Prorates

Metz, Mark A., Winterton, Shaun L. & Irwin, Michael E., 2002, Notes on the functional morphology of terminalia from Prorates ballmeri Nagatomi and Liu (Diptera: Scenopinidae: Proratinae) collected while in copula, with a description of the previously unknown female, Zootaxa 76 (1), pp. 1-12 : 3-4

Taxonomy of Prorates

Melander (1906) originally described Prorates claripennis as an empidid, but he later transferred this species to Bombyliidae : Heterotropinae ( Melander 1928) . The placement of this and subsequently described species of Prorates remained problematic with various authors ( Efflatoun 1945, Melander 1950, Hull 1973) suggesting a possible closer affinity with species of scenopinids. Using a quantitative cladistic analysis based on morphology, Yeates (1992) hypothesized a monophyletic group including Prorates frommeri Hall , Alloxytropus anomala Bezzi , and Caenotoides californica Hall relative to other scenopinid taxa. He erected a separate subfamily within Scenopinidae, Proratinae , containing the species in these genera and supported a sister group relationship between Prorates and Alloxytropus . Alloxytropus was previously considered a synonym of Prorates by Melander (1928, 1950), Hall (1972), and Hull (1973).

The sister­group relationship of Prorates and Alloxytropus was supported by two synapomorphic character states: 1) the inner margin of the male eyes indented at the level of the antennal bases and, 2) the modified setae of tergite 2 composed of large, truncate setae with flattened or slightly rounded apices creating a triangular area at the posterior margin ( Yeates 1992). Yeates (1992) also reported, however, that Alloxytropus possesses only a single antennal flagellomere, an apparent symplesiomorphy with the other scenopinids, while Prorates and Caenotoides possess two antennal flagellomeres. Nagatomi et al. (1994) deferred from making a single hypothesis of the relationships of the proratine genera, but acknowledged that Prorates and Alloxytropus were “closely related” and reported that Prorates could be distinguished from Alloxytropus by “having the cord­like phallus (just behind [the] hanging­bell phallus) forked anteriorly.” Nagatomi et al. (1994) also erected a new proratine genus, Jackhallia Nagatomi and Liu , determined to be “closely related to Prorates and Alloxytropus ” from a single female specimen from Santa Cruz, Argentina. They distinguished this genus based on the veins M1 and M2 arising independently from cell d instead of M2 arising from M1. Examination of this character among several specimens of Prorates suggests it is quite variable within a species. The validity of the species and their placement in these genera will require future phylogenetic investigation.

Prorates is represented by eight described species from the southwestern portion of the United States: arctos Hall, 1972 , ballmeri Nagatomi and Liu, 1994 , boydi Hall, 1972 , claripennis Melander, 1906 , frommeri Hall, 1972 , melanderi Hall, 1972 , nigrescens Hall, 1972 , and painteri Nagatomi and Liu, 1994 . A revision of the species of Prorates and their placement among the other proratine genera is the subject of ongoing study by coauthor Irwin.

The gonocoxal dorsal process ( Fig. 2 , GDP) ( Nagatomi et al. 1994) and the amount of its posterior extension is herein considered an artifact and not a firm character among species. This is part of a sclerotized connection between tergite 9 and the gonocoxite, and the length of its projection varies depending on how it was dissected. Other characters among the species are diagnostic but are not included in the keys. The issue of species diagnosis will be addressed in the upcoming revision of the genus.

Figures

FIGURES 1 ­ 5. Male genitalia and tergite 2. 1, Lateral view of the male aedeagal apparatus showing only the left distiphallus tip, dorsal bridge and gonocoxal apodeme removed; 2, Dorsal view of gonocoxite and aedeagal apparatus; 3, Ventral view of gonocoxite; 4, Dorsal view of tergite 9, cerci, and hypoproct; 5, Dorsal view of tergite 2 with patch of modified setae. Cordlike phallus and dorsal bridge shown in gray to help clarify structures. Measure bar a is for all genitalia, measure bar b is for tergite 2 only. bp, basiphallus; cp, cordlike phallus; db, dorsal bridge; dp, distiphallus; eap, ejaculatory apodeme; ga, gonocoxal apodeme; gdp, gonocoxal dorsal process; gs, gonostylus; hp, hanging bell phallus.