Phoridae

McAlpine, David, 2011, Observations on Antennal Morphology in Diptera, with Particular Reference to the Articular Surfaces between Segments 2 and 3 in the Cyclorrhapha, Records of the Australian Museum 63 (2), pp. 113-166 : 127-128

The Phoridae (including Sciadoceridae )

It has been clear for some time that the Phoridae and Sciadoceridae are very closely related to each other. Disney (2001) combined the two families, and Brown (2007) demonstrated the difficulty of supporting a monophyletic group Sciadoceridae (or Sciadocerinae ) when the numerous fossil taxa are considered. Study of phorid antennal structure has been limited because of the difficulty in separating segments 2 and 3 to expose the conus without fragmentation.

Segment 2 of Sciadocera rufomaculata White ( Figs 31, 32 ) is very largely concealed in the intact antenna. This is because the main body of the segment is reduced to a narrowly or scarcely visible flange representing the rim, and the large conus is deeply embedded within the basal hollow of segment 3. After removal of segment 3, the conus is seen to be relatively slender basally, with a large, rounded distal club bearing the foramen of articulation on the centre of its apical surface ( Fig. 31 ). The foramen is surrounded by an annular ridge bearing ridge-like denticles. The button is situated dorsolaterally on the distal surface of the conus ( Fig. 32 ). Much of the surface of the conus is covered with tile-like microtrichose ridges as described for Lindneromyia sp. above (family Platypezidae ). In contrast to that of most cyclorrhaphans, the region of the rim lacks obvious setulae.

In the Phoridae s.str. (or Euphorida of Brown, 2007) segment 2 shows the essential features described above for Sciadocera (see also Disney, 1988; 1994). This is the reason why many phorids appear to have only two prearistal segments in the antenna. In specimens of several genera I find the conus to have similar surface sculpture and annular ridge and a similarly situated button to that of Sciadocera . The rim may bear a few moderately small, socket-based setulae.

Segment 3 of Sciadocera has a deep basal hollow enclosing the conus and bears a subterminal three-segmented arista ( Hennig, 1976: fig. 62; Disney, 2001: fig. 7). It lacks macrotrichia and typical sacculi, but the general surface has diverse microtrichia and sensilla, and the dorsobasal external surface bears numerous (more than 25) saucer-shaped pits packed with trichoid sensilla (author’s observations). These pits bear some resemblance to the sensory pits of Cryptochetum (family Cryptochetidae , see Figs 69 , 70 ), but in that genus they coexist with a typical schizophoran sacculus. Both Sciadocera and Diplonevra sp. (examined by me) have neither sacculi (as described above and under Ironomyiidae ) nor the subcuticular pit sensilla (SPS) described by Disney (2003) and Pfeil et al. (1994) for certain phorids. Sukontason et al. (2005) and Chen & Fadamiro (2008) described the surface sensilla on segment 3 of certain phorids, demonstrating some diversity in these.

The arista of various phorids is not consistently terminal and consists of one to three segments, or it may be absent (Peterson, 1987; Disney, 1994).

A general condition for the Phoridae , sometimes noted by specialists, is the presence of barbed (“feathered”, or “fringed”) larger macrotrichia on many parts of the insect (see Peterson, 1987: fig. 99). The barbed condition is confirmed by our SEM work on such phylogenetically diverse phorids as Diplonevra nigrita (Malloch) and Sciadocera rufomaculata , and is therefore probably in the groundplan of the family. Detailed SEM examination of representatives of each of the other families of lower (noneumuscomorphan) Cyclorrhapha ( Opetiidae , Platypezidae , Lonchopteridae , Ironomyiidae , also Apystomyiidae ) suggests the absence of barbs on all macrotrichia for these families. Extensive experience also suggests that barbed macrotrichia may be absent from the numerous other cyclorrhaphous families, but a thorough search has not been made. The barbed condition is therefore likely to be, to a large extent, diagnostic for the Phoridae , though reduced or perhaps lost in some highly derived phorid taxa.

Figures

Figures 31, 32. Sciadocera rufomaculata White (fam. Phoridae). (31) Left antenna, seg. 2 after removal of seg. 3, lateral view. (32) Part of distal surface of conus, showing button. ar, annular ridge; bu, pedicellar button.

Figures 68–69. Antenna of Cryptochetum sp. (fam. Cryptochetidae). (68) Left seg. 2, dorsolateral view, conus broken. (69) Sensilla in sensory pit of seg. 3; scale = 2 µm.

Figures 70–72.Antennae of Cryptochetidae.(70) Cryptochetum sp., seg. 3 of left antenna, medial view.(71) Librella sp., left seg.2, lateral view. (72) The same, left seg. 3, medial view. bf, basal foramen; bh, basal hollow; pi, sensory pits; sc, sacculus.