Gonocephalum sericeum (Baudi, 1875)

Steiner Jr., Warren E. & Swearingen, Jil M., 2015, New Records of Three Non-Native Darkling Beetles (Coleoptera: Tenebrionidae) Established in California and Nevada, USA, The Coleopterists Bulletin (mo 14) 69, pp. 22-26 : 22-23

Gonocephalum sericeum (Baudi, 1875)

Gonocephalum Solier is a large genus of several hundred species worldwide (Iwan et al. 2010). No members are native to the Americas, but some adventive specimens have been noted previously. Occurrences of Gonocephalum bilineatum Walker on the eastern and western coasts of North America were reviewed by Aalbu and Triplehorn (1985), with notes on its taxonomic history and conclusion that these apparently did not result in established introductions. The genus was therefore not included in recent keys to North American opatrine Tenebrionidae . However, a second species newly reported here, G. sericeum , apparently is established in southern California, based on recent collections and images of live beetles. This species was recently recognized and separated among a complex of similar synanthropic species (Ferrer 2010) that are prone to colonization in regions outside their known native range. Some are considered to be agricultural pests, damaging various vegetable crop seedlings and young plants (Medvedev 1968; Rodríguez et al. 2008).

During December 2010 in Orange County, California, the collection of a series of female beetles, immediately recognized as a species of Gonocephalum , prompted a search for other records and a possible species identification. It was soon discovered that images of identical live beetles from nearby localities had been posted by insect photographers on the popular website BugGuide (2015a), with the following data: “Shipley Nature Center, Huntington Beach, Orange County, California, USA, May 26, 2008; Found three of these on the underside of a piece of dead bark on the path” (photograph by Elliotte Rusty Harold); “Palos Verdes Peninsula, Los Angeles County, California, USA, June 18, 2011 ” (photograph by Emile). With a “search image” for this species, a single male specimen was located among unsorted specimens of Blapstinus Sturm in the USNM collection, which had been found by Robert F. Denno at the same locality 30 years prior to the collection above.

Specimens Examined. “ C A L I F O R N I A: Orange Co., Newport Beach , 26 December 1980 , R. F. Denno ” (1 male); “ CALIFORNIA: Orange Co., Newport Beach, Back Bay, 33°38′02″N, 117°53′06″W, 16 December 2010, under matted dead grass at roadside, sandy soil / W. E. Steiner, J. M. Swearingen, N. J. Vandenberg, M. A. Brown, collectors” (8 females) .

While this species has been established in California for at least 35 years, it has apparently not spread as aggressively as have some other exotic species. Its native distribution includes northwestern Africa and the Arabian Peninsula, and it has been introduced to Spain (Ferrer 2010; Iwan et al. 2010).

Diagnosis. In keys to the genera of North American Opatrini (Aalbu and Triplehorn 1985; Aalbu et al. 2002), Gonocephalum runs to the couplet containing the monotypic genera Ephalus LeConte and Pseudephalus Casey , which are flightless, convex, and very different in appearance from Gonocephalum species. The following couplet is inserted in the key of Aalbu et al. (2002) to separate Gonocephalum from these genera:

3a(2). Body form broadly oval, convex; front tibiae apically broad, spatulate.............3b

- Body form elongate oval, not very convex; front tibiae unmodified..... Gonocephalum

3b. Elytra without striae, but with dense, confused granules............................. Ephalus

- Elytra with punctate striae, fine granules on intervals only................ Pseudephalus

Gonocephalum sericeum is dark brown to nearly black, 8.0– 9.5 mm long and widest at mid-length of elytra, 3.5–3.8 mm ( Fig. 1 ). Specimens have been confused with Blapstinus dilatatus LeConte , which are of similar size and may co-occur in sandy soil habitats. In G. sericeum , the cuticle is shiny, but in some specimens it may bear soil encrustations that obscure this. The eyes are deeply emarginate but not divided by the epistomal canthus as in species of Blapstinus . The epipleura end before the elytral apex, not entire as in Blapstinus species. The head and pronotum are granulate, not punctate, with decurrent, thick, golden setae; the elytra have punctate striae with relatively smooth intervals bearing similar setae ( Fig. 2 ).

No ant associations of G. sericeum have been recorded in California, but myrmecophily in a related Gonocephalum species has been reported (Bakr et al. 2007). In Orange County, G. sericeum co-occurs with the following species, a known facultative myrmecophile.

Figures

Fig. 1. Gonocephalum sericeum, female, dorsal and ventral view. Total body length = 8.9 mm.

Fig. 2. Gonocephalum sericeum, detail of elytron and suture.