Trigonorhinus alternatus (Say)

Janicki, Julia & Young, Daniel K., 2017, Nemonychidae and Anthribidae of Wisconsin (Coleoptera: Curculionoidea), Insecta Mundi 2017 (579), pp. 1-36 : 18-19

Trigonorhinus alternatus (Say)

(Fig. 25–26)

Anthribus alternatus Say 1826: 250 .

Brachytarsus alternatus (Say) ; Blatchley and Leng 1916: 38.

Brachytarsoides alternatus (Say) ; Pierce 1930: 30.

Trigonorhinus alternatus (Say) ; Valentine 1957: 9.

Description. Length 2.1–3.3mm (head excluded). Body elongate. Integument dark reddish-brown to black. Vestiture consisting of white and brown setae; pronotal setae white and brown intermixed with white, forming at least three longitudinal stripes; elytral setae silvery with numerous brown spots, with larger medial and basal spots; interstriae 3, 5 and 7 with numerous white setae, 1, 2, 4 and 6 with light brown and dark brown setae scattered in numerous small spots; tibial setal patterns annulate or spotted, with two dark and three pale areas; abdominal sternites each with one lateral spot of brown setae. Rostrum flattened, not transversely impressed, narrowed apically, medial 1/3 prolonged apically; surface densely punctate. Frons flattened, not transversely impressed; surface densely punctate, the rims of the punctures elevated. Pronotal width 1.2X length, widest at basal angles; weakly arcuate laterally, converging to narrowly rounded apical margin; disc evenly convex, weakly impressed before transverse carina; transverse carina basal, weakly emarginate, acutely elevated; surface densely punctate, the rims of the punctures not elevated, interpunctural space smooth, nitid. Elytral length 1.4X width, weakly arcuate laterally, broadly rounded apically; disc evenly convex; striae moderately impressed in even rows; interstriae flat, densely and finely punctate, 4.0X strial width.

Diagnosis. Trigonorhinus alternatus can be recognized by the tibiae that are biannulate or with dark spots, smooth interpunctural space on the elytra, and by the color pattern. Trigonorhinus alternatus has been misidentified as Eusphyrus walshii , but can be distinguished from it by the rostrum that is narrowed subapically, with the medial 1/3 longer than the sides apically, by the tibial vestiture consisting of two dark spots and three light spots, and by elytral interstriae 3, 5, and 7 possessing numerous white setae.

Natural history. Larvae of this species feed on stems surrounded by plant fragments and debris, then pupate in the stem or in the main stem ( Pierce 1930). Trigonorhinus alternatus has also been found in fungus galls and flower heads of numerous plant species, as well as overwintering in cotton bolls and ovipositing in kernels of dry corn ( Zea mays ). It has also been recorded from fungus-infested morning glories ( Valentine 2002). In Wisconsin, a specimen was collected by sweeping apple ( Malus spp. ).

Phenology. The two specimens collected from Wisconsin were found in June and July.

Collecting methods. The two Wisconsin specimens collected from two counties represent a NEW STATE RECORD. One specimen was collected by sweeping apple.