Dryocoetiops Schedl, 1957: 13

Beaver, Roger A., Smith, Sarah M. & Sanguansub, Sunisa, 2019, A review of the genus Dryocoetiops Schedl, with new species, new synonymy and a key to species (Coleoptera: Curculionidae: Scolytinae), Zootaxa 4712 (2), pp. 236-250 : 237-239

Genus Dryocoetiops Schedl, 1957: 13

Type species: Ozopemon laevis Strohmeyer 1911: 22

Diagnosis. The genus Dryocoetiops Schedl belongs in the tribe Dryocoetini ( Wood 1986; Alonso-Zarazaga & Lyal 2009). Generic boundaries in the tribe are not always clear ( Wood 1986), and Dryocoetiops is no exception. Many members of the tribe appear to have undergone mosaic evolution, and genera can be distinguished only by combinations of characters. Dryocoetiops is distinguished morphologically from other genera included in the tribe by the following combination of characters: 1) antennal funicle four-segmented (excluding the pedicel), club flattened or weakly obliquely truncate, sutures strongly displaced apically on posterior face, anterior face with basal segment confined to basal fifth or quarter, its apical margin convex to straight; and 2) eye emarginate, in a few species rather large, coarsely facetted and extending onto the frons; and 3) female frons without a brush of setae, sparsely setose, not aciculate; and 4) pronotum about as long as wide or wider than long, strongly declivous anteriorly, usually with rather coarse, rasp-like asperities, unequal in size and larger antero-laterally, the summit obtuse, humped, at or a little behind the middle, a weak to distinct transverse impression behind it, disc flat in lateral view, usually granulate-punctate; and 5) elytra with distinct striae and interstriae; and 6) elytral declivity steep, convex, interstriae granulate except in one species; and 7) protibiae with four socketed teeth (rarely five) in apical half, without further smaller teeth on external margin more basally.

Description. Female. Antenna with 4-segmented funicle (excluding the pedicel), club flattened or weakly obliquely truncate, without septum, sutures strongly displaced apically on posterior face, basal segment not extending beyond basal quarter on anterior face, its apical margin convex, sinuate or approximately straight. Eyes distinctly but not deeply emarginate anteriorly, either of normal size, finely faceted, or in a few species enlarged, more coarsely faceted, and extending onto frons. Frons punctate or granulate-punctate, usually with a median raised line, sometimes with a median tubercle. Pronotum strongly declivous anteriorly, rising to an obtuse hump-like elevation, approximately in the middle, with a weak to distinct transverse impression behind it. Anterior slope of pronotum with rasp-like asperities, often extending to anterior margin, usually increasing in size antero-laterally, the disc flat in lateral view, granulate-punctate. Elytra convex, striae and interstriae distinct, strial punctures with short, fine, recumbent setae, interstrial punctures with stouter, longer, erect setae, occasionally flattened on declivity. Elytral declivity steep, convex, striae 1, and less often striae 2–3 impressed, interstriae usually granulate, 1–3 raised and costate in two species. Procoxae usually narrowly separated, and prosternal process pointed, but contiguous and prosternal process blunt in a few species. Protibiae with four socketed teeth (rarely five), meso- and metatibiae usually with six teeth. Body length 1.9–4.0 mm.

Male. Unknown. Presumed to be dwarfed and flightless as in Coccotrypes Eichhoff, 1878a .

Distribution. The genus is primarily palaeotropical in its distribution from India through South-East Asia and Indonesia to New Guinea and northern Australia. Two species ( D. apatoides , D. moestus ) occur as far north as Japan.

Relationships. Early phylogenetic studies ( Jordal et al. 2000, 2002) suggested that Dryocoetiops should be included within the genus Coccotrypes . The studies were based on D. coffeae and D. cf. eugeniae [sic]. Both D. coffeae and D. eugeniae are now considered to be synonyms of D. moestus (see below). Later phylogenetic studies ( Jordal & Cognato 2012; Gohli et al. 2017) suggest that Dryocoetiops should rather be considered as a sister genus to Coccotrypes . It appears to have the same haplo-diploid breeding system as Coccotrypes ( Jordal et al. 2002) , but is morphologically distinct. Species of Dryocoetiops can be distinguished from Coccotrypes most easily by characters of the pronotum. In Dryocoetiops , 1) pronotum dome-shaped with a distinct summit near the middle, as wide as or wider than long, steeply sloping anteriorly, asperities often increasing in size antero-laterally, anterior margin broadly rounded, without a distinct row of asperities on the margin, slightly to distinctly impressed behind summit, disc flat in lateral view; and 2) frons without aciculation. In Coccotrypes , the pronotum is usually longer than wide, and if there is a distinct summit, it is often behind the middle. The anterior slope is less steep, and the asperities usually smaller, and not increasing in size antero-laterally. In some species, there is a row of larger asperities on the anterior margin only. The species of Dryocoetiops are myelophagous (Kirkendall et al. 2015) breeding in the pith of small branches and twigs; those of Coccotrypes breed in a variety of habitats, including fruits and seeds, phloem, leafstalks, and mangrove propagules ( Browne 1961; Jordal et al. 2002), but almost never in the pith of twigs.

Besides Coccotrypes , the genus is most similar morphologically to Taphrorychus ( Schedl 1957) , although it is not very closely related ( Jordal & Cognato 2012; Gohli et al. 2017), and has a very different biology and breeding system (see below). However, the two genera have been confused in the past, and some species now placed in Dryocoetiops have previously been placed in Taphrorychus (see below). Hence, we provide distinguishing characters here. Dryocoetiops can be most easily distinguished morphologically as follows: 1) basal segment of labial palp enlarged, barrel-shaped; 2) frons without a brush of setae; and 3) pronotum with distinct summit and steep anterior slope; and 4) pronotal asperities coarse, increasing in size antero-laterally; and 5) elytra with distinct striae and interstriae; and 6) without a circular impression on the elytral declivity; and 7) protibiae without additional small denticles. In Taphrorychus , the basal segment of the labial palp is of normal size. The other characters can vary depending on the species and the sex of the individual, but the combination of all of them is never present.

Biology. The biology of Dryocoetiops has been investigated only in D. moestus ( Browne 1961; Kalshoven 1958, both as Dryocoetes coffeae ), but is probably similar in other species. The species are inbreeding, polyphagous twig-borers. Only the female disperses and constructs the nest. A longitudinal tunnel is constructed in the centre of the twig, usually extending both upwards and downwards from the entrance. Browne (1961) notes that the eggs are laid in clusters and are very variable in size. The larvae feed on the tissues surrounding the gallery, and eventually pupate in single file ( Browne 1961). Browne (1961) also states that the species is monogamous with both parents playing a part in the care of the nest and the young brood. However, this part of his account of the biology is mistaken. As noted above, all known adults are female, and the male remains unknown. It is likely that Browne observed two females occupying the same gallery system. Dissections of females of D. moestus caught in ethanol traps show that the spermathecae contain sperm, indicating that the species is not parthenogenetic.

By contrast, the morphologically similar species of Taphrorychus are outbreeding bark beetles, making gallery systems below the bark of angiosperm trees, particularly of the family Fagaceae . Both male and female are of the same size, and the sex ratio at emergence is approximately 1: 1. Both sexes are capable of flight, disperse, and are involved in gallery construction. The males are harem polygynous (Kirkendall et al. 2015), with more than one female associated with each male in most gallery systems.