Ceratomerinae, Collin, 1928

Bradley J Sinclair, 2003, Taxonomy, Phylogeny and Zoogeography of the Subfamily Ceratomerinae of Australia (Diptera: Empidoidea), Records of the Australian Museum 55, pp. 1-44 : 4-5

Ceratomerinae

Ceratomerinae Collin, 1928: 3 . Type genus Ceratomerus Philippi, 1865 .

This subfamily includes the following genera: Ceratomerus Philippi , Glyphidopeza Sinclair , and Icasma Collin.

Diagnosis. Dichoptic in both sexes, usually lacking ommatrichia. Long projecting antennae generally inserted high on head; first antennal segment (scape) more than twice as long as the second segment (pedicel), bearing long dorsal and ventral setae; pedicel with finger-like condyle or conus on which postpedicel is inserted laterally; postpedicel (first flagellomere) elongate, often strap-like. Proboscis long and projected, longer than length of head; pseudotracheae lacking, except Glyphidopeza ; lacinia freely projected, except fused to labium in Glyphidopeza .

Scutum with restricted rows of bristles, sometimes reduced in number and size. Dorsal mesepimeral pocket present; laterotergite bare.

Wing narrow, lacking anal lobe; Sc complete, or incomplete in Icasma ; R 4+5 branched or unbranched; cell cu p absent, except Glyphidopeza ; 2 veins usually emitted from cell dm, or M 1+2 petiolate, except Glyphidopeza with 3 veins.

Male terminalia arched dorsally; ejaculatory apodeme plate-like, narrowly fused to base of phallus; epandrial lamellae not connected anterodorsally; surstyli usually weakly articulated with epandrium. Female terminalia truncate withdrawn into segment 7; sclerites of segment 8 articulated anterolaterally; anterior margin of tergite 8 with median or pair of flattened plates or none; tergite 10 (acanthophorites) arched dorsally, bearing spines or stout setae; cercus heavily sclerotized, projecting dorsally; spermatheca with single spherical receptacle.

Historical review of the classification of the Ceratomerinae

The genus Ceratomerus was described by Philippi (1865) for a highly modified male species from Chile which has a large protuberance or horn on the mid femur. Melander (1928) tentatively included Ceratomerus in the subfamily Clinocerinae because its slender legs and shortened front coxa are similar to that of the latter. In his revision of New Zealand Empididae, Collin (1928) erected a new subfamily Ceratomerinae for this genus, and has been followed ever since. In this revision, four new species of Ceratomerus and a new monotypic genus Icasma were described. Collin (1933) later described two species of Ceratomerus from southern Chile. In Australia, Hardy (1930) and Paramonov (1961) described four and one new species, respectively. No additional species of this subfamily were described until Plant (1990, 1991) described one and seven new species of Icasma and Ceratomerus , respectively.

Most recently, Sinclair (1997) described five new species of Icasma and two new species of a new genus Glyphidopeza , all endemic to New Zealand. In an ongoing revision of this subfamily, many new species remain to be described from New Zealand and there are at least two undescribed genera from South America ( Sinclair, 1998).

Chvála (1983) assigned the subfamily as the sister group to the Clinocerinae , but provided little evidence for such an arrangement, except for general resemblance of the male terminalia with that of the Clinocerinae . Ceratomerinae was considered the sister group to Hemerodromiinae + ( Brachystomatinae + Clinocerinae ) by Wiegmann et al. (1993), but these relationships are weakly supported as discussed by Sinclair (1995: 671, 719). Presently, the Ceratomerinae is considered most closely related to the Trichopezinae and Brachystomatinae because of unique similarities of the female terminalia and form of the male ejaculatory apodeme ( Sinclair, 1995; Cumming et al., 1995; Cumming & Sinclair, 2000). These three subfamilies comprise a probable new family group within the Empidoidea ( Cumming & Sinclair, 2000).

In contrast to its phylogenetic position within the Empidoidea, the monophyly of the Ceratomerinae has never been questioned. A number of characters are derived in comparison to the Trichopezinae and Brachystomatinae including: a small conus projecting from the second antennal segment into the postpedicel, scape 2–3 times longer than pedicel, inner face of base of scape flattened, males dichoptic, R 1 terminates proximally to mid-length of wing, and dorsal bridge of epandrial lamellae lacking.

Bionomics

The Ceratomerinae of Australia are confined to the area immediately within and along rocky, cascading streams of the eastern ranges. These streams are surrounded by a range of rainforest vegetation types that have been classified into numerous floral systems, comprehensively appraised by Adam (1992). Rainforest is discontinuously distributed in eastern Australia, and represent remnants of a widespread wet vegetation that predominated in the Late Paleocene and Early Eocene ( White, 1994; Bickel, 1994). Since this time, the progressive drying phases which accelerated during the Miocene have fragmented the rainforest into disjunct refugia. However, many of these pockets of rainforest are not completely isolated, but are connected through “gallery” or gully forests—a mixture of sclerophyll-rainforest vegetation along streams ( Adam, 1992; Bickel, 1994). These strips of rainforest along watercourses may extend well beyond lower rainfall regions and provide continuity and pathways among major stands. This is especially true around Sydney, which is surrounded by dry sclerophyll and heathlands, with narrow strips or patches of rainforests with closed overhead canopies growing along streams flowing through narrow valleys. It is in these habitats that a number of fairly widespread species of Ceratomerinae were collected, especially in the coastal lowlands around Sydney (e.g., Bola, Couranga and Waterfall Creeks).

The Australian species of Ceratomerinae are both steno- and eurythermic, some being found in a variety of stream temperatures. For example, C. victoriae n.sp. is known only from heavily shaded, cool streams cascading through temperate rainforests usually dominated by Nothofagus . In Victoria, these habitats are now confined to small patches, predominantly in deep ravines and consequently the populations of C. victoriae n.sp. are rather isolated ( Fig. 28). In contrast, C. orientalis n.sp. is tolerant of a wide range of stream temperatures. This tolerance has facilitated its widespread distribution, and it is the most commonly collected species of Ceratomerinae in Australia.

Most Australian species are found primarily in streams, running about on emergent rocks (especially C. ordinatus group) with their antennae outstretched. Only one species, C. albistylus is most commonly collected more distantly from streams. A large number of specimens of C. victoriae n.sp. were collected by sweeping fronds of tree ferns that were overhanging streams.

Although several distinct larval empidoid types have been identified from stream and river surveys, the larval and pupal stages of Ceratomerinae remain unknown. In addition, the mating habits have not been observed.Attempts were made to identify the immature stages by collecting live females and inducing oviposition by decapitation (see Cumming & Cooper, 1993), but these attempts failed. Since adults of most species of Australian Ceratomerus are present nearly year round, prediction of the emergence period(s) is difficult. In collections examined, some female specimens collected in October and November appeared to have swollen abdomens indicating a gravid condition. This is possibly the most appropriate period for attempts at either collection of immature stages of this subfamily or decapitation of gravid females.

Adults are believed to be predacious (except probably the C. virgatus group from New Zealand). Adults of C. ordinatus Hardy were observed feeding on conspecific flies that were squashed on emergent rocks. Numerous adults of this species were observed running about on emergent rocks in the Franklin River (Tasmania). They easily and quickly found the squashed corpses and extended their long proboscises obliquely while feeding. The morphology of the labrum (i.e., presence of apical epipharyngeal blades) supports predacious habits. Chvála (1983: 78) hypothesized that adults of Ceratomerinae were flower visitors on the basis of their long Empis -like proboscis, but only specimens of the C. virgatus group from New Zealand have been collected on flowers.