Usia turaco, 2011

Gibbs, David, 2011, 2960, Zootaxa 2960, pp. 1-77 : 22-24

20. turaco Gibbs sp. nov.

Diagnosis. Small, intensely black species differing from all other Usiini by the combination of entirely black vestiture and mid-tibia apicoventrally lacking stiff, suberect spines. All are shining black species with no more than a hint of aeneous or bluish iridescence. Discs of mesonotum and tergites never with the black cuticle entirely obscured by dust, any dusting present thin and whitish grey with ground colour clearly evident.

The male genitalia are generally large relative to the size of the insect, often larger than the remainder of the abdomen. The form of the epandrium, gonocoxite and epiphallus is very variable with no characters that seem to be of use for subgeneric diagnosis. However, gonostyli relatively simple, never bifurcate, differentiating them from U. versicolor .

Female genitalia less diverse than male genitalia but still with numerous forms. Furca usually fairly simple V- or U-shaped more or less sclerotised. Vaginal plate usually membranous and transparent, pigmented in very few species. The apical sternite is much more variable in Micrusia than in much of the rest of the Usiini , providing useful specific characters.

Excluded species. The following species were included in the subgenus Micrusia by Evenhuis & Greathead (1999) but have been found to be affiliated to Usia sensu stricto, Parageron or are sufficiently distinct to require a species-group of their own. The first three of these species will be dealt with in the second part ( Usia sensu stricto) and third part ( Parageron ) of this revision.

Usia aurata Fabricius, 1794

Usia loewi Becker, 1906

Usia sicula Egger, 1859

Usia versicolor Fabricius, 1787 given its own species group in this part.

Historical overview of Micrusia Evenhuis, 1990 . This subgenus was erected by Evenhuis (1990) based on the non-scrobiculate integument, the non-clavate apex of the third antennal segment and the usually very large genitalia of the males; Usia forcipata Brullé being designated the type species. Evenhuis (1990) cited seven species as belonging in Micrusia , one extra being added and one of the original synonymised in Evenhuis & Greathead (1999). However, examination of the full range of known species of Usia and Parageron demands a rather different interpretation. Of the eight taxa that have been placed in Micrusia , three of them ( U. aurata Fabricius , U. loewi Becker and U. sicula Egger ) are clearly closer to Parageron or Usia sensu stricto than they are to the type species of Micrusia . Also U. versicolor (Fabricius) , while having many characters in common with Micrusia , seems to differ from it as much as Micrusia does from Usia . Of the diagnostic characters cited, the non-scrobiculate integument is more applicable to species of Parageron and many Usia also have non-scrobiculate integument, for instance U. transcaspica Paramonov , which has male and female genitalia that place it close to U. bicolor Macquart. The non-clavate third antennal segment is mainly a feature of U. versicolor , in U. forcipata this is highly variable and many individuals have a clavate third antennal segment. The very large genitalia is indeed a useful characteristic of the Micrusia group, but some such as U. turaco sp. nov. have relatively small genitalia while U. vestita Macquart of Usia sensu stricto has male genitalia almost as large relative to the insect as does the typical Micrusia .

If Micrusia is to be retained as a subgenus then it needs to be restricted to the small, black-haired, intensely black species that usually have large male genitalia and lack dense dusting. This is very likely to prove to be a monophyletic group, especially with U. versicolor excluded, and it is this concept that is followed here. However, it also seems very possible that many of the discernable groups of species in Usia sensu stricto. and, especially, Parageron are at least as strongly differentiated as is Micrusia . Should it ever be possible to do a full phylogenetic analysis, it is probable that Micrusia will be subsumed or, if it is to be retained, then the Usiini will have to be split into numerous smaller genera and subgenera of equivalent divergence. Until this is done, and because it does seem to be monophyletic, it is best to retain Micrusia as a convenient label for all the black-haired species other than U. versicolor .

In his revision of Usia, Becker (1906) recognised “der schwarzhaarigen Arten” which he designated as Groupe III and equates with the concept of Micrusia recognised here apart from his inclusion of U. versicolor . Becker (1906) keyed and redescribed four species in his Groupe III ( U. versicolor , U. pusilla , U. novakii Strobl and U. forcipata ) and described three new species ( U. ignorata Becker , U. carmelitensis Becker and U. pallescens Becker ). He also treated U. hyalipennis Macquart as a synonym of U. versicolor which is difficult to understand as Becker should have had these types available to him. He offers no explanation so perhaps he was merely following established usage and did not look sufficiently closely enough at the two Macquart syntypes. One of his new species ( U. pallescens ) has proved in this study to be a synonym of U. ignorata (see account of U. ignorata for discussion).

Engel (1932) did not arrange the species into groups but keyed all the black-haired species together. He keyed only six of the seven described species omitting U. pallescens while in the text simply repeating Becker’s (1906) description verbatim. Despite the absence of any taxonomic revision of the Micrusia group, for the first time useable illustrations of the male genitalia were provided, including four Micrusia species. Engel’s illustration of the U. forcipata epipygium (his Textfig. 28) is quite adequate to permit identification in most cases. His illustration of U. novakii (Textfig. 32) also seem to be reasonably accurate. However, his illustration of U. ignorata (Textfig. 29), while probably this species, is difficult to interpret and not very helpful. Finally U. pusilla (Textfig. 35) is not this species but an example of U. susanae sp. nov.

Efflatoun (1945) recognised only one species from Egypt, which he identified as U. ignorata . His illustrations do indeed seem to be this species and are far more accurate than Engel’s attempt. However, there is reason to believe that Efflatoun in fact had at least two species in his series, thus his descriptions and distributional notes need to be treated with caution.

Paramonov (1950) followed Becker (1906) in recognising the black haired species as distinctive but called them group II — Usia versicolor group. Unfortunately, he did not revisit any of Becker’s decisions, making no comment on either the synonymy of U. hyalipennis or validity of U. pallescens . However, Paramonov did, for the first time, recognise Becker’s error in describing female specimens of U. carmelitensis as males commenting that all the types are females and that the male is still unknown. Paramonov (1950) described two new species, U. syriaca from two females and U. engeli from both sexes, bringing the total of the black-haired Usia to nine plus one synonym. In common with the vast majority of Paramonov’s work, this revision contained no illustrations leaving identification for the non-specialist a very frustrating exercise.

No further species of the Micrusia group were described subsequently, but considerable further research was done by Oskar Theodor. Unfortunately, he died before he could publish any new species. In his review of the genitalia of Bombyliidae ( Theodor 1983) , he presented detailed illustrations of the macerated male and female genitalia for the first time. These included seven species of Micrusia accurately drawn such that they are readily identified. Unfortunately, Theodor’s taxonomy could not compete with his skill as an illustrator as he applied the correct name to just one of them. Of the seven species he illustrated, U. forcipata is correctly identified, U. ignorata = U. carmelitensis , U.? carmelitensis = undescribed, U.? pusilla = undescribed, sp. no. 4 = U. syriaca , sp. no. 5 = U. ignorata and sp. no. 6 = undescribed.

Theodor seems to have examined few types, amongst the Micrusia only U. carmelitensis , which he borrowed in 1976. In a letter to the Berlin Museum dated August 1976, he explained that the type of U. carmelitensis received on loan from them was a female, therefore was not helpful for his research (J. Ziegler pers. comm. 2010). Given the errors in Becker’s original revision, followed and added to by subsequent authors, it is hardly surprising that Theodor failed to resolve his species. It was the discovery that two distinct Spanish species both ran to U. pusilla in all the available keys that motivated this revision. Having examined most of the extant types and numerous specimens from European Museums and private collections, the Micrusia group now stands at 21 species, more than doubling the total known to Paramonov (1950). Usia hyalipennis Macquart, 1840 is raised from synonymy, U. pallescens Becker, 1906 is synonymised under U. ignorata and 12 species are newly described.