Temnorhynchus retusus

Pest

Common name(s)

plate-faced beetle

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Temnorhynchus Species: Temnorhynchus retusus (Fabricius, 1781)

Adult diagnosis

Total body length 16.0–20.0 mm (0.63–0.79 in). Body wide, oval-shaped. Color black. Head lacking horns or tubercles; with distinctive cranial "face" plate; cranial plate notched medially, more deeply notched in males than females. Pronotum with anteromedial concavity in male; female pronotum lacking concavity; pronotum lacking horns or tubercles. Elytra weakly striated.

Larval diagnosis

Undescribed. For Dynastinae (Ritcher, 1966): Grub C-shaped, not hump-backed, cylindrical, whitish. Maxilla with galea and lacinia fused or nearly so. Lacinia of maxilla with 3 well developed unci. Maxillary stridulatory teeth truncate. Legs 4-segmented. Anal opening transverse, straight or slightly curved. Plegmatia absent.

Native range

Africa. This species is best known from southern Africa, where it has been recorded in South Africa, Namibia, and Lesotho. Isolated records also exist from Sudan, Eritrea, and Tanzania (Krell, 1993).

Plant host(s)

Adults and larvae of Temnorhynchus retusus are associated with grasses (Krell and Hangay, 1998). In Hawaii, adults have been found on the saline-tolerant turf species, seashore paspalum (Paspalum vaginatum) (Jameson et al., 2009). In South Africa, this species has been recorded damaging potatoes (Visser and Stals, 2012).

Life history

Poorly known. In Australia, adults of Temnorhynchus retusus are most abundant in September (Jameson et al., 2009) and are often found in or near watered, grassy areas in suburban and urban settings (Krell and Hangay, 1998). Both larvae and adults of this species appear to feed upon grasses (Krell and Hangay, 1998). It is likely that this species, like other Dynastinae, lays eggs in soil where larvae then feed on plant roots (Visser and Stals, 2012).

Pest potential

Minor. Though this species is closely associated with grasses (Krell and Hangay, 1998), it is not a significant grass pest in either horticultural or agricultural systems. The only record of this species causing appreciable damage comes from South Africa, where it has been associated with damage to potato tubers (Visser and Stals, 2012). This species does have a history of establishment beyond its native range, having spread to Australia in the 1980's (Krell and Hangay, 1998).

Status in Hawaii

Possibly established. In Hawaii, this species is known only from Big Island where it was found at Mauna Lani in Waikoloa in 2007 (Jameson et al., 2009).

Status in Guam

Not established or recorded. There are no records of this species from Guam.

Potential distribution and dispersal pathway

Adults of this species rarely come to lights (Krell and Hangay, 1998). It is likely that transportation occurs in the egg or larval stage, with immatures being moved with pallets of soil, in commercial turf, or around the roots of potted plants (Jameson et al., 2009).

Similar species

This scarab is superficially similar to the Tomarus species and the taro beetles (Papuana spp.) in color and size. However, the presence of the cranial plate is unique to Temnorhynchus retusus and easily separates it from all other scarabs recorded from Hawaii or Guam.

Other names (synonyms)

Scarabaeus retusus Fabricius

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Temnorhynchus retusus male; photo by M.L. Jameson

Temnorhynchus retusus male; photo by M.L. Jameson

Temnorhynchus retusus male head, frontal view; photo by M.L. Jameson

Temnorhynchus retusus male head, frontal view; photo by M.L. Jameson

Temnorhynchus retusus male genitalia, caudal view; photo by M.L. Jameson

Temnorhynchus retusus male genitalia, caudal view; photo by M.L. Jameson

distribution map for Temnorhynchus retusus

distribution map for Temnorhynchus retusus