, surface flat; lateral margins weakly elevated, punctate; surface finely punctate, with short, grey recumbent setae. Frons weakly convex, surface finely punctate, with short, grey recumbent setae. Pronotal width 1.3X length, widest at basal angles; sides weakly arcuate, strongly converging to narrowly rounded apex; disc evenly convex, weakly, transversely impressed before transverse carina, transverse carina basal, acutely elevated, forming a shallow V-shape; surface with shallow, irregularly placed, inconspicuous punctures, interpunctural space finely granulose-punctate. Elytral length 1.2X width, sides evenly arcuate to broadly rounded apex, disc evenly convex; striae narrowly and weakly impressed, with small punctures that are slightly more deeply impressed; interstriae flat, finely granulose-punctate, 4.0X strial width.

Diagnosis. Trigonorhinus tomentosus can be distinguished from other Trigonorhinus species by its small size ( T. rotundatus is also small but T. tomentosus has well-developed pronotal hind angles), by the acutely elevated, basal transverse pronotal carina that forms a shallow V-shape, and by the diffuse color pattern. It can be easily confused with T. limbatus at first glance, but the above characters should be sufficient to distinguish the two species.

Natural history. This species is the most abundant Trigonorhinus and anthribid species in Wisconsin; it is generally associated with smut fungi on grasses, which are ubiquitous. Pierce (1916) recorded that this species is found on the common ragweed ( Ambrosia artemisiifolia ). Bright (1993) reported that the adults oviposit in flowers of the same species. Other records of plants associations include dwarf cherry ( Prunus fruticosa ), prairie dropseed ( Sporobolis heterolepis ), sideoats grama ( Bouteloua curtipendula ), little bluestem ( Schizachyrium scoparium ), raspberry ( Rubus spp. ), and mullein ( Verbascum thapsus ).

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

Collecting methods. The 203 Wisconsin specimens examined from 32 counties represent a NEW STATE RECORD. This species is most commonly collected by sweeping. Many specimens have been collected in Malaise traps, one was collected with a vacuum, one was found at a blacklight trap, and one was “found on Mullein, Verbascum thapsus .”