Platystomatidae

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 : 154-157

The Platystomatidae and Tephritidae

Antennal structure in the Platystomatidae reflects some of the general diversity occurring in the family. I therefore divide the selection of taxa examined for antennal morphology into four categories for descriptive purposes. These categories (types A to D) are not necessarily sharply defined, nor do they consistently follow a natural classification.

Type A ( Figs 139–143 ). Examples studied: Achias kurandanus Hennig , Duomyia spp. , Euprosopia vitrea McAlpine , E. armipes McAlpine , Lamprogaster stenoparia Hendel , Lenophila achilles McAlpine & Kim , Loxonevra sp. (western Sumatra), Plagiostenopterina sp. (near enderleini Hendel), Platystoma gemmationis (Rondani) . This is the most frequent type in the family, particularly in the subfamily Platystomatinae , and is perhaps the groundplan condition for the Platystomatidae , the other types being derived from it. It resembles the condition commonly found in the Tephritidae .

Segment 2 has a long dorsal cleft extending near its base ( Figs 139 , 152 , pc). The distal articular surface immediately within the rim is flattened to slightly concave, but centrally it abruptly gives way to a capacious cup ( Fig. 140 ). The collar separating the distal articular surface from the cup (as seen in the Chloropidae ) is here at most slightly developed and dorsally interrupted. In some species of Duomyia it is almost obsolete, so that the surface of the cup is not so sharply differentiated from that of the surrounding articular surface. The short conus is often almost bilaterally symmetrical and almost symmetrically placed on the segment, but is tilted so that the annular ridge and distal foram face somewhat dorsally. Thus there is often a slight ventral chin and the dorsal extremity of the annular ridge is scarcely raised above the floor of the cup. Because of its small size, the conus does not nearly fill the cavity of the cup. The annular ridge and foraminal ring are vertically elongate, the latter usually with a dorsal and a ventral cusp. The button is located near the dorsolateral part of the annular ridge, virtually on the floor of the cup. Segment 3 is most often elongate, with both sacculus and arista located not far from its base. The basal hollow is generally present but small and there may be slight development of the basal stem. The basal foramen is asymmetrically placed at or near the margin of the hollow. The arista is commonly three-segmented, but in numerous species of Euprosopia and some of other genera segments 5 and 6 are fused.

Type B ( Figs 144–147 ). Examples studied: Cleitamia astrolabei (Macquart) , Peltacanthina sp. (Karen, Kenya), Scholastes cinctus (Guérin-Méneville) . The morphology of this group may not be well understood but a more detailed study should be completed by future students.

The most distinctive apparent feature is the deep, narrow cup of segment 2, which is almost plugged by the stout, apparently subcylindrical conus with distal foramen of greater area than usual. However, in all disarticulated specimens the conus has snapped or crumbled so that the features of its distal surface cannot be accurately ascertained. The tendency of the conus to break up may indicate that its distal part is flexible and incompletely sclerotized, as in the pyrgotid genus Adapsilia . Segment 3 appears not to have a typical hollow or sub-basal stem, but there is a narrow caecum next to the basal foramen, at least in Peltacanthina sp. ( Fig. 144 ), and the cuticle of the convex basal zone of the segment is covered with a dense set of fine encircling ridges.

Mezona sp. (Sokoke Forest, Kenya, in AM) appears to have several sacculi on segment 3, but available material is too limited for detailed study. This genus is perhaps closely related to Peltacanthina .

Type C ( Figs 148–150 ). Examples studied: Microepicausta “sp. 1” (New South Wales, in AM), Rhytidortalis averni McAlpine .

These taxa resemble those listed under type A, but the cup is absent or incompletely differentiated from the surrounding articular surface of segment 2. The condition of the base of the conus is therefore not very different from that of such lower tephritoid families as Piophilidae and Ulidiidae , though the resemblance is probably secondary.

Type D ( Figs 151–155 ). Examples studied: Atopognathus complens (Walker) , Mesanopin biplexum Whittington , Xiria sp. (West Malaysia, in AM).

The cup is deep and capacious but not very sharply demarcated at its periphery. The conus is much reduced or shortened, but in Mesanopin it retains a degree of ventral prominence. In Atopognathus and Xiria the annular ridge is only slightly raised above the floor of the cup. In all three genera the basal hollow of segment 3 is absent and the basal stem is well developed, with the foramen near its extremity. Mesanopin is unusual in having the sacculus located beyond mid-length of segment 3. Atopognathus differs from the other two examples in having segments 5 and 6 fused (arista twosegmented as in some Euprosopia spp. ).

Examples of the family Tephritidae examined for this study include the following: Bactrocera tryoni (Froggatt) , Euphranta marina Permkam & Hancock , Spathulina acroleuca (Schiner) (see Figs 156–158 ). It is a family of great taxonomic diversity and these taxa are unlikely to show the full range of variation.

Segment 2 shows the main features described above for platystomatid type A. The conus is short in Euphranta and Spathulina , longer and more ventrally prominent in Bactrocera . Segment 3 has a small basal hollow, broader and shallower in Euphranta than in the other two genera. There is a short subacute basal stem, with the foramen on its ventral surface. The arista is three-segmented, with segment 4 very short.

Figures

Figures 139–144.Antennae of Platystomatidae. (139) Duomyia curta McAlpine, left seg. 2, distodorsal view, seg. 3 removed. (140) Lamprogaster stenoparia Hendel, left seg. 2, lateral view, seg. 3 removed. (141) The same, parts contained in cup of seg. 2. (142) Loxonevra sp. (West Sumatra), part of left seg. 3, medial view. (143) Euprosopia armipes McAlpine, the same. (144) Peltacanthina sp. (Karen, Kenya), left seg. 3, medial view. bf, basal foramen of seg. 3; bh, basal hollow; bs, incipient basal stem; bu, pedicellar button; c, conus; cu, pedicellar cup; da, distal articular surface of seg. 2; fc, foraminal cusp; pc, pedicellar cleft; sc, sacculus.

Figures 151–155. Antennae of Platystomatidae. (151) Atopognathus complens (Walker), left seg. 2, distal view, seg. 3 removed. (152) The same, dorsal view of left seg. 2. (153) Mesanopin biplexum Whittington, pedicellar cup and contents. (154) A. complens, part of left seg. 3, medial view. (155) M. biplexum, the same parts. bf, basal foramen of seg. 3; bs, basal stem of seg. 3; bu, pedicellar button; c, conus; fc, foraminal cusps; pc, pedicellar cleft.

Figures 145–150. Antennae of Platystomatidae. (145) Peltacanthina sp. (Karen, Kenya), left seg. 2, distal view, seg. 3 removed. (146) Cleitamia astrolabei (Macquart), the same.(147) Scholastes cinctus (Guérin-Méneville), the same.(148) Microepicausta “sp. 1” (inAM), the same. (149) Rhytidortalis averni McAlpine, the same. (150) The same sp., part of left seg. 3, medial view. bu, pedicellar button; c, conus; fc, foraminal cusp.

Figures 156–158.Antennae of Tephritidae. (156) Euphranta marina Permkam & Hancock, left seg. 2, distal view, seg. 3 removed. (157) Spathulina acroleuca (Schiner), the same parts.(158) E. marina, left seg. 3, medial view. ar, annular ridge; bu, pedicellar button; c, conus; cu, pedicellar cup; fc, foraminal cusp.