Wakarumbia Bocak 1999

Wakarumbia Bocak, 1999: 166

Type species: Wakarumbia gracilis Bocak, 1999: 167 (by original designation).

Relationships and differential diagnosis. Wakarumbia is classified in the metriorrhynchine subtribe Hemiconderina which can be easily distinguished by the characteristic, slender, straight carinae forming only five areoles on the pronotal disc, the head without rostrum and the primary costae 1 and 3 weaker apically (Bocak 2002, Bocak & Bocakova, 2008). Additionally, all genera placed in Hemiconderina share a slender, delicate appearance, the parallel-sided elytra, very slender legs, slender and relatively long maxillary palpi, slightly securiform apical maxillary palpomere, minute labial palpi and absence of tibial spurs. Wakarumbia is the only genus of Hemiconderina, that lacks the longitudinal secondary costae in elytra. The apical part of the phallus is often characteristically rotated and there is one complex spine at base of the phallus in most species (Figs 1–4, 7–20). Only W. hanae sp. nov. has two separate spines (Figs 5–6).

Redescription. Soft-bodied beetles, body small, delicate, slightly dorsoventrally compressed, mostly dark brown to black, seldom brightly yellow, very slender in general appearance, with slender legs and antennae. Head small, hypognathous, without rostrum, mouthparts tiny, maxillary palpi slender, 4-segmented, labial palpi 3-segmented, apical palpomeres of both palpi securiform, with irregular apical tubercles. Antennae compressed, moderately long, reaching behind middle of elytral length, slightly serrate to parallel-sided, gradually narrowed to apex. Pronotum flat, frontal margin slightly projected forward, anterior angles obtuse, lateral margins often parallel-sided in frontal half, widened posteriorly, posterior angles acute, projecting. Pronotal disc with five areoles, pronotal carinae straight and slender, median areola rhomboidal. Elytra almost parallel-sided, flat, flexible, weakly sclerotized, with four longitudinal primary costae, secondary costae absent, only seldom vestiges present at bases of elytra, primary costae 1 and 3 weak. Transverse costae well developed, mostly regular, elytral cells mostly square-shaped. Legs slender, with five tarsomeres, claws simple. Phallus slender, either symmetrical or apical part rotated in various degrees, internal sac with one, complex basal spine in most species (Figs 3–4), only W. hanae with two separate simple spines (Figs 5–6).

Distribution. Australian Region: Sulawesi, Buton Island. Altogether 31 species are classified in Wakarumbia. Wakarumbia, similarly with several other net-winged beetle genera, is endemic to Sulawesi and does not occur in Borneo. The Makassar Strait was never subaerial (Voris 2001) and represents the effective barrier for many net-winged beetles. Only a few genera with high number of species in the Australian region, e.g. Metriorrhynchus, Microtrichalus Pic, 1921 and Diatrichalus Kleine, 1926, occur in the Great Sundas. The Sulawesi is supposed to serve as a stepping stone during their dispersal to Asia (Bocak & Yagi, in press).

Remark. There are three distantly related genera of Metriorrhynchini in Sulawesi, Sulabanus, Wakarumbia and some Broxylus, which are similar in the body size and shape and share also similar color patterns in the syntopically occurring species. Similar body shape, size and coloration was found also in Plateros (Lycinae: Platerodini). We compared the structure of genitalia of externally similar species and we found that the similar genitalia are often present in species exhibiting different color patterns. As net-winged beetles are protected by some bitter and smelling substances (Brown & Moore 1981, Eisner et al. 2008), the evolution of mimicry is a possible explanation of the observed distribution of the color patterns in Wakarumbia.