Metriorrhynchus Gemminger & Harold, 1869

Bocak, Ladislav, 2007, A Revision Of Metriorrhynchus (Coleoptera: Lycidae) From The Greater Sunda Islands And Continental Asia, Raffles Bulletin of Zoology 55 (2), pp. 253-260 : 253-254

Metriorrhynchus Gemminger & Harold, 1869

Type species. – Lycus parallelus Guérin-Méneville, 1835 .

Differential diagnosis. – Most species of Metriorrhynchinae share a characteristic pattern of pronotal carinae, which form a median lanceolate areole, four areolae at the frontal margin and two posterior to them. Metriorrhynchus differ from other Oriental genera with seven pronotal areolae in the short and stout rostrum, serrate antennae in both sexes, the characteristic shape of the internal sac in the male genitalia and the shape of the ovipositor (Figs. 1–11). Bocak (2002) revised the Metriorrhynchinae where a key to genera was given.

Redescription. – Body small- to medium-sized, parallelsided. All species brightly coloured at least in humeral part of elytra. Head small, partly-hidden by pronotum, with short, stout rostrum. Labrum about as long as wide, simply-rounded frontally. Mandibles small, slightly curved, without any teeth. Maxillary palpi 4-segmented, labial palpi 3-segmented, apical palpomeres parallel-sided in both palpi. Pronotum wider than long, with seven distinct areolae. Elytra parallel-sided, 3.6–4.9 times longer than their combined width at humeri. Each elytron with four primary costae and five secondary longitudinal costae, which differ slightly in strength. Transverse costae dense, elytral areolae strongly transverse. Ventral part of body regularly with blue metallic shine. Male genitalia with sclerotized phallobasal membrane, strong straight phallus, which is widened in middle part and with sclerotized, spiral internal sac (Figs. 1–8, 10). Ovipositor small, slightly sclerotized and firmly attached to terminal abdominal sclerites. Vagina membranous in Oriental species (Figs. 9, 11).

Distribution. – Metriorrhynchus is a genus of Australian origin ( Bocak, 2002; Bocak et al., 2006) and reaches its northwestern limit of distribution in the eastern part of the Oriental region. The northernmost records are available from northern Vietnam, northern Laos and northern Thailand; the range reaches to eastern India in the northwest. Although several old specimens were found with the locality “ India ” in the collection of the Natural History Museum in London, all precisely given records are from Manipur, Nagaland (Patkai Mountains) or Bangladesh (Sylhet). No records are available from areas west of these localities. Bocak et al. (2006) showed the close relationship of the Oriental and Sulawesi Metriorrhynchus faunae and hypothesized that speciation occurred after dispersal across the Wallace line. There is no modern revision of Metriorrhynchus in the Australian Region, so we can only estimate from the material in collections that more than two hundred species occur in New Guinea and Australia. The Oriental fauna is much poorer with five species in the Greater Sunda Islands and continental Asia and 12 species in the Philippines.

Ecology. – Larvae live under bark and in rotten wood with an estimated length of development of two to four years. Unlike most Oriental lycids they are able to colonize large dead tree trunks in sunny places, which can become considerably desiccated in the dry season. This fact supports the hypothesis of invasion from the Australian region, which is characterized by strong seasonality of precipitation. The larval morphology of several Metriorrhynchus species was described by Bocak & Matsuda (2003). Adults are free-living and commonly rest on leaves or visit flowers. They can even be collected on carrot flowers ( Daucus spp. L.) in recently established fields, where few other species of Metriorrhynchinae occur. All Metriorrhynchus species resemble in colour pattern and body shape sympatrically occurring species from other lycid genera as well as various beetles from other families and even other insect orders. Lycidae have distasteful and foul smelling compounds in their bodies (Moore & Brown, 1981) and their similarity to unrelated insects is ascribed to the evolution of Muellerian mimicry. Details about mimicry patterns are discussed further under individual species treatments.